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  • 1.
    Abd Alrahman, Chadi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cavity-enhanced optical frequency comb spectroscopy of high-temperature H2O in a flame2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 11, p. 13889-13895Article in journal (Refereed)
    Abstract [en]

    We demonstrate near-infrared cavity-enhanced optical frequency comb spectroscopy of water in a premixed methane/air flat flame. The detection system is based on an Er:fiber femtosecond laser, a high finesse optical cavity containing the flame, and a fast-scanning Fourier transform spectrometer (FTS). High absorption sensitivity is obtained by the combination of a high-bandwidth two-point comb-cavity lock and auto-balanced detection in the FTS. The system allows recording high-temperature water absorption spectra with a resolution of 1 GHz and a bandwidth of 50 nm in an acquisition time of 0.4 s, with absorption sensitivity of 4.2 x 10 (9) cm(-1) Hz(-1/2) per spectral element.

  • 2.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    NICE-OHMS – frequency modulation cavity-enhanced spectroscopy: principles and performance2014In: Cavity-Enhanced Spectroscopy and Sensing / [ed] Gianluca Gagliardi and Hans-Peter Loock, Berlin: Springer Berlin/Heidelberg, 2014, p. 221-251Chapter in book (Refereed)
    Abstract [en]

    Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is a sensitive technique for detection of molecular species in gas phase. It is based on a combination of frequency modulation for reduction of noise and cavity enhancement for prolongation of the interaction length between the light and a sample. It is capable of both Doppler-broadened and sub-Doppler detection with absorption sensitivity down to the 10−12 and 10−14 Hz−1/2 cm−1 range, respectively. This chapter provides a thorough description of the basic principles and the performance of the technique.

  • 3.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz-Matyba, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    NICE-OHMS – Frequency modulation cavity-enhanced spectroscopy: principles and performanceManuscript (preprint) (Other academic)
  • 4.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Physics. Umeå University, Faculty of Science and Technology, Physics.
    Sub-Doppler dispersion and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy revised2008In: Journal of the Optical Society of America B, Vol. 25, no 7, p. 1166-1177Article in journal (Refereed)
    Abstract [en]

    An expression for the peak-to-peak sub-Doppler optical phase shift of two counter-propagating modes of light, to which the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) dispersion signal is proportional, valid for arbitrary degree of saturation, is derived.

    For low degrees of saturation it agrees with the expression for weakly saturating (ws) conditions, [(1+S)-1/2-(1+2S)-1/20/2, where S is the degree of saturation and α0 the unsaturated peak absorption.

    However, the new expression, which can be written as 0.45S(1+S)-1α0/2, does not predict a distinct maximum as the ws-expression does; instead it predicts an optical phase shift that increases monotonically with S and levels off to 0.45α0/2 for large S. This alters the optimum conditions for the sub-Doppler NICE-OHMS technique and improves its shot-noise-limited detectability.

    The new expression is based upon the same explicit assumptions as the ws-expression but not the Kramers-Kronig’s relations, which are not valid for nonlinear responses, and is supported by experimental results up to S = 100. The new expression is expected to be valid for all techniques measuring sub-Doppler dispersion signals

  • 5.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gustafsson, Jörgen
    Omenetto, Nicoló
    Winefordner, James D.
    Absorption spectrometry by narrowband light in optically saturated and optically pumped collision and doppler broadened gaseous media under arbitrary optical thickness conditions2006In: Applied Spectroscopy, ISSN 0003-7028, E-ISSN 1943-3530, Vol. 60, no 11, p. 1217-1240Article in journal (Refereed)
    Abstract [en]

    This work examines absorption spectrometry by narrowband light in gaseous media with arbitrary optical thickness when the light induces optical saturation or optical pumping. Two quantities are defined: the observed absorbance, Aobs, and the true absorbance, Atrue. The former is the absorbance that is measured under the existing conditions, whereas the latter represents the absorbance one would measure if the light acted solely as a probe of the populations of the various levels, and it is therefore directly proportional to the concentration or density of absorbers. A general integral equation for the propagation of light in media of arbitrary optical thickness in which the light influences the populations of the levels involved is derived. This expression is transcendental in the observed absorbance and cannot be solved analytically. It is shown that an analytical expression can be derived by investigating the inverse relationship, i.e., Atruef(Aobs). Inasmuch as collision and Doppler broadened media react differently to optical saturation, they are considered separately. It is shown that a nonlinear response results if the medium is optically saturated (or pumped) and not optically thin. Expressions for the error introduced if the technique of standard additions is uncritically applied to such a system are derived.

  • 6.
    Ehlers, Patrick
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Use of etalon-immune distances to reduce the influence of background signals in frequency-modulation spectroscopy and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy2014In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 12, p. 2938-2945Article in journal (Refereed)
    Abstract [en]

    The detection sensitivity of phase-modulated techniques such as frequency-modulation spectroscopy (FMS) and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is often limited by etalon background signals. It has previously been shown that the impact of etalons can be reduced by the use of etalon-immune distances (EIDs), i.e., by separating the surfaces that give rise to etalons by a distance of q. L-m, where L-m is given by c/2n nu(m), where, in turn, n and nu(m) are the index of refraction between the components that make up the etalon (thus most often that of air) and the modulation frequency, respectively, and where q is an integer (i.e., 1, 2, 3,.) or half-integer (i.e., 1/2, 1, 3/2,.) for the dispersion and absorption modes of detection, respectively. An etalon created by surfaces separated by an EID will evade detection and thereby not contribute to any background signal. The concept of EIDs in FMS and NICE-OHMS is in this work demonstrated, scrutinized, and discussed in some detail. It is shown that the influence of EIDs on the absorption and dispersion modes of detection is significantly different; signals detected at the dispersion phase are considerably less sensitive to deviations from exact EID conditions than those detected at the absorption phase. For example, the FM background signal from an etalon whose length deviates from an EID by 2.5% of L-m (e.g., by 1 cm for an L-m of 40 cm), detected in dispersion, is only 9% of that in absorption. This makes the former mode of detection the preferred one whenever a sturdy immunity against etalons is needed or when optical components with parallel surfaces (e.g., lenses, polarizers, or beam splitters) are used. The impact of the concept of EIDs on NICE-OHMS is demonstrated by the use of Allan-Werle plots.

  • 7.
    Ehlers, Patrick
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry incorporating an optical circulator2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 2, p. 279-282Article in journal (Refereed)
    Abstract [en]

    To reduce the complexity of fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry, a system incorporating a fiber-coupled optical circulator to deflect the cavity-reflected light for laser stabilization has been realized. Detection near the shot-noise limit has been demonstrated for both Doppler-broadened and sub-Doppler signals, yielding a lowest detectable absorption and optical phase shift of 2.2 x 10(-12) cm(-1) and 4.0 x 10(-12) cm(-1), respectively, both for a 10 s integration time, where the former corresponds to a detection limit of C2H2 of 5 ppt. (C) 2014 Optical Society of America

  • 8.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Noise-immune cavity-enhanced optical heterodyne molecular spectro-metry (NICE-OHMS) is one of the most sensitive laser-based absorption techniques. The high sensitivity of NICE-OHMS is obtained by a unique combination of cavity enhancement (for increased interaction length with a sample) with frequency modulation spectrometry (for reduction of noise). Moreover, sub-Doppler detection is possible due to the presence of high intensity counter-propagating waves inside an external resonator, which provides an excellent spectral selectivity. The high sensitivity and selectivity make NICE-OHMS particularly suitable for trace gas detection. Despite this, the technique has so far not been often used for practical applications due to its technical complexity, originating primarily from the requirement of an active stabilization of the laser frequency to a cavity mode.

    The main aim of the work presented in this thesis has been to develop a simpler and more robust NICE-OHMS instrumentation without compro-mising the high sensitivity and selectivity of the technique. A compact NICE-OHMS setup based on a fiber laser and a fiber-coupled electro-optic modulator has been constructed. The main advantage of the fiber laser is its narrow free-running linewidth, which significantly simplifies the frequency stabilization procedure. It has been demonstrated, using acetylene and carbon dioxide as pilot species, that the system is capable of detecting relative absorption down to 3 × 10-9 on a Doppler-broadened transition, and sub-Doppler optical phase shift down to 1.6 × 10-10, the latter corresponding to a detection limit of 1 × 10-12 atm of C2H2. Moreover, the potential of dual frequency modulation dispersion spectrometry (DFM-DS), an integral part of NICE-OHMS, for concentration measurements has been assessed.

    This thesis contributes also to the theoretical description of Doppler-broadened and sub-Doppler NICE-OHMS signals, as well as DFM-DS signals. It has been shown that the concentration of an analyte can be deduced from a Doppler-broadened NICE-OHMS signal detected at an arbitrary and unknown detection phase, provided that a fit of the theoretical lineshape to the experimental data is performed. The influence of optical saturation on Doppler-broadened NICE-OHMS signals has been described theoretically and demonstrated experimentally. In particular, it has been shown that the Doppler-broadened dispersion signal is unaffected by optical saturation in the Doppler limit. An expression for the sub-Doppler optical phase shift, valid for high degrees of saturation, has been derived and verified experimentally up to degrees of saturation of 100.

  • 9.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Characterization of fiber-laser-based sub-Doppler NICE-OHMS for quantitative trace gas detection2008In: Optics Express, Vol. 16, no 19, p. 14689-14702Article in journal (Refereed)
    Abstract [en]

    The potential of fiber-laser-based sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry for trace gas detection is scrutinized. The non-linear dependence of the on-resonance sub-Doppler dispersion signal on the intracavity pressure and power is investigated and the optimum conditions with respect to these are determined. The linearity of the signal strength with concentration is demonstrated and the dynamic range of the technique is discussed. Measurements were performed on C2H2 at 1531 nm up to degrees of saturation of 100. The minimum detectable sub-Doppler optical phase shift was 5 x 10-11 cm-1 Hz-1/2, corresponding to a partial pressure of C2H2 of 1 x 10-12 atm for an intracavity pressure of 20 mTorr, and a concentration of 10 ppb at 400 mTorr.

  • 10.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry signals from optically saturated transitions under low pressure conditions2008In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, no 7, p. 1156-1165Article in journal (Refereed)
    Abstract [en]

    The influence of optical saturation on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) signals from purely Doppler-broadened transitions is investigated experimentally. It is shown that the shape and the strength of the dispersion signal are virtually unaffected by optical saturation, whereas the strength of the absorption signal decreases as (1+G+-1)-1/2, where G+-1 is the degree of saturation induced by the sideband of the frequency modulated triplet, in agreement with theoretical predictions. This implies, first of all, that Doppler-broadened NICE-OHMS is affected less by optical saturation than other cavity enhanced techniques but also that it exhibits nonlinearities in the power and pressure dependence for all detection phases except pure dispersion. A methodology for assessments of the degree of saturation and the saturation power of a transition from Doppler-broadened NICE-OHMS signals is given. The implications of optical saturation for practical trace species detection by Doppler-broadened NICE-OHMS are discussed.

  • 11.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wavelength modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy signal line shapes in the Doppler limit2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 7, p. 1384-1394Article in journal (Refereed)
    Abstract [en]

    A thorough analysis of the shape and strength of Doppler-broadened wavelength modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy signals is presented and their dependence on modulation frequency, modulation amplitude and detection phase is investigated in detail. The conditions that maximize the on-resonance signal are identified. The analysis is based on the standard frequency modulation spectroscopy formalism and the Fourier description of wavelength modulation spectroscopy and verified by fits to experimental signals from C2H2 and CO2 measured at 1531 nm. In addition, the line strengths of two CO2 transitions in the v2→3v1+v2+v3 hot band [Pe(7) and Pe(9)] were found to differ by ~20% from those given in the HITRAN database.

  • 12.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, USA.
    Maslowski, P.
    JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, CO, 80309-0440, USA and Instytut Fizyki, Uniwersytet Mikołaja Kopernika, Torun, Poland.
    Fleisher, A. J.
    JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, CO, 80309-0440, USA.
    Bjork, B. J.
    JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, CO, 80309-0440, USA.
    Ye, J.
    JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, CO, 80309-0440, USA.
    Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared application to trace detection of hydrogen peroxide2013In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 110, no 2, p. 163-175Article in journal (Refereed)
    Abstract [en]

    We demonstrate the first cavity-enhanced optical frequency comb spectroscopy in the mid-infrared wavelength region and report the sensitive real-time trace detection of hydrogen peroxide in the presence of a large amount of water. The experimental apparatus is based on a mid-infrared optical parametric oscillator synchronously pumped by a high-power Yb:fiber laser, a high-finesse broadband cavity, and a fast-scanning Fourier transform spectrometer with autobalancing detection. The comb spectrum with a bandwidth of 200 nm centered around 3.76 μm is simultaneously coupled to the cavity and both degrees of freedom of the comb, i.e. the repetition rate and carrier envelope offset frequency, are locked to the cavity to ensure stable transmission. The autobalancing detection scheme reduces the intensity noise by a factor of 300, and a sensitivity of 5.4×10-9 cm-1 Hz-1/2 with a resolution of 800 MHz is achieved (corresponding to 6.9×10-11 cm-1 Hz-1/2 per spectral element for 6000 resolved elements). This yields a noise equivalent detection limit for hydrogen peroxide of 8 parts-per-billion (ppb); in the presence of 2.8 % of water the detection limit is 130 ppb. Spectra of acetylene, methane, and nitrous oxide at atmospheric pressure are also presented, and a line-shape model is developed to simulate the experimental data.

  • 13.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gustafsson, Jörgen
    School of Engineering, Jönköping University, Jönköping, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wavelength modulation absorption spectrometry from optically pumped collision broadened atoms and molecules2007In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 108, no 2, p. 220-238Article in journal (Refereed)
    Abstract [en]

    A theoretical investigation of the influence of optical pumping on wavelength modulation absorption spectrometry (WMAS) signals from collision broadened atoms and molecules is presented. General expressions for the nf-WMAS signal from atomic and molecular systems, modeled as three-level systems that can accommodate both optical saturation and optical pumping, are derived by the use of a previously developed Fourier series-based formalism in combination with rate equations solved under steady-state conditions. The expressions are similar to those describing the nf-WMAS signal from two-level systems that can accommodate optical saturation [Schmidt FM, Foltynowicz A, Gustafsson J, Axner O, WMAS from optically saturated collision-broadened transitions. JQSRT 2005;94:225–54], the difference being the value of the saturation flux, wherefore the general parametric dependence of WMAS signals from optically pumped systems is the same as that from optically saturated systems. The additional effect of optical pumping on the WMAS signal is investigated for three typical cases: molecules or atoms in an ordinary atmosphere, atoms in an inert atmosphere, and atoms or molecules possessing metastable states. The possibility to describe any of these systems with a two-level model is investigated.

  • 14.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Noise-immune cavity-enhanced optical heterodyne molecular spectrometry: Current status and future potential2008In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 92, no 3, p. 313-326Article in journal (Refereed)
    Abstract [en]

    As a result of a combination of an external cavity and modulation techniques, noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is one of the most sensitive absorption techniques, capable of reaching close-to-shot-noise sensitivities, down to 5×10-13 fractional absorption at 1 s averaging. Due to its ability to provide sub-Doppler signals from weak molecular overtone transitions, the technique was first developed for frequency standard applications. It has since then also found use in fields of molecular spectroscopy of weak overtone transitions and trace gas detection. This paper describes the principles and the unique properties of NICE-OHMS. The historical background, the contributions of various groups, as well as the performance and present status of the technique are reviewed. Recent progress is highlighted and the future potential of the technique for trace species detection is discussed.

  • 15.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Distributed-feedback-laser-based NICE-OHMS
in the pressure-broadened regime2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 18, p. 18580-18591Article in journal (Refereed)
    Abstract [en]

    A compact noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) system based on a narrow linewidth distributed-feedback laser and fiber-coupled acousto-optic and electro-optic modulators has been developed. Measurements of absorption and dispersion signals have been performed at pressures up to 1/3 atmosphere on weak acetylene transitions at 1551 nm. Multiline fitting routines were implemented to obtain transition parameters, i.e., center frequencies, linestrengths, and pressure broadening coefficients. The signal strength was shown to be linear with pressure and concentration, and independent of detection phase. The minimum detectable on-resonance absorption with a cavity with a finesse of 460 was 2 × 10−10 cm−1 for 1 minute of integration time.

  • 16.
    Foltynowicz-Matyba, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Reduction of background signals in fiber-based NICE-OHMS2011In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 28, no 11, p. 2797-2805Article in journal (Refereed)
    Abstract [en]

    Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) based on a fiber-coupled electro-optic modulator (EOM) provides a compact and versatile experimental setup. It has, however, been limited by background signals originating from an imbalance of the phase modulated triplet created by a cross-coupling between the principal axes of the polarization maintaining fibers and the extraordinary axis of the EOM. Two strategies for reducing these background signals are investigated: (i) using an EOM with a titanium diffused waveguide, in which the balance of the triplet is controlled by active feedback, and (ii) using an EOM with a proton exchanged waveguide that does not support light propagation along the ordinary axis. It is shown that both approaches significantly reduce drifts and noise in the system. Using a cavity with a finesse of 5700, an absorption sensitivity of 3: 2 x 10(-12) cm(-1) in 1 min of integration time (i.e., 1: 8 x 10(-11) cm(-1) Hz(-1/2)) is demonstrated for Doppler-broadened detection, the lowest reported so far for Doppler-broadened NICE-OHMS. For sub-Doppler detection, a minimum detectable optical phase shift of 1: 3 x 10(-12) cm(-1) in 400s of integration time is obtained. (C) 2011 Optical Society of America

  • 17.
    Johansson, Alexandra C.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Filipsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Maslowski, Piotr
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    CO2 Line Parameter Retrieval Beyond the Voigt Profile Using Comb-Based Fourier Transform Spectroscopy2018In: Conference on Lasers and Electro-Optics, Optical Society of America, 2018Conference paper (Refereed)
    Abstract [en]

    We measure absorption spectra of the CO213 band at 1.57 μm using optical frequency comb Fourier transform spectroscopy with sub-nominal resolution and retrieve line shape parameters using multiline fitting with the speed-dependent Voigt profile.

  • 18.
    Johansson, Alexandra C.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Filipsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhao, Gang
    Umeå University, Faculty of Science and Technology, Department of Physics. 2 State Key Laboratory of Quantum Optics and Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 16, p. 20633-20648Article in journal (Refereed)
    Abstract [en]

    We present broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS), a technique for calibration-free determination of the complex refractive index of entire molecular bands via direct measurement of transmission modes of a Fabry-Perot cavity filled with the sample. The measurement of the cavity transmission spectrum is done using an optical frequency comb and a mechanical Fourier transform spectrometer with sub-nominal resolution. Molecular absorption and dispersion spectra (corresponding to the imaginary and real parts of the refractive index) are obtained from the cavity mode broadening and shift retrieved from fits of Lorentzian profiles to the individual cavity modes. This method is calibration-free because the mode broadening and shift are independent of the cavity parameters such as the length and mirror reflectivity. In this first demonstration of broadband CE-CRIS we measure simultaneously the absorption and dispersion spectra of three combination bands of CO2 in the range between 1525 nm and 1620 nm and achieve good agreement with theoretical models. This opens up for precision spectroscopy of the complex refractive index of several molecular bands simultaneously. 

  • 19.
    Johansson, Alexandra C.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Signal line shapes of Fourier-transform cavity-enhanced frequency modulation spectroscopy with optical frequency combs2017In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 34, no 2, p. 358-365Article in journal (Refereed)
    Abstract [en]

    We present a thorough analysis of the signal line shapes of Fourier-transform-based noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS). We discuss the signal dependence on the ratio of the modulation frequency, f(m), to the molecular linewidth, G. We compare a full model of the signals and a simplified absorption-like analytical model that has high accuracy for low f(m)/G ratios and is much faster to compute. We verify the theory experimentally by measuring and fitting the NICE-OFCS spectra of CO2 at 1575 nm using a system based on an Er: fiber femtosecond laser and a cavity with a finesse of similar to 11000. 

  • 20.
    Johansson, Alexandra C.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Westberg, Jonas
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wysocki, Gerard
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Faraday Rotation Spectroscopy Using an Optical Frequency Comb2017In: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Summary form only given. The mid-infrared (MIR) part of the optical spectrum (3-12 μm) houses the fundamental absorption bands of a multitude of environmentally important molecules, but the abundance of water absorption often causes interference with the target species and makes concentration measurement inaccurate. The broad spectral coverage of optical frequency comb spectroscopy (OFCS) provides access to entire ro-vibrational bands and allows more accurate concentration quantification and retrieval of sample temperature. To further improve detection sensitivity of paramagnetic species in the presence of interfering species, we combine a MIR optical frequency comb with the Faraday rotation spectroscopy (FRS) technique [I], which is insensitive to interferences from diamagnetic molecules, such as H 2 O, CO 2 , and CO. In FRS, the rotation of the polarization induced by an external magnetic field in the vicinity of paramagnetic molecular transitions is translated to an intensity change by the use of a polarization analyzer, which effectively removes the influence of any non-paramagnetic species. In the proof of principle demonstration of OFC-FRS we detect nitric oxide (NO) in the presence of water at 5.3 μm using a Fourier transform spectrometer.

  • 21.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Abd Alrahman, Chadi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Noise-immune cavity-enhanced optical frequency comb spectroscopy2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 17, p. 5034-5037Article in journal (Refereed)
    Abstract [en]

    We present a new method of optical frequency comb spectroscopy that combines cavity enhancement with frequency modulation to obtain immunity to laser frequency-to-amplitude noise conversion by the cavity modes and, thus, high absorption sensitivity over a broad spectral range. A frequency comb is locked to a cavity with a free spectral range (FSR) equal to 4/3 times the repetition rate of the laser, and phase-modulated at a frequency equal to the cavity FSR. The transmitted light is analyzed by a Fourier transform spectrometer with a high bandwidth detector. Phase-sensitive detection of the interferogram yields a noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS) signal. In the first demonstration, we record NICE-OFCS signals from the overtone CO2 band at 1575 nm with absorption sensitivity of 4.3 x 10(-10) cm(-1) Hz(-1/2) per spectral element, close to the shot noise limit.

  • 22.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Badarla, Venkata R.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lee, Kevin F.
    Jiang, J.
    Mohr, C.
    Fermann, Martin E.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical Frequency Comb Spectroscopy at 3.3 and 5.2 mu m by a Tm:fiber-Laser-Pumped Optical Parametric Oscillator2016In: Proceedings Conference on Lasers and Electro-Optics, 2016Conference paper (Refereed)
    Abstract [en]

    Using a doubly-resonant femtosecond optical parametric oscillator in combination with a multipass cell and a Fourier transform spectrometer we measure broadband CH4 and NO absorption spectra at fundamental transition wavelengths.

  • 23.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Noise-immune cavity-enhanced optical frequency comb spectroscopy: a sensitive technique for high-resolution broadband molecular detection2015In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 119, no 1, p. 87-96Article in journal (Refereed)
    Abstract [en]

    Noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS) is a recently developed technique that utilizes phase modulation to obtain immunity to frequency-to-amplitude noise conversion by the cavity modes and yields high absorption sensitivity over a broad spectral range. We describe the principles of the technique and discuss possible comb-cavity matching solutions. We present a theoretical description of NICE-OFCS signals detected with a Fourier transform spectrometer (FTS) and validate the model by comparing it to experimental CO2 spectra around 1,575 nm. Our system is based on an Er:fiber femtosecond laser locked to a cavity and phase-modulated at a frequency equal to a multiple of the cavity free spectral range (FSR). The NICE-OFCS signal is detected by a fast-scanning FTS equipped with a high-bandwidth commercial detector. We demonstrate a simple method of passive locking of the modulation frequency to the cavity FSR that significantly improves the long-term stability of the system, allowing averaging times on the order of minutes. Using a cavity with a finesse of ~9,000, we obtain absorption sensitivity of 6.4 × 10−11 cm−1 Hz−1∕2 per spectral element and concentration detection limit for CO2 of 450 ppb Hz−1/2, determined by multiline fitting.

  • 24.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fourier-Transform-Based Noise-Immune Cavity-Enhanced Optical Frequency Comb Spectroscopy2015In: 2015 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO), 2015Conference paper (Refereed)
    Abstract [en]

    We achieve absorption sensitivity of 6.4 x 10(-11) cm(-1) Hz(-1/2) per spectral element with near-infrared Fourier-transform-based noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS), which allows detection of CO2 at ppb concentration levels.

  • 25.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Abd Alrahman, Chadi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cavity-Enhanced Optical Frequency Comb Spectroscopy of High-Temperature Water in a Flame2015In: 2015 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO), 2015Conference paper (Refereed)
    Abstract [en]

    We demonstrate detection of broadband high-temperature water spectra in a laminar, premixed methane/air flat flame using high-resolution near-infrared cavity-enhanced optical frequency comb spectroscopy incorporating a fast-scanning Fourier transform spectrometer.

  • 26.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ramaiah-Badarla, Venkata
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lee, Kevin F.
    Jiang, Jie
    Mohr, Christian
    Fermann, Martin E.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fourier transform and Vernier spectroscopy using an optical frequency comb at 3-5.4 μm2016In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 41, no 11, p. 2541-2544Article in journal (Refereed)
    Abstract [en]

    We present a versatilemid-infrared frequency comb spectroscopy system based on a doubly resonant optical parametric oscillator tunable in the 3-5.4 mu m range and two detection methods: a Fourier transform spectrometer (FTS) and a continuous-filtering Vernier spectrometer (CF-VS). Using the FTS with a multipass cell, we measure high precision broadband absorption spectra of CH4 at 3.3 mu m and NO at 5.25 mu m, the latter for the first time with comb spectroscopy, and we detect atmospheric species (CH4, CO, CO2, and H2O) in air in the signal and idler ranges. Multiline fitting yields minimum detectable concentrations of 10-20 ppbHz-1/2 for CH4, NO, and CO. For the first time in the mid-infrared, we perform CF-VS using an enhancement cavity, a grating, and a single detector, and we measure the absorption spectrum of CH4 and H2O in ambient air at similar to 3.3 m mu, reaching a 40 ppb concentration detection limit for CH4 in 2 ms. 

  • 27.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Morville, Jerome
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Soboń, Grzegorz
    Umeå University, Faculty of Science and Technology, Department of Physics. Faculty of Electronics, Wrocław University of Science and Technology, Wrocław, Poland.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cavity-Enhanced Continuous-Filtering Vernier Spectroscopy at 3.3 mu m using a Femtosecond Optical Parametric Oscillator2017In: 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC), IEEE , 2017, p. CH_2_2-Conference paper (Refereed)
    Abstract [en]

    Optical frequency comb spectroscopy in the mid-infrared fingerprint region combines broad spectral bandwidth with high detection sensitivity and allows simultaneous detection of trace amounts of many molecular species. We have recently demonstrated a continuous-filtering Vernier spectrometer based on a mid-infrared optical frequency comb and an enhancement cavity for fast and sensitive detection of CH4 [1]. Here we present an improved, fully automatized and frequency calibrated continuous-filtering Vernier spectrometer, schematically shown in Fig. 1(a). The comb source is a doubly resonant optical parametric oscillator (DROPO) based on an orientation-patterned GaAs crystal synchronously pumped by a Tm:fiber femtosecond laser (125 MHz repetition rate, frep). The signal comb (3.1–3.4 µm, 30 mW) is mode matched to a 60-cm long Vernier enhancement cavity with a finesse of ~350 at 3.25 μm, placed in an enclosure that can be filled with the gas sample. The output mirror is attached to a PZT and mounted on a translation stage. When the cavity free spectral range is perfectly matched to twice the frep (250 MHz) every other signal comb mode is transmitted through the cavity. By detuning the cavity length from this perfect match position the cavity resonances act as a filter and transmit groups of comb modes called Vernier orders [2]. A diffraction grating mounted on a galvo-scanner separates these orders after the cavity and the chosen order is sent to the detection system. The Vernier order is tuned across the signal comb spectrum by scanning the cavity length (at 20 Hz) and the grating is rotated synchronously to fix the order in space and allow acquisition of the entire spectrum in 25 ms. Any residual mismatch between the cavity length scan and the grating rotation is compensated by a feedback loop acting on the frep of the pump laser and the PZT of the Vernier cavity [2]. A Fabry-Perot etalon is used for frequency calibration of the spectrometer. Figure 1(b) shows in black the normalized transmission spectrum of a sample containing 5.0 ppm CH4 and 160 ppm water. The red and blue curves show the corresponding fit of the Vernier spectrum [3] of CH4 and water, respectively, calculated using Voigt profiles, line parameters from the HITRAN database, and the experimentally determined cavity finesse. The figure of merit of the spectrometer is 1×10−9cm−1 Hz−1∕2 per spectral element and multiline fitting yields minimum detectable concentration of CH4 of 2 ppb in 25 ms, translating into 400 ppt Hz−1∕2 Since the spectrum of the signal comb covers the fundamental C-H stretch transitions we expect low detection limits for other hydrocarbons as well. In conclusion, mid-infrared comb-based continuous-filtering Vernier spectroscopy allows fast and highly sensitive measurement of broadband absorption spectra using a robust and compact detection system.

  • 28.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Morville, Jérôme
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator2017In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, no 210Article in journal (Refereed)
    Abstract [en]

    We present a continuous-filtering Vernier spectrometer operating in the 3.15-3.4 mu m range, based on a femtosecond doubly resonant optical parametric oscillator, a cavity with a finesse of 340, a grating mounted on a galvo scanner, and two photodiodes. The spectrometer allows acquisition of one spectrum spanning 250 nm of bandwidth in 25 ms with 8 GHz resolution, sufficient to detect molecular lines at atmospheric pressure. An active lock ensures good frequency and intensity stability of the consecutive spectra and enables continuous signal acquisition and efficient averaging. The relative frequency scale is calibrated using a Fabry-Perot etalon or, alternatively, the galvo scanner position signal. We measure spectra of a calibrated CH4 gas sample as well as dry and laboratory air and extract CH4 and -H2O concentrations by multiline fitting of model spectra. The figure of merit of the spectrometer is 1.7 x 10(-9) cm(-1) Hz(-1/2) per spectral element and the minimum detectable concentration of CH4 is 360 ppt Hz(-1/2), averaging down to 90 ppt after 16 s.

  • 29.
    Khodabakhsh, Amir
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Morville, Jérôme
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Soboń, Grzegorz
    Umeå University, Faculty of Science and Technology, Department of Physics. Faculty of Electronics, Wrocław University of Science and Technology, Wrocław, Poland.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Continuous-Filtering Vernier Spectroscopy at 3.3 mu m Using a Femtosecond Optical Parametric Oscillator2017In: 2017 conference on lasers and elecro-optics (CLEO): Science and innovations, IEEE , 2017, article id SW1L.5Conference paper (Refereed)
    Abstract [en]

    Using a cavity-enhanced continuous-filtering Vernier spectrometer based on a femtosecond optical parametric oscillator we measure broadband spectra of atmospheric water and CH4 around 3.3 mu m reaching 4 ppb detection limit for CH4 in 15 ms.

  • 30.
    Ma, Weiguang
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Theoretical description of Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectroscopy under optically saturated conditions2008In: Journal of the Optical Society of America B, Vol. 25, no 7, p. 1144-1155Article in journal (Refereed)
    Abstract [en]

    A theoretical description of Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) under optically saturated conditions is presented. Expressions for the strength and shape of the Doppler-broadened NICE-OHMS signals are given for both absorption and dispersion phase, in the Voigt regime as well as in the Doppler limit. It is shown that Doppler-broadened NICE-OHMS is affected less by optical saturation than other cavity enhanced techniques; in the Doppler limit the absorption signal decreases by a factor of (1+G+-1)-1/2, where G+-1 is the degree of saturation for one of the frequency modulation sidebands, whereas the dispersion signal is virtually unaffected by optical saturation. In the Voigt regime both signals show additional dependence on optical saturation. The concept of saturation-insensitive detection is introduced and its conditions are identified.

  • 31. Maslowski, P.
    et al.
    Kowzan, G.
    Charczun, D.
    Lisak, D.
    Trawinski, R.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lee, K. F.
    Fermann, M. E.
    Optical Frequency Comb Spectroscopy for Gas Metrology and Trace Gas Detection2017In: 2017 Conference on lasers and electro-optics (CLEO), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    We report recent developments of comb-based broadband absorption spectroscopy. The comb-line resolving approaches and Fourier transform spectroscopy with sub-nominal resolution overcome the frequency resolution limits of conventional techniques. Advantages for various applications will be discussed.

  • 32. Maslowski, Piotr
    et al.
    Lee, Kevin F.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kowzan, Grzegorz
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mills, Andrew A.
    Mohr, Christian
    Jiang, Jie
    Fermann, Martin E.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Surpassing the path-limited resolution of Fourier-transform spectrometry with frequency combs2016In: Physical Review A, ISSN 2469-9926, Vol. 93, no 2, article id 021802Article in journal (Refereed)
    Abstract [en]

    We overcome the resolution limit of Fourier-transform spectrometry and measure instrumental line-shape-free broadband molecular spectra with lines narrower than the optical path-limited resolution. We do this by using an optical frequency comb and precisely matching the maximum delay range of the spectrometer to the comb line spacing to measure the intensities of the individual comb lines. This method allows measurements of undistorted high-resolution spectra with acquisition time and interferometer length reduced by orders of magnitude and with frequency scale accuracy given by the comb.

  • 33.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Kyuberis, Aleksandra A.
    Zobov, Nikolai F.
    Polyansky, Oleg L.
    Yurchenko, Sergei N.
    Tennyson, Jonathan
    An experimental water line list at 1950 K in the 6250–6670 cm−1 region2018In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 205, p. 213-219Article in journal (Refereed)
    Abstract [en]

    An absorption spectrum of (H2O)-O-16 at 1950 K is recorded in a premixed methane/air flat flame using a cavity-enhanced optical frequency comb-based Fourier transform spectrometer. 2417 absorption lines are identified in the 6250-6670 cm(-1) region with an accuracy of about 0.01 cm(-1). Absolute line intensities are retrieved using temperature and concentration values obtained by tunable diode laser absorption spectroscopy. Line assignments are made using a combination of empirically known energy levels and predictions from the new POKAZATEL variational line list. 2030 of the observed lines are assigned to 2937 transitions, once blends are taken into account. 126 new energy levels of (H2O)-O-16 are identified. The assigned transitions belong to 136 bands and span rotational states up to J = 27.

  • 34.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Broadband and High Resolution Direct Measurement of Cavity Resonances2017In: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Summary form only given. Optical frequency combs offer unprecedented combination of broad bandwidth and high resolution and their coupling to enhancement cavities provides high sensitivity for spectroscopic measurements. Here we use a frequency-comb-based Fourier transform spectrometer (FTS) to measure the narrow resonances of a high-finesse cavity over a bandwidth of 100 nm around 1.55 μm and derive the group delay dispersion (GDD) of the cavity mirrors with precision below 1 fs 2 from the cavity resonance frequencies. We do this using a method that allows precise sampling of the comb intensities using an FTS with nominal resolution matched to the comb repetition rate (f rep ) [1, 2], and we demonstrate that sub-MHz resolution is achieved.

  • 35.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mechanical Fourier Transform Spectrometer with kHz Resolution2017In: 2017 conference on lasers and electro-optics (CLEO): Science and innovations, IEEE, 2017, article id SW4J.6Conference paper (Refereed)
    Abstract [en]

    We measure simultaneously 11000 resonances of a high-finesse cavity with kHz level resolution using optical frequency comb Fourier transform spectroscopy and retrieve the dispersion of the cavity mirrors from the cavity mode spacing.

  • 36.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Maslowski, Piotr
    Kowzan, Grzegorz
    Lee, Kevin F.
    Mills, Andrew A.
    Mohr, Christian
    Jiang, Jie
    Fermann, Martin E.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical Frequency Comb Fourier Transform Spectroscopy with Resolution beyond the Path Difference Limit2016In: Proceedings Conference on Lasers and Electro-Optics Part of CLEO: 2016 5–10 June 2016, San Jose, California, United States, 2016Conference paper (Refereed)
    Abstract [en]

    We overcome the resolution limit of Fourier transform spectrometry and measure instrumental-lineshape-free high-resolution broadband molecular spectra by matching the spectrometer's optical path difference to the line spacing of an optical frequency comb.

  • 37.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Valiev, Damir
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Lodi, Lorenzo
    Yurchenko, Sergey
    Polyansky, Oleg L.
    Tennyson, Jonathan
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Detection of OH and H2O in an Atmospheric Flame by Near-Infrared Optical Frequency Comb Spectroscopy2017In: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Absorption spectroscopy is attractive for combustion diagnostics because it allows in-situ and calibration-free quantification of reactants/products and thermometry. However, spectra measured at atmospheric pressure in the near-infrared telecom range, where laser sources and optical components are readily available, suffer from strong water interference. Cavity-enhanced optical frequency comb spectroscopy (CE-OFCS) is well suited for detection of other species, as it provides broad bandwidth with high signal-to-noise ratio and resolution, and allows de-convolving the spectra hidden among water transitions. Here we report detection of OH in the presence of H2O in an atmospheric premixed methane/air flat flame by CE-OFCS at 1.57 μm. We demonstrate a new water line list that is more accurate than HITEMP [1] and we isolate the OH lines by dividing spectra taken at different heights above the burner (HABs) to retrieve OH concentration and flame temperature.

  • 38.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Valiev, Damir
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tkacz, Arkadiusz
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Detection of OH in an atmospheric flame at 1.5 μm using optical frequency comb spectroscopy2016In: Photonics Letters of Poland, ISSN 2080-2242, E-ISSN 2080-2242, Vol. 8, no 4, p. 110-112Article in journal (Refereed)
    Abstract [en]

    We report broadband detection of OH in a premixed CH4/air flat flame at atmospheric pressure using cavity-enhanced absorption spectroscopy based on an Er:fiber femtosecond laser and a Fourier transform spectrometer. By taking ratios of spectra measured at different heights above the burner we separate twenty OH transitions from the largely overlapping water background. We retrieve from fits to the OH lines the relative variation of OH concentration and flame temperature with a height above the burner and compare them with the 1D simulations of flame structure.

  • 39.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhao, Gang
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 18, p. 21711-21718Article in journal (Refereed)
    Abstract [en]

    Optical cavities provide high sensitivity to dispersion since their resonance frequencies depend on the index of refraction. We present a direct, broadband, and accurate measurement of the modes of a high finesse cavity using an optical frequency comb and a mechanical Fourier transform spectrometer with a kHz-level resolution. We characterize 16000 longitudinal cavity modes spanning 16 THz of bandwidth in terms of center frequency, linewidth, and amplitude. Using the center frequencies we retrieve the group delay dispersion of the cavity mirror coatings and pure N2 with 0.1 fs2 precision and 1 fs2 accuracy, as well as the refractivity of the 3ν13 absorption band of CO2 with 5 × 10‒12 precision. This opens up for broadband refractive index metrology and calibration-free spectroscopy of entire molecular bands.

  • 40.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Valiev, Damir M.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lodi, Lorenzo
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ghorbani, Ramin
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Polyansky, Oleg L.
    Jin, Yuwei
    Tennyson, Jonathan
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Measurement of H2O and OH in a Flame by Optical Frequency Comb Spectroscopy2016In: Proceedings Conference on Lasers and Electro-Optics, 2016Conference paper (Refereed)
    Abstract [en]

    We measure broadband H2O and OH spectra in a flame using near-infrared cavity-enhanced Fourier transform optical frequency comb spectroscopy, we retrieve temperature and OH concentration, and compare water spectra to an improved line list.

  • 41.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Masłowski, Piotr
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical frequency comb Fourier transform spectroscopy with sub-nominal resolution and precision beyond the Voigt profile2018In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 204, p. 63-73Article in journal (Refereed)
    Abstract [en]

    Broadband precision spectroscopy is indispensable for providing high fidelity molecular parameters for spectroscopic databases. We have recently shown that mechanical Fourier transform spectrometers based on optical frequency combs can measure broadband high-resolution molecular spectra undistorted by the instrumental line shape (ILS) and with a highly precise frequency scale provided by the comb. The accurate measurement of the power of the comb modes interacting with the molecular sample was achieved by acquiring single-burst interferograms with nominal resolution matched to the comb mode spacing. Here we describe in detail the experimental and numerical steps needed to achieve sub-nominal resolution and retrieve ILS-free molecular spectra, i.e. with ILS-induced distortion below the noise level. We investigate the accuracy of the transition line centers retrieved by fitting to the absorption lines measured using this method. We verify the performance by measuring an ILS-free cavity-enhanced low-pressure spectrum of the 3ν1 + ν3 band of CO2 around 1575 nm with line widths narrower than the nominal resolution. We observe and quantify collisional narrowing of absorption line shape, for the first time with a comb-based spectroscopic technique. Thus retrieval of line shape parameters with accuracy not limited by the Voigt profile is now possible for entire absorption bands acquired simultaneously.

  • 42.
    Sadiek, Ibrahim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mikkonen, Tommi
    Vainio, Markku
    Toivonen, Juha
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical frequency comb photoacoustic spectroscopy2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 44, p. 27849-27855Article in journal (Refereed)
    Abstract [en]

    We report the first photoacoustic detection scheme using an optical frequency comb—optical frequency comb photoacoustic spectroscopy (OFC-PAS). OFC-PAS combines the broad spectral coverage and the high resolution of OFCs with the small sample volume of cantilever-enhanced PA detection. In OFC-PAS, a Fourier transform spectrometer (FTS) is used to modulate the intensity of the exciting comb source at a frequency determined by its scanning speed. One of the FTS outputs is directed to the PA cell and the other is measured simultaneously with a photodiode and used to normalize the PA signal. The cantilever-enhanced PA detector operates in a non-resonant mode, enabling detection of a broadband frequency response. The broadband and the high-resolution capabilities of OFC-PAS are demonstrated by measuring the rovibrational spectra of the fundamental C–H stretch band of CH4, with no instrumental line shape distortions, at total pressures of 1000 mbar, 650 mbar, and 400 mbar. In this first demonstration, a spectral resolution two orders of magnitude better than previously reported with broadband PAS is obtained, limited by the pressure broadening. A limit of detection of 0.8 ppm of methane in N2 is accomplished in a single interferogram measurement (200 s measurement time, 1000 MHz spectral resolution, 1000 mbar total pressure) for an exciting power spectral density of 42 μW/cm−1. A normalized noise equivalent absorption of 8 × 10−10 W cm−1 Hz−1/2 is obtained, which is only a factor of three higher than the best reported with PAS based on continuous wave lasers. A wide dynamic range of up to four orders of magnitude and a very good linearity (limited by the Beer–Lambert law) over two orders of magnitude are realized. OFC-PAS extends the capability of optical sensors for multispecies trace gas analysis in small sample volumes with high resolution and selectivity.

  • 43.
    Schmidt, Florian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gustafsson, Jörgen
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wavelength modulation absorption spectrometry from optically saturated collision-broadened transitions2005In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 94, no 2, p. 225-254Article in journal (Refereed)
    Abstract [en]

    A theoretical investigation of the influence of optical saturation on wavelength modulation absorption spectrometry (WMAS) signals from collision-broadened transitions is presented. Expressions are derived for the nth Fourier coefficient of the analytical detector signal, and thereby also for the nth harmonic signal from a WMAS instrumentation (i.e. the nf-WMAS signal), from a wavelength modulated collision-broadened transition exposed to optical saturation. The flux- (or irradiance-) and modulation-amplitude dependences of the nf-WMAS signal on resonance are scrutinized in detail. It is shown that the nth Fourier coefficient of the wavelength modulated analytical detector signal from an optically saturated collision-broadened transition can be written as a product of a flux-dependent (φ) bleaching function, given by (1+φ/φsat)-1 and identical to that appearing for ordinary, unmodulated absorption spectrometry (AS), and a flux-, detuning-, and modulation-amplitude-dependent wavelength modulated peak-normalized saturation-broadened Lorentzian lineshape function, specific for the WMAS technique. It is found that the nf-WMAS signal on resonance decreases faster than an ordinary AS signal as a function of laser flux when smaller-than-optimum modulation amplitudes are used, but slower when larger-than-optimum modulation amplitudes are used. When optimum (or close-to-optimum) modulation amplitudes are being used, on the other hand, the flux dependence of the WMAS signal resembles to a large degree that of ordinary AS. The conditions for when WMAS from collision-broadened transitions has the same flux dependence as ordinary AS are identified.

  • 44.
    Schmidt, Florian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz-Matyba, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lock, Tomas
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Doppler-broadened fiber-laser-based NICE-OHMS: improved detectability2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 17, p. 10822-10831Article in journal (Refereed)
    Abstract [en]

    The performance of fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) has been improved by elimination of the technical constraints that limited its first demonstration. Doppler-broadened detection of C2H2 and CO2 at ~1531 nm is demonstrated using a cavity with a finesse of 4800. Frequency and wavelength modulated detection at absorption and dispersion phase are compared and the optimum mode of detection is discussed. A minimum detectable absorption of 8 × 10-11 cm-1, which corresponds to a detection limit of 4.5 ppt (2 ppt·m) for C2H2, was obtained for an acquisition time of 0.7 s by lineshape fitting. The linearity of the pressure dependence of the signal strengths is investigated for both C2H2 and CO2.

  • 45.
    Schmidt, Florian M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Axner, Ove
    Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry for Doppler-broadened detection of C2H2 in the parts per trillion range2007In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 24, no 6, p. 1392-1405Article in journal (Refereed)
  • 46.
    Schmidt, Florian M.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Highly sensitive dispersion spectroscopy by probing the free spectral range of an optical cavity using dual-frequency modulation2010In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 101, no 3, p. 497-509Article in journal (Refereed)
    Abstract [en]

    Dual-frequency modulation (DFM) has been used to continuously track the frequency shifts of optical cavity modes in the vicinity of an optical transition of a gas inside the cavity for assessment of the gas concentration. A theoretical description of the size and lineshape of the DFM dispersion spectroscopy (DFM-DS) signal is given. Since the signal is measured in terms of a radio frequency the technique is insensitive to laser intensity fluctuations. The signal strength, which can accurately be obtained by curve fitting, only depends on fundamental parameters (including the line strength), thus enabling quantitative detection without calibration procedure. In a first demonstration, using a compact setup based on a narrowband fiber laser, the change in free spectral range around a value of 379.9 MHz due to an acetylene transition near 1531 nm was measured with a resolution of 6 Hz (i.e. with an accuracy of 1.5 parts in 10(8)) in 12.5 s acquisition time, which corresponds to a minimum detectable integrated absorption (SNR=3) of 3x10(-9) cm(-1)

  • 47.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A dual Fabry-Perot cavity for fast assessments of gasnumber densityManuscript (preprint) (Other academic)
  • 48.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zelan, Martin
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Arrhen, Fredrik
    Pendrill, Leslie
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical measurement of the gas number density in a Fabry-Perot cavity2013In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 24, no 10, p. 105207-Article in journal (Refereed)
    Abstract [en]

    An optical method for measuring the gas density by monitoring the refractive index inside a high-finesse Fabry-Perot cavity is presented. The frequency of a narrow linewidth Er:fiber laser, locked to a mode of the cavity, is measured with the help of an optical frequency comb while the gas density inside the cavity changes. A resolution of 1.4 x 10(-6) mol m(-3) is achieved in 3 s for nitrogen, which allows measurement of a relative gas density change of 3.4 x 10(-8) at atmospheric pressure.

  • 49.
    Sobon, Grzegorz
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Laser & Fiber Electronics Group, Faculty of Electronics, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland.
    Martynkien, Tadeusz
    Mergo, Pawel
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-power frequency comb source tunable from 2.7 to 4.2 mu m based on difference frequency generation pumped by an Yb-doped fiber laser2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 9, p. 1748-1751Article in journal (Refereed)
    Abstract [en]

    We demonstrate a broadband mid-infrared (MIR) frequency comb source based on difference frequency generation (DFG) in periodically poled lithium niobate crystal. MIR radiation is obtained via mixing of the output of a 125 MHz repetition rate Yb-doped fiber laser with Raman-shifted solitons generated from the same source in a highly nonlinear fiber. The resulting idler is tunable in the range of 2.7-4.2 mu m, with average output power reaching 237 mW and pulses as short as 115 fs. The coherence of the MIR comb is confirmed by spectral interferometry and heterodyne beat measurements. Applicability of the developed DFG source for laser spectroscopy is demonstrated by measuring absorption spectrum of acetylene at 3.0-3.1 mu m. (C) 2017 Optical Society of America

  • 50.
    Soboń, Grzegorz
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Faculty of Electronics, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland .
    Martynkien, Tadeusz
    Mergo, Pawel
    Marangoni, Marco
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-power broadband source tunable from 2.8 to 4 μm based on difference frequency generation2017In: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Mid-infrared (MIR) frequency comb sources enable high-speed and accurate detection of various species, since many molecules possess their fingerprints in this wavelength range. Usually, broadband radiation in this spectral region is obtained from optical parametric oscillators (OPOs), which provide high output power and broad tuning capabilities [1]. However, OPO sources require locking of the cavity to the pumping oscillator, which increases the complexity. MIR sources based on difference frequency generation (DFG) are interesting alternatives to OPOs, due to their simplicity, single-pass configuration, broad tunability, and fully passive cancellation of the carrier-envelope offset in the generated idler pulses. However, the conversion efficiency of the DFG process is usually insufficient to reach the output power levels easily achieved in OPO systems. Here, we demonstrate a widely tunable DFG source based on a mode-locked Yb-doped fiber laser, with average MIR output power reaching 165 mW, which is more than in previous reports on similar DFG systems [2,3].

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