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  • 1.
    Hausmaninger, Thomas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zhao, Gang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ma, Weiguang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Depletion of the vibrational ground state of CH4 in absorption spectroscopy at 3.4 μm in N2 and air in the 1-100Torr range2018Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 205, s. 59-70Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model presented in an accompanying work predicts that mid-IR absorption signals from methane in trace concentrations in various buffer gases detected at pressures in the 1-100Torr range can be reduced and distorted due to depletion of the vibrational ground state if the molecules are exposed to laser powers in the tens of mW range or above. This work provides experimental evidence of such depletion in a resonant cavity under a variety of conditions, e.g. for intracavity laser powers up to 2W and for buffer gases of N-2 or dry air, and verifies the applicability of the model. It was found that the degree of depletion is significantly larger in N-2 than dry air, and that it increases with pressure for pressures up to around 10Torr (attributed to a decreased diffusion rate) but decreases with pressure for pressures above 20Torr (caused by an increased collisional vibrational decay rate). The maximum degree of depletion (similar to 80%) was obtained for methane in N-2 at around 15Torr. This implies that absorption spectrometry of methane can experience significant non-linear dependencies on laser power, pressure, as well as buffer gas composition. It is shown that depletion takes place also in (CH4)-C-13, which verifies the applicability of the model also for this isotopologue, and that NICE-OHMS signals detected in absorption phase are less affected by depletion than in dispersion. It was concluded that the absorption mode of detection can provide concentration assessments that are virtually free of influence of depletion for intracavity powers below 0.8 W. 

  • 2.
    Johansson, Alexandra C.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rutkowski, Lucile
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Filipsson, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zhao, Gang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. 2 State Key Laboratory of Quantum Optics and Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb2018Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, nr 16, s. 20633-20648Artikel i tidskrift (Refereegranskat)
    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. 

  • 3.
    Rutkowski, Lucile
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Johansson, Alexandra C.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zhao, Gang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Quantum Optics and Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Khodabakhsh, Amir
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution2017Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, nr 18, s. 21711-21718Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Zhao, Gang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China .
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ma, Weiguang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China .
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Differential noise-immune cavity-enhanced optical heterodyne molecular spectroscopy for improvement of the detection sensitivity by reduction of drifts from background signals2017Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, nr 23, s. 29454-29471Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The detection sensitivity of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is often limited by background signals that bring in drifts. A novel realization of NICE-OHMS, termed differential NICE-OHMS, that both reduces such drifts and enlarges the molecular signal is presented. It is based on simultaneous detection of NICE-OHMS signals in reflection and transmission, followed by a subtraction of the former (properly weighted) from the latter. An Allan plot analysis shows that the instrumentation could demonstrate a noise equivalent absorption per unit length (NEAL) of 4.7 × 10−14 cm−1, obtained for an integration time of 170 s.

  • 5.
    Zhao, Gang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China.
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ma, Weiguang
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shot-noise-limited Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry2018Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, nr 4, s. 715-718Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shot-noise-limited Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) has been realized by implementation of balanced detection. A characterization of the system based on Allan-Werle plots of the absorption coefficient, retrieved by fitting a model function to data, shows that the system has a white noise equivalent absorption per unit length per square root of bandwidth of 2.3 x 10(-13) cm(-1) Hz(-1/2), solely 44% above the shot noise limit, and a detection sensitivity of 2.2 x 10(-14) cm(-1) over 200 s, both being unprecedented for Db NICE-OHMS. The white noise response follows the expected inverse square root dependence on power that is representative of a shot-noise-limited response, which confirms that the system is shot-noise-limited. 

  • 6.
    Zhao, Gang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Shanxi Univ, Inst Laser Spect, State Key Lab Quantum Opt & Quantum Opt Devices, Taiyuan 030006, Shanxi, Peoples R China; Shanxi Univ, Collaborat Innovat Ctr Extreme Opt, Taiyuan 030006, Shanxi, Peoples R China.
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ma, Weiguang
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Whispering-gallery-mode laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry2017Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, nr 16, s. 3109-3112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The whispering-gallery-mode (WGM) laser is a type of laser that has an exceptionally narrow linewidth. Noise-immune cavity-enhanced optical heterodyne molecular spectrometry, which is a detection technique with extraordinary properties that benefit from narrow linewidth lasers, has been realized with a WGM laser. By locking to a cavity with a finesse of 55 000, acetylene and carbon dioxide could be simultaneously detected down to an unprecedented noise equivalent absorption per unit length of 6.6 x 10(-14) cm(-1) over 150 s, corresponding to 5 ppt of C2H2.

  • 7.
    Zhao, Gang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China.
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Ma, Weiguang
    State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    High resolution ultra-sensitive trace gas detection by use of cavity-position-modulated sub-Doppler NICE-OHMS - Application to detection of acetylene in human breathManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    A sensitive high resolution spectrometer for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species by sub-Doppler (sD) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is presented. The setup is based on a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. An additional layer of modulation is added to reduce the influence of narrow etalons and improve the sensitivity for sD detection. By dithering synchronously the positions of the two cavity mirrors, the effect of residual etalons between one of the cavity mirrors and another surface in the system could be reduced without affecting the frequencies of the cavity mode. This reduced the drifts in the system, allowing for an Allan deviation of the absorption coefficient of 2.2×10−13 cm−1 for an integration time of 60 s, which, for the targeted C2H2 transition at 6518.4858 cm−1, corresponds to a 3σ detection sensitivity of 130 ppt. Sub-Doppler trace gas detection is demonstrated by measuring ppb levels of C2H2 in the exhaled breath of smokers. A procedure was worked out for simultaneous detection of CO2, based on the Db response. It is shown that despite significant spectral interference from CO2, which precludes Db detection of C2H2 in breath, acetylene could be detected in breath from smokers with good spectral resolution by the use of sD NICE-OHMS.

  • 8.
    Zhao, Gang
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. State Key Laboratory of Quantum Optics & Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, 030006 Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006 Taiyuan, China .
    Hausmaninger, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. National Metrology Institute VTT MIKES, Tekniikantie 1, FI-02044 VTT, Finland.
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Ma, Weiguang
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    High-resolution trace gas detection by sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry: application to detection of acetylene in human breath2019Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, nr 13, s. 17940-17953Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A sensitive high-resolution sub-Doppler detecting spectrometer, based on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS), for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species is presented. It is designed around a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. By synchronous dithering the positions of the two cavity mirrors, the effect of residual etalons between the cavity and other surfaces in the system could be reduced. An Allan deviation of the absorption coefficient of 2.2 × 10-13 cm-1 at 60 s, which, for the targeted transition in C2H2, corresponds to a 3σ detection sensitivity of 130 ppt, is demonstrated. It is shown that despite significant spectral interference from CO2 at the targeted transition, which precludes Db detection of C2H2, acetylene could be detected in exhaled breath of healthy smokers.

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