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  • 1.
    Foltynowicz, Aleksandra
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. 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 peroxide2013Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 110, nr 2, s. 163-175Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    Foltynowicz, Aleksandra
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schmidt, Florian M
    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.
    Noise-immune cavity-enhanced optical heterodyne molecular spectrometry: Current status and future potential2008Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 92, nr 3, s. 313-326Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    Ghorbani, Ramin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Real-time breath gas analysis of CO and CO2 using an EC-QCL2017Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, nr 5, artikkel-id 144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Real-time breath gas analysis is a promising, non-invasive tool in medical diagnostics, and well-suited to investigate the physiology of carbon monoxide (CO), a potential biomarker for oxidative stress and respiratory diseases. A sensor for precise, breath-cycle resolved, simultaneous detection of exhaled CO (eCO) and carbon dioxide (eCO2) was developed based on a continuous wave, external-cavity quantum cascade laser (EC-QCL), a low-volume multi-pass cell and wavelength modulation spectroscopy. The system achieves a noise-equivalent (1σ) sensitivity of 8.5 × 10−8 cm−1 Hz−1/2 and (2σ) detection limits of 9 ± 2 ppbv and 650 ± 7 ppmv at 0.14 s spectrum acquisition time for CO and CO2, respectively. Integration over 15 s yields a precision of 0.6 ppbv for CO. The fact that the eCO2 expirograms measured by capnography and laser spectroscopy have essentially identical shape confirms true real-time detection. It is found that the individual eCO exhalation profiles from healthy non-smokers have a slightly different shape than the eCO2 profiles and exhibit a clear dependence on exhalation flow rate and breath-holding time. Detection of indoor air CO and broadband breath profiling across the 93 cm−1 mode-hop-free tuning range of the EC-QCL are also demonstrated.

  • 4. Heissler, P.
    et al.
    Barna, A.
    Mikhailova, J. M.
    Ma, Guangjin
    Khrennikov, K.
    Karsch, S.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Földes, I. B.
    Tsakiris, G. D.
    Multi‑μJ harmonic emission energy from laser‑driven plasma2015Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 118, nr 2, s. 195-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on simultaneous efficiency and divergence measurements for harmonics from solid targets generated by the relativistic oscillating mirror mechanism. For a value of the normalized vector potential of aL≃1.5aL≃1.5, we demonstrate the generation of 30 μJ high-harmonic radiation in a 17±317±3 mrad divergence cone. This corresponds to a conversion efficiency of ≳≳ 10−4 in the 17–80 nm range into a well-confined beam. Presuming phase-locked harmonics, our results predict unprecedented levels of average power for a single attosecond pulse in the generated pulse train. Results of PIC simulations raise the prospect of attaining efficiencies of a few percent at higher laser intensities.

  • 5. Henderson, Ben
    et al.
    Khodabakhsh, Amir
    Metsälä, Markus
    Ventrillard, Irène
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Romanini, Daniele
    Ritchie, Grant A. D.
    te Lintel Hekkert, Sacco
    Briot, Raphaël
    Risby, Terence
    Marczin, Nandor
    Harren, Frans J. M.
    Cristescu, Simona M.
    Laser spectroscopy for breath analysis: towards clinical implementation2018Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 124, nr 8, artikkel-id 161Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.

  • 6.
    Johansson, Alexandra C.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Westberg, Jonas
    Wysocki, Gerard
    Foltynowicz, Aleksandra
    Optical frequency comb Faraday rotation spectroscopy2018Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 124, nr 5, artikkel-id 79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate optical frequency comb Faraday rotation spectroscopy (OFC-FRS) for broadband interference-free detection of paramagnetic species. The system is based on a femtosecond doubly resonant optical parametric oscillator and a fast-scanning Fourier transform spectrometer (FTS). The sample is placed in a DC magnetic field parallel to the light propagation. Efficient background suppression is implemented via switching the direction of the field on consecutive FTS scans and subtracting the consecutive spectra, which enables long-term averaging. In this first demonstration, we measure the entire Q- and R-branches of the fundamental band of nitric oxide in the 5.2–5.4 μm range and achieve good agreement with a theoretical model.

  • 7.
    Khodabakhsh, Amir
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Johansson, Alexandra C.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Noise-immune cavity-enhanced optical frequency comb spectroscopy: a sensitive technique for high-resolution broadband molecular detection2015Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 119, nr 1, s. 87-96Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    Khodabakhsh, Amir
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Rutkowski, Lucile
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Morville, Jérôme
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator2017Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, nr 210Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 9. Kluczynski, P.
    et al.
    Jahjah, M.
    Naehle, L.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Belahsene, S.
    Fischer, M.
    Koeth, J.
    Rouillard, Y.
    Westberg, Jonas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Vicet, A.
    Lundqvist, S.
    Detection of acetylene impurities in ethylene and polyethylene manufacturing processes using tunable diode laser spectroscopy in the 3-mu m range2011Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 105, nr 2, s. 427-434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using recently developed GaInAsSb/AlGaInAsSb DFB lasers, tunable diode laser spectroscopy (TDLS) has been extended into the 3-mu m wavelength region for the detection of acetylene impurities in hydrocarbon compounds encountered in ethylene manufacturing. Measurements of acetylene in pure polymer grade ethylene and in a gas mixture of ethylene and ethane typical of the process stream around a hydrogenation reactor have been performed. Using a procedure incorporating subtraction of a hydrocarbon background spectrum a detection limit of 5 ppb m was achieved under ordinary laboratory conditions. Under forced temperature cycling conditions, the detection limit deteriorated to 180 ppb m, due to temperature drift caused by optical interferences generated by reflections in the laser TO8 can.

  • 10. Kluczynski, Pawel
    et al.
    Lundqvist, Stefan
    Westberg, Jonas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Faraday rotation spectrometer with sub-second response time for detection of nitric oxide using a cw DFB quantum cascade laser at 5.33 µm2011Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 103, nr 2, s. 451-459Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Faraday modulation spectrometer for sensitive and fast detection of nitric oxide at 5.33 μm utilizing a room temperature continuous wave distributed feedback quantum cascade laser and a Peltier cooled MCT detector is presented. The magnetic field was modulated at 7.4 kHz whereas the laser wavelength was scanned at 20 Hz across the most favorable rotational-vibrational transition for FAMOS, Q3/2(3/2), at 5.33 μm. Using a 15 cm optical path and lineshape fitting, the spectrometer provides a detection limit of 4.5 ppb for a response time of 1 s. An Allan variance analysis demonstrates that the system has an excellent stability, up to several hours of operation.

  • 11.
    Petra, Stefan JH
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    van Leeuwen, KAH
    Feenstra, L
    Hogervorst, W
    Vassen, W
    Atom lithography with two-dimensional optical masks2004Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 79, nr 3, s. 279-283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With a two-dimensional (2D) optical mask at lambda=1083 nm, nanoscale patterns are created for the first time in an atom lithography process using metastable helium atoms. The internal energy of the atoms is used to locally damage a hydrophobic resist layer, which is removed in a wet etching process. Experiments have been performed with several polarizations for the optical mask, resulting in different intensity patterns, and corresponding nanoscale structures. The results for a linear polarized light field show an array of holes with a diameter of 260 nm, in agreement with a computed pattern. With a circularly polarized light field a line pattern is observed with a spacing of lambdaroot2=766 nm. Simulations taking into account many possible experimental imperfections can not explain this pattern.

  • 12.
    Qu, Zhechao
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    In situ H2O and temperature detection close to burning biomass pellets using calibration-free wavelength modulation spectroscopy2015Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 119, nr 1, s. 45-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The design and application of an H2O/temperature sensor based on scanned calibration-free wavelength modulation spectroscopy (CF-WMS) and a single tunable diode laser at 1.4 μm is presented. The sensor probes two H2O absorption peaks in a single scan and simultaneously retrieves H2O concentration and temperature by least-squares fitting simulated 1f-normalized 2f-WMS spectra to measured 2f/1f-WMS signals, with temperature, concentration and nonlinear modulation amplitude as fitting parameters. Given a minimum detectable absorbance of 1.7×10-5 cm-1 Hz-1/2, the system is applicable down to an H2O concentration of 0.1 % at 1000 K and 20 cm path length (200 ppm·m). The temperature in a water-seeded lab-scale reactor (670-1220 K at 4 % H2O) was determined within an accuracy of 1 % by comparison with the reactor thermocouple. The CF-WMS sensor was applied to real- time in situ measurements of H2O concentration and temperature time histories (0.25 s time resolution) in the hot gases 2 to 11 mm above biomass pellets during atmospheric combustion in the reactor. Temperatures between 1200 and 1600 K and H2O concentrations up to 40 % were detected above the biofuels. 

  • 13.
    Schmidt, Florian M.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ma, Weiguang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Foltynowicz, Aleksandra
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Highly sensitive dispersion spectroscopy by probing the free spectral range of an optical cavity using dual-frequency modulation2010Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 101, nr 3, s. 497-509Artikkel i tidsskrift (Fagfellevurdert)
    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)

  • 14.
    Schmidt, Florian M.
    et al.
    University of Helsinki.
    Vaittinen, O.
    Metsala, M.
    Kraus, P.
    Halonen, L.
    Direct detection of acetylene in air by continuous wave cavity ring-down spectroscopy2010Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 101, nr 3, s. 671-682Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diode laser-based continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared region has been used to measure the mixing ratio of acetylene (C(2)H(2)) in ambient air. Detection limits of 120 parts per trillion by volume (pptv) for 20 min and 340 pptv for 70 s acquisition time were achieved without sample pre-concentration, measuring on a C(2)H(2) absorption line at 6565.620 cm(-1) (similar to 1523 nm). Several indoor and outdoor air samples were collected at different locations in the Helsinki metropolitan area and analyzed using static-cell measurements. In addition, flow measurements of indoor and outdoor air have been performed continuously over several days with a time resolution of down to one minute. Baseline acetylene levels in the range of 0.4 to 3 parts per billion by volume (ppbv), with a maximum around midday and a minimum during the night, were measured. Sudden high mixing ratios of up to 60 ppbv were observed in outdoor air during daytime on a minute time scale. In general, the indoor mixing ratios were found to be higher than those in outdoor air. The acetylene levels correlated with the ambient CO levels and with outdoor temperature.

  • 15.
    Shao, Jie
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lathdavong, Lemthong
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kluczynski, Pawel
    Siemens AB.
    Lundqvist, Stefan
    Siemens AB.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Methodology for temperature measurements in water vapor using wavelength-modulation tunable diode laser absorption spectrometry in the telecom C-band2009Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 97, nr 3, s. 727-748Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A methodology based upon wavelength modulation and two-line thermometry for assessment of gas temperature by tunable diode laser absorption spectroscopy utilizing a standard tunable distributed feedback (DFB) diode laser working in the telecom C-band has been developed. Due to the high density of water lines in this wavelength region at elevated temperatures the methodology does not make use of two individual lines, but rather two groups of lines. The two groups identified have been found to have favorable properties for accurate temperature assessment in the 200-1000 ºC range, primarily a separation that is within a single DFB laser scan (~20 GHz), an adequate linestrength, and sufficient difference in temperature dependence; the ratio of the peak-values of the 2f-wm-signals, R, was found to increase monotonically with temperature, T, with a relative sensitivity, (ΔR/R)/(Δ/T), above or around unity for most of the pertinent temperature range. The standard deviation of a temperature measurement with a 1 s integration time was found to be below 0.3 %. The dependence of the temperature assessment on water concentration and modulation amplitude has also been investigated.

  • 16. Tan, Wei
    et al.
    Qiu, Xiaodong
    Zhao, Gang
    Jia, Mengyuan
    Ma, Weiguang
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institute of Laser Spectroscopy, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China.
    Yan, Xiaojuan
    Dong, Lei
    Zhang, Lei
    Tong, Zhaomin
    Yin, Wangbao
    Feng, Xiaoxia
    Xiao, Liantuan
    Axner, Ove
    Jia, Suotang
    High-efficiency frequency upconversion of 1.5 mu m laser based on a doubly resonant external ring cavity with a low finesse for signal field2017Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, nr 2, artikkel-id 52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A doubly resonant external ring cavity with a low finesse for the signal field is used to improve the frequency upconversion efficiency of a weak 1583 nm signal laser to 636 nm by mixing with a resonance power enhanced 1064 nm pump laser in a 25 mm periodically poled lithium niobate crystal. The process of frequency upconversion is described and optimized by the doubly resonant cavity-enhanced sum frequency generation theory under the condition of undepleted pump approximation. By selecting the suitable reflectivity of the signal input mirror and the incident pump power, a cavity-enhanced frequency conversion efficiency of 94.6% was obtained for signal powers up to 25 mW with an input pump power of 780 mW.

  • 17.
    Westberg, Jonas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lineshape asymmetries in Faraday modulation spectroscopy2014Inngår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 116, nr 2, s. 467-476Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Faraday modulation/rotation spectroscopy (FAMOS/FRS) is a spectroscopic technique for detection of paramagnetic species in gas phase. Although the prevailing theoretical description predicts fully symmetrical lineshapes, experiments do not in general provide such. This work shows that asymmetries in FAMOS can have at least two origins; (i) a frequency dependent laser intensity and (ii) polarization imperfections, which both are scrutinized here. A general analytical description for the latter, derived under the assumption that both the polarization imperfections and the relative absorption are small, is presented, conveniently expressed in terms of 1st Fourier coefficients of modulated dispersion and absorption lineshape functions. The resulting expression, which is thus an extension to the conventional FAMOS expression, can thereby be swiftly evaluated and allows for on-line fitting to measured asymmetric FAMOS signals. Curve fits to experimentally obtained data from nitric oxide measured both in the ultra-violet and the mid-infrared region demonstrate the applicability of the methodology.

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