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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. Amotchkina, Tatiana
    et al.
    Trubetskov, Michael K.
    Pervak, Yurij
    Veisz, Laszlo
    Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Pervak, Vladimir
    Stress compensation with antireflection coatings for ultrafast laser applications: from theory to practice2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 24, p. 30387-30393Article in journal (Refereed)
    Abstract [en]

    Each complicated coating, in particular, a dispersive mirror consists of dozens of layers. Thin films layers have mechanical stresses. After summing up stresses from all layers, the resulting stress is high enough to bend even a relatively thick substrate. To avoid this effect we suggest depositing an antireflection coating (AR) at the back-side of the substrate which together with suppression of unwanted reflections from the back side will also compensate this stress. We demonstrate unique, extremely thick and sophisticated AR coating consisting of 71 layers with the total physical thickness of 7.5 µm. This AR coating completely compensates stress from the dispersive mirror coated on the front side and minimizes unwanted reflections.

  • 3. Centeno, R.
    et al.
    Mandon, J.
    Cristescu, S. M.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Harren, F. J. M.
    External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 5, p. 6277-6282Article in journal (Refereed)
    Abstract [en]

    We combine an external cavity diode laser with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using current modulation. With a finesse of 1600, we demonstrate noise equivalent absorption sensitivities of 4.1 x 10(-10) cm(-1) Hz(-1/2), resulting in sub-ppbv detection limits for Doppler-broadened transitions of CH4 at 6132.3 cm(-1), C2H2 at 6578.5 cm(-1) and HCN at 6541.7 cm(-1). The system is used for hydrogen cyanide detection from sweet almonds.

  • 4.
    Cheddad, Abbas
    et al.
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Nord, Christoffer
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Hörnblad, Andreas
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Prunskaite-Hyyryläinen, Renata
    Oulu Center for Cell-Matrix Research, Biocenter Oulu, Laboratory of Developmental Biology and Department of Medical Biochemistry and Molecular Biology, Institute of Biomedicine, University of Oulu, Finland.
    Eriksson, Maria
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Georgsson, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Vainio, Seppo
    Oulu Center for Cell-Matrix Research, Biocenter Oulu, Laboratory of Developmental Biology and Department of Medical Biochemistry and Molecular Biology, Institute of Biomedicine, University of Oulu, Finland.
    Ahlgren, Ulf
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Improving signal detection in emission optical projection tomography via single source multi-exposure image fusion2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 14, p. 16584-16604Article in journal (Refereed)
    Abstract [en]

    We demonstrate a technique to improve structural data obtained from Optical Projection Tomography (OPT) using Image Fusion (IF) and contrast normalization. This enables the visualization of molecular expression patterns in biological specimens with highly variable contrast values. In the approach, termed IF-OPT, different exposures are fused by assigning weighted contrasts to each. When applied to projection images from mouse organs and digital phantoms our results demonstrate the capability of IF-OPT to reveal high and low signal intensity details in challenging specimens. We further provide measurements to highlight the benefits of the new algorithm in comparison to other similar methods.

  • 5.
    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.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization of fiber-laser-based sub-Doppler NICE-OHMS for quantitative trace gas detection2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, 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.

  • 6.
    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.

  • 7.
    Ghorbani, Ramin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 11, p. 12743-12752Article in journal (Refereed)
    Abstract [en]

    We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a low-volume circular multipass cell and wavelength modulation absorption spectroscopy. A fringe-limited (1σ) sensitivity of 6.5 × 10−8 cm−1Hz-1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy. Integration over 10 s increases the precision to 0.6 ppbv. The setup also allows measuring the stable isotope 13CO in breath. We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking. Isotope ratio analysis indicates depletion of 13CO in breath compared to natural abundance.

  • 8.
    Hausmaninger, Thomas
    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.
    Narrowing of the linewidth of an optical parametric oscillator by an acousto-optic modulator for the realization of mid-IR noise-immune cavity-enhanced optical heterodyne molecular spectrometry down to 10(-10) cm(-1) Hz(-1/2)2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 26, p. 33641-33655, article id UNSP 252446Article in journal (Refereed)
    Abstract [en]

    The linewidth of a singly resonant optical parametric oscillator (OPO) has been narrowed with respect to an external cavity by the use of an acousto-optic modulator (AOM). This made possible an improvement of the sensitivity of a previously realized OPO-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry instrument for the 3.2 - 3.9 mu m mid-infrared region by one order of magnitude. The resulting system shows a detection sensitivity for methane of 2.4 x 10(-10) cm(-1) Hz(-1/2) and 1.3 x 10(-10) cm(-1) at 20 s, which allows for detection of both the environmentally important (CH4)-C-13 and CH3D isotopologues in atmospheric samples. (C) 2015 Optical Society of America

  • 9.
    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. 

  • 10. Krzempek, Karol
    et al.
    Tomaszewska, Dorota
    Gluszek, Aleksander
    Martynkien, Tadeusz
    Mergo, Pawel
    Sotor, Jaroslaw
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sobon, Grzegorz
    Stabilized all-fiber source for generation of tunable broadband fCEO-free mid-IR frequency comb in the 7–9 µm range2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 26, p. 37435-37445Article in journal (Refereed)
    Abstract [en]

    A compact and robust all-fiber difference frequency generation-based source of broadband mid-infrared radiation is presented. The source emits tunable radiation in the range between 6.5 µm and 9 µm with an average output power up to 5 mW at 125 MHz repetition frequency. The all-in-fiber construction of the source along with active stabilization techniques results in long-term repetition rate stability of 3 Hz per 10 h and a standard deviation of the output power better than 0.8% per 1 h. The applicability of the presented source to laser spectroscopy is demonstrated by measuring the absorption spectrum of nitrous oxide (N2O) around 7.8 µm. The robustness and good long- and short-term stability of the source opens up for applications outside the laboratory.

  • 11. Liu, Jianxin
    et al.
    Zhou, Yueting
    Guo, Songjie
    Hou, Jiajuan
    Zhao, Gang
    Ma, Weiguang
    Wu, Yongqian
    Dong, Lei
    Zhang, Lei
    Yin, Wangbao
    Xiao, Liantuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    A novel methodology to directly pre-determine the relative wavelength response of DFB laser in wavelength modulation spectroscopy2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 2, p. 1249-1261Article in journal (Refereed)
    Abstract [en]

    A novel methodology to directly pre-determine the relative wavelength response (RWR) of a DFB laser, in terms of a combined current linearly scanned wavelength response and current modulated wavelength response (CMWR), in wavelength modulation spectroscopy (WMS) is presented. It is shown that the assessed RWR can be used to mimic the measured response with standard deviation of discriminations that are below 3.4 x 10(-3)cm(-1) under a variety of conditions. It is also shown that its performance supersedes two commonly used assessment models of the CMWR but is slightly worse than that of the third model. however with the benefit of solely using a single fitting parameter (the concentration) instead of more. When the novel method is applied to the assessment of CO2 concentration in a Herriot-type multipass cell by using the technique of calibration-free WMS, the results show that there is virtually no difference compared to that by use of the best of the other methods. It is concluded that the novel method is more robust and simplifies the retrieval process of gas concentration.

  • 12.
    Lu, Chuang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vieira, Francisco Senna
    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.
    Time-resolved continuous-filtering Vernier spectroscopy of H2O and OH radical in a flame2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 21, p. 29521-29533Article in journal (Refereed)
    Abstract [en]

    We use broadband near-infrared continuous-filtering Vernier spectroscopy (CF-VS) for time-resolved detection of H2O and OH radical in a premixed CH4/air flat flame. The CF-VS spectrometer is based on a femtosecond Er:fiber laser, an external cavity that contains the flame, and a detection system comprising a rotating diffraction grating and photodetectors. Spectra of H2O and OH radical around 1570 nm are continuously recorded with 6.6 GHz spectral resolution, 4.0 x 10-7 cm-1 absorption sensitivity, and 25 ms time resolution, while the fuel-air equivalence ratio is periodically modulated with a square wave. The concentrations of the two analytes are retrieved with percent level precision by a fit of a Vernier model to each spectrum spanning 13 nm. The temporal profiles of both concentrations in each modulation cycle are repeatable and the steady-state concentration levels are in good agreement with predictions based on one-dimensional simulations of a static flat flame. The robust CF-VS spectrometer opens up for quantitative monitoring of multiple products of time-varying combustion processes with relatively simple data acquisition procedures.

  • 13. Ma, Guangjin
    et al.
    Yu, Wei
    Yu, M. Y.
    Shen, Baifei
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Intense circularly polarized attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 9, p. 10057-10065Article in journal (Refereed)
    Abstract [en]

    We have investigated the polarization of attosecond light pulses generated from relativistic few-cycle laser pulse interaction with the surface of overdense plasmas using particle-in-cell simulation. Under suitable conditions, a desired polarization state of the generated attosecond pulse can be achieved by controlling the polarization of the incident laser. In particular, an elliptically polarized laser pulse of suitable ellipticity can generate an almost circularly polarized attosecond pulse without compromising the harmonic generation efficiency. The process is thus applicable as a new tabletop circularly-polarized XUV radiation source for probing attosecond phenomena with high temporal resolution.

  • 14.
    Qu, Zhechao
    et al.
    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.
    Valiev, Damir
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Calibration-free scanned wavelength modulation spectroscopy – application to H2O and temperature sensing in flames2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 12, p. 16492-16499Article in journal (Refereed)
    Abstract [en]

    A calibration-free scanned wavelength modulation spectroscopy scheme requiring minimal laser characterization is presented. Species concentration and temperature are retrieved simultaneously from a single fit to a group of 2f/1f-WMS lineshapes acquired in one laser scan. The fitting algorithm includes a novel method to obtain the phase shift between laser intensity and wavelength modulation, and allows for a wavelengthdependent modulation amplitude. The scheme is demonstrated by detection of H2O concentration and temperature in atmospheric, premixed CH4/air flat flames using a sensor operating near 1.4 μm. The detection sensitivity for H2O at 2000 K was 4 × 10−5 cm−1 Hz-1/2, and temperature was determined with a precision of 10 K and absolute accuracy of ~50 K. A parametric study of the dependence of H2O and temperature on distance to the burner and total fuel mass flow rate shows good agreement with 1D simulations.

  • 15.
    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.

  • 16.
    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.

  • 17.
    Tan, Jeryl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Forget, Nicolas
    Borot, Antonin
    Kaplan, Daniel
    Tournois, Pierre
    Muschet, Alexander
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Dispersion control for temporal contrast optimization2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 19, p. 25003-25012Article in journal (Refereed)
    Abstract [en]

    We investigate the temporal contrast of the Light Wave Synthesizer 20 (LWS-20): a powerful, few-cycle source based on the optical parametric synthesizer principle. Saturation effects in the RF amplifier driving the acousto-optic programmable dispersive filter (AOPDF) were found to degrade the coherent contrast for non-monotonic group delay corrections. We subsequently present a new dispersion scheme and design a novel transmission grism-based stretcher optimized for LWS-20. The resulting temporal contrast of the amplified, compressed output pulses is improved by 2-4 orders of magnitude compared to the former design.

  • 18. Valerio, Aline de Matos
    et al.
    Kampel, Milton
    Vantrepotte, Vincent
    Ward, Nicholas D.
    Sawakuchi, Henrique Oliveira
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Universidade de São Paulo, USP/CENA, Piracicaba, SP, Brazil .
    Da Silva Less, Diani Fernanda
    Neu, Vania
    Cunha, Alan
    Richey, Jeffrey
    Using CDOM optical properties for estimating DOC concentrations and pCO2 in the Lower Amazon River2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 14, p. A657-A677Article in journal (Refereed)
    Abstract [en]

    Coloured dissolved organic matter (CDOM) is one of the major contributors to the absorption budget of most freshwaters and can be used as a proxy to assess non-optical carbon fractions such as dissolved organic carbon (DOC) and the partial pressure of carbon dioxide (pCO2). Nevertheless, riverine studies that explore the former relationships are still relatively scarce, especially within tropical regions. Here we document the spatial-seasonal variability of CDOM, DOC and pCO2, and assess the potential of CDOM absorption coefficient (aCDOM(412)) for estimating DOC concentration and pCO2 along the Lower Amazon River. Our results revealed differences in the dissolved organic matter (DOM) quality between clearwater (CW) tributaries and the Amazon River mainstream. A linear relationship between DOC and CDOM was observed when tributaries and mainstream are evaluated separately (Amazon River: N = 42, R2 = 0.74, p<0.05; CW: N = 13, R2 = 0.57, p<0.05). However, this linear relationship was not observed during periods of higher rainfall and river discharge, requiring a specific model for these time periods to be developed (N = 25, R2 = 0.58, p<0.05). A strong linear positive relation was found between aCDOM(412) and pCO2(N = 69, R2 = 0.65, p<0.05) along the lower river. pCO2 was less affected by the optical difference between tributaries and mainstream waters or by the discharge conditions when compared to CDOM to DOC relationships. Including the river water temperature in the model improves our ability to estimate pCO(2) (N = 69; R2 = 0.80, p<0.05). The ability to assess both DOC and pCO2 from CDOM optical properties opens further perspectives on the use of ocean colour remote sensing data for monitoring carbon dynamics in large running water systems worldwide.

  • 19.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China .
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China .
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Differential noise-immune cavity-enhanced optical heterodyne molecular spectroscopy for improvement of the detection sensitivity by reduction of drifts from background signals2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 23, p. 29454-29471Article in journal (Refereed)
    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.

  • 20.
    Zhao, Gang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. 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 University, Faculty of Science and Technology, Department of Physics. National Metrology Institute VTT MIKES, Tekniikantie 1, FI-02044 VTT, Finland.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ma, Weiguang
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-resolution trace gas detection by sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry: application to detection of acetylene in human breath2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 13, p. 17940-17953Article in journal (Refereed)
    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.

  • 21. Zhao, Gang
    et al.
    Tan, Wei
    Hou, Jiajia
    Qiu, Xiaodong
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University ; Collaborative Innovation Center of Extreme Optics, Shanxi University.
    Li, Zhixin
    Dong, Lei
    Zhang, Lei
    Yin, Wangbao
    Xiao, Liantuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    Calibration-free wavelength-modulation spectroscopy based on a swiftly determined wavelength-modulation frequency response function of a DFB laser2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 2, p. 1723-1733Article in journal (Refereed)
    Abstract [en]

    A methodology for calibration-free wavelength modulation spectroscopy (CF-WMS) that is based upon an extensive empirical description of the wavelength-modulation frequency response (WMFR) of DFB laser is presented. An assessment of the WMFR of a DFB laser by the use of an etalon confirms that it consists of two parts: a 1st harmonic component with an amplitude that is linear with the sweep and a nonlinear 2nd harmonic component with a constant amplitude. Simulations show that, among the various factors that affect the line shape of a background-subtracted peak-normalized 2f signal, such as concentration, phase shifts between intensity modulation and frequency modulation, and WMFR, only the last factor has a decisive impact. Based on this and to avoid the impractical use of an etalon, a novel method to pre-determine the parameters of the WMFR by fitting to a background-subtracted peak-normalized 2f signal has been developed. The accuracy of the new scheme to determine the WMFR is demonstrated and compared with that of conventional methods in CF-WMS by detection of trace acetylene. The results show that the new method provides a four times smaller fitting error than the conventional methods and retrieves concentration more accurately.

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