| 1. |
- Foltynowicz, Aleksandra, 1981-, et al.
(author)
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Cavity-enhanced optical frequency combs spectroscopy in the near- and mid-infrared
- 2016
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In: Imaging and applied optics 2016. - : OSA - The Optical Society. - 9781943580156
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Conference paper (peer-reviewed)abstract
- We present the recent developments in high-resolution Fourier transform spectroscopy based on optical frequency combs for precision measurements and combustion diagnostics, and the first implementation of continuous-filtering Vernier spectroscopy in the mid-infrared wavelength range for fast multispecies detection.
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| 2. |
- Foltynowicz, Aleksandra, 1981-, et al.
(author)
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Measurement and assignment of double-resonance transitions to the 8900-9100- cm-1 levels of methane
- 2021
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 103:2
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Journal article (peer-reviewed)abstract
- Optical-optical double-resonance spectroscopy with a continuous wave pump and frequency comb probe allows measurement of sub-Doppler transitions to highly excited molecular states over a wide spectral range with high frequency accuracy. We report on assessment and characterization of sub-Doppler double-resonance transitions in methane measured using a 3.3-μm continuous wave optical parametric oscillator as a pump and a 1.67-μm frequency comb as a probe. The comb spectra were recorded using a Fourier transform spectrometer with comb-mode-limited resolution. With the pump tuned to nine different transitions in the ν3 fundamental band, we detected 36 ladder-type transitions to the 3ν3 overtone band region, and 18 V-type transitions to the 2ν3 overtone band. We describe in detail the experimental approach and the pump stabilization scheme, which currently limits the frequency accuracy of the measurement. We present the data analysis procedure used to extract the frequencies and intensities of the probe transitions for parallel and perpendicular relative pump-probe polarization. We compare the center frequencies and relative intensities of the ladder-type transitions to theoretical predictions from the TheoReTS and ExoMol line lists, demonstrating good agreement with TheoReTS.
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| 3. |
- Foltynowicz, Aleksandra, 1981-, et al.
(author)
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Sub-Doppler Double-Resonance Spectroscopy of Methane Using a Frequency Comb Probe
- 2021
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 126:6
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Journal article (peer-reviewed)abstract
- We report the first measurement of sub-Doppler molecular response using a frequency comb by employing the comb as a probe in optical-optical double-resonance spectroscopy. We use a 3.3 μm continuous wave pump and a 1.67 μm comb probe to detect sub-Doppler transitions to the 2ν3 and 3ν3 bands of methane with ∼1.7 MHz center frequency accuracy. These measurements provide the first verification of the accuracy of theoretical predictions from highly vibrationally excited states, needed to model the high-temperature spectra of exoplanets. Transition frequencies to the 3ν3 band show good agreement with the TheoReTS line list.
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| 4. |
- Foltynowicz, Aleksandra, 1981-, et al.
(author)
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Sub-doppler double-resonance spectroscopy of methane using a frequency comb probe
- 2020
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In: Conference on Lasers and Electro-Optics. - : Optica Publishing Group (formerly OSA). - 9781943580767 - 9781728144184
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Conference paper (peer-reviewed)abstract
- We use a 3.3 µm continuous wave optical parametric oscillator as a pump and a 1.67 µm frequency comb as a probe to record 36 sub-Doppler double-resonance transitions in the 3v3 band of methane (including 26 previously unreported) with ~1.5 MHz center frequency accuracy.
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| 5. |
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| 6. |
- Hjältén, Adrian, 1988-, et al.
(author)
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Accurate measurement and assignment of high rotational energy levels of the 3v3 ← v3 band of methane
- 2023
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In: 2023 conference on lasers and electro-optics, CLEO 2023. - : IEEE. - 9781957171258 - 9781665455688
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Conference paper (peer-reviewed)abstract
- We use optical-optical double-resonance spectroscopy with a high-power continuous wave pump and a cavity-enhanced comb probe to expand sub-Doppler measurements of the 3v3 ← v3 band of CH4 to higher rotational levels. We assign the final states using combination differences, i.e., by reaching the same state using different pump/probe combinations.
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| 7. |
- Johansson, Alexandra C., et al.
(author)
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Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb
- 2018
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In: Optics Express. - : Optical Society of America. - 1094-4087. ; 26:16, s. 20633-20648
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Johansson, Alexandra C., 1987-, et al.
(author)
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Broadband Complex Refractive Index Spectroscopy via Measurement of Cavity Modes
- 2018
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In: 2018 Conference on Lasers and Electro-Optics (CLEO). - : IEEE. - 9781943580422
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Conference paper (peer-reviewed)abstract
- We retrieve high precision absorption and dispersion spectra of the 3v(1)+v(3) band of CO2 from direct measurement of cavity transmission modes using an optical frequency comb and a mechanical Fourier transfolin spectrometer with sub-nominal resolution.
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| 9. |
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| 10. |
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| 11. |
- Johansson, Alexandra C., et al.
(author)
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Faraday rotation spectroscopy using an optical frequency comb
- 2017
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In: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC). - : IEEE. - 9781509067367
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Conference paper (peer-reviewed)abstract
- 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.
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| 12. |
- Johansson, Alexandra C., 1987-, et al.
(author)
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Fourier-transform-based noise-immune cavity-enhanced optical frequency comb spectroscopy
- 2016
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In: Light, Energy and the Environment. - : Optica Publishing Group (formerly OSA). - 9781557528209
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Conference paper (peer-reviewed)abstract
- We describe the principles and implementation of Fourier-transform-based cavityenhanced optical frequency comb spectroscopy that uses phase modulation at the cavity free spectral range frequency to achieve high sensitivity over broad spectral range.
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| 13. |
- Johansson, Alexandra C., 1987-, et al.
(author)
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Precise comb-based fourier transform spectroscopy for line parameter retrieval
- 2019
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In: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference (CLEO/EUROPE-EQEC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728104690
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Conference paper (peer-reviewed)abstract
- Accurate parameters of molecular transitions are needed for data analysis in many applications, ranging from atmospheric research to astrophysics and determination of fundamental constants. Optical frequency comb Fourier transform spectroscopy (OFC-FTS) is particularly well-suited for high-precision measurements of broadband molecular spectra. From these spectra, the parameters of individual transitions - all measured simultaneously under the same experimental conditions - can be determined. We use a mechanical OFC-FTS spectrometer with sub-nominal resolution [1, 2] to perform precise broadband measurements of entire molecular bands of CO2 using either direct absorption spectroscopy or cavity-enhanced complex refractive index spectroscopy (CE-CRIS) [3] and we extract line parameters for line shapes beyond the Voigt profile.
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| 14. |
- Johansson, Alexandra C., et al.
(author)
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Signal line shapes of Fourier-transform cavity-enhanced frequency modulation spectroscopy with optical frequency combs
- 2017
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In: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 34:2, s. 358-365
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Journal article (peer-reviewed)abstract
- 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.
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| 15. |
- Khodabakhsh, Amir, et al.
(author)
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Cavity-Enhanced Continuous-Filtering Vernier Spectroscopy at 3.3 mu m using a Femtosecond Optical Parametric Oscillator
- 2017
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In: 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC). - : IEEE. - 9781509067367 ; , s. CH_2_2-
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Conference paper (peer-reviewed)abstract
- 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.
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| 16. |
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| 17. |
- Khodabakhsh, Amir, et al.
(author)
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Cavity-Enhanced Optical Frequency Comb Spectroscopy of High-Temperature Water in a Flame
- 2015
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In: 2015 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO). - 9781557529688
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Conference paper (peer-reviewed)abstract
- 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.
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| 18. |
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| 19. |
- Khodabakhsh, Amir, et al.
(author)
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Fourier transform and Vernier spectroscopy using an optical frequency comb at 3-5.4 μm
- 2016
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In: Optics Letters. - 0146-9592 .- 1539-4794. ; 41:11, s. 2541-2544
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Journal article (peer-reviewed)abstract
- 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.
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| 20. |
- Khodabakhsh, Amir, et al.
(author)
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Fourier transform and vernier spectroscopy with a mid-infrared optical frequency comb
- 2016
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In: Light, energy and the environment. - : Optica Publishing Group (formerly OSA). - 9780960038046
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Conference paper (peer-reviewed)abstract
- We present a versatile frequency comb spectroscopy system based on a doubly resonant optical parametric oscillator tunable between 3-5.4 μm and two detection methods: a Fourier transform spectrometer and a continuous-filtering Vernier spectrometer.
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| 21. |
- Khodabakhsh, Amir, et al.
(author)
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Fourier-Transform-Based Noise-Immune Cavity-Enhanced Optical Frequency Comb Spectroscopy
- 2015
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In: 2015 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO). - 9781557529688
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Conference paper (peer-reviewed)abstract
- 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.
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| 22. |
- Khodabakhsh, Amir, 1983-, et al.
(author)
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Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator
- 2017
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In: Applied physics. B, Lasers and optics (Print). - : Springer. - 0946-2171 .- 1432-0649. ; 123
-
Journal article (peer-reviewed)abstract
- We present a continuous-filtering Vernier spectrometer operating in the 3.15–3.4 µm 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 × 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.
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| 23. |
- Khodabakhsh, Amir, et al.
(author)
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Near-infrared Fourier transform cavity-enhanced optical frequency comb spectroscopy
- 2014
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In: Fourier Transform Spectroscopy. - : OSA - The Optical Society. - 9780960038046 ; , s. 3-
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Conference paper (peer-reviewed)abstract
- Using Fourier transform-based cavity-enhanced optical frequency comb spectroscopy around 1.57 μm we measure high precision low pressure spectra of the 3v1+ v3 band of CO2 and high temperature H2O and OH spectra in a premixed methane/air flat flame.
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| 24. |
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| 25. |
- Lu, Chuang, et al.
(author)
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Cavity-Enhanced Frequency Comb Vernier Spectroscopy
- 2022
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In: Photonics. - : MDPI. - 2304-6732. ; 9:4
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Research review (peer-reviewed)abstract
- Vernier spectroscopy is a frequency comb-based technique employing optical cavities for filtering of the comb and for enhancement of the interaction length with the sample. Depending on the ratio of the cavity free spectral range and the comb repetition rate, the cavity transmits either widely spaced individual comb lines (comb-resolved Vernier spectroscopy) or groups of comb lines, called Vernier orders (continuous-filtering Vernier spectroscopy, CF-VS). The cavity filtering enables the use of low-resolution spectrometers to resolve the individual comb lines or Vernier orders. Vernier spectroscopy has been implemented using various near- and mid-infrared comb sources for applications ranging from trace gas detection to precision spectroscopy. Here, we present the principles of the technique and provide a review of previous demonstrations of comb-resolved and continuous-filtering Vernier spectroscopy. We also demonstrate two new implementations of CF-VS: one in the mid-infrared, based on a difference frequency generation comb source, with a new and more robust detection system design, and the other in the near-infrared, based on a Ti:sapphire laser, reaching high sensitivity and the fundamental resolution limit of the technique.
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