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1. Fabry–Perot Effect Suppression in Gas Cells Used in THz Absorption Spectrometers. Experimental Verification

Author

George K. Raspopin, Alexey V. Borisov, Arnaud Cuisset, Francis Hindle, Semyon V. Yakovlev, and Yury V. Kistenev

Subjects
amplitude modulation spectroscopy, Fabry–Perot effects, frequency modulation spectroscopy, terahertz gas absorption spectroscopy, Chemical technology, TP1-1185
Abstract

A standard measuring gas cell used in absorption spectrometers is a cylinder enclosed by two transparent windows. The Fabry–Perot effects caused by multiple reflections of terahertz waves between these windows produce significant variations in the transmitted radiation intensity. Therefore, the Fabry–Perot effects should be taken into account to correctly measure absorption spectra in Bouguer law-based absorption spectroscopy. One approach to reducing the Fabry–Perot effects is based on inserting an additional external movable window with the standard measuring gas cell. This was proposed and numerically analyzed in our previous work. This paper is aimed at the experimental validation of this method when using amplitude modulation (AM) spectroscopy. Also, a comparison of the efficiency of reducing the Fabry–Perot effects using this method is experimentally compared to frequency modulation spectroscopy. The latter was shown to effectively reduce the Fabry–Perot effects compared to AM spectroscopy with the standard measuring gas cell, and the use of the external movable window was shown to further improve the elimination of Fabry–Perot effects.

Published
2024
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2. Optically Pumped Terahertz Molecular Laser: Gain Factor and Validation up to 5.5 THz

Author

Marie-Hélène Mammez, Zachary Buchanan, Olivier Pirali, Marie-Aline Martin-Drumel, Joan Turut, Guillaume Ducournau, Sophie Eliet, Francis Hindle, Stefano Barbieri, Pascale Roy, Gaël Mouret, and Jean-François Lampin

Subjects
ammonia, mid-infrared quantum cascade laser pump, optical gain factor, THz molecular laser, Applied optics. Photonics, TA1501-1820, Optics. Light, QC350-467
Abstract

Quantum cascade laser‐pumped terahertz (THz) gas lasers are at the edge of revolutionizing THz science where powerful yet tunable sources have long been lacking. Maybe one of the last remaining drawbacks to a wider use of these instruments lies in the lack of available databases of potentially lasing transitions for users. A new figure of merit, the molecular gain factor is proposed, that allows to discriminate transitions by their lasing potential. Using this factor, catalogs of THz laser lines of ammonia, both 14NH3 and 15NH3, up to 10 THz are reported. Demonstration of the use of these two catalogs, and of the pertinence of the molecular gain factor, is made by experimentally observing 32 laser lines of 14NH3 and 5 lines of 15NH3 up to 5.5 THz. Prospects to generalize the use of this molecular gain factor to a wide range of molecules are discussed.

Published
2022
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3. Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths

Author

Arnaud Cuisset, Francis Hindle, Gaël Mouret, Robin Bocquet, Jonas Bruckhuisen, Jean Decker, Anastasiia Pienkina, Cédric Bray, Éric Fertein, and Vincent Boudon

Subjects
greenhouse gases, terahertz, long interaction path-lengths, rotational spectroscopy, trace gas monitoring, Technology, Engineering (General). Civil engineering (General), TA1-2040, Biology (General), QH301-705.5, Physics, QC1-999, Chemistry, QD1-999
Abstract

Even if on-board mm-wave/THz heterodyne receivers have been developed to measure greenhouse gases (GHGs) atmospheric profiles, rotational spectroscopy rests under-exploited for their monitoring unlike IR rovibrational spectroscopy. The present study deals with the ability of THz spectroscopy using long interaction path-lengths for GHG laboratory investigations. High-resolution THz signatures of non-polar greenhouse molecules may be observed by probing very weak centrifugal distortion induced rotational transitions. To illustrate, new measurements on CH4 and CF4 have been carried out. For CH4, pure rotational transitions, recorded by cw-THz photomixing up to 2.6 THz in a White type cell adjusted to 20 m, have allowed to update the methane line list of atmospheric databases. Concerning CF4, Fabry-Perot THz absorption spectroscopy with a km effective pathlength was required to detect line intensities lower than 10−27 cm−1/(moleccm−2). Contrary to previous synchrotron-based FT-FIR measurements, the tetrahedral splitting of CF4 THz lines is fully resolved. Finally, quantitative measurements of N2O and O3 gas traces have been performed in an atmospheric simulation chamber using a submm-wave amplified multiplier chain coupled to a Chernin type multi-pass cell on a 200 m path-length. The THz monitoring of these two polar GHGs at tropospheric and stratospheric concentrations may be now considered.

Published
2021
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4. Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy

Author

Guillaume Ducournau, Tahsin Akalin, Robin Bocquet, Emilien Peytavit, Karine Blary, Jean-François Lampin, Arnaud Cuisset, Gael Mouret, Chun Yang, and Francis Hindle

Subjects
THz, photomixing, high-resolution spectroscopy, gas phase, Chemical technology, TP1-1185
Abstract

A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements.

Published
2009
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6. Dielectric Lined Waveguides for Low Loss Millimeter Wave and Terahertz Transmission

Author

Kyle Thackston, John Doane, James Anderson, Mhamad Chrayteh, and Francis Hindle

Abstract

By coating the inside of an overmoded, smooth wall metallic waveguide with a thin dielectric layer, one can obtain similar boundary conditions to corrugated waveguides and achieve extremely low transmission loss propagating the HE11 mode. As presented here, dielectric lined waveguides are a cost-effective alternative to corrugated waveguides for broadband microwave transmission, particularly at frequencies above 300 GHz. A theoretical model provides an analytic method for computing attenuation. The propagation mode of a prototype dielectric lined waveguide is characterized using low power transmission measurements to analyze the beam radiated from the waveguide aperture. Results indicate HE11 mode purity of approximately 98%. Furthermore, we quantified attenuation with low power Fabry-Perot measurements, verifying low loss performance of the experimental prototype. These results demonstrate that dielectric lined waveguides could have applications in many fields demanding low attenuation millimeter and terahertz transmission, such as radar, high-frequency communication systems, THz dynamic nuclear polarization, and electron cyclotron heating in magnetically confined fusion experiments.

Published
2022
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9. Terahertz time domain spectroscopy data processing: analysing uncertainties to push boundaries

Author

Mélanie Lavancier, Sophie Eliet Barois, Elsa Denakpo, Juliette Vlieghe, Nabil Vindas, Francis Hindle, Arnaud Cuisset, Romain Peretti, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL), Photonique THz - IEMN (PHOTONIQUE THZ - IEMN), Université catholique de Lille (UCL)-Université catholique de Lille (UCL)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Plateforme de Caractérisation Multi-Physiques - IEMN (PCMP - IEMN), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), no information, and PCMP CHOP

Subjects
[SPI]Engineering Sciences [physics], Terahertz, Time Domain Spectroscopy, super-resolution, signal processing
Abstract

International audience; Terahertz spectroscopy provides information on the motion of the charges in a sample at a picosecond scale. To recover this information from Terahertz time-domain spectroscopy (THz-TDS), one usually extracts the experimental refractive index then fits these curves. This approach suffers from several limitations, among them the difficulty to compare models of motions, provide the error bar associated with the extracted magnitude and a resolution limitation coming from the Fourier criteria of the fast Fourier transform. By adopting a Bayesian framework taking into account the experimental uncertainties and directly fitting the time-domain trace, we overcame these limitations. When correlated and epistemic uncertainties/noise are present, the algorithm considers its distribution as part of the data to fit and can mistake it for real physical features. Hence, it offers poor discrimination between good models and bad ones. After a thorough analysis of the experimental noise, we developed a preprocessing software removing epistemic noise on the time traces and providing an estimate of the noise correlation matrix (generalization of the standard deviation). It allows the proper weighting of the error function of the fit using these uncertainties and therefore the derivation of the Akaike information criteria, a metric enabling to calculate the most probable model from a set of models one wants to compare. In addition, by being in the time domain we avoid the Fourier criteria for the resolution and thus could get information on experimental lines down to 30 MHz with a commercial THz-TDS system.

Published
2022
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11. Thz Cavity Ring-Down Quantitative Gas Phase Spectroscopy

Author

Coralie Elmaleh, Fabien Simon, Jean Decker, Julien Dumont, Fabrice Cazier, Marc Fourmentin, Robin Bocquet, Arnaud Cuisset, Gaël Mouret, and Francis Hindle

Subjects
History, Polymers and Plastics, Business and International Management, Industrial and Manufacturing Engineering, Analytical Chemistry
Published
2022
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12. MULTICHARME: A modified Chernin-type multi-pass cell designed for IR and THz long-path absorption measurements in the CHARME atmospheric simulation chamber

Author

Weixiong Zhao, Jean Decker, Arnaud Cuisset, Eric Fertein, Pierre Kulinski, Cécile Coeur, Robin Bocquet, Nicolas Houzel, Gaël Mouret, Guillaume Dhont, Francis Hindle, Jonas Bruckhuisen, and Bo Fang

Subjects
Absorbance, Wavelength, Materials science, Optics, Atmospheric pressure, Terahertz radiation, business.industry, Excited state, Rotational spectroscopy, Rotational–vibrational spectroscopy, business, Absorption (electromagnetic radiation)
Abstract

We have developed MULTICHARME, a modified Chernin-type multi-pass cell especially designed for IR and THz long-path absorption measurements in the CHamber for Atmospheric Reactivity and Metrology of the Environment (CHARME). By measuring the output power using a near-IR diode-laser and a THz amplified multiplication chain, we have established that the effective reflectivity of MULTICHARME is better than 94 % over approximately three decades of frequency. Absorption measurements of N2O have been performed by probing highly excited rovibrational transitions in the near-IR and ground state rotational transitions at submillimeter wavelengths. In each case the linearity of the absorbance with the path lengths was verified. Finally, we demonstrate that THz spectroscopy is able to study the isotopic composition of greenhouse polar gases such as N2O and to absolutely quantify stable (N2O) and reactive (O3) species at trace levels. At low pressure the ozone concentration was continuously monitored and its decay characterized. The deduced ozone lifetime of 3.4 ± 0.1 h is shorter compared with previous measurements performed in CHARME at atmospheric pressure. For the first time, the ability of THz rotational spectroscopy to monitor, with a very high degree of selectivity, stable and reactive polar compounds at trace level in an atmospheric simulation chamber is demonstrated. However, the sensitivity of the THz monitoring needs to be improved to reach atmospheric trace levels. For this purpose, it is necessary to fully understand the origin of the observed baseline variations caused by the complex multiple standing waves present in MULTICHARME.

Published
2021
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14. Cavity based high resolution THz spectrometer

Author

Coralie Elmaleh, Marc Fourmentin, Anastasiia Pienkina, Arnaud Cuisset, Robin Bocquet, Francis Hindle, Gaël Mouret, Jonas Bruckhuisen, and Fabien Simon

Subjects
Materials science, Spectrometer, business.industry, Terahertz radiation, Physics::Optics, Finesse, Optics, Path length, Attenuation coefficient, Physics::Accelerator Physics, Photonics, business, Absorption (electromagnetic radiation), Sensitivity (electronics)
Abstract

A high finesse cavity operating around 620 GHz has been constructed to improve the sensitivity limit for the measurement of weakly absorbing gases. An effective path length of 1 km is achieved significantly improving the available sensitivity. The measurement of the cavity decay time allows the quantification of the absorption coefficient.

Published
2021
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15. New laser lines from a terahertz ammonia laser pumped by a quantum cascadelaser and their application to high-resolution spectroscopy

Author

Z. Buchanan, Guillaume Ducournau, S. Eliet, S. Barbieri, Gaël Mouret, Marie-Aline Martin-Drumel, Francis Hindle, D. Mammez, J-F. Lampin, Olivier Pirali, T. S. Hearne, Pascal Roy, Marie-Hélène Mammez, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université catholique de Lille (UCL)-Université catholique de Lille (UCL), Photonique THz - IEMN (PHOTONIQUE THZ - IEMN), Université catholique de Lille (UCL)-Université catholique de Lille (UCL)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Groupe de spectrométrie moléculaire et atmosphérique (GSMA), Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), University of California [Davis] (UC Davis), University of California (UC), Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Plateforme de Caractérisation Multi-Physiques - IEMN (PCMP - IEMN), Ligne AILES, Synchrotron SOLEIL, no information, PCMP CHOP, Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), University of California, and Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Heterodyne, Materials science, Spectrometer, quantum cascade lasers, Terahertz radiation, business.industry, submillimetre wave lasers, Local oscillator, Physics::Optics, Laser, ammonia, law.invention, [SPI]Engineering Sciences [physics], law, Optoelectronics, Figure of merit, Physics::Atomic Physics, Quantum cascade laser, business, Spectroscopy, Astrophysics::Galaxy Astrophysics, optical pumping
Abstract

oral; International audience; We present an experimental investigation into new continuous-wave laser lines from a terahertz ammonia laser pumped by a quantum cascade laser. These lines were investigated with the help of a molecular figure of merit calculated from spectroscopic parameters available in molecular databases. We also demonstrate the use of this laser as a local oscillator in a heterodyne high-resolution spectrometer between 1 and 3.4 THz.

Published
2021
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16. Super resolution of A 400 MHz rotational line doublet with a TDS using a 850 ps long delay line

Author

Francis Hindle, Romain Peretti, Arnaud Cuisset, Jean-François Lampin, S. Eliet, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Plateforme de Caractérisation Multi-Physiques - IEMN (PCMP - IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS), Photonique THz - IEMN (PHOTONIQUE THZ - IEMN), The authors want to thanks the 'Région Hauts-de-France' for the International Chair of Excellence 'ThOTroV. Part of the work was done in the CHOP platform., PCMP CHOP, Université catholique de Lille (UCL)-Université catholique de Lille (UCL), Université catholique de Lille (UCL)-Université catholique de Lille (UCL)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), and Université du Littoral Côte d'Opale (ULCO)

Subjects
Physics, Terahertz radiation, business.industry, terahertz wave spectra, Line length, Reconstruction algorithm, CMOS integrated circuits, image reconstruction, terahertz spectroscopy, Superresolution, biomedical ultrasonics, [SPI.TRON]Engineering Sciences [physics]/Electronics, catheters, Optics, Limit (music), [SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic, Thz time domain spectroscopy, Spectral resolution, [SPI.NANO]Engineering Sciences [physics]/Micro and nanotechnologies/Microelectronics, business, delay lines, image resolution, Line (formation)
Abstract

oral; International audience; We improved the spectral resolution of THz time domain spectroscopy beyond the limit given by the delay line length. The constraint reconstruction algorithm used successfully depicted the 1.21 THz NH 3 doublet separated by ~400MHz in experimental data despite the 1.2 GHz delay line limitation.

Published
2021
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18. OPTICALLY-PUMPED AMMONIA TERAHERTZ LASER UP TO 5.5 THz

Author

Sophie Eliet, Jean-François Lampin, Francis Hindle, Gaël Mouret, Pascal Roy, Marie-Hélène Mammez, Olivier Pirali, Stefano Barbieri, and Marie-Aline Martin-Drumel

Subjects
Ammonia, chemistry.chemical_compound, Materials science, chemistry, Terahertz radiation, business.industry, Far-infrared laser, Optoelectronics, business
Published
2021
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19. THZ FABRY-PEROT SPECTROMETER

Author

Gaël Mouret, Francis Hindle, Coralie Elmaleh, Arnaud Cuisset, Anastasiia Pienkina, Fabien Simon, and Robin Bocquet

Subjects
Optics, Materials science, Spectrometer, business.industry, Terahertz radiation, business, Fabry–Pérot interferometer
Published
2021
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20. THE HEROES OF TERAHERTZ SYNCHROTRON SPECTROSCOPY

Author

Pascal Roy, Dominique Mammez, Francis Hindle, Olivier Pirali, Jean-François Lampin, Marie-Aline Martin-Drumel, Gaël Mouret, Thomas Hearne, and Marie-Hélène Mammez

Subjects
Materials science, law, business.industry, Terahertz radiation, Optoelectronics, business, Spectroscopy, Synchrotron, law.invention
Published
2021
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21. AN HETERODYNE SPECTROMETER FOR TERAHERTZ SPECTROSCOPY

Author

Dominique Mammez, Marie-Aline Martin-Drumel, Jean-François Lampin, Francis Hindle, Thomas Hearne, Sophie Eliet, Gaël Mouret, Olivier Pirali, and Marie-Hélène Mammez

Subjects
Heterodyne, Materials science, Optics, Spectrometer, business.industry, business, Terahertz spectroscopy and technology
Published
2021
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22. Broadband super-resolution Terahertz Time domain spectroscopy applied to Gas analysis

Author

Sophie Eliet, Francis Hindle, Romain Peretti, Arnaud Cuisset, Jean-Francois Lampin, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Plateforme de Caractérisation Multi-Physiques - IEMN (PCMP - IEMN), Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Photonique THz - IEMN (PHOTONIQUE THZ - IEMN), PCMP CHOP, Université catholique de Lille (UCL)-Université catholique de Lille (UCL), Université catholique de Lille (UCL)-Université catholique de Lille (UCL)-Centrale Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), no funding indication, Institut d’Électronique, de Microélectronique et de Nanotechnologie (IEMN) - UMR 8520 (IEMN), Ecole Centrale de Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Ecole Centrale de Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Ecole Centrale de Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA)-Ecole Centrale de Lille-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-JUNIA (JUNIA), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 [IEMN], Plateforme de Caractérisation Multi-Physiques - IEMN [PCMP - IEMN], Laboratoire de Physico-Chimie de l'Atmosphère [LPCA], and Photonique THz - IEMN [PHOTONIQUE THZ - IEMN]

Subjects
Materials science, Terahertz radiation, [PHYS.PHYS.PHYS-BIO-PH]Physics [physics]/Physics [physics]/Biological Physics [physics.bio-ph], FOS: Physical sciences, Physics::Optics, Terahertz gas spectroscopy, Applied Physics (physics.app-ph), Measure (mathematics), Spectral line, Optics, Broadband, Physics - Biological Physics, Time domain, Electrical and Electronic Engineering, Terahertz time-domain spectroscopy, Spectroscopy, super resolution spectroscopy, [PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics], Radiation, business.industry, Resolution (electron density), Physics - Applied Physics, Biological Physics (physics.bio-ph), [SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic, Time domain spectroscopy, business, Optics (physics.optics), Physics - Optics
Abstract

Terahertz (THz) Time domain spectroscopy (THz-TDS) is a broadband spectroscopic technique spreading its uses in multiple fields: in science from material science to biology, in industry where it measures the thickness of a paint layer during the painting operation. Using such practical commercial apparatus with broad spectrum for gas spectroscopy could be a major asset for air quality monitoring and tracking of atmospheric composition. However, gas spectroscopy needs high resolution and the usual approach in THz-TDS, where the recorded time trace is Fourier transform, suffers from resolution limitation due to the size of the delay line in the system. In this letter, we introduce the concept of constraint reconstruction for super-resolution spectroscopy based on the modeling of the spectroscopic lines in a sparse spectrum. Light molecule gas typically shows sparse and narrow lines on a broad spectrum and we propose an algorithm reconstructing these lines with a resolution improvement of 10 the ultimate resolution reachable by the apparatus. We envision the proposed technique to lead to broadband, selective, rapid and cheap gas monitoring applications.

Published
2021
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23. Super resolution spectroscopy for THz-TDS: application to gas spectroscopy

Author

Meriem Mouelhi, J.-F. Lampin, Romain Peretti, Arnaud Cuisset, S. Eliet, Francis Hindle, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Photonique THz - IEMN (PHOTONIQ THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), PCMP CHOP, and Photonique THz - IEMN (PHOTONIQUE THz - IEMN)

Subjects
Materials science, 010304 chemical physics, Terahertz radiation, Resolution (electron density), Reconstruction algorithm, 01 natural sciences, Spectral line, Computational physics, 010309 optics, symbols.namesake, [SPI]Engineering Sciences [physics], Fourier transform, 0103 physical sciences, symbols, Time domain, Spectroscopy, Line (formation)
Abstract

International audience; Time Domain Spectroscopy resolution is usually limited by the Fourier Heisenberg criteria (FHC) coming from the length of the delay line. We will present a method to exploit THz-TDS spectra providing a 10-fold resolution improvement reaching 120 MHz for width measurements. These results were obtained by modeling and the implementation of a constraint reconstruction algorithm. We tested the methods on temporal traces from gaseous NH3 and were in very good agreement with the values from literature [1] down to a pressure of 5 mbar.

Published
2020
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24. Continuous-wave lines up to 5.5 THz from the ammonia laser pumped by a quantum cascade laser

Author

J-F. Lampin, Olivier Pirali, S. Barbieri, Marie-Aline Martin-Drumel, Martin Mičica, Gaël Mouret, S. Eliet, Francis Hindle, Zachary Buchanan, Marie-Hélène Mammez, Pascal Roy, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Photonique THz - IEMN (PHOTONIQ THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), University of California [Davis] (UC Davis), University of California, Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), PCMP CHOP, Photonique THz - IEMN (PHOTONIQUE THz - IEMN), University of California (UC), and ANR-16-CE30-0020,HEROES,Conception de détecteurs heterodyne optimisés pour les sources synchrotron(2016)

Subjects
Materials science, business.industry, Terahertz radiation, External cavity, Physics::Optics, Laser, 7. Clean energy, 3. Good health, law.invention, [SPI]Engineering Sciences [physics], law, Optoelectronics, Continuous wave, Physics::Atomic Physics, Stimulated emission, business, Quantum cascade laser
Abstract

International audience; We have recently demonstrated a continuous wave molecular laser emission based on ammonia optically pumped by a quantum cascade laser. We report here new results obtained with an optimized laser prototype pumped by a tunable external cavity quantum cascade laser. New laser lines with high output power are demonstrated at frequencies between 1 and 5.5 THz.

Published
2020
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25. Characterization of the Observed Electric Field and Molecular Relaxation Times for Millimeter-Wave Chirped Pulse Instrumentation

Author

Gaël Mouret, Daniele Fontanari, Kevin M. Hickson, Guillaume Dhont, Francis Hindle, Arnaud Cuisset, Robin Bocquet, Cédric Bray, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Institut des Sciences Moléculaires (ISM), Université Montesquieu - Bordeaux 4-Université Sciences et Technologies - Bordeaux 1-École Nationale Supérieure de Chimie et de Physique de Bordeaux (ENSCPB)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and Université Montesquieu - Bordeaux 4-Université Sciences et Technologies - Bordeaux 1-École Nationale Supérieure de Chimie et de Physique de Bordeaux (ENSCPB)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.ASTR.IM]Physics [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], Rabi frequency, 01 natural sciences, Coherent transients, Article, 010309 optics, Optics, Electric field, Polarization, 0103 physical sciences, Classical electromagnetism, Chirped pulse, Electrical and Electronic Engineering, Instrumentation, ComputingMilieux_MISCELLANEOUS, 010302 applied physics, Physics, [PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics], Radiation, business.industry, Relaxation time, Condensed Matter Physics, Polarization (waves), Bloch equations, Amplitude, Millimeter, business, Microwave
Abstract

International audience; In a chirped pulse experiment, the strength of the signal level is proportional to the amplitude of the electric field, which is weaker in the millimeter or submillimeter region than in the microwave region. Experiments in the millimeter region thus require an optimization of the coupling between the source and the molecular system and a method to estimate the amplitude of the electric field as seen by the molecular system. We have developed an analytical model capable of reproducing the coherent transient signals obtained with a millimeter wave chirped pulse setup operated in a monochromatic pulse mode. The fit of the model against the experimental data allowed access to the amplitude of the electric field and, as a byproduct, to the molecular relaxation times T 1 and T 2 .

Published
2020
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27. Self and N2 broadening coefficients of H2S probed by submillimeter spectroscopy: Comparison with IR measurements and semi-classical calculations

Author

Francis Hindle, C. Jellali, Robin Bocquet, Hassen Aroui, S. Galalou, Arnaud Cuisset, F. Rohart, Gaël Mouret, Meriem Mouelhi, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523 (PhLAM), and Université de Lille-Centre National de la Recherche Scientifique (CNRS)

Subjects
Voigt profile, Physics, [PHYS]Physics [physics], Radiation, 010504 meteorology & atmospheric sciences, Spectrometer, Terahertz radiation, Broadening coefficients, H2S, Rotational–vibrational spectroscopy, Semi-classical calculation, 01 natural sciences, Submillimeter-wave spectroscopy, Atomic and Molecular Physics, and Optics, Spectral line, Formalism (philosophy of mathematics), Intermolecular interaction, Rotational dependencies, Atomic physics, Spectroscopy, Speed-dependence effects, 0105 earth and related environmental sciences
Abstract

International audience; High-resolution lines of H2S self-perturbed and perturbed by N2 have been recorded at room temperature using a frequency modulated THz spectrometer at pressures of H2S ranging from 0.1 to 1.0 mbar. A non-linear least squares fitting of these spectra has been performed to retrieve self- and N2-broadening coefficients of pure rotational transitions (mainly in the RQ sub-branch) of H2S in the submillimeter region. We show that the lineshapes are well reproduced by the Speed-Dependent Voigt profile accounting for the speed dependence of relaxation rates which display linear pressure dependencies. Using the Robert and Bonamy formalism, these coefficients were calculated, showing the need to account for all contributions of the intermolecular interaction for N2-broadening. The calculated coefficients are consistent with the measured data and the average accuracy of the line parameters has been estimated to be about 5%. The observed J″ and Ka″ rotational dependences have been analyzed using an empirical model and compared to previous rovibrational studies in the ν2 fundamental band. In our study the self- and the N2-broadening coefficients decreases monotonically with Ka″ and J″, respectively.

Published
2020
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28. Full Conformational Landscape of 3-Methoxyphenol Revealed by Room Temperature mm-wave Rotational Spectroscopy Supported by Quantum Chemical Calculations

Author

Francis Hindle, Arnaud Cuisset, Daniele Fontanari, Robin Bocquet, Guillaume Dhont, Cédric Bray, Gaël Mouret, Atef Jabri, and Anthony Roucou

Subjects
Quantitative Biology::Biomolecules, Materials science, 010304 chemical physics, 010402 general chemistry, 01 natural sciences, Molecular physics, Atomic and Molecular Physics, and Optics, 0104 chemical sciences, Excited state, 0103 physical sciences, Polar, Molecule, Rotational spectroscopy, Physics::Chemical Physics, Physical and Theoretical Chemistry, Ground state, Conformational isomerism, Excitation, Microwave
Abstract

Room temperature millimeter-wave rotational spectroscopy supported by high level of theory calculations have been employed to fully characterise the conformational landscape of 3-Methoxyphenol, a semi-volatile polar oxygenated aromatic compound precursor of secondary organic aerosols in the atmosphere arising from biomass combustion. While previous rotationally-resolved spectroscopic studies in the microwave and in the UV domains failed to observe the complete conformational landscape, the 70-330 GHz rotational spectrum measured in this study reveals the ground state rotational signatures of the four stable conformations theoretically predicted. Moreover, rotational transitions in the lowest energy vibrationally excited states were assigned for two conformers. While the inertial defect of methoxyphenol does not significantly change between conformers and isomers, the excitation of the methoxy out-of-plane bending is the main contribution to the non-planarity of the molecule.

Published
2018
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29. Spectral lines of methane measured up to 2.6 THz at sub-MHz accuracy with a CW-THz photomixing spectrometer: Line positions of rotational transitions induced by centrifugal distortion

Author

Gaël Mouret, Francis Hindle, Cédric Bray, Robin Bocquet, Arnaud Cuisset, and Vincent Boudon

Subjects
Physics, Radiation, 010504 meteorology & atmospheric sciences, Spectrometer, business.industry, 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, Atomic and Molecular Physics, and Optics, Hot band, Spectral line, Photomixing, Frequency comb, Optics, Distortion, Rotational spectroscopy, HITRAN, Atomic physics, 0210 nano-technology, business, Spectroscopy, 0105 earth and related environmental sciences
Abstract

Several Doppler-limited rotational transitions of methane induced by centrifugal distortion have been measured with an unprecedented frequency accuracy using a THz photomixing synthesizer based on a frequency comb. Compared to previous synchrotron based FT-Far-IR measurements of Boudon et al. (Ref. [1] ), the accuracy of the line frequency measurements is improved by one order of magnitude; this yields a corresponding increase of two orders of magnitude to the weighting of these transitions in the global fit. The rotational transitions in the ν 4 ← ν 4 hot band are measured for the first time by the broad spectral coverage of the photomixing CW-THz spectrometer providing access up to R(5) transitions at 2.6 THz. The new global fit including the present lines has been used to update the methane line list of the HITRAN database. Some small, but significant variations of the parameter values are observed and are accompanied by a reduction of the 1- σ uncertainties on the rotational ( B 0 ) and centrifugal distortion ( D 0 ) constants.

Published
2017
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30. Chirped Pulse Spectrometer Operating at 200 GHz

Author

Cédric Bray, Gaël Mouret, Kevin M. Hickson, Robin Bocquet, Daniele Fontanari, Francis Hindle, Meriem Mouelhi, Arnaud Cuisset, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), and Université du Littoral Côte d'Opale (ULCO)

Subjects
Physics - Instrumentation and Detectors, Materials science, Instrumentation, FOS: Physical sciences, 02 engineering and technology, 01 natural sciences, 010309 optics, symbols.namesake, Optics, 0103 physical sciences, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], Electrical and Electronic Engineering, Radiation, Spectrometer, business.industry, Pulse duration, Linearity, Instrumentation and Detectors (physics.ins-det), 021001 nanoscience & nanotechnology, Condensed Matter Physics, Pulse (physics), Fourier transform, symbols, Rotational spectroscopy, 0210 nano-technology, business, Microwave
Abstract

International audience; The combination of electronic sources operating at high frequencies and modern microwave instrumentation has enabled the recent development of chirped-pulse spectrometers for the millimetre and THz bands. This type of instrument can operate at high resolution which is particularly suited to gas phase rotational spectroscopy. The construction of a chirped pulse spectrometer operating at 200 GHz is described in detail while attention is paid to the phase stability and the data accumulation over many cycles. Validation using carbonyl sulphide has allowed the detection limit of the instrument to be established as function of the accumulation. A large number of OCS transitions were identified using a 10 GHz chirped pulse and include the 6 most abundant isotopologues, the weakest line corresponding to the fundamental R(17) transition of 16 O 13 C 33 S with a line strength of 4.3 x 10-26 cm-1 /(molec.cm-2). The linearity of the system response for different degrees of data accumulation and transition line strength was confirmed over 4 orders of magnitudes. A simple analysis of the time domain data was demonstrated to provide the line broadening coefficient without the need for conversion by a Fourier transform. Finally, the pulse duration is discussed and optimal values are given for both Doppler limited and collisional regimes.

Published
2017
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31. CH3D photomixing spectroscopy up to 2.5 THz: New set of rotational and dipole parameters, first THz self-broadening measurements

Author

Gaël Mouret, Francis Hindle, Cédric Bray, Brian J. Drouin, Arnaud Cuisset, Robin Bocquet, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), and Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Physics, Radiation, 010504 meteorology & atmospheric sciences, Spectrometer, business.industry, Terahertz radiation, Rotational–vibrational spectroscopy, 01 natural sciences, Atomic and Molecular Physics, and Optics, Photomixing, Frequency comb, Dipole, Optics, 0103 physical sciences, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], Atomic physics, Spectroscopy, business, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Line (formation)
Abstract

Several previously unmeasured transitions of 12 CH 3 D have been recorded by a terahertz photomixing continuous-wave spectrometer up to Q R (10) branch at 2.5 THz. An improved set of rotational constants has been obtained utilizing a THz frequency metrology based on a frequency comb that achieved an averaged frequency position better than 150 kHz on more than fifty ground-state transitions. A detailed analysis of the measured line intensities was undertaken using the multispectrum fitting program and has resulted in a determination of new dipole moment parameters. Measurements at different pressures of the Q R (7) transitions provide the first determination of self-broadening coefficients from pure rotational CH 3 D lines. The THz rotational measurements are consistent with IR rovibrational data but no significant vibrational dependence of self-broadening coefficient may be observed by comparison.

Published
2017
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32. Spoilage of Salmon fillets as observed by THz waves

Author

Frank Devlieghere, Francis Hindle, Lotta Kuuliala, Robin Bocquet, Gaël Mouret, Arnaud Cuisset, Meriem Mouelhi, Mathias Vanwolleghem, Cédric Bray, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Photophysique Moléculaire (PPM), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Dynamique Interactions et Réactivité (LADIR), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Photonique THz - IEMN (PHOTONIQ THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Food Safety and Food Quality, Universiteit Gent = Ghent University [Belgium] (UGENT), European Project, Université du Littoral Côte d'Opale (ULCO), Photonique THz - IEMN (PHOTONIQUE THz - IEMN), Universiteit Gent = Ghent University (UGENT), and NONE FOUND.

Subjects
Monitoring, Measurement uncertainty, Hydrogen sulfide, Food spoilage, 02 engineering and technology, Frequency conversion, 01 natural sciences, [SPI]Engineering Sciences [physics], chemistry.chemical_compound, Thz waves, Bars, Food science, Fillet (mechanics), Spectroscopy, 010401 analytical chemistry, Time measurement, 021001 nanoscience & nanotechnology, 0104 chemical sciences, Trace gas, Tray, chemistry, 13. Climate action, Environmental science, 0210 nano-technology, Plastics
Abstract

International audience; The minimization of food wastage is an important challenge for today's society. Microbial activity during the storage of foodstuffs packed under a protective atmosphere, will lead to the generation of a complex mixture of trace gases that may be used as food spoilage indicators. THz waves have been used to monitor the generation of hydrogen sulfide in the headspace of a sealed plastic tray containing a salmon fillet portion.

Published
2019
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33. Free induction decay signals stimulated by photomixing

Author

Arnaud Cuisset, F. Bavedila, Francis Hindle, Robin Bocquet, J-F. Lampin, Emilien Peytavit, Cédric Bray, Guillaume Ducournau, Gaël Mouret, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Photonique THz - IEMN (PHOTONIQUE THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Institut des Sciences Moléculaires (Bordeaux), NONE FOUND, Photonique THz - IEMN (PHOTONIQ THz - IEMN), and Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Optical devices, Materials science, Physics::Optics, 02 engineering and technology, 01 natural sciences, Signal, Photomixing, [SPI]Engineering Sciences [physics], 0103 physical sciences, Chirp, Bars, Photoconducting materials, Stimulated emission, Astrophysics::Galaxy Astrophysics, 010302 applied physics, [PHYS]Physics [physics], Spectrometer, business.industry, Optical polarization, 021001 nanoscience & nanotechnology, Pulse (physics), Free induction decay, High-speed optical techniques, Optoelectronics, 0210 nano-technology, business
Abstract

International audience; An optically driven photoconductor device is electrically pulsed to provide a powerful pulse around 206 GHz. The pulsed radiation polarizes the OCS gas which emits a free induction decay signal that is observed after the end of the pulse. This is the first step in the development of a photonic chirped pulsed spectrometer.

Published
2019
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34. Broadband terahertz heterodyne spectrometer exploiting synchrotron radiation at sub-megahertz resolution

Author

Francis Hindle, Gaël Mouret, S. Eliet, Joan Turut, Pascal Roy, M.-A. Martin-mel, Olivier Pirali, Zachary Buchanan, J.-F. Lampin, Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Photonique THz - IEMN (PHOTONIQUE THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), and Photonique THz - IEMN (PHOTONIQ THz - IEMN)

Subjects
Heterodyne, Materials science, Spectrometer, business.industry, Terahertz radiation, Synchrotron radiation, Laser, Synchrotron, law.invention, [SPI]Engineering Sciences [physics], Optics, Beamline, law, Heterodyne detection, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], business
Abstract

International audience; A new spectrometer on the AILES beamline of the SOLEIL synchrotron facility to achieve sub-MHz resolution in the THz and far-IR regions is currently being developed. Thanks to a dedicated heterodyne detection by use of a new kind of molecular laser as local oscillator along with a Fast Fourier Transform Spectrometer, several pure rotation absorption lines of H 2 S and CH 3 OH around 1.073 THz have been recorded.

Published
2019
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35. Enlarging the Frontiers of Research in the IR/mm Range Using Synchrotron Radiation

Author

T. Souske, Gaël Mouret, Clement Evain, Benjamin Langerome, Francis Hindle, Marie-Aline Martin-Drumel, Francesco Capitani, Eléonore Roussel, J-B. Brubach, Marine Verseils, Sophie Eliet, Olivier Pirali, Thomas Timusk, C. Szwaj, Serge Bielawski, J.F. Lampin, Pascale Roy, Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Muséum national d'Histoire naturelle (MNHN)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de recherche pour le développement [IRD] : UR206-Centre National de la Recherche Scientifique (CNRS), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Photonique THz - IEMN (PHOTONIQUE THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Ligne AILES, Synchrotron SOLEIL, Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523 (PhLAM), Université de Lille-Centre National de la Recherche Scientifique (CNRS), NONE FOUND, Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de recherche pour le développement [IRD] : UR206-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS), Photonique THz - IEMN (PHOTONIQ THz - IEMN), and Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Brightness, Range (particle radiation), Materials science, Temperature measurement, Infrared, Terahertz radiation, business.industry, Optical films, [PHYS.PHYS.PHYS-ACC-PH]Physics [physics]/Physics [physics]/Accelerator Physics [physics.acc-ph], Synchrotron radiation, Reflectivity, Optical filters, Interferometry, Optics, Optical interferometry, Optical reflection, Frequency measurement, [PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph], business, Optical filter, ComputingMilieux_MISCELLANEOUS
Abstract

International audience; Abstract:Optical probes are among the most important techniques for characterizing new physical states induced by changes of temperature and/or pressure. In link with its high brightness and wide spectral coverage, infrared synchrotron radiation is ideally suited for such studies when the quantity of material to investigate is limited or when the system needs to be probed down to the sub mm domain.

Published
2019

36. BUILDING A DATABASE FOR QCL PUMPED FAR-IR LASERS

Author

Francis Hindle, Marie-Aline Martin-Drumel, Joan Turut, Olivier Pirali, Zachary Buchanan, Sophie Eliet, Jean-François Lampin, and Gaël Mouret

Subjects
Materials science, business.industry, law, Optoelectronics, business, Laser, law.invention
Published
2019
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38. Conformational landscape and inertial defect of methoxyphenol isomers studied by mm-wave spectroscopy and quantum chemistry calculations

Author

Cédric Bray, Atef Jabri, Daniele Fontanari, Arnaud Cuisset, Guillaume Dhont, Francis Hindle, Gaël Mouret, Anthony Roucou, Robin Bocquet, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), and Université du Littoral Côte d'Opale (ULCO)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Electron density, Materials science, 010304 chemical physics, General Physics and Astronomy, Rotational–vibrational spectroscopy, 010402 general chemistry, 7. Clean energy, 01 natural sciences, Quantum chemistry, Molecular physics, Spectral line, 0104 chemical sciences, [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, [SPI.ELEC]Engineering Sciences [physics]/Electromagnetism, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], 13. Climate action, Excited state, 0103 physical sciences, [SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic, Physical and Theoretical Chemistry, Spectroscopy, Ground state, Conformational isomerism
Abstract

International audience; Because methoxyphenols (MP) are emitted in significant quantities during biomass fires and contribute to the secondary organic aerosols formation which impacts the climate, their gas phase monitoring in the atmosphere is crucial and requires accurate rovibrational cross sections determined with a good knowledge of their ground state (GS) and vibrationally excited state (ES) molecular parameters. Therefore, the rotational spectra of the two isomers, 2-MP (guaïacol) and 4-MP (mequinol), have been measured in absorption and in emission at room temperature using a frequency multiplication chain and a mm-wave Fourier transform chirped-pulse spectrometer, respectively. Guided by quantum chemistry calculations, the conformational landscape has been characterised and the observation of only one rotamer in the spectra of 2-MP and 4-MP has been explained. For 2-MP, the most stable conformation is justified by an intramolecular O-H⋯OCH 3 hydrogen-bond which has been characterised by a topology analysis of the electron density. In a global fit including more than 30 000 line assignments, rotational and quartic centrifugal constants of the GS and the three lowest energy ES have been determined allowing to reproduce the millimeter-wave spectra at the experimental accuracy. The same work has been performed on the cis-rotamer of 4-MP highlighting some perturbations marring the fit quality for two vibrationally ES. Finally, the isomeric dependence of the negative inertial defect ∆I agrees with that of the lowest energy out of plane mode ν 45 , and the variation of ∆I with the degree of vibrational excitation allows a fine estimation of v 45 = 1 vibrational wavenumber.

Published
2019
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39. Broadband terahertz heterodyne spectrometer exploiting synchrotron radiation at megahertz resolution

Author

Gaël Mouret, Pascal Roy, Olivier Pirali, Joan Turut, Marie-Aline Martin-Drumel, Francis Hindle, Sophie Eliet, Zachary Buchanan, J.F. Lampin, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Photonique THz - IEMN (PHOTONIQ THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), University of California [Davis] (UC Davis), University of California, Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS), Université du Littoral Côte d'Opale (ULCO), Photonique THz - IEMN (PHOTONIQUE THz - IEMN), University of California (UC), French Renatech network, CPER Wavetech, Laboratoire d’excellence Physique Atomes Lumière Matière, Funding. This project received fundings from the Agence Nationale de la Recherche (ANR) (HEROES, ANR-16-CE30-0020-00), partial fundings from the LABoratoire d’EXcellence PALM (University Paris-Saclay) and from the SATT-Nord 'TERAPOMPE' project., Acknowledgment. The authors acknowledge SOLEIL for provision of synchrotron radiation under beamtime proposal 20180684 and we would like to thank J.-B. Brubach and K.Raddler for technical assistance. ZSB acknowledges support from the Chateaubriand Fellowship of the Office for Science & Technology of the Embassy of France in the United States., and ANR-16-CE30-0020,HEROES,Conception de détecteurs heterodyne optimisés pour les sources synchrotron(2016)

Subjects
Heterodyne, [PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics], Materials science, Spectrometer, business.industry, Terahertz radiation, Local oscillator, Synchrotron radiation, 02 engineering and technology, 021001 nanoscience & nanotechnology, Laser, 7. Clean energy, 01 natural sciences, Atomic and Molecular Physics, and Optics, law.invention, 010309 optics, symbols.namesake, Optics, law, 0103 physical sciences, symbols, 0210 nano-technology, business, Quantum cascade laser, Doppler effect
Abstract

International audience; A new spectrometer allowing both high resolution and broadband coverage in the terahertz (THz) domain is proposed. This instrument exploits the heterodyne technique between broadband synchrotron radiation and a quantum cascade laser (QCL) based molecular THz laser that acts as the local oscillator (LO). Proof of principle for exploitation for spectroscopy is provided by the recording of molecular absorptions of hydrogen sulfide (H 2 S) and methanol (CH 3 OH) around 1.073 THz. Ultimately, the spectrometer will enable to cover the 1-4 THz region in 5 GHz windows at Doppler resolution.

Published
2019
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40. Terahertz Frequency-Domain Spectroscopy of Low-Pressure Acetonitrile Gas by a Photomixing Terahertz Synthesizer Referenced to Dual Optical Frequency Combs

Author

Takeo Minamikawa, Takeshi Yasui, Francis Hindle, Tetsuo Iwata, Yasuhiro Mizutani, Hiroto Kimura, Hirotsugu Yamamoto, Kenta Hayashi, Kaoru Minoshima, Yi-Da Hsieh, and Hajime Inaba

Subjects
Frequency synthesizer, Radiation, Materials science, business.industry, Terahertz radiation, 02 engineering and technology, Frequency standard, 021001 nanoscience & nanotechnology, Condensed Matter Physics, Laser, 01 natural sciences, Photodiode, law.invention, 010309 optics, Photomixing, Nuclear magnetic resonance, law, 0103 physical sciences, Optoelectronics, Frequency offset, Electrical and Electronic Engineering, 0210 nano-technology, business, Spectroscopy, Instrumentation
Abstract

A terahertz (THz) frequency synthesizer based on photomixing of two near-infrared lasers with a sub-THz to THz frequency offset is a powerful tool for spectroscopy of polar gas molecules due to its broad spectral coverage; however, its frequency accuracy and resolution are relatively low. To tune the output frequency continuously and widely while maintaining its traceability to a frequency standard, we developed a photomixing THz synthesizer phase-locked to dual optical frequency combs (OFCs). While the phase-locking to dual OFCs ensured continuous tuning within a spectral range of 120 GHz, in addition to the traceability to the frequency standard, use of a broadband uni-traveling carrier photodiode for photomixing enabled the generation of CW-THz radiation within a frequency range from 0.2 to 1.5 THz. We demonstrated THz frequency-domain spectroscopy of gas-phase acetonitrile CH3CN and its isotope CH3 13CN in the frequency range of 0.600–0.720 THz using this THz synthesizer. Their rotational transitions were assigned with a frequency accuracy of 8.42 × 10−8 and a frequency resolution of 520 kHz. Furthermore, the concentration of the CH3CN gas at 20 Pa was determined to be (5.41 ± 0.05) × 1014 molecules/cm3 by curve fitting analysis of the measured absorbance spectrum, and the mixture ratio of the mixed CH3CN/CH3 13CN gas was determined to be 1:2.26 with a gas concentration of 1014–1015 molecules/cm3. The developed THz synthesizer is highly promising for high-precision THz-FDS of low-pressure molecular gases and will enable the qualitative and quantitative analyses of multiple gases.

Published
2016
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41. Adaptive-sampling near-Doppler-limited terahertz dual-comb spectroscopy with a free-running single-cavity fiber laser

Author

Francis Hindle, Takahiko Mizuno, Takeshi Yasui, Takeo Minamikawa, Zheng Zheng, Kazuki Nitta, Xin Zhao, and Jie Chen

Subjects
Materials science, 010504 meteorology & atmospheric sciences, business.industry, Terahertz radiation, Physics::Optics, General Medicine, Laser, 01 natural sciences, law.invention, 010309 optics, symbols.namesake, law, Fiber laser, 0103 physical sciences, symbols, Optoelectronics, Spectral resolution, business, Spectroscopy, Absorption (electromagnetic radiation), Doppler effect, Ultrashort pulse, 0105 earth and related environmental sciences
Abstract

Mode-resolved dual-comb spectroscopy (DCS) is an emerging spectroscopic tool with the potential to simultaneously achieve a broad spectral coverage and ultrahigh spectral resolution in terahertz (THz) spectroscopy. However, the need for two independently stabilized ultrafast lasers significantly hampers the potential application of DCS techniques. In this article, we demonstrate mode-resolved DCS in the THz region based on a free-running single-cavity dual-comb fiber laser with adaptive sampling. Low-pressure spectroscopy of acetonitrile gas with absorption features approaching the Doppler limit is demonstrated by comb-mode-resolved measurements with a spectral sampling spacing of 48.8 MHz, a spectral resolution of less than 5 MHz and a signal-to-noise ratio of ~50 dB. The successful demonstration of the proposed method clearly indicates the great potential for the realization of low-complexity, MHz-resolution THz spectroscopy instrumentation.

Published
2020
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42. Corrigendum to ‘CH3D photomixing spectroscopy up to 2.5 THz: new set of rotational and dipole parameters, first THz self-broadening measurements’ [Journal of Quantitative Spectroscopy and Radiative Transfer 189 (2017) 198–205]

Author

Gaël Mouret, Robin Bocquet, Francis Hindle, Cédric Bray, Arnaud Cuisset, and Brian J. Drouin

Subjects
Photomixing, Physics, Dipole, Radiation, Terahertz radiation, Radiative transfer, Atomic physics, Spectroscopy, Atomic and Molecular Physics, and Optics
Published
2020
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43. Monitoring of food spoilage by high resolution THz analysis

Author

Mathias Vanwolleghem, Meriem Mouelhi, Lotta Kuuliala, Arnaud Cuisset, Gaël Mouret, Frank Devlieghere, Robin Bocquet, Cédric Bray, Francis Hindle, Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO), Laboratoire de Photophysique Moléculaire (PPM), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Dynamique Interactions et Réactivité (LADIR), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Photonique THz - IEMN (PHOTONIQUE THz - IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF)-Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Food Safety and Food Quality, Universiteit Gent = Ghent University (UGENT), Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS), Photonique THz - IEMN (PHOTONIQ THz - IEMN), and Universiteit Gent = Ghent University [Belgium] (UGENT)

Subjects
Materials science, Hydrogen sulfide, Food spoilage, Salmo salar, Analytical chemistry, Mass spectrometry, 01 natural sciences, Biochemistry, Mass Spectrometry, Analytical Chemistry, chemistry.chemical_compound, 0404 agricultural biotechnology, [CHIM.ANAL]Chemical Sciences/Analytical chemistry, Limit of Detection, Electrochemistry, Acetone, Environmental Chemistry, Animals, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], Hydrogen Sulfide, Spectroscopy, Detection limit, Terahertz Spectroscopy, 010401 analytical chemistry, Butanone, 04 agricultural and veterinary sciences, 040401 food science, 0104 chemical sciences, Trace gas, chemistry, Food Storage, 13. Climate action, Food Microbiology, Dimethyl sulfide, Food Analysis
Abstract

International audience; High resolution rotational Terahertz (THz) spectroscopy has been widely applied to the studies of numerous polar gas phase molecules, in particular volatile organic compounds (VOCs). During the storage of foodstuffs packed under a protective atmosphere, microbial activity will lead to the generation of a complex mixture of trace gases that could be used as food spoilage indicators. Here we have demonstrated that the THz instrumentation presently available provides sufficient sensitivity and selectivity to monitor the generation of hydrogen sulfide (H2S) in the headspace of packed Atlantic salmon (Salmo salar) fillet portions. A comprehensive comparison was made by selective-ion flow-tube mass spectrometry (SIFT-MS) in order to validate the THz measurements and protocol. The detectivity of a range of alternative compounds for this application is also provided, based on the experimental detection limit observed and molecular spectroscopic properties. Molecules like ethanol, methyl mercaptan and ammonia are suitable indicators with the presently available sensitivity levels, while dimethyl sulfide, acetone and butanone may be considered with a sensitivity improvement of 2 orders of magnitude.

Published
2018
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46. Frequency comb for THz metrology and spectroscopy

Author

Francis Hindle, Cédric Bray, Arnaud Cuisset, J-F. Lampin, and Gaël Mouret

Subjects
Materials science, 010504 meteorology & atmospheric sciences, business.industry, Terahertz radiation, Physics, QC1-999, 01 natural sciences, Metrology, 010309 optics, Frequency comb, 0103 physical sciences, Optoelectronics, business, Spectroscopy, 0105 earth and related environmental sciences
Published
2018

47. Continuous Monitoring of Formaldehyde Photolysis Products by THz Spectroscopy

Author

Cécile Coeur-Tourneur, Abdelaziz Omar, Guillaume Dhont, Gaël Mouret, Francis Hindle, Robin Bocquet, S. Eliet, and Arnaud Cuisset

Subjects
Detection limit, Zeeman effect, Spectrometer, Terahertz radiation, Photodissociation, Formaldehyde, Analytical chemistry, Dissociation (chemistry), chemistry.chemical_compound, symbols.namesake, chemistry, symbols, Electrical and Electronic Engineering, Instrumentation, Carbon monoxide
Abstract

A terahertz sensor system based on a commercially available multiplier chain operating in the range 600–900 GHz is used to monitor the photolysis of formaldehyde H2CO. The exposure of formaldehyde to solar radiation provokes dissociation via two pathways: 1) the molecular channel producing molecular carbon monoxide CO and 2) the radicalar channel giving formyl HCO. Monitoring the concentrations of CO and H2CO via pure rotational transitions, allowed us to obtain the kinetic rate constants for these two channels. In order to establish the detection limit of HCO, a modified spectrometer configuration employing the Zeeman modulation was used with acetaldehyde CH3CHO and photosensitization by mercury.

Published
2015
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48. Towards the Detection of Explosive Taggants: Microwave and Millimetre-Wave Gas-Phase Spectroscopies of 3-Nitrotoluene

Author

Manuel Goubet, Arnaud Cuisset, W. Leo Meerts, Gaël Mouret, Robin Bocquet, Isabelle Kleiner, Francis Hindle, Anthony Roucou, Sabath Bteich, Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA (UMR_7583)), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523 (PhLAM), Université de Lille-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS), Université du Littoral Côte d'Opale (ULCO), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), and Centre National de la Recherche Scientifique (CNRS)-Université du Littoral Côte d'Opale

Subjects
Materials science, 010304 chemical physics, Spectrometer, Molecular and Biophysics, 010402 general chemistry, 01 natural sciences, Atomic and Molecular Physics, and Optics, Spectral line, 0104 chemical sciences, Rotational energy, Excited state, 0103 physical sciences, Rotational spectroscopy, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], Physical and Theoretical Chemistry, Atomic physics, Ground state, Hyperfine structure, Microwave, ComputingMilieux_MISCELLANEOUS
Abstract

The monitoring of gas-phase mononitrotoluenes is crucial for defence, civil security and environmental interests because they are used as taggant for TNT detection and in the manufacturing of industrial compounds such as dyestuffs. In this study, we have succeeded to measure and analyse at high-resolution a room temperature rotationally resolved millimetre-wave spectrum of meta-nitrotoluene (3-NT). Experimental and theoretical difficulties have been overcome, in particular, those related to the low vapour pressure of 3-NT and to the presence of a CH3 internal rotation in an almost free rotation regime (V3 =6.7659(24) cm-1 ). Rotational spectra have been recorded in the microwave and millimetre-wave ranges using a supersonic jet Fourier Transform microwave spectrometer (Trot

Published
2017
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49. Rotational structure of the five lowest frequency fundamental vibrational states of dimethylsulfoxide

Author

Arnaud Cuisset, Dmitrií A. Sadovskií, Francis Hindle, Marie-Aline Martin Drumel, and Gaël Mouret

Subjects
Spectrometer, Chemistry, Internal rotation, Solid-state, General Physics and Astronomy, Rotational–vibrational spectroscopy, Low frequency, Spectral line, Gas phase, symbols.namesake, symbols, Physical and Theoretical Chemistry, Atomic physics, Hamiltonian (quantum mechanics)
Abstract

We report on the successful extended analysis of the high-frequency (200–700 GHz) part of the gas phase (sub)mm-wave spectra of dimethylsulfoxide (DMSO). The spectrum was recorded at 100 kHz resolution using a solid state subTHz spectrometer. The five lowest energy fundamental vibrational states of DMSO with frequencies below 400 cm−1 were observed as sidebands along with the main 0 ← 0 band. Neglecting the internal rotation of methyls, our rotational Hamiltonian reproduced the spectrum to the subMHz accuracy. We have found that the asymmetric bending state ν 23 is the only low frequency fundamental vibrational state with the “anomalous” rotational structure uncovered in Cuisset et al. [1] . dmsomw 2013-09-04 15:03 © 2013 Elsevier

Published
2013
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50. Terahertz Comb Spectroscopy Traceable to Microwave Frequency Standard

Author

Takeshi Yasui, Yoshinori Takahashi, Masashi Yoshimura, Hajime Inaba, Shuko Yokoyama, Francis Hindle, Yusuke Mori, Tsutomu Araki, Yi-Da Hsieh, Kaoru Minoshima, Yuki Iyonaga, and Yoshiyuki Sakaguchi

Subjects
Radiation, Materials science, Spectrometer, Terahertz radiation, business.industry, Laser, Terahertz spectroscopy and technology, law.invention, Frequency comb, Laser linewidth, Optics, law, Electrical and Electronic Engineering, Spectral resolution, Spectroscopy, business
Abstract

The fine-structured spectrum of a terahertz (THz) frequency comb has been observed using asynchronous-optical-sampling THz time-domain spectroscopy with an extended time window covering multiple THz pulses. Fourier transformation of 10 consecutive THz pulses enables us to obtain the spectrum of THz comb mode having a linewidth of 25 MHz at intervals of 250 MHz. Further expansion of time window up to 100 consecutive THz pulses reduces the linewidth of THz comb mode down to 2.5 MHz while conserving interval of 250 MHz. The observed THz comb mode can be used as a precise and accurate frequency marker for broadband THz spectroscopy because it is phase-locked to a microwave frequency standard by laser control. The spectroscopy of pharmaceutical tablets and low-pressure molecular gas is used to demonstrate the utility of this approach, indicating a spectral resolution of 250 MHz. The proposed method enables frequency calibration of the THz spectrometer based on a microwave frequency standard.

Published
2013
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