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Kubarev V. Periodical properties of the ray transfer matrix and generation of sideband modes in a stable laser resonator. OPTICS LETTERS 2023; 48:4785-4788. [PMID: 37707902 DOI: 10.1364/ol.501366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Accepted: 08/15/2023] [Indexed: 09/15/2023]
Abstract
The paper describes a subclass of stable laser cavities, periodic stable laser cavities, in which perturbations consisting of deviations of the mode axis from the ideal direction are of a strictly periodic oscillatory nature. In such resonators, in addition to unperturbed longitudinal-transverse spatial modes with an ideal direction of the optical axis, additional modes can appear at sideband frequencies, associated with the resonant buildup of perturbation oscillations. These modes have approximately the same spatial structure as those of the unperturbed fundamental modes, and their frequency detuning from the frequencies of the fundamental modes is governed by the resonator geometry and the periodicity parameter, i.e., the number of passes in the resonator in one period of perturbation oscillations. For many repetitively pulsed laser systems emitting comb spectrum structures, such as free electron lasers, modern frequency standards using femtosecond lasers, and various comb spectrometers, it is desirable to avoid such periodic stable cavities in order to preserve the purity of the comb spectrum used in them. This may also be important for CW lasers with extreme radiation monochromaticity. In some repetitively pulsed lasers, on the contrary, it may be desirable to use such periodic stable laser cavities for a more complete frequency filling and higher quasi-continuity of their emission spectra.
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2
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Funkner S, Niehues G, Nasse MJ, Bründermann E, Caselle M, Kehrer B, Rota L, Schönfeldt P, Schuh M, Steffen B, Steinmann JL, Weber M, Müller AS. Revealing the dynamics of ultrarelativistic non-equilibrium many-electron systems with phase space tomography. Sci Rep 2023; 13:4618. [PMID: 36944670 PMCID: PMC10030633 DOI: 10.1038/s41598-023-31196-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 03/07/2023] [Indexed: 03/23/2023] Open
Abstract
The description of physical processes with many-particle systems is a key approach to the modeling of numerous physical systems. For example in storage rings, where ultrarelativistic particles are agglomerated in dense bunches, the modeling and measurement of their phase-space distribution is of paramount importance: at any time the phase-space distribution not only determines the complete space-time evolution but also provides fundamental performance characteristics for storage ring operation. Here, we demonstrate a non-destructive tomographic imaging technique for the 2D longitudinal phase-space distribution of ultrarelativistic electron bunches. For this purpose, we utilize a unique setup, which streams turn-by-turn near-field measurements of bunch profiles at MHz repetition rates. To demonstrate the feasibility of our method, we induce a non-equilibrium state and show that the phase-space distribution microstructuring as well as the phase-space distribution dynamics can be observed in great detail. Our approach offers a pathway to control ultrashort bunches and supports, as one example, the development of compact accelerators with low energy footprints.
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Affiliation(s)
- Stefan Funkner
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany.
| | - Gudrun Niehues
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
| | - Michael J Nasse
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
| | - Erik Bründermann
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
| | - Michele Caselle
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
| | - Benjamin Kehrer
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
| | - Lorenzo Rota
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
- SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Patrik Schönfeldt
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
- DLR (Deutsches Zentrum für Luft und Raumfahrt) Institute of Networked Energy Systems, Carl-von-Ossietzky-Str.15, 26129, Oldenburg, Germany
| | - Marcel Schuh
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
| | - Bernd Steffen
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany
| | | | - Marc Weber
- Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany
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Karataev P, Fedorov K, Naumenko G, Popov K, Potylitsyn A, Vukolov A. Ultra-monochromatic far-infrared Cherenkov diffraction radiation in a super-radiant regime. Sci Rep 2020; 10:20961. [PMID: 33262360 PMCID: PMC7708415 DOI: 10.1038/s41598-020-76996-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 11/04/2020] [Indexed: 11/29/2022] Open
Abstract
Nowadays, intense electromagnetic (EM) radiation in the far-infrared (FIR) spectral range is an advanced tool for scientific research in biology, chemistry, and material science because many materials leave signatures in the radiation spectrum. Narrow-band spectral lines enable researchers to investigate the matter response in greater detail. The generation of highly monochromatic variable frequency FIR radiation has therefore become a broad area of research. High energy electron beams consisting of a long train of dense bunches of particles provide a super-radiant regime and can generate intense highly monochromatic radiation due to coherent emission in the spectral range from a few GHz to potentially a few THz. We employed novel coherent Cherenkov diffraction radiation (ChDR) as a generation mechanism. This effect occurs when a fast charged particle moves in the vicinity of and parallel to a dielectric interface. Two key features of the ChDR phenomenon are its non-invasive nature and its photon yield being proportional to the length of the radiator. The bunched structure of the very long electron beam produced spectral lines that were observed to have frequencies upto 21 GHz and with a relative bandwidth of 10–4 ~ 10–5. The line bandwidth and intensity are defined by the shape and length of the bunch train. A compact linear accelerator can be utilized to control the resonant wavelength by adjusting the bunch sequence frequency.
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Affiliation(s)
- P Karataev
- John Adams Institute at Royal Holloway, University of London, Egham, TW20 0EX, Surrey, UK.
| | - K Fedorov
- John Adams Institute at Royal Holloway, University of London, Egham, TW20 0EX, Surrey, UK.,National Research Tomsk Polytechnic University, Lenin Ave. 30, 634050, Tomsk, Russia
| | - G Naumenko
- National Research Tomsk Polytechnic University, Lenin Ave. 30, 634050, Tomsk, Russia
| | - K Popov
- National Research Tomsk Polytechnic University, Lenin Ave. 30, 634050, Tomsk, Russia
| | - A Potylitsyn
- National Research Tomsk Polytechnic University, Lenin Ave. 30, 634050, Tomsk, Russia
| | - A Vukolov
- National Research Tomsk Polytechnic University, Lenin Ave. 30, 634050, Tomsk, Russia
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Zhang H, Wang W, Jiang S, Li C, He Z, Zhang S, Jia Q, Wang L, He D. Chirp control of tunable terahertz synchrotron radiation. OPTICS LETTERS 2020; 45:4674-4677. [PMID: 32870828 DOI: 10.1364/ol.396722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 07/21/2020] [Indexed: 06/11/2023]
Abstract
It is of scientific significance to explore the terahertz radiation source with the performances of high power, tunable frequency, and controllable chirp for the realization of coherent control of quantum systems. How to realize frequency chirp control of terahertz synchrotron radiation is the last puzzle to be completed. In this Letter, we propose a method to control the radiation frequency chirp with precision. A novel photomixing scheme is presented to generate a longitudinally modulated laser pulse with non-uniform time intervals between the adjacent micro-peaks, which means that there is a chirp in the modulation frequency, and this chirp can be continuously tuned. The interaction is made to occur between an electron beam and the modulated laser pulse in a modulator (an undulator tuned at the laser wavelength), then terahertz synchrotron radiation with the same spectrum characteristics as the modulated laser will be generated when the electron beam passes through the following bending magnet. We expect that this method will open a new way for the coherent control of quantum systems in the terahertz regime.
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Abstract
Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. These micro-instabilities are investigated at the electron storage ring BESSY II by means of cross-correlation of the THz fields from successive bunches. The investigations allow deriving the longitudinal length scale of the micro bunch fluctuations and show that it grows faster than the current-dependent bunch length. Our findings will help to set the limits for the possible time resolution for pump-probe experiments achieved with coherent THz synchrotron radiation from a storage ring.
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Lampin JF, Pirali O, Buchanan ZS, Eliet S, Martin-Drumel MA, Turut J, Roy P, Hindle F, Mouret G. Broadband terahertz heterodyne spectrometer exploiting synchrotron radiation at megahertz resolution. OPTICS LETTERS 2019; 44:4985-4988. [PMID: 31613245 DOI: 10.1364/ol.44.004985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 09/08/2019] [Indexed: 06/10/2023]
Abstract
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-based molecular THz laser that acts as the local oscillator. Proof of principle for exploitation for spectroscopy is provided by the recording of molecular absorptions of hydrogen sulfide (H2S) and methanol (CH3OH) around 1.073 THz. Ultimately, the spectrometer will enable to cover the 1-4 THz region in 5 GHz windows at Doppler resolution.
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Kampfrath T, Wolf M, Sajadi M. The sign of the polarizability anisotropy of polar molecules is obtained from the terahertz Kerr effect. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2017.12.061] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Evain C, Roussel E, Le Parquier M, Szwaj C, Tordeux MA, Brubach JB, Manceron L, Roy P, Bielawski S. Direct Observation of Spatiotemporal Dynamics of Short Electron Bunches in Storage Rings. PHYSICAL REVIEW LETTERS 2017; 118:054801. [PMID: 28211708 DOI: 10.1103/physrevlett.118.054801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Indexed: 05/23/2023]
Abstract
In recent synchrotron radiation facilities, the use of short (picosecond) electron bunches is a powerful method for producing giant pulses of terahertz coherent synchrotron radiation. Here we report on the first direct observation of these pulse shapes with a few picoseconds resolution, and of their dynamics over a long time. We thus confirm in a very direct way the theories predicting an interplay between two physical processes. Below a critical bunch charge, we observe a train of identical THz pulses (a broadband Terahertz comb) stemming from the shortness of the electron bunches. Above this threshold, a large part of the emission is dominated by drifting structures, which appear through spontaneous self-organization. These challenging single-shot THz recordings are made possible by using a recently developed photonic time stretch detector with a high sensitivity. The experiment has been realized at the SOLEIL storage ring.
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Affiliation(s)
- C Evain
- Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523 Centre d'Études et de Recherches Lasers et Applications, FR CNRS 2416, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex, France
| | - E Roussel
- Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 in AREA Science Park,34149 Basovizza, Trieste, Italy
| | - M Le Parquier
- Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523 Centre d'Études et de Recherches Lasers et Applications, FR CNRS 2416, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex, France
| | - C Szwaj
- Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523 Centre d'Études et de Recherches Lasers et Applications, FR CNRS 2416, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex, France
| | - M-A Tordeux
- Synchrotron SOLEIL, Saint Aubin, BP 34, 91192 Gif-sur-Yvette, France
| | - J-B Brubach
- Synchrotron SOLEIL, Saint Aubin, BP 34, 91192 Gif-sur-Yvette, France
| | - L Manceron
- Synchrotron SOLEIL, Saint Aubin, BP 34, 91192 Gif-sur-Yvette, France
| | - P Roy
- Synchrotron SOLEIL, Saint Aubin, BP 34, 91192 Gif-sur-Yvette, France
| | - S Bielawski
- Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523 Centre d'Études et de Recherches Lasers et Applications, FR CNRS 2416, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex, France
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Cossel KC, Waxman EM, Finneran IA, Blake GA, Ye J, Newbury NR. Gas-phase broadband spectroscopy using active sources: progress, status, and applications. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. B, OPTICAL PHYSICS 2017; 34:104-129. [PMID: 28630530 PMCID: PMC5473295 DOI: 10.1364/josab.34.000104] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Broadband spectroscopy is an invaluable tool for measuring multiple gas-phase species simultaneously. In this work we review basic techniques, implementations, and current applications for broadband spectroscopy. We discuss components of broad-band spectroscopy including light sources, absorption cells, and detection methods and then discuss specific combinations of these components in commonly-used techniques. We finish this review by discussing potential future advances in techniques and applications of broad-band spectroscopy.
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Affiliation(s)
- Kevin C. Cossel
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Eleanor M. Waxman
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Ian A. Finneran
- Division of Chemistry & Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
| | - Geoffrey A. Blake
- Division of Chemistry & Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
| | - Jun Ye
- JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, CO 80309, USA
| | - Nathan R. Newbury
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
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Steinmann JL, Blomley E, Brosi M, Bründermann E, Caselle M, Hesler JL, Hiller N, Kehrer B, Mathis YL, Nasse MJ, Raasch J, Schedler M, Schönfeldt P, Schuh M, Schwarz M, Siegel M, Smale N, Weber M, Müller AS. Frequency-Comb Spectrum of Periodic-Patterned Signals. PHYSICAL REVIEW LETTERS 2016; 117:174802. [PMID: 27824451 DOI: 10.1103/physrevlett.117.174802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Indexed: 06/06/2023]
Abstract
Using arbitrary periodic pulse patterns we show the enhancement of specific frequencies in a frequency comb. The envelope of a regular frequency comb originates from equally spaced, identical pulses and mimics the single pulse spectrum. We investigated spectra originating from the periodic emission of pulse trains with gaps and individual pulse heights, which are commonly observed, for example, at high-repetition-rate free electron lasers, high power lasers, and synchrotrons. The ANKA synchrotron light source was filled with defined patterns of short electron bunches generating coherent synchrotron radiation in the terahertz range. We resolved the intensities of the frequency comb around 0.258 THz using the heterodyne mixing spectroscopy with a resolution of down to 1 Hz and provide a comprehensive theoretical description. Adjusting the electron's revolution frequency, a gapless spectrum can be recorded, improving the resolution by up to 7 and 5 orders of magnitude compared to FTIR and recent heterodyne measurements, respectively. The results imply avenues to optimize and increase the signal-to-noise ratio of specific frequencies in the emitted synchrotron radiation spectrum to enable novel ultrahigh resolution spectroscopy and metrology applications from the terahertz to the x-ray region.
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Affiliation(s)
- Johannes L Steinmann
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Edmund Blomley
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Miriam Brosi
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Erik Bründermann
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Michele Caselle
- Institute for Data Processing and Electronics, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | | | - Nicole Hiller
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Benjamin Kehrer
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Yves-Laurent Mathis
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Michael J Nasse
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Juliane Raasch
- Institute of Micro- und Nanoelectronic Systems, Karlsruhe Institute of Technology, 76187 Karlsruhe, Germany
| | - Manuel Schedler
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Patrik Schönfeldt
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Marcel Schuh
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Markus Schwarz
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Michael Siegel
- Institute of Micro- und Nanoelectronic Systems, Karlsruhe Institute of Technology, 76187 Karlsruhe, Germany
| | - Nigel Smale
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Marc Weber
- Institute for Data Processing and Electronics, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
| | - Anke-Susanne Müller
- Institute for Beam Physics and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
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11
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Szwaj C, Evain C, Le Parquier M, Roy P, Manceron L, Brubach JB, Tordeux MA, Bielawski S. High sensitivity photonic time-stretch electro-optic sampling of terahertz pulses. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:103111. [PMID: 27802701 DOI: 10.1063/1.4964702] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Single-shot recording of terahertz electric signals has recently become possible at high repetition rates, by using the photonic time-stretch electro-optic sampling (EOS) technique. However the moderate sensitivity of time-stretch EOS is still a strong limit for a range of applications. Here we present a variant enabling to increase the sensitivity of photonic time-stretch for free-propagating THz signals. The ellipticity of the laser probe is enhanced by adding a set of Brewster plates, as proposed by Ahmed et al. [Rev. Sci. Instrum. 85, 013114 (2014)] in a different context. The method is tested using the high repetition rate terahertz coherent synchrotron radiation source of the SOLEIL synchrotron radiation facility. The signal-to-noise ratio of our terahertz digitizer could thus be straightforwardly improved by a factor ≈6.5, leading to a noise-equivalent input electric field below 1.25 V/cm inside the electro-optic crystal, over the 0-300 GHz band (i.e., 2.3 μV/cm/Hz). The sensitivity is scalable with respect to the available laser power, potentially enabling further sensitivity improvements when needed.
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Affiliation(s)
- C Szwaj
- Laboratoire PhLAM, UMR CNRS 8523, Université Lille 1, Sciences et Technologies, 59655 Villeneuve d'Ascq, France
| | - C Evain
- Laboratoire PhLAM, UMR CNRS 8523, Université Lille 1, Sciences et Technologies, 59655 Villeneuve d'Ascq, France
| | - M Le Parquier
- Centre d'Étude Recherches et Applications (CERLA), 59655 Villeneuve d'Ascq, France
| | - P Roy
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France
| | - L Manceron
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France
| | - J-B Brubach
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France
| | - M-A Tordeux
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France
| | - S Bielawski
- Laboratoire PhLAM, UMR CNRS 8523, Université Lille 1, Sciences et Technologies, 59655 Villeneuve d'Ascq, France
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Good JT, Holland DB, Finneran IA, Carroll PB, Kelley MJ, Blake GA. A decade-spanning high-resolution asynchronous optical sampling terahertz time-domain and frequency comb spectrometer. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:103107. [PMID: 26520940 DOI: 10.1063/1.4932567] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present the design and capabilities of a high-resolution, decade-spanning ASynchronous OPtical Sampling (ASOPS)-based TeraHertz Time-Domain Spectroscopy (THz-TDS) instrument. Our system employs dual mode-locked femtosecond Ti:Sapphire oscillators with repetition rates offset locked at 100 Hz via a Phase-Locked Loop (PLL) operating at the 60th harmonic of the ∼80 MHz oscillator repetition rates. The respective time delays of the individual laser pulses are scanned across a 12.5 ns window in a laboratory scan time of 10 ms, supporting a time delay resolution as fine as 15.6 fs. The repetition rate of the pump oscillator is synchronized to a Rb frequency standard via a PLL operating at the 12th harmonic of the oscillator repetition rate, achieving milliHertz (mHz) stability. We characterize the timing jitter of the system using an air-spaced etalon, an optical cross correlator, and the phase noise spectrum of the PLL. Spectroscopic applications of ASOPS-THz-TDS are demonstrated by measuring water vapor absorption lines from 0.55 to 3.35 THz and acetonitrile absorption lines from 0.13 to 1.39 THz in a short pathlength gas cell. With 70 min of data acquisition, a 50 dB signal-to-noise ratio is achieved. The achieved root-mean-square deviation is 14.6 MHz, with a mean deviation of 11.6 MHz, for the measured water line center frequencies as compared to the JPL molecular spectroscopy database. Further, with the same instrument and data acquisition hardware, we use the ability to control the repetition rate of the pump oscillator to enable THz frequency comb spectroscopy (THz-FCS). Here, a frequency comb with a tooth width of 5 MHz is generated and used to fully resolve the pure rotational spectrum of acetonitrile with Doppler-limited precision. The oscillator repetition rate stability achieved by our PLL lock circuits enables sub-MHz tooth width generation, if desired. This instrument provides unprecedented decade-spanning, tunable resolution, from 80 MHz down to sub-MHz, and heralds a new generation of gas-phase spectroscopic tools in the THz region.
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Affiliation(s)
- Jacob T Good
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | - Daniel B Holland
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | - Ian A Finneran
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | - P Brandon Carroll
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | - Matthew J Kelley
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | - Geoffrey A Blake
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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