Abstract-Broadband terahertz heterodyne spectrometer exploiting synchrotron radiation at megahertz resolution

J.-F. Lampin, O. Pirali, Z. S. Buchanan, S. Eliet, M.-A. Martin-Drumel, J. Turut, P. Roy, F. Hindle, G. Mouret

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-20-4985

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${\mathrm{H}}_2\mathrm{S}$) and methanol (CH3OH${\mathrm{CH}}_3\mathrm{OH}$) around 1.073 THz. Ultimately, the spectrometer will enable to cover the 1–4 THz region in 5 GHz windows at Doppler resolution.

© 2019 Optical Society of America

Abstract-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

• C. Bray^a, 
• A. Cuisset^a, 
• F. Hindle^a, 
• G. Mouret^a, 
• R. Bocquet^a, 
• V. Boudon^b

• ^a Laboratoire de Physico-Chimie de l'Atmosphàre, CNRS EA-4493 - Université du Littoral Côte d'Opale, 59140 Dunkerque, France
• ^b Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS - Université Bourgogne Franche-Comté, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France
• 
  

http://www.sciencedirect.com/science/article/pii/S0022
40731730047X

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 ν₄←ν₄${}_{\mathrm{}}{}_{\mathrm{}}$ 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 (B₀) and centrifugal distortion (D₀) constants.

Abstract-High density terahertz frequency comb produced by coherent synchrotron radiation

S. Tammaro,

O. Pirali,

P. Roy,

J.-F. Lampin,

G. Ducournau,

A. Cuisset,

F. Hindle

& G. Mouret

http://www.nature.com/ncomms/2015/150720/ncomms8733/full/ncomms8733.html

Frequency combs have enabled significant progress in frequency metrology and high-resolution spectroscopy extending the achievable resolution while increasing the signal-to-noise ratio. In its coherent mode, synchrotron radiation is accepted to provide an intense terahertz continuum covering a wide spectral range from about 0.1 to 1 THz. Using a dedicated heterodyne receiver, we reveal the purely discrete nature of this emission. A phase relationship between the light pulses leads to a powerful frequency comb spanning over one decade in frequency. The comb has a mode spacing of 846 kHz, a linewidth of about 200 Hz, a fractional precision of about 2 × 10⁻¹⁰ and no frequency offset. The unprecedented potential of the comb for high-resolution spectroscopy is demonstrated by the accurate determination of pure rotation transitions of acetonitrile.