Institut des Sciences Moléculaires d'Orsay



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Accueil > Équipes scientifiques > Systèmes Moléculaires, Astrophysique et Environnement (SYSTEMAE) > Offres de stages, thèses et post-docs > Frequency metrology in the THz, news means for new perspectives in molecular quantum physics

M2 internship

Frequency metrology in the THz, news means for new perspectives in molecular quantum physics

M2 or PhD

Contact : Olivier Pirali

The project aims at developing a new generation of THz (300-6 000 GHz) instrumentation to perform ultra- high resolution (sub-kHz) and highly precise spectroscopy of molecules isolated in the gas phase. When applied to the study of fundamental species such as NH3, H2O, CH3OH, and small radicals (OH, NH2), these new type of spectrometers will provide energy values of the rotational quantum numbers (including fine and hyperfine effects) with unprecedented precision. This will be a great interest for astrophysics, molecular physics models and, for some species, may carry the fingerprint of a possible time variance of the electron- to-proton mass ratio due to cosmological expansion.

During the internship we propose to develop and test two different approaches : I) Mixing THz synchrotron radiation with lasers :
Our team benefitted of a national grant to develop a new spectrometer whose operating principle is based on the heterodyne mixing of the THz synchrotron continuum (extracted by the AILES beamline of SOLEIL) with a new generation of local oscillators (LOs) emitting in the 1-6 THz region. These LOs are molecular lasers optically pumped by a 10 μm Quantum Cascade Laser. We recently performed a first test experiment (Lampin et al., Optics Letters 2019) which demonstrated the validity of our approach but showed important limitations in terms of frequency metrology and intensity stability. During the internship, we will work on two axes of improvement of the spectrometer : i) Improve the LO frequency metrology by mixing the laser output with a THz frequency comb (acting as a highly accurate frequency ruler in the THz) generated by a femto second laser. ii) Study new molecular gain media and QCL frequencies to produce a great wealth of new laser lines in the THz. Finally, in June 2022 the team will have 5 days access to synchrotron radiation to measure with this heterodyne instrument the pure rotational spectrum of the NH2 radical, highly relevant for astrophysics, and which exhibits a complicated fine and hyperfine structure never resolved in the THz.

II) Photomixing of high spectral purity distributed feedback lasers :
The availability of metrological signal at ISMO (lambda = 1.542 μm), delivered by the SYRTE laboratory using a fibered network (project REFIMEV), opens the possibility of mixing the high spectral purity emissions from two distributed feedback (DFB) lasers, which frequencies are separated by few THz, to generate a high precision tunable THz source. During the internship, we propose to perform the very first tests of THz generation by photomixing technique at ISMO laboratory exploiting a THz mixer and newly available high sensitivity THz detector.
The activities linked to these two developments are highly tunable, depending on the scientific interests of the master 2 students. Emphasis on either one or the other project can easily be proposed. In addition, high- resolution spectroscopic measurements on stable or reactive species can also be done during the internship. Proofs of concept performed during the internship will lead to numerous perspectives which can be explored during a PhD thesis. The candidate will be trained to state of the art instrumentation and requires good understanding of molecular quantum physics, optics, electronics, laser technologies and a taste for experimental explorations !

Voir en ligne : Systèmes moléculaires, Astrophysique et Environnement