The DPM brings together experimentalists and theorists working towards a more precise understanding of the structure of molecules and/or radicals of interest.
Experimentally, we are building spectrometers offering both absorption sensitivity and frequency accuracy. These spectrometers are developed to be compatible with the uniform supersonic flows of the DPM but also with shock tubes. Our goal is to produce experimental data capable of validating or constraining the theoretical models calculating the energy levels of the molecules we measure.
Cavity enhanced spectroscopy
Optical cavities are very sensitive to changes in absorption and refractive index characteristic of molecular transitions.
Optical frequency comb spectroscopy
Mode-locked femtosecond lasers emit a characteristic comb-like spectrum of optical frequencies (see the following figure). Each mode of the comb oscillates at an optical frequency depending only on the repetition rate frep, and the offset frequency fceo (0 < fceo < frep). fceo and frep are two radio frequencies (0-10 GHz) and can be detected and controlled by acting on the femtosecond oscillator.
These sources can be used directly as probes for high precision absorption spectroscopy using both their frequency stability and their coupling with optical cavities.
Fourier transform spectrometers
A Fourier transform spectrometer is a Michelson interferometer. For this reason, measuring spectra with high resolution requires the use of bulky instruments. The combination of a Fourier transform spectrometer and a frequency comb allows to dramatically optimize the resolution of small interferometers (resolution < 3.10-5 cm-1 for 30 cm step difference, for example).