Resonant optical cavity system with optical feedback, suitable for detecting traces of gas by raman spectroscopy

A device for analyzing gas by Raman spectrometry, the device comprising an optical cavity into which a laser beam emitted by a laser source is introduced, the device further comprising:

• a processor;
• and
• a memory coupled to the processor, the memory comprising instructions that, when executed by the processor, cause the device to:
• apply a control signal to the laser source to produce a laser beam sweeping a range of frequencies including frequencies of multiple resonant modes of an optical cavity holding gases to be analyzed, the width of the frequency range being less than the resolution of a Raman spectrometer,
• supply the laser beam to an entrance of the optical cavity,
• extract a feedback beam from the optical cavity,
• adjust a phase and an amplitude of the feedback beam,
• send the phase and amplitude adjusted feedback beam to the laser source,
• during sweeping of the frequency range, measure light intensity variations of the laser beam in the optical cavity, and detect light intensity peaks in the light intensity variations, each light intensity peak corresponding to a resonance mode of the optical cavity, the phase of the feedback beam being adjusted to reduce a deviation between a median time and the time of occurrence of an apex of one of the light intensity peaks, the amplitude of the feedback beam being adjusted to reduce at least an interval of zero intensity between the light intensity peaks, and
• acquire, with a spectrometer sensor, measurements of the spectrum of light inelastically scattered by the laser beam in the optical cavity to determine the nature and/or concentration of gases in the optical cavity.