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

The disclosure relates to a gas analysis method by Raman spectrometry, the method comprising the steps of generating by a laser source a laser beam sweeping a range of frequencies including a plurality of resonance modes of an optical cavity holding gases to be analyzed; delivering the laser beam into the cavity; extracting from the cavity a feedback beam that is sent adjusted in phase and amplitude to the source; during the frequency range sweeping, detecting light intensity peaks in the laser beam in the cavity, the phase of the feedback beam being adjusted to reduce shape asymmetries of the peaks, the amplitude of the feedback beam being adjusted to reduce intervals of zero intensity between the peaks; and performing a spectral analysis of the light inelastically scattered in the cavity, to determine the composition of the gases to be analyzed.