Stimulated emission spectrum of a laser with narrow-band intracavity absorption and temporal modulation of the gain

Near the absorption lines of a gas filling a resonator there is a range of dispersion of the refractive index within which axial modes become nonequidistant. Periodic modulation of the active-medium gain results in mode locking and an abrupt rise in the lasing intensity in those spectral ranges where the intermode spacing is the same as the modulation frequency. The effect observed may be used to control the laser emission spectrum and also to measure the oscillator strength of spectral lines having an unknown broadening.