Increasing the spectral contrast of optical signals by the intracavity laser spectroscopy method

A method of calculation is proposed and used as the basis of a numerical analysis of the processes occurring when a weak optical signal is injected into the resonator of a broad-band laser generating a pulse of microsecond duration. It is shown that the synchronous addition, to the spontaneous radiation power density, of 10 ^– 8 W/cm² in an assigned mode, induces a measurable response in the lasing spectrum. The use of frequency-spatial filtering of the radiation in a nonlinear absorber placed inside the resonator of this laser makes it possible to lower the detection limit of a weak narrow-band signal to 10 ^– 10 or 10 ^– 15 W/cm² for overall laser pulse durations of 8 or 13 μs, respectively.