Fine structure of the spectra of giant pulses from actively $Q$-switched solid-state lasers with injection of external radiation

A theoretical and experimental investigation was made of the problem of controlling the mode structure of the spectra of giant pulses from actively $Q$-switched solid-state lasers by injection of external radiation at a frequency independent of the natural frequencies of the resonator. A marked difference was observed between the spectral kinetic characteristics of giant pulses from neodymium-glass and ruby lasers. On the basis of a comparison with previously established differences in the free-lasing dynamics, an explanation of this observation by nonlinear mode interaction is proposed and confirmed theoretically and experimentally. A method of improving the mode selection efficiency under giant pulse conditions using passive negative feedback is proposed and implemented experimentally using a neodymium-glass laser. Giant pulse generation with a spectral width of $\leqslant5\cdot10^{-4}$ cm${}^{-1}$ and a power of 20 MW was obtained using an actively $Q$-switched neodymium-glass laser.