Dynamics of a Q-Switched Laser

Abstract

The most effective method of generating giant pulses of coherent light — “Q-modulation” (“Q-switching”) of a laser — was proposed by Hellwarth [1]. The first theoretical investigations [1–6] of the energy, maximum power, and the rate of rise and decay of the giant pulse were based on equations balancing the total energy of the radiation field and the total number of active particles in the resonator. Such equations represent a simple model in which the density of the inverse population and the energy density of the radiation field are assumed homogeneous over the volume of the resonator. Hence, such a model ignores the electrodynamic effects responsible for the spatial and temporal development of the generation field, and the effect of the initial spatial distribution of the inverse population and the resonator geometry on the dynamics of pulse generation. The delay time, length, and shape of the giant pulse calculated for such a simplified model can differ considerably (even qualitatively [7]) from the actual values. As will be shown below, this is due to transverse development of the generation region during a time of the order of the length of the giant pulse. The need to consider the spatial development of the generation region in a Q-switched laser was pointed out in [8].