Gas laser
A gas laser uses gas as a working substance to generate laser light. It is composed of three main parts: the activated gas in the discharge tube, a resonant cavity composed of a pair of mirrors, and an excitation source. The main excitation methods are electrical excitation, pneumatic excitation, light excitation and chemical excitation. Among them, electrical excitation is the most commonly used. Under proper discharge conditions, gas particles are selectively excited to a certain high energy level by using electron collision excitation and energy transfer excitation, thereby forming a population inversion with a certain low energy level, resulting in a stimulated emission transition.