The principle of Q-switching is that the resonator is in a state of high loss and low Q value at the initial stage of pumping, which means that the threshold of laser oscillation is very high, even if the inversion number of particle density accumulates to a very high level, it will not produce oscillation; When the inversion number of particle number density reaches the peak, the Q value of the cavity suddenly increases, which will cause the gain of the laser ring to greatly exceed the threshold and oscillate very fast. This means that the energy stored in metastable state will soon be converted into photon energy, and the photon will grow at a very high speed like an avalanche, and the laser can output laser giant pulses with high peak power and narrow width. The technology of adjusting the Q value of resonant cavity to obtain laser giant pulse becomes laser Q-switched technology.

Commonly used Q-switching technology: mechanical rotating mirror Q-switching technology, electro-optic Q-switching technology, saturable absorption dye Q-switching technology, acousto-optic Q-switching technology.