First, the particles in the high energy state transition to the low energy state under the excitation of external light, which is called spontaneous radiation;

Second, the particles in the high energy state transition to the low energy state under the excitation of external light, which is called stimulated radiation;

Third, the transition of the particles in the low energy state to absorb the energy of the foreign light is called excited absorption.

Spontaneous radiation, even two particles from a high energy state to a low energy state transition at the same time, they emit light phase, polarization state, emission direction may also be different, but the excited radiation is different, when the particles located in the high energy state under the excitation of the low energy state transition, emit in frequency, phase, polarization state and other aspects of the foreign photon exactly the same light. In a laser, the radiation that occurs is stimulated radiation, and the laser emitted by it is exactly the same in terms of frequency, phase, polarization state, and so on. Any stimulated optical system, that is, there is stimulated radiation, there is also stimulated absorption, only the stimulated radiation is dominant, in order to amplify the external light and emit laser. The general light source is dominated by excited absorption, and only the equilibrium state of the particles is broken, so that the number of particles in the high energy state is greater than the number of particles in the low energy state (such a situation is called ion number inversion), in order to emit laser

In-line diode manufacturers