808nm diode laser manufacturers tell you that laser diodes include single heterojunction, double heterojunction and quantum well laser diodes. Quantum well semiconductor lasers have the advantages of low threshold current and high output power. It is the mainstream product of market application. Compared with lasers, laser diodes have the advantages of high efficiency, small size and long service life, but their output power is small (generally less than 2MW), poor linearity and monochromaticity are not very good, so they are used in cable TV systems. Being greatly restricted, it cannot transmit multi-channel, high-performance analog signals. The 808nm diode laser manufacturer tells you that in the return module of the bidirectional optical receiver, the quantum well semiconductor laser is usually used as the light source for the upward emission.

Before discussing the mechanism of laser generation, let's talk about stimulated emission. There are three radiation processes in light radiation,
1. It is the spontaneous transition of high-energy particles to low-energy particles, which is called spontaneous emission.
2. Under the excitation of external light, particles in a high-energy state are transformed into a low-energy state, which is called stimulated emission.
3. The transition from the external light energy absorbed by the particles in the low energy state to the high energy state is called stimulated absorption.
808nm diode laser manufacturers tell you spontaneous emission, even if two particles transition from high energy state to low energy state at the same time, their optical phase, polarization state and emission direction may be different, but stimulated emission is different. When particles in a high-energy state transition to a low-energy state upon excitation by an external photon, they emit light identical to the external photon in frequency, phase, and polarization state. The 808nm diode laser manufacturer tells you that in the laser, the generated radiation is stimulated radiation. In the polarization state, the frequency of the laser emission is exactly the same. Any stimulated optical system has stimulated emission and stimulated absorption. It amplifies external light and emits laser light only when stimulated emission dominates. Generally speaking, stimulated absorption dominates in light sources. Only when the equilibrium state of the particles is broken, and the number of particles in the high-energy state is greater than the number of particles in the low-energy state (a situation called population inversion), can the laser be emitted.
The three conditions for the generation of laser light are: realizing the population inversion, satisfying the threshold condition and the resonance condition. The 808nm diode laser manufacturer tells you that the main condition for the stimulated emission of light is the inversion of the particle number. In semiconductors, it is necessary to pump electrons in the valence band to the conduction band.