What is the laser diode

Laser-a device capable of emitting laser light. The first microwave quantum amplifier was made in 1954, and a highly coherent microwave beam was obtained. In 1958, A.L. Xiaoluo and C.H. Towns extended the principle of microwave quantum amplifier to the optical frequency range. In 1960, T.H. Mayman and others made the first ruby laser. In 1961, A. Jia Wen and others made a helium-neon laser. In 1962, R.N. Hall and others created a gallium arsenide semiconductor laser. In the future, there will be more and more types of lasers. According to the working medium, lasers can be divided into four categories: gas lasers, solid lasers, semiconductor lasers and dye lasers. Free electron lasers have also been developed recently. High-power lasers are usually pulsed output.

History:

The key concept in laser technology was established as early as 1917 when Einstein proposed "stimulated emission". The term laser was once controversial; Gordon Gould was the first person to use this term in records.
In 1953, the American physicist Charles Harde Towns and his student Arthur Xiao Luo made the first microwave quantum amplifier and obtained a highly coherent microwave beam.
In 1958, C.H. Towns and A.L. Xiao Luo extended the principle of microwave quantum amplifiers to the optical frequency range.
In 1960, T.H. Theodore Mayman made the first ruby laser.
In 1961, Iranian scientist A. Javin and others made a helium-neon laser.
In 1962, R.N. Hall and others created a gallium arsenide semiconductor laser.
In 2013, researchers from the National Laser Center of the South African Science and Industry Research Council developed the world's first digital laser, opening up new prospects for laser applications. The research results were published in the British journal Nature Communications on August 2, 2013.

Types and applications of lasers:
The quality of the light emitted by the laser is pure and the spectrum is stable, which can be used in many ways.
Ruby laser: The original laser was that ruby was excited by a bright flashing bulb, and the laser produced was a "pulse laser" rather than a continuous and stable beam. The quality of the beam produced by this laser is essentially different from the laser produced by the laser diode we are using now. This intense light emission that lasts only a few nanoseconds is very suitable for capturing easily moving objects, such as holographic portraits of people. The first laser portrait was born in 1967. Ruby lasers require expensive rubies and can only produce short pulsed light.
He-Ne laser: In 1960, scientists Ali Javan, William R. Brennet Jr. and Donald Herriot designed a He-Ne laser. This is the first gas laser. This type of laser is commonly used by holographic photographers. Two advantages: 1. Produce continuous laser output; 2. Do not need flash bulb for light excitation, but use electric excitation gas.
Laser diode: The laser diode is one of the most commonly used lasers. The phenomenon of spontaneous recombination of electrons and holes on both sides of the PN junction of the diode to emit light is called spontaneous emission. When the photon generated by spontaneous radiation passes through the semiconductor, once it passes the vicinity of the emitted electron-hole pair, it can excite the two to recombine and produce new photons. This photon induces the excited carriers to recombine and emit new photons. The phenomenon is called stimulated emission. If the injected current is large enough, the carrier distribution opposite to the thermal equilibrium state will be formed, that is, the population inversion. When the carriers in the active layer are in a large number of inversions, a small amount of spontaneous radiation produces induced radiation due to the reciprocating reflection at both ends of the resonant cavity, resulting in frequency-selective resonant positive feedback, or gaining a certain frequency. When the gain is greater than the absorption loss, a coherent light with good spectral lines-laser light can be emitted from the PN junction. The invention of the laser diode allows laser applications to be rapidly popularized. Various types of information scanning, optical fiber communication, laser ranging, lidar, laser discs, laser pointers, supermarket collections, etc., are constantly being developed and popularized.