A semiconductor laser (or Laser Diode) is a device that causes laser oscillation by flowing an electric current to a semiconductor.
The semiconductor laser is regarded as “the laser of the future.” It is because that the semiconductor laser is one of the most practical and important types of laser. It is small in size and appearance, long in life, low power consumption. It is compact and can be pumped by a simple current injection. It has great potentials for mass production, can be easily integrated as well, where its properties are improved rapidly. Nowadays, it is becoming more and more powerful and efficient and has found widespread use as pumps for solid-state lasers.
Due to the difference in material structure, the specific processes of different types of lasers are different. Gallium arsenide (GaAs), Cadmium sulfide (CdS), Indium phosphide (InP), Zinc sulfide (ZnS) are the commonly used working materials. And, electrical injection, electron beam excitation, and optical pumping are the three types of excitation methods. Semiconductor laser devices can be divided into homojunction, single heterojunctions, and double heterojunctions. Homojunction lasers and single heterojunction lasers mostly become pulsed devices at room temperature, while double heterojunction lasers can work continuously at room temperature.
Semiconductor lasers work by injecting carriers. Three basic conditions must be met for laser emission:
(1) To produce sufficient population inversion distribution, that is, the number of high-energy state particles is sufficiently larger than that of the low-energy state;
(2) There must be a suitable resonant cavity that can play a feedback function, so that the stimulated emission photons are proliferated, thereby generating laser oscillation;
(3) Certain threshold conditions must be met to make the photon gain equal to or greater than the photon loss.
The working principle of the semiconductor laser is excitation mode. Semiconductor materials (i.e. electrons) are used to emit light between energy bands. The cleavage surface of semiconductor crystal is used to form two parallel mirrors as mirrors to form a resonant cavity, which makes the light oscillate and feedback to generate light radiation amplification and output laser.
The variety of semiconductor lasers has developed rapidly and has a wide range of applications. There are currently more than 300 types. Such as,
1.Industry and technology
1)Optical fiber communication. The semiconductor laser is the only practical light source for optical fiber communication system, and optical fiber communication has become the mainstream of contemporary communication technology.
2)CD access. The use of blue and green lasers can greatly increase the storage density of optical discs.
3)Spectral analysis. Far-infrared tunable semiconductor lasers have been used for environmental gas analysis, monitoring air pollution, automobile exhaust, etc.
4)Optical information processing. Semiconductor lasers have been used in optical information management systems. The two-dimensional array of surface-emitting semiconductor lasers is an ideal light source for optical parallel processing systems and will be used in computers and optical neural networks.
2.Medical and life science research
1)Laser surgery treatment.
2)Laser dynamic therapy.
3)3) Life science research.
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