The production of laser must choose the appropriate working medium, which can be a normal body, a liquid, a solid or a semiconductor.In this medium, the number of particles can be reversed to create the necessary conditions for obtaining the laser.
Structure of laser:
1. Working medium of laser
Production of lasers must choose the appropriate working medium, which can be a normal body, a liquid, a solid or a semiconductor.In this medium,the number of particles can be reversed to create the necessary conditions for obtaining the laser.As the core of the laser, it is composed of activated particles and matrix. The energy level structure of the activated particles determines the laser characteristics such as spectral characteristics and fluorescence life of the laser, and the matrix mainly determines the physical and chemical properties of the working substances.According to the level structure of the active particle, it can be divided into three level system and four level system.There are four main types of working material: cylindrical, flat, disc and tubular.
2. Motivation source
In order to cause the inversion of the number of particles in the working medium, a certain method must be used to excite the atomic system to increase the number of particles in the upper energy level.In general, the method of gas discharge can be used to use electrons with kinetic energy to excite medium atoms, which is called electric excitation.Pulse light source can also be used to illuminate the working medium, which is called light excitation.There are also thermal excitation, chemical excitation and so on.The various forms of excitation are referred to visually as pumping or pumping.In order to get a continuous laser output, it is necessary to keep pumping more particles in the upper level than in the lower level.
3. Condensing system
There are two functions of the condenser cavity. One is to effectively coupling the pump source with the working material.The other is to determine the distribution of the pumping optical density on the laser material, which affects the uniformity, divergence and optical distortion of the output beam.Both the working material and pump source are installed in the condenser cavity, so the quality of the condenser cavity directly affects the efficiency and performance of the pump.
It is composed of total reflector and partial reflector and is an important part of solid state laser.The optical resonator not only provides the optical positive feedback to maintain the laser continuous oscillation to form the excited beam, but also restricts the direction and frequency of the oscillating beam to ensure the high monochromatism and high directivity of the output laser.The optical resonator of the most simple and commonly used solid state laser is composed of two plane mirrors or spherical mirrors placed in opposite directions.
5. Cooling and filtering system
Cooling and filtering systems are essential auxiliary devices for lasers.Solid state laser work will produce more serious thermal effect, so usually to take cooling measures.It is mainly used to cool the laser working material, pumping system and concentrator to ensure the normal use of the laser and the protection of the equipment.Cooling methods include liquid cooling, gas cooling and conduction cooling, but liquid cooling is the most widely used method at present.In order to obtain a high monochromatic laser beam, the filter system plays a very important role.The filter system can filter most of the pumping light and some other interfering light, making the output laser very monochromatic.
Type of laser:
1) Ruby laser:
Original laser was a "pulse laser" of rubies excited by a bright flashing bulb, rather than a steady stream of light.The beam quality produced by such a laser is substantially different from that produced by the laser diodes we use today.The bright light lasts only a few nanoseconds, making it ideal for capturing easily moving objects, such as holographic portraits first taken in 1967.Ruby lasers require expensive rubies and produce only brief pulses of light.
2) Helium-Neon laser:
He-ne laser is a kind of gas laser, which is often used by holographers.It has two advantages:
1. Generate continuous laser output
2, do not use flashlight for light excitation, but electrically excited gas.
3) Laser diode:
Laser diode is one of the most commonly used lasers.The spontaneous combination of electrons and holes on both sides of the DIODE PN junction and the phenomenon of luminescence is called spontaneous radiation.When a photon emitted by spontaneous radiation passes through a semiconductor, it can stimulate the combination of the two to produce new photons once it passes near the electron-hole pair being emitted.This photon-induced excited carrier binds and releases new photons, called stimulated emission.When the injected current is large enough, the carrier distribution opposite to the thermal equilibrium state will be formed, that is, the number of particles will reverse.