Laser is a kind of device that can transmit laser. According to working medium, laser can be divided into 4 categories: gas laser, solid laser, semiconductor laser and dye laser. Recently, free electron lasers have been developed. High power lasers are usually pulsed output.
The working principle of laser
In addition to free electron lasers, the basic working principle of all lasers is the same. The indispensable condition for laser generation is that the population inversion and gain are greater than the loss, so the essential components of the device are the excitation (or pumping) source and the working medium with metastable energy levels. Excitation is the work medium that absorbs external energy and then excites it into an excited state, creating conditions for achieving and maintaining population inversion. Incentives include optical, electrical, chemical, and nuclear energy.
The working medium has a metastable energy level so that the stimulated radiation dominates, thereby realizing light amplification. The common component of the astronomy laser pointer is the resonant cavity, but the resonant cavity (see the optical resonant cavity) is not an integral part. The resonant cavity allows the photons in the cavity to have a consistent frequency, phase, and direction of travel, so that the laser has Good directionality and coherence. Moreover, it can well shorten the length of the working substance, and also can adjust the mode of the generated laser by changing the length of the cavity (ie, mode selection), so the general laser has a resonant cavity.
A laser is usually composed of three parts:
1. Working substance: The core of the laser, only the substances that can realize the energy level transition can be used as the working substance of the laser.
2. Incentive energy: Its role is to give energy to the working substance and to excite atoms from low energy levels to high energy levels. Usually there can be light energy, thermal energy, electricity energy, chemical energy, etc.
3. The optical cavity: the first one is to make the stimulated radiation of the working substance continuous; the second is to accelerate the photon; the third is to limit the direction of the laser output. The simplest optical resonant cavity consists of two parallel mirrors placed at both ends of a HeNe laser. When some helium atoms undergo transitions between the two energy levels that achieve population inversion and radiate photons parallel to the direction of the laser, these photons will be reflected back and forth between the two mirrors, and they will continue to cause stimulated radiation. A very strong laser is produced very quickly.
The quality and purity of light emitted by lasers can be applied in many ways.
Ruby lasers: The original laser was a ruby that was excited by a bright flash light bulb. The laser produced was a "pulsed laser" rather than a continuously stable beam. The quality of the light produced by this laser is fundamentally different from the laser light produced by the laser diodes we use today. This strong light emission, which lasts only a few nanoseconds, is ideal for capturing easily moving objects such as holographic portraitures. The first laser portrait was born in 1967. Ruby lasers require expensive ruby and can only generate short-pulse light.
Laser Diodes: Laser diodes are one of the most commonly used lasers. The phenomenon of spontaneous recombination of electrons and holes on the sides of a PN junction of a diode is called spontaneous emission. When the photons generated by spontaneous emission pass through the semiconductor, once they pass near the emitted electron-hole pairs, they can stimulate the two to recombine to produce new photons, which induce the recombination of excited carriers and emit new photons. The phenomenon is called stimulated radiation.
If the injection current is sufficiently large, a carrier distribution opposite to the thermal equilibrium state is formed, ie, the number of particles is reversed. When carriers in the active layer are reversed in large numbers, photons generated by a small amount of spontaneous radiation generate inductive radiation due to the reciprocal reflection of both ends of the resonant cavity, resulting in selective frequency resonant feedback, or gain for a certain frequency. When the gain is greater than the absorption loss, a coherent light with a good spectral line-laser can be emitted from the PN junction. The invention of laser diodes allows rapid popularization of laser applications. Various types of applications, such as information scanning, optical fiber communications, laser ranging, laser radar, laser discs, laser pointers, supermarket receipts, etc., are constantly being developed and popularized.