Solid-state laser: operating principle, application

This article shows what are the sources of monochromatic radiation and what advantages the laser has in solid-state before other species. Here it is told how the generation of coherent radiation occurs, why the pulse device is more powerful, for which it is necessary to engrave. Also, three compulsory elements of the laser and the principle of its operation are considered here.

Zone theory

Before talking about how the laser works (solid-state, for example), you should consider some physical models. From school lessons, one remembers that the electrons are located around the atomic nucleus in certain orbits, or energy levels. If we have at our disposal not one atom, but many, that is, we consider any three-dimensional body, then there is one difficulty.

According to the Pauli principle, there can be only one electron in a given body with the same energy. In this case, even the smallest grain of sand contains a huge number of atoms. Nature in this case has found a very elegant way out - the energy of each electron differs from the energy of the neighboring electron by a very small, almost indiscernible value. In this case, all electrons of one level are "compressed" into one energy zone. The zone in which the electrons most distant from the core are called valence. The zone following it has a higher energy. In it, electrons move freely, and it is called the conduction band.

Emission and Absorption

Any laser (solid-state, gas, chemical) works on the principles of electron transfer from one zone to another. If a light falls on the body, the photon gives the electron enough strength to make it appear in a higher energy state. And vice versa: when an electron passes from the conduction band to the valence one, it emits one photon. If the substance is a semiconductor or dielectric, the valence and conductivity zones are separated by an interval in which there are no levels. Accordingly, electrons can not be there. This interval is called the forbidden zone. If the photon has sufficient energy, then the electrons overcome this interval abruptly.

Generation

The principle of operation of a solid-state laser is based on the fact that a so-called inverse level is created in the forbidden zone of matter. The lifetime of an electron at this level is higher than its time in the conduction band. Thus, in a certain period of time it is on it that electrons "accumulate". This is called inverse population. When a photon of the desired wavelength passes by such a level dotted with electrons, it causes simultaneous generation of a large number of light waves of equal length and phase. That is, the electrons of the avalanche all simultaneously go to the ground state, generating a beam of monochromatic photons of sufficiently high power. It is worth noting that the main problem of the developers of the first laser was the search for a combination of substances for which the inverse population of one of the levels would be possible. The first working substance was a doped ruby.

Composition of the laser

The solid-state laser for the main components does not differ from the other species. The working body, in which the inverse population of one of the levels occurs, is illuminated by some light source. It is called pumping. Often it can be a conventional incandescent lamp or a gas-discharge tube. Two parallel running ends of the working body (a solid-state laser means a crystal, a gas medium is a sparse medium) form a system of mirrors, or an optical resonator. He collects into the beam only those photons that run parallel to the outlet. Pumping of solid-state lasers usually occurs with the help of flash tubes.

Types of solid-state lasers

Depending on the method of output of the laser beam, continuous and pulsed lasers are distinguished. Each of them finds application and has its own peculiarities. The main difference is that pulsed solid-state lasers have a higher power. Since for each shot the photons seem to be "digging", then one pulse is capable of giving out more energy than continuous generation in the same period of time. The less the pulse lasts, the stronger each "shot". At the moment it is technologically possible to build a femtosecond laser. One of his impulses lasts about 10 ^-15 seconds. This dependence is related to the fact that the processes of reverse population described above last very, very little. The longer it takes to wait before the laser "shoots", the more electrons will have time to leave the inverse level. Accordingly, the concentration of photons and the energy of the output beam decrease.

Laser engraving

Patterns on the surface of metal and glass objects adorn the everyday life of a person. They can be applied mechanically, chemically or by laser. The latter way is the most modern. Its advantages over other methods are as follows. Since there is no direct impact on the surface being treated, it is almost impossible to damage a thing in the process of applying a pattern or inscription. The laser beam burns very shallow grooves: the surface with such engraving remains smooth, which means that the thing does not get damaged and will last longer. In the case of metal, the laser beam changes the structure of the substance itself, and the inscription will not be erased for many years. If you use a thing carefully, do not immerse it in acid and do not deform, then for several generations the pattern on it will be exactly preserved. The laser for engraving is best to choose a solid-state pulse for two reasons: it is easier to control the processes in a solid body, and it is optimal in terms of the ratio of power and price.

Installation

For engraving there are special settings. In addition to the laser itself, they consist of mechanical guides, through which the laser moves, and the monitoring equipment (computer). The laser machine is used in many branches of human activity. Above we talked about decorating household items. Nominal cutlery, lighters, glasses, watches will remain in the family for a long time and will remind you of happy moments.

However, not only domestic, but also industrial goods need laser engraving. Large factories, for example, automobile, produce details in huge numbers: hundreds of thousands or millions. Each such element must be labeled - when and who created it. The best way than laser engraving is not found: numbers, time of release, service life will remain for a long time even on moving parts, for which the risk of abrasion is increased. The laser machine in this case should be characterized by increased power, as well as safety. After all, if engraving, at least a fraction of percent, changes the property of a metal part, it can react differently to an external effect. For example, break at the place of inscription. However, a simpler and cheaper installation is suitable for domestic use.