T YPE AND DESIGN FEATURES OF COHERENT RADIATION SOURCES. Coherence. Spatial coherence determined by the angle of the light beam.. In addition, when assessing the coherence laser used parameters such as area, volume and time coherence. To obtain coherent radiation used in optoelectronics lasers. Depending on the type of environment in which the generation of optical vibrations, lasers are divided into gas, solid-state and semiconductor.

S OLID - STATE LASERS The first working laser was made on ruby American Theodore Maiman in 1960 in the research laboratory of Hughes Aircraft. The active medium is a solid-state lasers solid foundation in the form of a crystal, garnet or glass, which included impurities activator. Ruby is a crystal Al 2 O 3, in which individual ions Al 3+ ions are replaced by trivalent chromium. Pink ruby crystals grown from the melt is usually a mixture of Cr 2 О 3, Al 2 O 3. The scheme for energy levels shown in fig. 5.1 Fig Diagram of the energy levels of ruby laser.

L IQUID LASERS The active laser medium serves as a solution of inorganic compounds of rare earth elements or solutions of organic dyes. The loss of radiation in the active medium of these lasers is less than solid-state due to less heterogeneity and lack of defects. Cooling the environment at the expense of recycling. The main drawback is a small period of limited time, loss of sediment (1-2 months). Scheme liquid laser energy levels.

S EMICONDUCTOR LASERS. The distribution of electrons in the semiconductor energy levels described by the Fermi-Dirac where Pn (Q) - electron occupation probability level of energy Q; - The Fermi level. Such a distribution of holes is: The Fermi level is defined as the probability of settlement which the electron (hole) is 0.5. At T = 0 all levels below the Fermi level populated by electrons, and all levels above the Fermi level - free

T HE DESIGN AND PRINCIPLES OF GAS SOURCES OF COHERENT RADIATION. In gas lasers used for excitation of atoms in a gas discharge, due to the large size, high power, low efficiency and resistance to mechanical stress. However, these devices provide the best coherence and direction of radiation, which is very important in optical storage devices. Active laser centers in gas environments - is an atom in atomic lasers, ions - in ion and molecule - in molecular lasers. In atomic energy lasers distance between energy levels is 0.1 eV eV, corresponding to a wavelength of microns; in ionic gas lasers power distance eV ( microns); in molecular gas lasers eV microns).

In atomic helium-neon laser active medium is a mixture of helium and neon. In the gas discharge tube pressure helium Pa, and neon Pa. Active centers - neon atoms. Four-level scheme of energy levels of helium- neon laser is shown in Fig. 5.2, a simplified block diagram - Fig Fig Diagram of the energy levels of helium-neon laser.

The glow gas discharge in helium-neon mixture creates conditions for population inversion in neon laser levels. Helium is used for resonant excitation of neon. The collision of electrons Plaza we helium atoms moving in an excited state and in inelastic collisions with the atoms of neon transmit them to their energy. Neon atoms are selectively populate the upper laser level. Reduced levels of habitability 3p, 2p and 1s carried neon atoms in collisions with the walls of the gas discharge tube. The range of helium-neon lasers most broad and includes devices with multimode, single-mode and single-frequency generation up to 1 Watt (standard 0.1 W). Wavelength ; 1.15 and 3.39 microns. Top generating samples of the light beam with divergence close to the diffraction limit. The efficiency of the helium-neon laser - less than half percent. Ion gas lasers - the main source of coherent radiation in the blue-green region of the spectrum. In these lasers are used transitions between energy levels of ions of noble gases and vapors zinc; potassium, sulfur and other substances. Ion lasers have low efficiency (1%) require effective cooling.