The physical phenomenon of the laser (Light Amplification by Stimulated Emission) is based on optical energy exchange, which was first demonstrated with gas lasers. This phenomenon is a light amplification with which a coherent, monochromatic light beam can be generated that diverges only minimally even over longer distances.
Technically, a laser is a feedback amplifier in self- resonance. The resonance takes place in a space that forms the amplification medium. In this space, visible light, infrared light or ultraviolet radiation is reflected in such a way that it is amplified. The reflected wavelength depends on whether there is gas, liquid, semiconductor material or solid material in the cavity.
The reflection of the waves occurs at mirrors located at both ends of the cavity. Due to a narrow-band resonator, only modes of one or a few wavelengths are amplified, making the wavelength spectrum around the self-resonance extremely narrow and monochromatic. The generated wavelength can be in the visible range between 400 nm and 700 nm, but also in the infrared and ultraviolet or even in the X-ray range. The energy is injected from an external light source, and the amplified monochromatic wavelength is coupled out at one of the two mirrors, which is partially reflective. The total wavelength range is from about 100 nm up to 10,600 nm and depends on the laser technology and its field of application.
The different laser designs
Depending on the medium in the resonant cavity, a distinction is made between gas lasers, solid-state lasers, metal vapor lasers, fiber lasers, dye lasers and diode lasers or laser diodes. As far as gas lasers are concerned, the gases helium, neon, argon, nitrogen and carbon dioxide are used. In the case of solid-state lasers, ruby, titanium and rare earths are used to dope the base material. Examples are the different versions of the Yttrium Aluminum Garnet Laser(YAG). As for semiconductor lasers, some are based on aluminum compounds. The AlGaAs laser diode and the AlGaInP laser diode are worth mentioning. Other semiconductor lasers use indium compounds, such as the InGaN semiconductor laser and the InGaAs semiconductor laser.
From these basic techniques, the Distributed Feedback Laser( DFB) the Fabry Perot Laser( FPL), the laser diode, the Distributed Bragg Reflector( DBR) and the VCSEL laser, Vertical Cavity Surface Emitting Laser (VCSEL), have been developed for optical transmission technology. In addition to lasers with surface emitters, Surface Emitting, there are lasers with edge emitters, Edge-Emitting Lasers( EEL). Since lasers pose a risk to health and especially to eyesight, they have been classified into laser classes.
Lasers are used in CD drives, MO drives and DVD drives as well as in laser printers. Furthermore, in optical directional radio, in military and automotive technology, in cash registers, land surveying, in laser shows, as measuring and adjustment lasers as well as in research, medicine and material processing.