A laser is a device that converts pump energy (light, electrical, thermal, chemical, etc.) into the energy of a coherent, monochromatic, polarized and narrowly directed radiation flux.
The physical basis of laser operation is the quantum-mechanical phenomenon of stimulated (induced) radiation. Laser radiation can be continuous, with constant power, or pulsed, reaching extremely high peak powers. In some schemes, the working element of the laser is used as an optical amplifier for radiation from another source. There are a large number of types of lasers that use all aggregate states of matter as a working medium. Certain types of lasers, such as dye solution lasers or polychromatic solid-state lasers, can generate a range of frequencies (optical cavity modes) over a wide spectral range. Laser sizes range from microscopic for some semiconductor lasers to soccer field sizes for some neodymium glass lasers. The unique properties of laser radiation made it possible to use them in various branches of science and technology, as well as in everyday life, from reading and writing CDs to research in the field of controlled thermonuclear fusion.