The laser is one of the greatest achievements of physics in the 20th century, combining the strict principles of quantum mechanics with the poetry of light. Its appearance changed our understanding of what emission, energy, and precision are. Today, lasers permeate all areas of human activity — from surgery to astrophysics, from communication to art. But the path to creating controlled light was long and required an understanding of the very nature of the photon. Physics of Ordered Light The term "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation, meaning "light amplification by stimulated emission of radiation." The basis of the laser's operation lies in the quantum principle discovered by Albert Einstein in 1917: atoms are capable of not only absorbing but also emitting photons under the action of external influence. A conventional light source, such as a lamp, emits photons randomly, in different directions, and at different frequencies. A laser, however, creates a stream in which all light quanta move in unison, maintaining the same wavelength and phase. Such emission is called coherent. Thanks to this, the laser beam does not scatter but remains narrow and directed over long distances. Historical Prehistory and the Birth of the Laser The idea of controlled light originated in the mid-20th century when Soviet and American physicists independently began to seek a way to implement stimulated emission in practice. The first prototype was the maser — a device operating in the microwave range. In 1960, American physicist Theodore Maiman created the first optical laser on a ruby crystal. Its pulse lasted only fractions of a second, but became a symbol of a new era in science. Since then, lasers have developed rapidly. Scientists have created gas, semiconductor, solid-state, and fiber lasers, each opening up its own field of application. Over several decades, the technology has transformed from a laboratory experiment into the foundation ... Read more