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Laser basic knowledge Apr 12, 2018

Laser basics:

1, a brief history of laser development

      At the beginning of the last century, a group of theoretical physicists represented by big scientist Einstein laid one of the important disciplines of modern physics, quantum theory. Laser-LASER is an abbreviation for English Light-Amplification-Stimulated Emission of Radiation, meaning that it is amplified by laser radiation. Quantum theory predicts the possibility of stimulated radiation. Forty years ago, American scientists first used the ruby as a working medium to obtain laser output. About two years later, our scientists also developed the first ruby laser.

      When lasers first appeared, Chinese scholars translated them into lasers based on the pronunciation of English LASER. China, Taiwan and Hong Kong, also frequently used the term laser. Later, after the proposal of Qian Xuesen, the scientist, it was changed to laser and used today. After more than forty years of development, especially in the last ten years, the rapid development of laser technology has resulted in a wide variety of lasers and applications. Laser technology and its products have penetrated into many fields, including our daily lives.

2, the basic working principle of the laser

Quantum theory holds that all substances consist of a variety of microscopic "particles," such as molecules, atoms, protons, neutrons, and electrons. In the microcosm, all kinds of particles have their own energy level structure. When a particle falls from a high energy level to a low energy level, according to the law of conservation of energy, it releases the energy of the difference between the two energy levels. Usually this energy is released in both light and heat. The working principle of the ordinary electric light gun is that the filament absorbs the electric energy, and various particles in the filament are pushed to a higher energy level by the electric energy, because the high energy level is unstable, and it has a tendency of downward energy level transition. When a high-energy particle transitions to a low energy level, the filament glows and heats up.

      The luminescent radiation of the filament is random, and particles of various energy levels radiate light of different wavelengths when they transition downwards, and there is no correlation. This is called spontaneous emission. Unlike lasers, scientists have carefully designed the structure of the laser so that the radiation of one energy level pair is amplified, while the radiation of other energy level pairs is not amplified or suppressed. In a laser, when a particle radiates down and emits a photon, this photon will induce other particles to excite the same photon. This is an avalanche replication process, so the light emitted by the laser has a correlation. This process is called Excitation.

      The laser usually consists of three major components: the excitation source, the working substance, and the resonant amplification cavity. The working substance absorbs the energy of the excitation source and causes its internal "particles" to rise to high energy levels. The role of the resonant cavity is to oscillate and amplify the radiation of a certain energy level pair so as to realize stimulated radiation and output laser light.

3, the difference between laser and ordinary light source

      The main difference between laser and common light source is: laser's monochromaticity, directionality and high brightness. The so-called monochromaticity means that the laser wavelength is a single wavelength, usually a laser outputs only light of one wavelength or several wavelengths, and ordinary light sources output light of various wavelengths; square means that the radiation of a laser is concentrated in a certain In the direction, ordinary light sources have radiation in all directions; high brightness means that the energy of the laser is concentrated in a small spot, whereas the light of an ordinary light source is divergent.