19 16, Einstein published the article Quantum Theory of Radiation, and put forward the concept of stimulated radiation for the first time. According to this theory, a matter particle in a high-energy state will be transformed into a low-energy state under the action of a photon whose energy is equal to the energy difference between two energy levels, and a second photon will be generated and emitted at the same time as the first photon, which is stimulated radiation. The light output by this radiation is amplified and coherent, that is, the direction, frequency, phase and polarization of the two photons are exactly the same. With the establishment and development of quantum mechanics, people have a deeper understanding of the microstructure of matter and its motion law, and the energy level distribution, transition and photon radiation of microscopic particles have also been proved more forcefully, which objectively improves Einstein's radiation theory and lays a theoretical foundation for the generation of laser.
In the late 1940s, quantum electronics appeared, which mainly studied the interaction between electromagnetic radiation and various micro-particle systems, and developed corresponding devices. These advances in theory and technology prepared the conditions for the invention of laser. 195 1 year, American physicists purcell and Pound suddenly reversed the magnetic field applied to the working substance in the nuclear induction experiment, resulting in the reversal of the number of particles in the nuclear spin system and the stimulated radiation of 50 kHz per second, which is an experiment of great significance in the history of laser.
1954, American scientist Downs and his assistants Gordon and Zeg made the first ammonia molecular beam maser. This maser produced 1? The microwave power with a wavelength of 25 cm is very small, but it successfully creates a precedent of using molecular or atomic systems as coherent amplifiers or oscillators for microwave radiation, so it is of great significance. At the same time, Basov and ProHohloff of the former Soviet Union and Weber of the University of Maryland also independently put forward the idea of maser. Due to the success of maser, it is further considered that if the principle of maser is extended to optical frequency band, it is possible to make an oscillator or amplifier for coherent light radiation. The need of production and the development of science and technology also urge scientists to explore new luminous mechanisms and produce new light sources with excellent performance.
From 65438 to 0958, Sholo and Towns combined the knowledge of maser, optics and spectroscopy, put forward the key suggestion of using open resonator, and predicted the characteristics of laser such as coherence, directivity, linewidth and noise.
At the same time, Basov, ProHohloff and others also put forward the principle scheme to realize the optical amplification of stimulated radiation. 1960 In July, American young scientist Mayman successfully manufactured and operated the world's first laser. The working substance is artificial ruby, the excitation source is intense pulsed xenon lamp, and the wavelength is 0? 6943 micron red pulse laser. After the first laser came out, lasers developed rapidly, and many different types of lasers appeared in a short time. From 196 1 to 1964, Nd: YAG laser and Nd: YAG laser were made successively, and they and ruby laser are still widely used solid-state lasers. At the end of 1960, Jia Wan of Bell Telephone Laboratory and others made the first gas laser He-Ne laser.
1962, three groups of scientists invented the semiconductor junction laser almost simultaneously. 1966 An organic dye laser with continuously adjustable wavelength was developed. In addition, there are chemical lasers with high output energy and high power, which do not depend on the power grid. Because of its outstanding characteristics, laser was quickly applied to industry, agriculture, precision measurement and detection, communication and information processing, medical care, military and other aspects, and caused revolutionary breakthroughs in many fields. For example, with the concentration and extremely high energy of laser, various materials can be processed.
As a means to stimulate, mutate, cauterize and vaporize organisms, laser has achieved good results in medicine and agriculture. Militarily, in addition to communication, night vision, early warning and ranging, various laser weapons and laser-guided weapons have been put into practical use. In the future, with the further development of laser technology, the performance and cost of lasers will be further reduced, the application scope will be continuously expanded, and it will play an increasingly important role.