laser

History

The invention of the laser is a major achievement of science and technology in the 20th century. It enables people to finally have the ability to drive the light-emitting process of molecules and atoms with extremely small scales, large numbers, and extremely chaotic movements, so as to obtain the ability to generate and amplify coherent infrared rays, visible rays, and ultraviolet rays (as well as X-rays and gamma rays). The rise of laser science and technology has brought humans to a new level of understanding and utilization of light. The birth history of lasers can be roughly divided into several stages, among which the concept of stimulated radiation proposed by Einstein in 1916 is its important theoretical basis. This theory states that matter particles in a high-energy state are subjected to a photon whose energy is equal to the energy difference between the two energy levels, will transition to a low-energy state, and produce a second photon, which is emitted at the same time as the first photon, This is stimulated radiation. The light output by this radiation has been amplified, and it is coherent light, that is, the emission direction, frequency, phase, and polarization of multiple photons are exactly the same.

development stage

Since then, the establishment and development of quantum mechanics have enabled people to have a deeper understanding of the microscopic structure and laws of motion of matter. Issues such as energy level distribution, transitions, and photon radiation of microscopic particles have also been more powerfully proved. This is also an objective fact. In fact, Einstein’s theory of stimulated radiation has been improved, and the theoretical foundation for the production of lasers has been further established. In the late 1940s, after the birth of quantum electronics, it was quickly applied to the study of the interaction between electromagnetic radiation and various microscopic particle systems, and many corresponding devices were developed. The rapid development of these scientific theories and technologies has created conditions for the invention of lasers.

If a system has more particles in high-energy states than in low-energy states, a population inversion state occurs. Then as long as one photon is triggered, it will force an atom in a high-energy state to be stimulated to radiate an identical photon, and these two photons will trigger other atoms to be stimulated to radiate, thus achieving light amplification; The feedback effect of the appropriate resonant cavity on the laser will form optical oscillation, thus emitting laser light. This is how lasers work. In 1951, American physicists Purcell and Pound successfully caused the inversion of the number of particles in the experiment, and obtained the stimulated radiation of 50 kHz per second. Later, American physicist Charles Townes and Soviet physicists Masov and Prokhorov successively proposed the design of using the principle of stimulated radiation of atoms and molecules to generate and amplify microwaves.

However, most of the above-mentioned microwave spectroscopy theory and experimental research belonged to “pure science”, and it was still very elusive at that time whether the laser could be successfully developed.

mature stage

But scientists’ efforts finally paid off. In 1954, the aforementioned American physicist Towns finally made the first ammonia molecular beam maser, successfully creating a precedent for using molecular and atomic systems as coherent amplifiers or oscillators for microwave radiation.

The maser developed by Towns et al. only produced microwaves with a wavelength of 1.25 cm, and the power was very small. The need for continuous development of production and technology drives scientists to explore new light-emitting mechanisms to produce new light sources with excellent performance. In 1958, Towns and his brother-in-law Arthur Shaw combined the maser with the theoretical knowledge of optics and spectroscopy, and put forward the key suggestion of using an open resonator, and prevented the coherence and directionality of the laser. , linewidth and noise properties. At the same time, Basov, Prokhorov and others also proposed a principled scheme to realize light amplification by stimulated emission of radiation.

Since then, many laboratories around the world have been involved in a fierce research and development competition to see who can successfully manufacture and operate the world’s first laser.

In 1960, American physicist Theodore Maiman narrowly won the worldwide race to develop it in his research laboratory in Miami, Florida. He used a high-intensity flash tube to stimulate the chromium atoms in the ruby crystal, which produced a very concentrated thin beam of red light, which when it was directed at a certain point, could make that point reach a temperature higher than that of the sun.

The “Mayman Design” has aroused shock and suspicion in the scientific community, because what scientists have been watching and looking forward to is a helium-neon laser.

Although Maiman was the first scientist to introduce the laser into a practical field, there was a great controversy in court over who actually invented the technology. One of the contenders was Gordon Gould, the inventor of the term “laser” (short for “stimulated emission optical frequency amplifier”). He coined the term in 1957 while working on his doctorate at Columbia University. At the same time, the inventors of the maser, Towns and Xiao Luo, also developed the concept of laser light. In the final judgment of the court, Townes became the winner because the paperwork of the study was 9 months earlier than Gould. However, Maiman’s laser invention rights have not been shaken.

In December 1960, Jawan, an American scientist who was born in Iran, finally successfully manufactured and operated the world’s first gas laser, a helium-neon laser. In 1962, three groups of scientists invented the semiconductor laser almost simultaneously. In 1966, scientists developed an organic dye laser whose wavelength can be continuously adjusted within a certain range. In addition, there are also chemical lasers with large output energy, high power, and independent of the power grid.

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