Knowing the characteristics of laser, let's see how it was discovered.
We must start with Archimedes. Archimedes was a great scholar, and his stories were widely circulated. He invented the method of weighing the crown while taking a bath. No one will forget, but he is certainly not familiar with his intention to make weapons. The hometown of Archimedes, an ancient Greek scholar, is a beautiful place along the Mediterranean coast. According to legend, in the 3rd century BC, there were rich products and outstanding people here. People advocate science, pay attention to civilization, live a rich life, live and work in peace and contentment, and present a peaceful and quiet scene everywhere. But the Roman Empire on the other side of the Mediterranean was very jealous of this. They had been aggressive and coveted this rich land for a long time. However, due to years of fighting, I have no time to take care of it, and the time is not yet ripe.
Smart Greeks also know that their beautiful land is in danger of being invaded at any time. They are prepared for danger in times of peace and study countermeasures. At that time, the Greek king also sent letters to the whole country to mobilize the people of the whole country to study the good strategy to deal with the invasion.
The Greeks who advocated science naturally turned their attention to science, hoping that science could save the country. Because Archimedes' hometown is in the Mediterranean, and it was the first place invaded by the Roman Empire, the burden of history fell on Archimedes' shoulders. He promised his elders in his hometown that he would develop a secret weapon to defeat the army of the Roman Empire. But what weapon he used, no one knows.
Suddenly one day, on a sunny day, a huge Roman fleet appeared in the Mediterranean and headed for Archimedes' hometown Greece, seeing that this beautiful land was about to be trampled by invaders.
Someone reported to Archimedes that Archimedes told everyone to go to the seaside to watch the excitement, and he wanted to destroy the Roman fleet alone. People will be skeptical. I saw Archimedes riding on a fast horse and running quickly up the hill.
Besides, the Roman fleet, mighty, aggressive, and straight.
The ship in front reported to the commander and found that many people on the shore were stopping to watch, without much fear, as if watching the Roman fleet exercise. The commander was overjoyed and thought, they are not prepared at all, and we will surely win a great victory.
At that moment, a bright light cut through the sky like a sword. Soon, the wooden warships of the Roman fleet caught fire one after another. In an instant, they saw smoke billowing and flames soaring. Crying, crackling of fire, the sound of running into the water. ...
The powerful Roman fleet was defeated without a fight.
People looked down the bright light and saw a huge concave mirror shining on the top of the mountain. Archimedes is directing his assistant to get busy.
Archimedes defeated the Roman fleet with light weapons.
Although this legend is very exciting, it can't stand scrutiny.
/kloc-In the 8th century, a Frenchman named Pierre, perhaps inspired by Archimedes, also designed a "light cannon". It consists of 168 mirrors, each of which is15cm long and 20cm wide. The total area of this 168 mirror is about 50,000 square centimeters, which is equivalent to the area of a hemispherical mirror with a radius of 0.9 meters.
The sunlight gathered by this kind of light mirror can make the pine board 47 meters away burn in a few minutes. However, if the pine board moves a little more, the number of mirrors will increase greatly. If you want to burn the pine wood beyond 1 km in half a minute, then the radius of the reflector must be increased to about 1 km. Such a large mirror, not to mention that it could not be made under the technical conditions at that time, is a difficult task even in today's highly developed technology. Even if you make such a big mirror, you can't use it on the battlefield, because a bullet can smash it. Imagine how big a mirror Archimedes needed to design to burn an enemy ship. Archimedes' sadness is that human beings can only make the mirror bigger and bigger according to their own enlightenment.
In the development of human society, people have always maintained a very close relationship with light. In addition to making full use of natural light sources, human beings have also invented many artificial light sources, from ancient wood burning, oil lamps and candles to various electric lights today. But these are ordinary lamps, and their important use is lighting, so it is difficult to play a greater role. In the past, due to frequent wars, people fantasized about using light as a weapon for a long time and made great efforts to this end.
Fantasy is fantasy after all. No matter how hard you try, you can't use sunlight as a weapon to kill the enemy. Lasers are even more unimaginable.
When the history developed to 19 16, the famous great physicist Einstein put forward the theory of being irradiated by laser, which laid a theoretical foundation for the invention of laser. However, due to the limitation of science and technology at that time, the laser was not invented.
Later, with the development of radio technology, people developed new bands, especially in order to obtain high-quality electromagnetic directional beams. However, it is required in engineering that the antenna for transmitting radio waves should not be too large (because the longer the wavelength, the larger the antenna size), and it can only develop in the direction of short wave. Microwave wavelength is the shortest among radio waves, so it develops rapidly. 1954, American physicist Towns and others successfully developed the first mother board of ammonia molecular gas microwave quantum amplifier with the wavelength of 1.25 cm, which is translated as "maser". 1957, solid-state microwave quantum amplifier came out. Due to the advantages of extremely low noise and high sensitivity, such devices have great application potential in modern science and technology such as long-range microwave radar, artificial satellite, radio astronomy, communication, telemetry and remote control. Therefore, it developed very rapidly in theory and technology, and soon entered the practical stage from the laboratory. Because laser is actually a quantum amplifier in optical band, the invention and development of microwave quantum amplifier laid a solid material foundation for the advent of laser.
The material foundation and theoretical foundation are already available. As long as someone combines them, they may be invented, but it's not that simple.
1958, Towns and former Soviet scholar Basov and others put forward the theory of extending microwave quantum amplification technology to light wave band. Two years later, in July 1960, American scholar Mayman successfully tested the first solid ruby optical quantum amplifier in the laboratory. At that time, he used the crystal doped with chromium ions in corundum (namely ruby crystal) as the working substance. Maiman also hesitated when choosing this material. At that time, a paper pointed out that ruby crystal could not be expected as the working material of laser, because according to its energy level structure and characteristics, the required pumping intensity was extremely high, which was not easy to realize technically. Other papers point out that the luminous quantum efficiency of ruby is low, only about 1%. Therefore, Maiman also considered using alkali metal vapor as working medium, but after analysis and comparison, it was found that it was difficult to use this vapor as working medium. Maiman used ruby crystal in the development of the maser, knowing its optical characteristics, so he decided to try ruby crystal first to understand the specific requirements for working materials, and then cooperated with materials scientists to develop new working materials.
He re-measured the quantum efficiency of ruby crystal and found that it was not 1% in the literature, but as high as 75% (100% in later experiments). He also analyzed the conditions for realizing the energy level particle inversion of ruby crystal, and found that as long as there is a blackbody radiation source equivalent to 5000K and the color temperature of the xenon lamp can reach 8,000, the energy level particle inversion can be realized, so it is technically possible. After these analyses, Meman firmly chose ruby crystal as the working material of his amplifier. The pump source used in this amplifier, pulsed xenon lamp, is spiral. The diameter of ruby rod is 1cm, and the length is 2cm, which just coincides with the silver-plated films at both ends of the spiral xenon lamp to form a resonant cavity. In this way, the first laser was made. Maiman turned on the power and the switch, and a dazzling magical red light came out. Maiman succeeded. He made the first optical quantum amplifier in the world. In fact, the optical quantum amplifier is a laser. This magical light is called "laser", which means optical amplification of stimulated emission. Its abbreviation is "laser", which is translated as "laser" by Taiwan Province academic circles. "Laser" and "Xiao Er" are popular names in China.
A year later, scientists in China also made a laser. At that time, it was during the three-year natural disaster in China, and people's lives were extremely difficult. China scientists carried forward the spirit of hard struggle, and made the first laser in China with patriotic blood and intelligence without equipment. Developed by Changchun Institute of Optics and Fine Mechanics, China Academy of Sciences. The material used at that time was also ruby crystal with a diameter of 0.5 cm and a length of 3 cm. The pump source used is a straight pulse xenon lamp, not a spiral xenon lamp. The designer thinks that the pumping efficiency of direct xenon lamp can be the same as that of spiral xenon lamp, but the manufacturing process is simpler.
As soon as the first laser appeared, it immediately attracted great attention from scientists all over the world, and many different types of lasers were invented one after another. He-Ne gas laser appeared in 196 1 year, gallium arsenic semiconductor laser in 1962, liquid laser in 1963 and chemical laser in 1965. Since then, various lasers have mushroomed. At present, there are thousands of working substances that can generate laser. The wavelength range of laser is expanding, the long wave direction is extended to far infrared, connected with millimeter wave of radio waves, and the short wave direction is extended to ultraviolet to X-ray. Because laser has many excellent characteristics, various scientific and technological fields take laser as a powerful means, forming a new interdisciplinary and applied technology, and laser processing, laser detection, laser communication, laser medicine, laser chemistry, laser holography and applied laser technology have emerged, making laser technology an important new force in modern high-tech fields.
The laser is basically composed of three parts: the first part is the working substance used to generate stimulated emission. The working substance can be solid, such as crystal and glass, or gas, such as inert gas and carbon dioxide, or liquid. The second part is called energy excitation device (also known as pump source), which inputs energy into the working medium in a certain way, so that the working medium is in the state of inversion of particle number. The third part is called optical resonant cavity, which is composed of two optical mirrors in a certain way. The working substance is placed between two mirrors. The function of the resonant cavity is to make the laser emitted by the working medium go back and forth between the two mirrors many times, thus forming continuous oscillation in the cavity. The energy excitation device transfers energy to the working substance, so that the working substance is in the state of population inversion, thereby generating stimulated emission of light. At first, the intensity of this stimulated emission was very weak. Because of the existence of the optical resonator, the laser in a certain direction travels back and forth between the two mirrors for many times and passes through the working medium for many times, which excites some working medium to emit laser, that is, it experiences an optical amplification caused by stimulated emission. After going back and forth enough times to make the amplification degree of light equal to or greater than various losses in the cavity, stable and continuous coherent light oscillation can be established in the cavity, and part of the oscillating light is output to the outside of the cavity through a mirror with a certain transmittance, forming the laser we need, which is the basic process of laser generation. Because of the different working materials, working modes and working wavelengths of light excitation sources, lasers can be divided into many types. Common are solid-state lasers, gas lasers, semiconductor lasers, chemical lasers, free electron lasers and so on. Besides, there are dye lasers, liquid lasers, excimer lasers, X-ray lasers and other lasers. At present, these lasers have formed a huge family. Because of its magical characteristics, laser has a wide range of application values in many fields and has become a veritable generalist.