Find the data of laser ranging

Hu Haitang, former Deputy Director of Information Department of State Science and Technology Commission of Laser and Space Technology —— 1. Laser technology-1. What is laser and laser technology-laser is a kind of light that does not exist in nature and has the characteristics of good directivity, high brightness, good monochromaticity and good coherence after being excited. Physicists trace the mechanism of laser generation back to Einstein's hypothesis when he explained the law of blackbody radiation in 19 17, that is, the absorption and emission of light can go through three basic processes: stimulated absorption, stimulated radiation and spontaneous radiation. As we all know, the luminescence of any light source is related to the motion state of particles in its substance. When particles (atoms, molecules or ions) at a low energy level absorb external energy (light) at an appropriate frequency and are excited to jump to a corresponding high energy level (stimulated absorption), they always try to jump to a lower energy level and release excess energy in the form of photons. Without the action of foreign photons, light is spontaneously released (spontaneous radiation), and the light released at this time is ordinary light (such as electric lights and neon lights). ), which is characterized by inconsistent frequency, direction and rhythm of light. However, if the extra energy is released in the form of photons (stimulated radiation) when the foreign photons directly jump from high energy level to low energy level, the released photons are completely consistent with the foreign incident photons in frequency, phase and propagation direction, which means that the foreign light is strengthened, which is called optical amplification. Obviously, if the number of particles in the high-energy level is more than that in the low-energy level through stimulated absorption (the number of particles is reversed), this light amplification phenomenon will be more obvious, and it is possible to form a laser at this time. Laser is called magical light because it has four characteristics that ordinary light does not have at all. -1. Good directionality-Ordinary light sources (sun, incandescent lamp or fluorescent lamp) emit light in all directions, while the emission direction of laser can be limited to a solid angle less than a few milliradians (Figure 8-9), which increases the illumination in the irradiation direction by ten million times. Laser collimation, guidance and ranging all take advantage of this good directivity. -2. High brightness-Laser is the brightest light source in the contemporary era, which can only be compared with the intense flash at the moment when the hydrogen bomb explodes. The brightness of sunlight is about 103W/(cm2. Spherical), the brightness of high-power laser output light is 7 ~ 14 orders of magnitude higher than that of sunlight. In this way, although the total energy of laser is not necessarily large, due to the high concentration of energy, it is easy to produce high pressure and high temperature of tens of thousands of degrees Celsius or even millions of degrees Celsius at a tiny point. Laser drilling, cutting, welding and laser surgery all take advantage of this feature. Monochromatic light is electromagnetic wave. The color of light depends on its wavelength. The light emitted by ordinary light sources usually contains various wavelengths and is a mixture of various colors of light. Sunlight includes seven colors of visible light such as red, blue, yellow, green, cyan, blue and purple, and invisible light such as infrared light and ultraviolet light. The wavelength of a laser is only concentrated in a very narrow spectral band or frequency range. For example, the wavelength of He-Ne laser is 632.8 nm, and its wavelength variation range is less than one ten thousandth of a nanometer. Because of the good monochromaticity of laser, it provides an extremely favorable means for scientific experiments such as precision instrument measurement and stimulation of certain chemical reactions. -4. Good coherent interference is an attribute of wave phenomenon. Based on the characteristics of high directivity and monochromaticity of laser, it must have excellent coherence. This characteristic of laser makes holographic photography a reality. -The so-called laser technology refers to the exploration and development of various methods of generating laser, and the exploration and application of these characteristics of laser for the benefit of mankind. Since 1960, the United States successfully developed the world's first ruby laser, and 196 1 year, China also successfully developed the first domestic ruby laser, laser technology is regarded as another major scientific and technological achievement after quantum physics, radio technology, atomic energy technology, semiconductor technology and computer technology in the 20th century. In the past 30 years, laser technology has made great progress. Not only have lasers with different characteristics been developed, but the application fields of lasers have been continuously expanded, forming a series of emerging industries such as laser disc player, laser medical treatment, laser processing, laser holography, laser phototypesetting printing, laser printing, laser weapons and so on. The rapid development of laser technology makes it one of the "leading technologies" in the new technological revolution. (2) Various lasers —— In the light source, the inversion of the number of particles in the energy level is the premise of realizing light amplification, that is, the premise of generating laser. In order to realize the inversion of the number of particles, a large number of particles originally in the low energy level need to jump to the high energy level with the help of external light. This process is called "excitation". What we usually call a laser is a device that excites the particles in the light source to generate stimulated radiation transition, realizes the inversion of the number of particles, and then generates light amplification through stimulated radiation. Although there are many kinds of lasers, their task is to obtain lasers through excitation and stimulated radiation. Therefore, the basic composition usually consists of three parts: the active medium (i.e., the working medium that can generate particle number inversion after being excited), the excitation device (i.e., the energy source and the pumping source that can generate particle number inversion in the active medium) and the optical resonator (i.e., two plane mirrors that can repeatedly oscillate and amplify the light beam) (Figure 8-2). After more than 30 years of development, more than 200 kinds of practical lasers have been developed in various countries. There are many kinds, different characteristics and different uses. There are many ways to classify lasers: according to working substances, there are gas, glass, crystal, liquid, semiconductor, excimer and other lasers, as well as chemical lasers (excited by chemical reactions) and free electron lasers; According to the wavelength division, the wavelength range covered includes far infrared, infrared, visible light, ultraviolet and even far ultraviolet. Recently, X-ray lasers and gamma-ray optical devices have been developed. According to the different excitation methods, there are light excitation (light source or ultraviolet light excitation), gas discharge excitation, chemical reaction excitation, nuclear reaction excitation and so on. According to different output modes, there are continuous, single pulse, continuous pulse and ultrashort pulse. Judging from the size of power output, the continuous output power is as small as microwatts and as large as megawatts; The output energy of the pulse can range from microjoules to over 654.38+ million joules, and the pulse width can range from milliseconds to picoseconds or even femtoseconds (654.38+0.000 trillion). -The emergence of various lasers mentioned above is mainly to meet different application purposes. For example, laser processing and some military lasers require high-power lasers or high-energy lasers (so-called intense lasers). Some people want to shorten the pulse time as much as possible in order to do some research on express delivery process. Some also put forward high requirements for improving the monochromaticity of light, improving the mode of output light, improving the intensity distribution of light spots, and requiring adjustable wavelength, thus making the exploration depth and application breadth of laser unprecedented. The application of laser has penetrated into various fields and is miraculously changing our world. (3) The vigorous application of laser-laser is not only one of the most important inventions of the 20th century, but also the application of laser technology has been widely used in industry, agriculture, military, medicine and even all aspects of society, playing an increasingly important role in the progress of human society. -1. Application of laser in information field-Semiconductor laser and fiber amplifier are two key technologies of optical fiber communication. The laser emitted by the semiconductor laser is not only monochromatic and coherent, but also the frequency of light wave is ten thousand times higher than that of microwave. Therefore, optical fiber communication with laser as information transmission carrier and optical fiber as information transmission line not only has good communication quality, strong anti-interference ability and good confidentiality, but also has a communication capacity 10,000 times higher than that of microwave communication. An optical fiber thinner than a hair can transmit tens of thousands of telephone calls or thousands of TV programs at the same time, thus making communication truly a new network era leading to thousands of households. -Using laser technology for optical storage is a revolutionary leap in information storage. The recording density of CD audio disc is equivalent to 10 megabit /cm2, and it can record 78 minutes of music programs, which is several orders of magnitude better than that of optical disc. A CD-ROM with a diameter of 5 inches has a capacity of 650 megabits. A kind of LD (Laser Recording Disc), or the most popular VCD (Laser Video Disc) in recent years, and a new generation of DVD (Digital Video Disc) after VCD, whose video contains thousands of times more signals than CD, can record 100 minutes of high-definition video programs. CD, VCD and LD not only occupy a considerable share in the market of playback equipment, but also can be played on computers equipped with laser drivers. In addition, laser printers, laser fax machines, laser phototypesetting, laser large-screen color TV, optical fiber cable TV and atmospheric laser communication have also been widely used. 2. Application of Laser in Holography As a wave phenomenon, light is characterized by its physical quantities including wavelength (related to color), amplitude (related to light intensity) and phase (indicating the relationship between the starting point of wave and reference time). People can only use photosensitive photography to record wavelength and amplitude, so no matter how realistic the photos are, it is always different to see the real scenery. Laser has high coherence and can obtain all information of interference wave space, including phase. Therefore, holographic photography is carried out by laser, and all the information of the photographed object is recorded on the negative. Through the diffraction of light, a vivid three-dimensional image of the object can be reproduced. Today, on the basis of holography, new holographic technologies such as holographic interferometry, color holography, rainbow holography and panoramic holography have been further developed. Holography has the characteristics of three-dimensional imaging, which can be recorded repeatedly. Every small holographic negative can reproduce a complete three-dimensional image of an object, and it is widely used. It can be widely used in precise interferometry, nondestructive testing, holographic photoelasticity, micro-strain analysis, vibration analysis and other scientific research. Holographic interferometry has been widely used to study the combustion process of gas, the vibration mode of mechanical parts, the bonding quality of honeycomb structure and the detection of subcutaneous defects of automobile tires. Holography has become an industry as an anti-counterfeiting mark for goods and credit cards. Shooting precious works of art with holography not only makes people feel immersive, but also provides a reliable realistic basis for the restoration of works of art. The developing holographic TV will also add a new life enjoyment to people. -2. Space technology-(1) What is space technology-space technology, as its name implies, is the technology of exploring, developing and utilizing space. At present, space technology is also called space technology. But at present, experts have two understandings of "heaven": one is to call the infinite space outside the earth's atmosphere "heaven"; The other is to call the limited space outside the earth's atmosphere and inside the solar system "sky". According to previous understanding, space technology and space technology are completely the same thing; According to the latter understanding, space activities outside the earth's atmosphere and in the solar system are called aerospace, and space activities outside the solar system are called aerospace. In this way, space technology should cover space technology and space technology. However, for a long time, human beings have mainly carried out activities in the solar system, so today they have realized that space technology and space technology are synonyms. -China space experts summarized the main features of space technology into two aspects: First, space technology is a highly comprehensive science and technology, which is a comprehensive integration of many modern scientific and technological achievements. This mainly depends on the development of many advanced technologies such as electronic technology, automation technology, remote sensing technology and computer technology. Therefore, the achievements of a country's space technology can best reflect its scientific and technological level and is an important symbol to measure its scientific and technological strength. Secondly, space technology is a fast and large-scale science and technology, which can play the most important role in the macro. For example, communication satellites can cover the ground or even the whole world in a large area; Meteorological satellites can make global weather forecasts; Reconnaissance satellites can monitor military activities in a wide range in time and so on. These two characteristics of space technology, which are different from general conventional technology, make it play an unexpected strategic role in a country's strength and progress: it can produce high economic and social benefits in economy, and it is generally believed that the investment benefit of the development and utilization of outer space resources can reach more than1:10; Militarily, it can best show the military strength of a country. As long as a country has space advantages, it will take the initiative in military strategy. Politically, it has a far-reaching impact on improving a country's position in international activities. A major aerospace achievement often becomes a major bargaining chip in international negotiations; In science and technology, it can also promote the development of electronics, automation, remote sensing, biology and other disciplines, and form a number of new marginal sciences including satellite meteorology, satellite oceanography, space biology, space material technology and so on. (2) the great achievements of space technology-the creation and development of space technology is the magnificent cause of human exploration of space. Since its rise in the 1950s, space technology has attracted worldwide attention for its brilliant achievements in international politics and military affairs and its contribution to human economy and civilization. In the past decades, great achievements have been made in space technology, among which various satellites have shown their magical power.