The invention of the laser was a great achievement in 20th century science and technology. Finally it makes people have the ability to driving, quantity scale minimax, sports extremely chaotic luminescence process of molecules and atoms, thereby gaining generation, amplification coherent infrared, visible light and ultraviolet (to X rays, and gamma rays). The rise of laser science and technology has led to a new level of understanding and utilization of light.
The birth history of laser can be divided into several stages, including the concept of excited radiation proposed by Einstein in 1916 as its important theoretical basis. This theory points out that in high energy particles by an energy equal to the energy difference between the two levels of photons, will shift to the low-energy state, and generate a second photon, with the first photon emitted at the same time, this is stimulated radiation. The light from this radiation is amplified and coherent light, i.e. the emission direction, frequency, phase and polarization of multiple photons are identical.
Since then, the establishment and development of quantum mechanics on the microscopic structure of the materials and the motion law of a more in-depth understanding, the energy of a micro particle distribution, transition and photon radiation also got more powerful proof, this also objectively more perfected the Einstein's theory of stimulated radiation, laid a theoretical basis for the production of laser further. After the birth of quantum electronics in the late 1940s, it was quickly applied to study the interaction between electromagnetic radiation and various microscopic particle systems, and developed many corresponding devices. These scientific theories and the rapid development of technology have created the conditions for the invention of the laser.
If the number of particles in a system is higher than the number of particles in the lower energy state, the reverse state of the number of particles appears. So as long as there is a single photon, will force a atoms in the upper state of stimulated radiation out a the same photons, these two photons will cause other atoms stimulated radiation, thus realize the optical amplification; If the appropriate resonator feedback is added, the light oscillates and the laser is emitted. That's how lasers work. In 1951, American physicists Purcell and pound succeeded in causing the number of particles to reverse, and they received the radiation of 50 KHZ per second. Later, American physicist Charles townes and Soviet physicist horse krissoff and Mr Prokhorov successively put forward the use of the stimulated radiation principle of atoms and molecules to produce and microwave amplifier design.
1) hazard and protection of far-infrared laser: the commonly used carbon dioxide laser (10.6 mm) is absorbed by the cornea, which can't enter the eye. Since this laser is not visible to the laser and is generally more powerful, it burns the cornea, the conjunctiva and the eyelids. For corneal burns, little white cloud point is the lightest, 10 min after irradiation, only involves the corneal epithelium, edema, fade, no visible scar, the heavier formed from outside to inside cylindrical white spot, again heavy is routed soup wounded spot or perforation. Despite the strong, the protection is quite simple, just wear a pair of flat glass glasses. The threshold value of the co2 laser is 0.1 W/cm2. The carbon dioxide laser will be absorbed by the skin of 0.2mm thick, which can easily cause blisters or charred. When the power is large, it can be burned immediately, and the physiological reaction (such as pain) can not protect the body. The transverse stimulated atmospheric carbon dioxide laser can ionize the air. When using 30mJ carbon dioxide, the skin of the forearm surface is 0.5 ~ 0.25 s, and the spot diameter of the spot is 10 m, which is painful and burning when irradiated. After a few hours, erythema appeared, and after 24h, it expanded, edema, and finally edema. Protective measures wear gloves in overalls.
(2) general protection measures: the laser shall be enclosed in a possible manner. The laser beam should not leak outside the target. The laser beam should not be at the same level as the eye. The laser beam should be stopped from reflector and fire retardant material. Pulse laser should be safe to prevent laser explosion. For each application, the minimum radiation level of the target should be used.
Take appropriate measures:
(1) the laser emitted by a class a laser does not cause any biological hazards and may be exempted from control measures;
(2) class b laser is of low power range, with wavelength of 0.4 ~ 0.7 mm, and power less than 1mW. Long time fixation can cause retinal damage, so it is necessary to take protective measures and use warning signs.
(3) the range of power in a class c laser can cause biological damage due to short exposure, so control measures are indispensable. The laser diffuse beam of this kind of laser has no harm;
(4) the fourth class belongs to the high power laser range, can produce dangerous laser beam reflection of laser beam, short-term directly or diffuse the exposure of the human body can cause biological damage, the strict control measures must be taken.