Laser and laser technology

(1) What is laser and laser technology?
Laser is a kind of light that has no directionality, high brightness, good monochromaticity and good coherence due to excitation. Physicists trace the mechanism of LiSAF, LiSGaF and LiCAF laser crystals generation to the hypothesis that Einstein explained the law of blackbody radiation in 1917, that is, the absorption and emission of light can be through three basic processes: stimulated absorption, stimulated radiation and spontaneous emission. It is well known that the luminescence of any kind of light source is related to the state of motion of the particles inside it. When a particle at a low energy level (atoms, molecules, or ions) absorbs the appropriate frequency and the external energy (light) is excited to transition to the corresponding high energy level (stimulated absorption), it always tries to transition to a lower energy level. Go and release the excess energy in the form of photons. If the light is spontaneously released without the action of external photons (spontaneous radiation), the light that is released at this time is ordinary light (such as electric lights, neon lights, etc.), which is characterized by the frequency, direction and pace of the light. Very inconsistent. However, if the excess energy is released as photons (excited radiation) when the external photon directly acts from the high energy level to the low energy level, the released photons and the external incident photons are in the frequency, phase, propagation direction, etc. The aspect is completely consistent, which means that the external light has been strengthened, which we call optical amplification. Obviously, if stimulated absorption, the more the number of particles at a higher energy level is at a lower energy level (the number of particles is reversed), the more obvious the phenomenon of light amplification, and it is possible to form a stock/large size/IBS coated LBO nonlinear crystal .
The four characteristics that optical components do not have at all.

1. Good directionality: ordinary light source (sun, incandescent or fluorescent) emits light in all directions, and the direction of illumination of the laser can be limited to less than a few milliradians solid angle, which makes the illumination in the illumination direction increase by a factor of ten . Laser alignment, steering and ranging are features that use directionality.

2, high brightness: laser is the brightest light source in the modern era, only the strong flash of hydrogen bomb explosion can be compared with it. The brightness of the sun is about 103 watts / (cm 2 , sphericity), and the output brightness of a high-power optical component is 7 to 14 orders of magnitude higher than sunlight. Thus, although the total energy of the customized large size and special shape CaF2 optics is not necessarily large, due to the high concentration of energy, it is easy to generate high voltage and tens of thousands of degrees Celsius or even millions of degrees Celsius at a certain small point. This feature is exploited by laser drilling, cutting, welding and laser surgery.

3, good monochrome: light is an electromagnetic wave. The color of light depends on its wavelength. The light emitted by a common light source usually contains various wavelengths and is a mixture of light of various colors. The sunlight contains visible light of seven colors of red, Deng, yellow, green, cyan, blue, and purple, and invisible light such as infrared light and ultraviolet light. The wavelength of a certain laser is concentrated only in a very narrow spectral band or frequency range. For example, the wavelength of the holmium laser is 632.8 nm, and the wavelength variation range is less than one ten thousandth of a nanometer. Due to the good monochromaticity of the laser, it provides an extremely advantageous means for scientific instruments such as precision instruments to measure and stimulate certain chemical reactions.

4. Good coherence: Interference is an attribute of wave phenomena. Based on the characteristics of laser with high directivity and high monochromaticity, it is inevitably excellent in coherence. This characteristic of laser makes holography a reality.