Analysis of laser cooling principle of fiber laser marking machine

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Temperature is a physical quantity that indicates the degree of coldness and heat of an object. Microscopically speaking, it is the intensity of the thermal motion of an objects molecules. As we all k…


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Temperature is a physical quantity that indicates the degree of coldness and heat of an object. Microscopically speaking, it is the intensity of the thermal motion of an object's molecules. As we all know, all the molecules and atoms around us are in constant and random thermal movement. The essence of our refrigeration is to reduce the intensity of the overall thermal motion of these molecules or atoms, fiber laser marking machines. 1. A very important technology in laser refrigeration is Doppler cooling. The principle of Doppler cooling technology is to block the thermal movement of atoms by emitting photons from the laser, and this blocking process is to reduce the atom's momentum to Realized. So, how exactly does a laser reduce the momentum of these atoms? First, quantum mechanics proposes that atoms can only absorb photons of a specific frequency, thereby changing their momentum. The Doppler effect states that the frequency of a wave becomes higher as the wave source moves towards the observer, and the frequency becomes lower as the wave source moves away from the observer. The same conclusion can be reached when the observer moves. The same is true for atoms. When the atom moves in the opposite direction to the photon, the frequency of the photon will increase, and when the atom moves in the same direction as the photon, the frequency of the photon will decrease. Then, another physics principle is that although light has no static mass, it has momentum. So combining the above physics characteristics, we can build a simple model of laser cooling. 2. The frequency of the laser is adjustable within a certain range, and when the frequency of the laser is adjusted to a frequency slightly lower than the frequency that an atom can absorb, there will be unexpected results. This happens when a particular atom is illuminated with such a beam of light. If the atom is moving toward the laser beam, the frequency of the photon increases due to the Doppler effect of the light, and the original laser photon frequency is just slightly less than the absorbable frequency of the atom, then the Doppler effect is just Absorbed by the atom. This absorption appears as a change in momentum. Because the direction of photon movement is opposite to that of the atom, after the photon collides with the atom, the atom transitions to the excited state, and the momentum decreases, so the kinetic energy also decreases. For atoms in other directions of movement, the frequency of the corresponding photons will not increase, so the photons in the laser beam cannot be absorbed, so there is no increase in momentum, which is the same with respect to kinetic energy. When we use multiple laser beams to irradiate the atoms from different angles, the momentum of the atoms in different directions of motion will decrease, and the kinetic energy will decrease. And because the laser only reduces the momentum of the atoms, after the process continues for a period of time, the momentum of most of the atoms will reach a very low level, thereby achieving the purpose of cooling. However, most of the applications of this technology are for atomic cooling, and for molecules, this method is difficult to cool them to ultra-low temperatures. But supercooled molecules are more important than supercold atoms because of their more complex properties. Currently, the way to cool molecules is to combine supercooled base atoms together to produce a double base molecule. Not long ago, Yale University cooled strontium fluoride (SrF) to a few hundred micro-Ki. Another type of laser refrigeration, also called anti-Stokes fluorescence refrigeration, is a new concept of refrigeration that is being developed. The basic principle is the anti-Stokes effect, which uses the energy difference between scattered and incident photons to achieve refrigeration. The anti-Stokes effect is a special scattering effect in which the wavelength of scattered fluorescent photons is shorter than the wavelength of incident photons. Therefore, the energy of scattered fluorescent photons is higher than the energy of incident photons. The process can be simply understood as: low-energy laser photons are used to excite the light-emitting medium, and the light-emitting medium scatters high-energy photons, and the original energy in the light-emitting medium is taken out of the medium and cooled. . Compared with traditional cooling methods, lasers provide cooling power, while scattered anti-Stokes fluorescence is a heat carrier.

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2020-02

Analysis of laser co…

Temperature is a physical quantity that indicates the degree of coldness and heat of an object. Microscopically speaking, it is the intensit…… [Know More]

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