Analysis of Laser Cooling Principle of Fiber Laser Marking Machine

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Analysis of Laser Cooling Principle of Fiber Laser Marking Machine

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Temperature is the physical quantity that represents the degree of coldness and heat of an object. Microscopically speaking, it is the intensity of thermal motion of the object's molecules. It is well known that all the molecules and atoms around us are engaged in ceaseless and irregular thermal movements. And the essence of our refrigeration is to reduce the intensity of the overall thermal movement of these molecules or atoms.

One of the most important technologies in laser cooling is doppler cooling. Doppler cooling is based on the principle that the laser sends out photons to block the thermal motion of atoms, which is realized by reducing the momentum of atoms. So how does a laser actually reduce the momentum of these atoms?

First, quantum mechanics suggests that atoms can only change their momentum by absorbing photons of a particular frequency. Doppler effect indicates that the frequency of a wave is higher when the source is moving towards the observer, and lower when the source is moving away from the observer. The same conclusion can be reached when the observer moves.

The same is true for atoms. When the direction of motion of an atom is opposite to that of a photon, the frequency of the photon increases, and when the direction of motion of the atom is the same as that of the photon, the frequency of the photon decreases. And then, another physics principle is that light has momentum, although it has no static mass. In this way, we can build a simple model of lasing cool.

The frequency of the laser is adjustable within a certain range, and when the frequency of the laser is set slightly below that of an atom, the result will be unexpected. That's what happens when you shine a light beam on a particular atom. If the atom is moving towards the laser beam, the frequency of the photon increases due to the doppler effect of light, and the original laser photon's frequency is just less than the absorbed frequency of the atom, then the doppler effect is absorbed by the atom.

And this absorption behaves as a momentum change. Since the motion direction of the photon is opposite to that of the atom, after the collision between the photon and the atom, the atom jumps to the excited state, and the momentum decreases, so the kinetic energy decreases accordingly. For atoms in other directions of motion, the corresponding photon frequency will not increase, so the photon in the laser beam cannot be absorbed, so there will be no increase in momentum, which is the same as the kinetic energy.

When we use multiple lasers to illuminate 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 atom, after a certain period of time in the process, most of the atom's momentum will reach a very low level, so as to achieve the purpose of refrigeration.

But most of the range of this technology is applied for cooling the atoms, and for molecules the method is difficult to cool to ultra-low temperature. But supercooled molecules are more significant than supercooled atoms because their properties are more complex. Currently, the way to cool a molecule is to combine ultra-cold alkali atoms together to form a dibasic molecule. Not long ago, Yale university cooled strontium fluoride (SrF) to a few hundred microvolts.

Another type of laser cooling, also known as anti-Stokes fluorescence refrigeration, is a new concept of cooling methods being developed. Its basic principle is the anti-Stokes effect, which uses the energy difference between scattering and incident photons to achieve refrigeration. The inverse stokes effect is a special scattering effect, the wavelength of the scattered fluorescence photon is shorter than that of the incident photon.

Therefore, the scattered fluorescence photon energy is higher than the incident photon energy, the process can be simple to understand as follows: The low-energy laser photons are used to excite the luminescence medium, the luminescence medium scatters high-energy photons, and the original energy in the luminescent medium is taken out of the medium and cooled. Compared with the traditional refrigeration method, the laser provides the refrigeration power, while the scattered anti-stokes fluorescence is the heat carrier.
Perfect Laser - Fiber Laser Marking Machine
Perfect Laser - Fiber Laser Marking Machine
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