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. As we all know, all the molecules and atoms around us are undergoing a non-regular heat movement. And the essence of our refrigeration is to reduce the intensity of the thermal motion of these molecules or atoms in general, fiber laser marking machines.

1. A very important technology in laser cooling is Doppler cooling technology. The principle of Doppler cooling technology is to use lasers to emit photons to hinder the thermal motion of atoms. This obstruction process reduces the momentum of atoms. Realized. So, how does the laser actually 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 indicates that the frequency of the wave increases as the wave source moves toward the observer, and the frequency decreases as the wave source moves away from the observer. The same conclusion can also be obtained when the observer moves.

Similarly, the same is true for atoms. When the direction of motion of an atom is opposite to that of a photon, the frequency of this photon will increase. When the direction of atomic motion is the same in this direction of photon motion, the photon frequency will decrease. Then, another physics principle is that light has no momentum, but it has momentum. Then combining these several physics features, we can build a simple model of laser cooling.

2. The frequency of the laser can be adjusted within a certain range. When the frequency of the laser is adjusted to be slightly lower than the absorbable frequency of an atom, unexpected results can be obtained. This happens when such a beam of light is used to illuminate a particular atom. If the atoms move toward the laser beam, the frequency of the photons increases due to the Doppler effect of the light, and the frequency of the original laser photons is just slightly less than the absorbable frequency of the atoms, then the Doppler effect is just right. Atomic absorption.

And this absorption shows a change in momentum. Because the direction of photon motion is opposite to the direction of motion of the atoms, after the photon collides with atoms, the atoms transition to the excited state, and the momentum decreases, so the kinetic energy also decreases. For atoms in other directions of motion, the frequency of their corresponding photons does not increase, so they cannot absorb the photons in the laser beam, so there is no increase in momentum, which is also true for 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. Since the laser only reduces the momentum of the atom, after a certain period of time in the process, the momentum of most atoms will reach a very low level, so as to achieve the purpose of refrigeration.

However, the scope of this technology is mostly used for atomic cooling, but for molecules, this method is difficult to cool to ultra-low temperature. However, ultra-cold molecules are more significant than ultra-cold atoms because their properties are more complex. At present, the method of cooling molecules is to combine supercooled alkali atoms to produce double-base molecules. Not long ago, Yale University had cooled SrF to a few hundred microseconds.

Another type of laser refrigeration, 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 anti-Stokes effect is a special scattering effect, the wavelength of scattered fluorescence photons is shorter than the wavelength of the incident photon.

Therefore, the scattered fluorescence photon energy is higher than the incident photon energy, and the process can be simply understood as follows: a low-energy laser photon is used to excite a luminescent medium, a luminescence medium scatters a high-energy photon, and the original energy in the luminescence medium is taken out of the medium and refrigerated . Compared with the traditional cooling method, the laser plays a role in providing cooling power, and the scattered anti-Stokes fluorescence is a heat carrier.

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