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Analysis of laser cooling principle of optical fiber laser marking machine

Superwave Laser Technology Co.,Ltd | Updated: Mar 10, 2018

The temperature is the physical quantity which indicates the degree of cold and heat of the object, and the micro is the intensity of the thermal motion of the object molecules. It is well known that all the molecules and atoms around us are engaged in a perpetual, irregular heat movement. The essence of our refrigeration is to reduce the intensity of the overall thermal motion of these molecules or atoms, and the optical fiber laser marking machine.

1, laser cooling is a very important technology in the doppler cooling technology, the principle of doppler cooling technology is through the laser photons to block the thermal motion of the atom, which hinder the process by reducing the atomic momentum. So how exactly do lasers reduce the momentum of these atoms?
First, quantum mechanics suggests that atoms can only absorb photons of a particular frequency, changing their momentum. The doppler effect indicates that the frequency of the wave is higher when the source is shifted to the observer, and the frequency is lower when the source is far away from the observer. The same conclusion can be reached when the observer moves.

Also, for the atoms, when the movement direction of the atom and photon movement on the contrary, the frequency of the photon will increase, and when the atoms at the same time, the direction of movement direction on the photon is the photon frequency will decrease. And then the other principle of physics is that although light has no static mass, it has momentum. By combining the above physical features, we can build a simple model of laser cooling.

2. The frequency of the laser is adjustable in a certain range, while the frequency of the laser is adjusted to a slightly lower than the absorption frequency of an atom, and the result is unexpected. This happens when a particular atom is illuminated by such a beam of light. If the atom is towards the laser beam movement, caused by the doppler effect, the frequency of the photon to increase, and the frequency of the original laser photons is just slightly smaller than the atomic absorption frequency, is at this time due to the doppler effect is just by atomic absorption.

This absorption represents a change in momentum. Because the motion of the photon is opposite to the motion of the atom, after the collision of the photon with the atom, the atoms jump to the excited state, and the momentum decreases, so the kinetic energy decreases. Direction of motion with other atoms, then its corresponding to the frequency of the photon doesn't increase, so can't absorb the photons in a laser beam, so there will be no momentum increase the occurrence of this phenomenon, relative to the kinetic energy is the same.

When we illuminate the atom from different angles with a multi-beam laser, the momentum of the atoms in the different directions of the atom decreases, and the kinetic energy decreases. Since the laser only reduces the momentum of the atom, the momentum of most atoms will reach a very low level after a period of time, thus achieving the purpose of refrigeration.

But the technology is mostly used for atomic cooling, and for molecules, it's hard to cool it down to ultra-low temperatures. But ultra-cold molecules are more important than supercooled atoms because their properties are more complex. At present, the way to cool the molecules is to combine the supercooled base atoms together to produce a bibasic molecule. Not long ago, Yale university had cooled strontium fluoride (SrF) to hundreds of tiny pieces.

Another kind of laser cooling, also known as anti stokes fluorescent cooling, is developing the new concept of the cooling method of its basic principle is anti stokes effect, the scattering and the photon energy difference of refrigeration. The anti-stokes effect is a special scattering effect, whose wavelength is shorter than that of the incident photon.

Therefore, fluorescent scattering photon energy is higher than the incident photon energy, the process can be simple to understand as: with low energy laser photons luminous medium, light scattering medium of high-energy photons, will shine medium energy out of the original medium and refrigeration. Compared with the traditional cooling mode, the laser has the function of providing refrigeration power, while the anti-stokes fluorescence is the carrier of heat.