Magical Laser Refrigeration
As one of the four inventions of the twentieth century, which is commensurate with computers, and atomic energy, astronomy laser pointer technology has been widely used in many industries. However, when it comes to lasers, most people can think of their application in machining.
In fact, in addition to industrial cutting, welding, and medical beauty applications. There are many other uses for lasers, such as those used in refrigeration. The concept of laser cooling was first proposed by Soviet scholars in 1962, and it was only after a period of silence that it was only concerned by the academic circles. In 1985, the famous American Chinese scientist Zhu Yuwen successfully achieved the low temperature environment using laser frozen atoms, and won the 1997 Physics Award for this invention.
Doppler cooling technology
So why is the laser able to cool? Usually, the atoms of an object are always doing irregular motion, which is called thermal motion in physics. The more intense the movement of the atom, the higher the temperature of the object, and the lower the temperature. Therefore, if there is a way to reduce the rate of movement of the atom, the temperature of the object can be lowered. The principle of laser cooling can be generally understood as: the use of a large number of photons hinders the movement of atoms to reduce the rate of movement of atoms, thereby achieving the purpose of reducing the temperature of the object.
A burning laser pointer is a highly concentrated beam of light. Because of the uniform direction of the light particles it emits, these particles are very concentrated. When the laser beam is injected into the object, because the number of particles entering is so large that the particles in the object become very crowded, they cannot be "live and jump" as they are, thereby reducing the thermal motion of the molecules. This laser refrigeration technology Known as Doppler cooling technology.
In 1995, using Doppler cooling technology, the Danoke Group cooled the helium atoms to a low temperature of 2.8 nK. Physicists at the University of Berne, Germany, have used this technology to achieve high-density concentration of photons. This technology is very promising on solar cells, enabling solar cells to operate efficiently on cloudy days.
Anti-stokes fluorescence refrigeration technology
Doppler cooling is the most basic mechanism in laser cooling, and later developed an anti-Stokes fluorescence refrigeration technology. The idea of this technology was first proposed by P. Prinsheim in 1929. The basic principle of this refrigeration method is the anti-Stokes effect, which uses the energy difference between the scattering and incident photons to achieve refrigeration.
The anti-Stokes effect is a special scattering effect in which the scattered fluorescent photon wavelength is shorter than the incident photon wavelength. Therefore, the scattering fluorescent photon energy is higher than the incident photon energy, and the process can be simply understood as: the low-energy blue laser pointer photon is used to excite the luminescent medium, the illuminating medium scatters high-energy photons, and the original energy in the luminescent medium is taken out of the medium to be cooled. Compared with the traditional cooling method, the laser provides the function of providing refrigeration power, and the scattered anti-Stokes fluorescence is the heat carrier.
In 1995, Epstein and colleagues at the Space Refrigeration Technology Research Group of the Los Alamos National Laboratory in the United States successfully obtained measurable cooling capacity on solid materials by laser-induced anti-Stokes fluorescence.
In 1999, low temperature physicist E. Finkeipen used a doped sapphire laser to excite hole excitons of GaAs/GaAl semiconductor quantum well materials to achieve anti-Stokes fluorescence emission of hole excitons, giving refrigeration at different temperatures. The relationship between efficiency and cooling temperature.
In 2010, scientists used lasers to freeze molecules to near absolute zero. This is the first time that single-molecule laser refrigeration has reached such a low temperature, and it has taken a big step toward controlling the chemical and physical processes of substances and making quantum computers.
As technology continues to mature, green laser pointer cooling has begun to gain many applications. For example, atomic optics, atomic etching, atomic clocks, optical tweezers, high resolution and other basic research. This technique can also be used for metal welding and human surgery. I believe that in the future, this technology will definitely get a wider application.