The Theory Of Laser Cooling Without Spontaneous Emission Using The Bichromatic Force

Using laser cooling technology to reduce the temperature of atomic and molecular gases by laser light field,the temperatures of those gases are reduced to micro Kelvins or even nano Kelvins,which helps the realization of Bose-Einstein condensation and Fermion degeneracy system,developing the precision measurement technology and quantum simulation platform based on matter wave.However,except for a few atoms,most of the atoms in the periodic table can not be cooled by laser.In order to solve this problem,bichromatic cooling technology is proposed.The principle of this technique is to transfer the kinetic energy of the atomic gas to the bichromatic field by using the Landau Senner tunneling effect at the adiabatic energy level of the atomic gas and the bichromatic cooling system,so as to show the cooling of the atomic gas after the pulse light field is closed.However,its cooling efficiency is lower than other existing cooling technologies,which requires further theoretical exploration and optimization.In this paper,numerical simulation is used to optimize the adiabatic cooling process.The parameters linked with action time,velocity and spontaneous emission are changed to find the connection between those parameters and cooling effect of the bichromatic cooling system.It is found that there is an optimal action time to achieve the highest bichromatic cooling efficiency.In addition,it is also found that the initial velocity of atomic gas needs to be smaller because this method is the adiabatic evolution bewteen atomic gas and bichromatic system.Finally,the effect of spontaneous emission on the bichromatic cooling is explored.It is found that the effect is small when the light pulse is shorter than the spontaneous emission time,but after a long time,the spontaneous emission will significantly reduce the cooling effect.