Laser refrigeration is generally defined as an interaction between substances or a system and laser which has the effect of decreasing the temperature.In most cases,laser refrigeration refers to solid refrigeration excited by monochromatic light.In other words,for a physical system which has a certain inner degree of freedom,laser could be used to reduce its energy.Laser refrigeration of solids is usually based on the physical principle that the luminescence center induced by laser produces anti-Stokes fluorescence radiation.It is an all-optical refrigeration technology with no vibration,no noise,no electromagnetic pollution and other unique advantages.It has a vast development potential in special fields such as national defense industry,military industry and space remote sensing.Recently,laser refrigeration in various rare-earth?Yb,Tm and Er?doped solid materials is accomplished in several nations due to their researchers'work.The research of refrigeration of Tm ion doped crystal has got stuck,new refrigeration mechanism has to be proposed in order to increase laser refrigerating capacity.This paper is based on the SBE theory of anti-stokes fluorescence refrigeration.Combining the specialty of3F4 and3H6 energy level of Tm3+with laser refrigeration lighting theory,the conception of Tm-doped solid rare earth material is proposed,the energy level rate equation of Tm ion's three-level system model is established.The refrigeration power,refrigeration efficiency and thermal equilibrium dynamics of the refrigeration system under conditions of continuous excitation and pulse excitation are deduced in detail.Analysis of the property of Tm-doped solid for laser pulse refrigeration and scheme optimization are the key points of this paper.The net refrigeration power,refrigeration efficiency are calculated and the thermodynamics of temperature is analyzed.The optimized scheme of laser refrigeration is proposed by optimizing the system parameters numerically according to the dependencies of refrigeration capacity on the peak power,time span and repetition frequency of the pulse.By comparing the refrigeration capability of periodic modulated pulse with the one of continuous wave,we can draw the conclusion that the pulse pumping mechanism has many advantages in anti-Stokes fluorescence refrigeration. |