Theoretical Study On Laser Cooling Of Rare Earth-doped Materials

In recent years, the laser cooling technique of solid materials based on the anti-Stokes fluorescent scattering has obtained fast progress. In this thesis, the basic principle on laser cooling of solid and its technique are first briefly introduced. Second, all of new codling materials, schemes and results and their recent experimental progresses are reviewed in some detail. Meanwhile, different temperature measurement techniques are summarized. Finally, the applied prospect on laser cooling of solid materials and the development of optical refrigerators are briefly discussed and looked ahead.We propose a simplified two-level system to analyze the pumping and stimulated-emission processes. Using the model of Tm³⁺, a theoretical study of the relationship between the minimum energy gap and the laser pumping rate is performed. Under the different pumping rate, the relationship between the energy gap and cooling power and the relationship between the energy gap and heat-light converting efficiency are analyzed. We find the relationship between the optimal heat-light converting efficiency and the pumping rate, and thus prove the feasibility of laser cooling in Thulium-doped material. Meanwhile, the choice of host material is discussed.We propose a two-level model to analyze the absorption and stimulated-emission processes between the Yb^{3+ 2}F_7/2 ground-state manifold and the ²F_5/2 excited-state manifold, and discuss several parameters that influence the cooling power, and find some ways to improve the cooling power. The influences of the doped concentration, pumping power and the effective pump-spot area on laser cooling efficiency are particularly analyzed. At the same time, we make computer simulation about the cooling process and obtain the temperature as a function of the cooling time, it is similar to the experimental results. So this shows that our model is reasonable.