Cavity Enhanced Laser Cooling of Solids
Biao Zhong, Youhua Jia, Jianping Yi
Since the successful realization of laser cooling of solids in 19951, the optical cooling techniques2-5 have made fast development, and laser cooling experiments have obtained some important progress. However, how to improve the absorption of pump laser and enhance the temperature drops so as to realize the practical optical refrigeration, it has become a hot research point in applied physics. As early as 2002, the Heeg et. al proposed an extraor intra-cavity enhancement scheme to improve the laser cooling effect of solids2, and experimentally demonstrated their intra-cavity enhancement scheme in 2004, and found that there is no large temperature drops due to the experimental parameters were not optimized3. In 2003, Hoyt proposed a multiple-pass scheme to enhance the absorption of pump laser and did a series of experimental researches about the multiple-pass scheme4. As expected, a greater temperature drop was obtained. However, due to some limitation in the early work, it is difficulty to cool the sample to the cryogenics temperature, such as low absorption of cooling materials5, the coating of the sample surfaces3, the purity of the sample6, the load from the ambient1,7, etc. Therefore, people have done much work to improve the record of temperature drop. For example, to avoid the coating absorption deposited on the sample surface, they cut the sample with a Brewster angle along with the cavity axis8, or improve the purity of cooling material9-11, and so on. Mansoor. Seletskiy used the multi-pass scheme to do some meaningful experiments and obtain a milestone progress, that is, they cool a high pure Yb3+-doped YLF to cryogenic temperature12 in this year. To obtain an efficient absorption, another scheme was proposed to insert a Brewster-cut sample into a resonant cavity and make the cavity to be resonated with the pump laser, and then the maximum absorption of the pump laser can be achieved 2, 13-18. Seletskiy demonstrated this scheme in the experiment13. However, this scheme depends on the power of the pump laser. Fortunately, the intra-cavity scheme proposed by Heeg can solve this problem in the case of low absorption2. He also suggested that inserting a cooling sample into the resonant cavity of a laser with a gain (so-called intra-cavity enhancement scheme) to realize the maximum absorption of the pump laser2, 14, 19 and carried out it in the experiment3. Besides of enhancement laser cooling of bulk solids using resonant cavity, we propose another new scheme to optically cool some film materials (i.e., filmier solids) by using a high fineness planar waveguide, which is similar to the cavity enhanced cooling scheme. In our laser cooling scheme, the solid film as a high-index gap waveguide is separated from a prism by a low-index gap one, and an incident laser beam is resonantly coupled into a
InTech eBooks•Apr 1, 2011•0 citations