激光制冷中能级间距的选择

激光制冷问题的核心是材料的选择。荧光中心能级的间距是其中的一个关键指标。确定合理的能级间距有助于选择合适的激光制冷材料。能级间距决定了对激光制冷至关重要的两个因素:量子效率和无辐射跃迁速率。如果单纯地从制冷功率的角度来看,能级间距越大量子效率越高,也越有利于荧光制冷。但当能级间距宽到某一值后,制冷功率基本上保持不变。如果从热一光转换效率的观点来考察激光制冷的效率问题,能级间距宽度的合理取值就应该小得多。如果在选择激光制冷材料时,确定制冷功率具有第一位的重要性,那么,能级间距选择在5000cm^-1左右的宽度是比较合适的、这不仅可以确定较大的热－光转换效率,同时也基本上保证了很高的制冷功率。

Energy Gap Choosing in Laser Cooling

The main problem in laser cooling investigation is to choose materials. One of the keys is the energy width split out between ground state and excited state of luminescence center. Choosing the energy space reasonably will help us to determine laser-cooling media correctly. The energy gap of two states determines two important elements in laser cooling, quantum efficiency and multiphonon relaxation rate. Only as for cooling power in laser cooling, the more the energy gap splits, the higher quantum efficiency is and the more powerful is to fluorescent cooling. When the energy gap reaches a certain width or more, the cooling power will almost keep unchanging. If heat-light converting efficiency is considered in laser cooling, the energy gap in reason should be much narrower. If we confirm that it is the most important to keep cooling power at the highest level, then, it is more appropriate to choose the energy gap at 5000cm-l than 10 000cm-l of Yb3+, because, the choosing can not only confirm higher heat-light converting efficiency, but also ensure in substance a high cooling power.