Thermal load management of laser cooling of Yb³⁺:LuLiF₄ crystal

In order to study the thermal load management mechanism of Yb3+:LuLiF4 crystal in anti-Stokes fluorescence process, laser cooling experiment based on standard pressure (1.0105 Pa) and high vacuum(2.510-3 Pa) states were carried out. The 5 mol% doped sample was supported by two optical fibers, and was placed in chamber with different vacuum states. The sample was excited via a 1 020 nm, 3 W laser. A temperature drop from room temperature of the sample was about △T12 K under standard pressure, and △T26 K under high vacuum. As for standard pressure state, thermal convection load of air was about 11.23 mW, thermal conduction load of the fibers was about 0.03 mW, thermal radiation load of the chamber was about 4.8 mW. As for high vacuum state, convection load of air was about 0.03 mW, conduction load of the fibers was about 0.07 mW, radiation load of the chamber was about 10.4 mW. As experimental results show, with the decrease of the pressure of the chamber from -105 Pa to -103 Pa, convection load of air is almost negligible, radiation load of the chamber becomes the most important thermal load of the refrigeration sample.