Origin of laser-induced internal cooling of Yb3+-doped systems

摘要: Laser induced internal cooling has been investigated in a new fluorochloride glass (CNBZn) and a fluoride glass (BIG) doped with 2.1x1020 Yb3+ ions/cm3 and in a Kpb2Cl5 crystal doped with 5x1019 Yb3+ by using collinear photothermal deflection and conventional laser excitation spectroscopies under high photon irradiances. The cooling efficiency for CNBZn glass which is approximately 2% relative to the absorbed laser power at 1010 nm and 300 K falls about 20% at 77 K. The cooling efficiency for BIG glass was only approximately 6% at room temperature. For the Yb3+ doped Kpb2Cl5 crystal we have shown internal laser cooling with a cooling efficiency of about 0.2% at room temperature. This is the third ytterbium-doped crystal, after Kgd(WO4) (Ref.10) and YAG (Ref.11), in which anti-Stokes laser-induced internal cooling has been demonstrated. The observed temperature dependence of the cooling …