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We present a non-contact optical technique for the measurement of laser-induced temperature changes in solids. Two-band differential luminescence thermometry (TBDLT) achieves a sensitivity of 7 mK and enables a precise measurement of the net quantum efficiency of optical refrigerator materials. The TBDLT detects internal temperature changes by decoupling surface and bulk heating effects via time-resolved luminescence spectroscopy. Several Yb3+-doped fluorozirconate (ZrF4-BaF2-LaF3-AlF3-NaF-InF3, ZBLANI) glasses fabricated from precursors of varying purity and by different processes are analyzed in detail. A net quantum efficiency of (97.39 + or -0.01)% at 238 K (at a pump wavelength of 1020.5 nm) is found for a ZBLANI:1% Yb3+ laser-cooling sample produced from metal fluoride precursors that were purified by chelate-assisted solvent extraction and dried in hydrofluoric gas. In comparison, a ZBLANI:1% Yb3+ sample produced from commercial-grade metal fluoride precursors showed pronounced laser-induced heating that is indicative of a substantially higher impurity concentration. The TBDLT enables rapid and sensitive benchmarking of laser-cooling materials and provides critical feedback to the development and optimization of high-performance optical cryocooler materials., Published in Journal of the Optical Society of America B, v27 n3 p611-618, Mar 2010.

We present an efficient and numerically stable method to calculate time-dependent, laser-induced temperature distributions in solids and provide a detailed description of the computational procedure and its implementation. This study combines the two-dimensional heat equation with laser-induced heat generation and temperature-dependent luminescence. The time-dependent optical response of a system is obtained numerically by the Crank Nicolson method. This general model is applied to the specific case of optical refrigeration in ytterbium (Yb3+) doped fluorozirconate glass (ZBLAN). The laser-induced temperature change upon optical pumping and the respective transient luminescence response are calculated and compared to experimental data. The model successfully predicts the zero-crossing temperature, the net quantum efficiency, and the functional shape of the transients. We find that the laser-cooling transients have a fast and a slow component that are determined by the excited-state lifetime of the luminescent ion and the thermal properties of the bulk, respectively. The tools presented here may find application in the design of a wide range of optical and optoelectronic devices., Published in Journal of Applied Physics, v107 p063108-1/063108-9, 2010.

Laser cooling in semiconductor structures due to anti-Stokes luminescence is reviewed. Theoretical background considering luminescence trapping and red-shifting, the effect of free carrier and back-ground absorption, Pauli bandblocking and the temperature-dependence of various recombination mechanisms are discussed. Recent experimental results demonstrating record external quantum efficiencies (EQE) in GaAs/GaInP heterostructures are described, and conditions favorable for the first observation of laser cooling in semiconductors are discussed., Proceedings of SPIE Photonics West, 2006. Sponsored in part by NASA NAG5-10373. Additional AFOSR grant FA9550-04-1-0356. Prepared in collaboration with Los Alamos National Laboratories, Los Alamos, NM. Prepared in cooperation with the Department of Physics and Astronomy, University of New Mexico, Albuquerque.

Recent developments in cooling thulium-doped heavy-metal fluoride glass are presented. Thulium-doped fluorozirconate (ZBLANP) is cooled to 19 K below ambient with a multiple-pass pump scheme. This represents over an order of magnitude increase from the previously reported single-pass geometry. The results agree with a simple model for anti-Stokes fluorescence cooling that includes considerations of quantum efficiency and parasitic heating mechanisms. Issues relating to a practical optical refrigerator are examined, including a general model for the effects of multiple pump passes., Published in the Journal of the Optical Society of America B, v20 n5 p1066-, May 2003. Prepared in cooperation with the Department of Physics and Astronomy, University of New Mexico, Albuquerque. Sponsored in part by NASA NAG5-10373.

Coherent electromagnetic radiation is generated by the oscillation of longitudinal modes associated with optical phonons and bulk plasmons in InAs. Dramatic changes to the radiation spectra occur when the plasmon and phonon frequencies are in close spectral proximity, i.e., when the modes become strongly coupled., Published in Physical Review B, v65 article ID 233203, 29 May 2002. Prepared in cooperation with the Department of Physics and Astronomy and Center for High Technology Materials, University of New Mexico, Albuquerque.