We report the first observation of laser cooling in 1%Yb³⁺:KYW and discuss factors that limit the cooling efficiency. Cooling by 10 K from room temperature at atmospheric pressure was achieved in this crystal at a wavelength of 1025 nm using 8 W from a seeded fiber amplifier. The temperature of the sample was measured using a calibrated differential luminescence thermometry method and was verified with a thermal camera. Infrared imagery and 3-D modeling were used to analyze the impact of thermal conduction, thermal convection, black-body radiation, and background impurities. The simulated results agree with experimental measurements confirming that the chief limitation of laser cooling at room temperature and atmospheric pressure is thermal conduction from sample supports. Best results were obtained for samples mounted on silica aerogel. Theoretical improvement of cooling efficiency in vacuum by exploiting impurity absorption saturation is also discussed.

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Laura B. Andre, Long Cheng, Alexander J. Salkeld, Luis H. C. Andrade, Sandro M. Lima, Junior R. Silva, and Stephen C. Rand, "Laser cooling under ambient conditions in Yb3+:KYW," Proc. SPIE 10936, Photonic Heat Engines: Science and Applications, 109360E (Presented at SPIE OPTO: February 04, 2019; Published: 1 March 2019); https://doi.org/10.1117/12.2507325.