Lasing and up conversion from a nominally pure whispering gallery mode resonator

Abstract

We report on the experimental observation of green and infrared light emission from a whispering gallery mode resonator fabricated with calcium fluoride, when the resonator is pumped with 795 nm light. The spectrum of light exiting the resonator caused by residual impurities contains both infrared lines corresponding to the emission pattern of Nd3+ ions and green light originating from two-photon pumping and subsequent emission of Er3+ ions. The process takes place due to the high quality factor (Q > 1010) of the resonator, even when the expected concentration of the extrinsic impurities approaches a part per million level. The potential for optical cooling of a monolithic solid state resonator via the upconversion phenomenon is explored theoretically. © 2012 Optical Society of America.