Abstract
In this work we aim to explore applications of single crystalline whispering gallery mode resonators (WGMRs), in particular we construct WGMRs of yttrium lithium fluoride (YLF). We devise two experimental applications of Newton’s rings phenomena in WGMRs, firstly we successfully demonstrate an independent method of measuring prism-resonator separation distances utilizing Newton’s rings and further use this distance calibration to explore the properties of different modes in a YLF WGMR. Secondly, we show that Newton’s rings can be used to align light beams incident to resonators by prism coupling in both WGMR and in spherical resonators. Furthermore we explore YLF WGMRs for Kerr-type frequency comb generation with the aim of producing solitons, where some success was seen in observing multiple comb lines, however we were unsuccessful in generating stable solitons due to thermal oscillations which was explored. Lastly, an erbium doped yttrium lithium fluoride (Er:YLF) WGMR was fabricated and its fluorescence was studying when when pumped at 980 nm and 1550 nm. We observed very strong fluorescence at 550 nm when pumping at both 980 nm and 1550 nm, the processes were attributed to twofold and threefold upconversion by intraionic energy transfer, respectively.