Department of Physics


Department of Physics Apple - Gravity

Phone (701) 231-8974, fax (701) 231-7088


Seminar Abstract

December 16, 2004

"Properties and Applications of Whispering-Gallery Mode Resonances in Fused Silica Microspheres"

Dr. Jeromy Rezac
ITT Industries - Advanced Engineering and Sciences
Albuquerque, NM


Light is evanescently coupled into whispering-gallery modes (WGMs) of fused silica microspheres created from optical fiber. Coupling is performed using total internal reflection off the face of a prism or a taper optical fiber. The high quality factor (Q) of this microcavity results in a sharp resonance criterion that is observable as the frequency of a tunable laser is scanned. In the reflection spectrum the depth and width of this dip are determined by the coupling mechanisms between the coupler and the microsphere, and the intrinsic loss of the cavity. Introducing an absorber in the evanescent field of the microsphere WGM changes the intrinsic loss of the cavity and hence changes the dip depth and width. Absorbers studied include the vibrational overtones of CO2 gas at 1572 nm and indocyanine green dye in methanol at 800 nm. Additionally, the temperature dependence of the index of refraction of fused silica gives the WGM resonance frequency a temperature dependence of 1.6 GHz/K at 1550 nm. This allows the microsphere to be used as a microKelvin scale temperature probe for thermal studies, including thermal bistability of the cavity determined from the amount of power absorbed by the microspheres. Additionally, the high Q-factor of the microspheres allows temporal studies of the cavity to be performed. If time permits, this will lead into a brief introduction of cavity ring down spectroscopy and experiments performed using a traditional cavity.