Frequency tuning of the whispering-gallery modes of silica microspheres for cavity quantum electrodynamics and spectroscopy

We have tuned the whispering-gallery modes of a fused-silica microresonator over nearly 1 nm at 800 nm, i.e., over half a free spectral range, or 10(6 ) linewidths of the resonator. This result has been achieved by use of a ne w method based on the stretching of a two-stem microsphere. We describe dev ices that will permit new cavity QED experiments with this high-Q optical r esonator when it is desirable to optimize its coupling to emitters with giv en transition frequencies. The demonstrated tuning capability is compatible with both UHV and low-temperature operation, which should be useful for fu ture experiments with laser-cooled atoms or single quantum dots. (C) 2001 O ptical Society of America.