VERY HIGH-Q WHISPERING-GALLERY MODE RESONANCES OBSERVED ON FUSED-SILICA MICROSPHERES

We have studied by phase modulation spectroscopy the whispering-galler y modes (Mie resonances) of 60 to 200 mum diameter microspheres obtain ed by fusing with a CO2 law the end of a high-transmission silica fibr e. An evanescent wave at 780 nm was produced by total internal reflect ion of a phase-modulated semiconductor diode laser beam in a glass pri sm. It was coupled into the Mie mode of the microsphere positioned at a fixed distance from the prism face. The spectrum was obtained by mea suring the phase-to-amplitude conversion of the laser beam modulation as its carrier frequency was scanned. Record Q-factors greater-than-or -equal-to 2.10(9) were observed, corresponding to photon storage times longer than 1 mus. Applications of these resonances to fundamental an d applied projects are discussed.