Ultrahigh optical Q factors of crystalline resonators in the linear regime

Experimental demonstration of record optical quality factor of (6.3 +/- 0.8)x10(10) corresponding to cavity ring-down time of tau similar or equal to 36 mu s is made possible by avoiding nonlinear effects in a crystalline whispering gallery mode resonator. We discuss various loss mechanisms in CaF2 cavities and ways of achieving higher quality factors. Possible applications in quantum optics and photonics are discussed.