ULTRAHIGH LONG-TERM DIMENSIONAL STABILITY OF A SAPPHIRE CRYOGENIC OPTICAL-RESONATOR

We report on the ultrahigh long-term dimensional stability of a crysta lline cryogenic optical resonator (CORE) cooled to liquid-helium tempe rature. The frequency of a Nd:YAG laser stabilized to a CORE was compa red over long times with an independent laser system, a frequency-doub led Nd:YAG laser stabilized to a hyperfine line of molecular iodine at 532 nm. Over a 6-month period the drift was less than 3 kHz. The dime nsional stability of the CORE is thus more than 2 orders of magnitude higher than that of the best ultralow-expansion glass ceramic cavities at room temperature. (C) 1998 Optical Society of America OCIS codes: 120.0120, 140.0140, 300.0300, 120.3940, 120.4800, 140.4780.