Wavelength references for interferometry in air

Cavity-mode wavelengths in air are determined by measuring a laser's frequency while it is locked to the mode in vacuum during a calibration step and subsequently correcting the mode wavelength for atmospheric pressure compression, temperature difference, and material aging. Using a Zerodur ring cavity, we demonstrate a repeatability of +/- 2 X 10(-8) (3 sigma), with the wavelength accuracy limited to +/- 4 X 10(-8) by knowledge of the absolute helium gas temperature during the pressure calibration. Mirror cleaning perturbed the mode frequency by less than Delta v/v similar to 3 X 10(-9), limited by temperature correction residuals. (c) 2005 Optical Society of America.