Wavelength-Tracking Capabilities of a Fabry-Perot Cavity
Jack A. Stone Jr., Alois Stejskal
We have characterized the accuracy of atmospheric wavelength tracking based on a laser servolocked to a simple Fabry-Peron cavity. The motivations are (1) to explore a method for air refractive index measurement and (2) to determine the stability and accuracy of these cavities when employed as a length reference, with otential application to absolute distance interferometry, air-wavelength stabilized lasers or similar applications. The Fabry-Perot cavity consists of mirrors optically contacted to an ultra-low-expansion spacer with the interior of the cavity open along its length to the surrounding air. Changes in laser frequency are monitored to determine changes in the refractive index of the gas in the cavity. We have studied limitations of this technique that arise from humidity effects, thermal distortion, and (for absolute refractive index measurements where the cavity must be evacuated) pressure-induced distortions. Comparing results from two cavities with very different lengths gives us a very sensitive probe of errors associated with end effects, and pressure-induced distortions can be measured by filling the cavity with helium, whose index of refraction is believed to be well known from ab initio calculations. The uncertainty of refractive index measurements can be greatly reduced when these sources of error are measured and corrected.
Proceedings of SPIE
August 4, 2003
San Diego, CA
Recent Developments in Traceable Dimensional Measurements II; Jennifer E. Decker, Nicholas Brown, Editors November 2003
hellium, index of refraction, interferometry, refractive index, refractometer, wavelength tracker