Optical frequency references for laser interferometry

Abstract

Optical frequency references for laser standards based on molecular iodine absorption cells represent one of the most used tool for frequency stabilization of lasers operating in a visible spectral range. In the industry oriented laser measurements and similar laser interferometry applications performed at atmospheric conditions, a refractive index of air plays a role of main uncertainty contributor. In these cases there is no need to use technologically complicated and expensive iodine references made of pure fused silica with precise pressure control of absorpbing media. A set of iodine cells made of borosilicate glass was filled with certain amount of absorbing media to define the saturation point of iodine inside. A combination of these two approaches (pyrex material and controlled saturation pressure of iodine) allows us to simplify the laser stabilization setup (there is no need of additional iodine pressure level control) and reduce the overall reference's costs with ensuring of sufficient frequency stability of the system at the same time. Spectral properties of manufactured cells were tested by hyperfine transitions linewidth measurement and comparison with results from traditional fused silica cells was done to investigate the long-term iodine purity inside the references. As the transitions linewidth method shows a very high sensitivity to iodine purity level, this method is proposed to be an alternative approach in investigation of contamination in iodine absorption cells where traditionally used techniques -laser induced fluorescence (LIF) and absolute frequency shifts measurement -can not be used.