Laser frequency stability measurement using a Fabry-Perot based system

Abstract

Electronic circuitry utilising digital-to-analogue converters, in conjunction with a commercially available 300 MHz scanning Fabry-Perot (FP) interferometer, has been designed to monitor laser frequency variations between two laser modes of widely different wavelength (in this case a single mode HeNe laser operating at 543 nm (green) and a highly stable laser operating at 633 nm (red)). Measurements of the frequency variation of the green laser relative to the red laser have been performed over periods of several hours. The accuracy of the measurements has been measured at better than 1 MHz using two stabilised 633 nm HeNe lasers and excellent linearity has been achieved. Compensation circuitry to negate the effects of the observed thermal drift of the Fabry-Perot interferometer is also described. The addition of fairly standard laser heater control circuitry to the output of the measurement system enables stabilisation of any other laser to a 633 nm frequency stabilised HeNe laser (subject to the finesse of the FP cavity).