Abstract

The frequency noise of an external-cavity diode laser has been measured by converting the frequency fluctuations to amplitude fluctuations through absorption on an atomic transition. The frequency noise has also been measured by the standard technique of conversion to amplitude fluctuation by means of transmission by a Fabry-Perot interferometer, for comparison. The two techniques are largely equivalent. This work makes an important link between noise spectroscopy^1,2 and the characterization of the frequency noise of laser diodes. In particular, it has been noted that using an external-cavity laser diode (ECLD) reduces the frequency noise and so gives very small signals in noise spectroscopy.² However, calculations of the frequency noise of an ECLD show an enhancement of the frequency noise at multiples of the longitudinal-mode-spacing frequency v_LMS and a suppression at intermediate frequencies.³ We have confirmed this experimentally by using an ECLD tuned to the Cs D₂ atomic resonance. Thus, an ECLD can be used for noise spectroscopy, provided that the detection frequency is tuned to a multiple of v_LMS

© 1995 Optical Society of America