Optical heterodyne spectroscopy enhanced by an external optical cavity: toward improved working standards

Abstract

A study is made of the use of an external resonator to enhance sub-Doppler signals observable with the high-sensitivity techniques of optical heterodyne spectroscopy. The case of modulation-transfer spectroscopy in a ring resonator is considered in detail. Exciting the /sup 127/I/sub 2/ resonance at 612 nm with a low-power He-Ne laser made it possible to observe a S/N of 250:1 in a 10-kHz bandwidth. Used in an optimal control loop, this performance would provide a laser stability of 10 Hz at 1 s. Such a greater-than-hundredfold improvement in stability should lead to increases in accuracy as well.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>