PNNL

Abstract

We report a heterodyne beat with a line width of 5.6?0.6 Hz between two cavity-stabilized quantum cascade lasers operating at 8.5 micron. We also present a technique for this measurement that avoids the need for extreme isolation of the optical cavities from the environment; that the employing a third servo loop with a low bandwidth to force one cavity to track the slow drifts and low frequency flutuations of the other. While not fully independent, this technique gratly facilitates heterodyne beat measurements for evaluating the performances of cavity-locked lasers above the bandwidth of the third loop.