Eye-safe 2-μm master oscillators for precision velocity measurements

Abstract

Coherent laser radar and other demanding applications require extremely stable, environmentally immune cw laser sources to act as single frequency references in the Doppler measurement process. Powerful new techniques such as micro-Doppler remote vibration sensing place even greater demands on these reference oscillators, which require sub-kHz absolute reference frequency stability over several milliseconds to resolve sub-mm/sec vibration signatures at many ten's of kilometers range. We report on progress toward super-stable (1 - 100 Hz relative stability over relevant lidar times of flight) cw eyesafe master oscillators for such applications, incorporating active frequency stabilization techniques. We also describe wide band agile frequency offset locking between two frequency-stable oscillators, relevant to the problem of compensating for large platform-induced Doppler shifts in space-borne coherent lidar applications. In these experiments, two cw lasers were programmably offset locked across a +/- 4.5 GHz span, to an accuracy of 5 kHz.