Initial High-Power-CW-Laser Testing of Liquid-Crystal Optical Phased Arrays

摘要

The performance of liquid-crystal phase retarders and optical phased arrays may be gauged by examining their behavior when they are used as variable wave plates. We used this method to evaluate the performance of these devices as they are heated, and as they are exposed to high-power laser energy at 1.083 micrometer. The results indicate that at higher temperatures or higher power levels of laser exposure, the available phase-modulation depth is reduced, presumably due to heating in both cases. In some instances, normal phase- shifting behavior returned when the conditions of the tests were removed, while in others, the behavior eventually vanished entirely, never to return on its own. We developed a novel method for reviving (as well as extending the temperature range of) the performance of phase retarders after such impairments, by imposing a momentary, DC drive voltage (the 'DC Reset'). Also, as the high- power laser was activated (or deactivated), the LCoS (Liquid Crystal on Silicon) OPA's we examined exhibited thermal time constants in the neighborhood of 20 seconds. Petrographic-microscope images were recorded before and after the tests and, in spite of no apparent materials damage, showed LC migration in most of the devices, supposably due to thermal expansion and contraction. Additional petrographic images were recorded to show the visually apparent local phase-shifting behavior of the devices as the laser-energy level was increased.