We begin with a brief review of prior work relating to optical windows for use with high power laser beams. A typical window must provide pressure separation between system segments, ultra-low loss, and small wavefront distortion of the many outgoing laser beams and signal returns despite heating by the high energy laser (HEL) beam. Historically, two approaches have been examined to improve such windows. The first uses positive thermo-optic coefficient materials, but with very low HEL absorptance glass to minimize the thermal distortion optical path differences (OPDs). The second approach uses negative thermo-optic coefficient materials for which the optical path can be made to remain fixed, and the OPDs small, even though the HEL increases the temperature and physical thickness. Recently, a U.S. Navy contractor developed a new fluoride glass which appears to possess superior stability and robustness properties compared to their earlier counterpart thermo-optic materials. Using preliminary properties for this glass, we have performed simulations that examine its ability to avoid deleterious Airborne Laser Beam Control System OPD effects-possible increase of localized irradiance on downstream optics and decrease of local loop beam Strehl. Even with the present glass formulation, not optimized for the ABL wavelength, the performance is exceptional in preventing these effects. Encouraged by this, a small window was exposed to the COIL laser beam at RADICL, demonstrating reasonable bulk absorptance and robustness against abrupt beam turn-on thermal shock. In view of these successful predictions and tests, the ABL program has chosen this "Oxyfluoride Glass (OFG)" as its candidate material and is following a Technology Roadmap to develop OFG windows. This presentation will discuss current progress along this development path.
Development of low-OPD windows for airborne laser
2001
12 Seiten, 15 Quellen
Aufsatz (Konferenz)
Englisch