Laser damage in multispectral optical coatings for the ABL

Coatings designed for use in the Airborne Laser (ABL) have stringent requirements for reflectance over several spectral bands in addition to extremely low absorption and high damage threshold at the 1315nm output of the chemical oxygen iodine laser(COIL). The complexity of these coatings leads to difficulty in design and fabrication particularly on curved optical surfaces with large apertures. A series of witness samples were fabricated to evaluate the state-of-the-art for this type of coating and provide appropriate design criteria for the ABL optical train. Damage testing at 1315nm under CW conditions, was performed at the RADICL* laser facility at Kirtland AFB, Limited optical characterization before and after the tests was performed at the OCEL* facility to evaluate the quality of the samples and to identify damage. The results of these tests and characterization will be discussed.