James Gerard Fagan

Conformal window for the airborne laser aircraft

The Airborne Laser (ABL) program requires a large aperture, highly transparent window to allow the high energy laser beam to be focused on targets. This window presents many challenges as it is thin, large in diameter and very highly curved. Additionally, the window must be made from a material highly transparent at 1.315 micrometers, the chemical oxygen-iodine laser wavelength, have good transmission from the visible through 3 micrometers and be able to withstand the rigors of operations on a tactical aircraft. To manufacture this window, a unique partnership between two companies, Heraeus and Corning, was forged to demonstrate the process and manufacture the window blanks. Infrasil 302, a Heraeus product, is the only material with low absorption at 1.31 micrometers that can be produced in large enough quantities to make a window blank of the required size. Corning has developed the technology to flow- out and sag glass products to make highly curved optics without the need to machine them out of a cylindrical block. Using their experience and a common desire to support the ABL program, the two companies worked together to develop the processes that produce the window blanks. Contraves Brashear Systems of Pittsburgh will polish the blank in to its final form, with coatings applied by Optical Coating Laboratories, Inc. of Santa Rosa to maximize transmission.