Radiation Hardened Optical Filters for Focal Plane Assemblies

Critical space and missile defense systems include high performance infrared (IR) sensors consisting of cryogenically cooled IR focal plane arrays and IR band-pass filters, which are both degraded by ionizing radiation. One aspect of this problem is the absence of intentionally radiation hardened by design (RHBD) cryogenic IR band-pass filters. The current filters used in IR sensors are either radiation soft or radiation hard by accident. All of the previous proposed solutions to prevent radiation induced darkening of IR filters have been shown to be invalid. This leaves IR sensor designers with two options: 1) Complete the development of radiation hardened by design cryogenic IR filters, or 2) iteratively develop, fabricate, and characterize IR filters in the hope that some are accidentally radiation hard enough. Option 1 will provide MDA and other agencies with intentionally radiation hardened designs capable of operation in environments that exceed total doses of 100 krad(Si). Subsequent programs may then choose a rad-hard by design filter, resulting in reduced cost and schedule risks to the program. Option 2 will not only dramatically increase cost and schedule risks, but it will also leave the space and radiation community without a known solution and only limited radiation hardness.