Infrared Measurement System for Visibly Opaque Freeform Windows

Project goals: To test visibly opaque windows by flexible optical ray metrology using an infrared camera with a thermal source, to improve test usability by automating test window positioning, and to quantitatively characterize test subsystem performance. Flexible optical ray metrology measures complex aspheric windows in transmission. The transmitted wavefront error and surface quality of these windows are determined by measuring off-nominal deflections of a known patterned source. Tightly toleranced spatial control of the optic in pitch, yaw and roll was achieved by designing a kinematic optical mount for the free-form optic under test. A software package and graphical user interface were created in LabView to automate spatial positioning of the optic and subsequent image acquisition. Mechanical performance of the motorized optic mount was characterized with a laser tracker, and an infrared modulation transfer function test was designed and implemented to verify optical performance modeled in Zemax. The improved flexible optical ray metrology system overcomes challenges associated with free-form window metrology, and could lead to higher-quality fabrication processes for visibly opaque conformal windows.