Device and Method for Subaperture Stray Light Detection and Diagnosis

A device for identifying sources of stray light in an optical system to be tested having an aperture through which light may enter the system and a detection surface, comprising:

• a source of a test light beam having a propagation axis and a selected width at a selected location along the propagation axis of the test light beam, including a test light beam width magnifier whereby the cross sectional area of the test light beam may be made less than the cross sectional area of the aperture the optical system to be tested;
• a relative lateral positioning stage;
• an angular test light beam directing stage, the lateral test light beam positioning stage and the angular test light beam directing stage be adapted to launch the test light beam into the aperture at a selected position and selected directional angles with respect to a selected optical axis;
• a detector adapted to be located at the detection surface;
• and
• a data processing system responsive to the detector for identifying stray light that reaches the detector and producing a data set relating the presence of stray light at the detector to the location and direction angles of the test light beam at the aperture.

A light trap and test light beam delivery system for identifying actual sources of stray light in and optical system having an aperture through which light may enter the system, comprising:

• a light beam delivery system for placement between the light trap and the optical system;
• and
• a light trap having a specular surface disposed at an acute angle to the axis of the test light beam and a diffuse surface disposed nominally parallel to the axis of the test light beam;
• the light beam delivery system including a diffuse surface disposed to interact with the specular surface of the light trap and a specular surface disposed to interact with the diffuse surface of the light beam delivery system, the test light beam being delivered to the optical system through a window in the specular surface of the light beam delivery system.