Optical systems design for focal plane testing using direct write scene generation

Infrared Focal Plane Array (FPA) sensors are commonly tested using various means of scene generation. At the Arnold Engineering Development Center a Direct Write Scene Generator (DWSG) is being developed. The DWSG projects the scene onto the focal plane array by scanning a rake of beams across the sensor. The rake consists of up to 256 synchronous beams generated by passing a single laser beam through an acousto-optic deflector (AOD). A complex radio frequency signal input into the AOD diffracts the laser beam into multiple beams. Each pixel of the focal plane is illuminated by one of the beams in the rake. The Direct Write Scene Generator is being designed to test a focal plane area as large as a 512 X 512 pixel array. Scan optics focus an expanded laser beam to a spot smaller than the focal plane pixel pitch over the entire test area. Several optical configurations and multiple AODs are needed to achieve the test requirements at various wavelengths. Some important considerations in the optical design are spot size, crosstalk, and background radiation.