In Direct Write Scene Generation (DWSG) a critical lens design parameter is the optical crosstalk, or the undesired energy incident on adjacent pixels (EOAD). Crosstalk must be minimized to obtain the proper scene projection fidelity. The laser scan lens systems used in this scene generation technique are typical fO and can be optimized by adjusting the diameter of the input gaussian beam in relation to the entrance pupil. The optimum gaussian beam diameter is dependent on the resolution requirements placed on a system and the test article metrics. Optical cross talk calculations are used to gauge the performance of systems with square and circular entrance pupils. This paper will address the calculated relationship between crosstalk and the truncation of the Gaussian input beam.

Various means of scene generation are used to test infrared focal plane sensors. At Arnold Engineering Development Center a Direct Write Scene Generator is being developed. A scene is projected onto the focal plane array by scanning a rake of beams across the surface of the sensor. The rake consists of 1 28 synchronous beams generated by passing a single laser beam through an acousto-optic cell with a complex radio frequency signal input. Each pixel of the focal plane is illuminated by one of the beams in the rake. The beam is blanked as the rake scans from one row of pixels to the nexton the focal plane array. The Direct Write Scene Generator is being designed to test focal planes as large as a 512 x 512 pixel array. Scan optics were designed to focus an expanded laser beam to a spot smaller than the focal plane pixel pitch over the entire test area. Several optical configurations are needed to achieve the requirements at various wavelengths. SCENE PROJECTION COMPONENTSThe Direct Write Scene Generator (DWSG) 1,2,3 is designed to test focal planes at three different wavelengths (0.514 tm, 1.06 rim, and 5.4 rim), with additional diagnostic capabilities at 10.6 rim. The standard projection configurations are for pixel sizes of 50 jim for visible and 100 pm for infrared over a 512 x 5 12 pixel area, although other sizes and configurations are possible. The optical components in this system are shown in the schematic drawing in Fig. 1 . The first component is the laser system. High power continuous wave lasers were selected with output wavelengths compatible with the acousto-optic (AO) cells and the focal plane array (FPA). While a focal plane can be tested at a number of wavelengths, only one wavelength can be used to test an FPA at a time, since each wavelength requires a separate set of optics. First, the laser beam passes through a stabilizer to reduce noise in the laser output. Next the beam goes through a blanker, which blocks the beam during transition between columns to reduce illumination between pixels. The beam expander enlarges and collimates the beam to fill the AO cell aperture, and a diverging lens is needed at longer wavelength configurations to produce the required diverging input beam to the AO deflectors. Up to sixteen AO cells receive input radio frequency (RF) signals and break the input beam into a number of deflected beams. The AO cell consists of two AO deflectors and creates a two-axis scan; the first deflector produces a beam that is scanned across the FPA, and the second breaks this beam into a rake. The scan lens focuses the AO deflected beams through the dewar window and laser-line filter and onto the FPA.

The viability of extending the Direct Write Scene Generator (DWSG) to project to a sensor system with an optical telescope installed has been investigated. The test approach requires development of transmissive or reflective screens andlor collimator systems to expand the DWSG output to the sensor telescope. Several optical configurations have been examined to accommodate this capability. Measurements of the optical spot size on a camera with a zoom lens have been compared to CODE V predictions. Analysis has been performed to determine the practical limitations of this configuration with regard to testing sensors with a set field of view (FOV). A demonstration of operation of the DWSG through camera optics has been accomplished. The utility of this new capability to closed-loop operation has also been examined.

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This paper describes the investication and potential utility ot usino the l)ircct Write Scene (kaicrator (I )VvS( to proJect onto a sensor system's local plane array (FPA) throuizh its optical telescope. The test approach requires dcveloimicnl of inaonifier/collimator systems to expand the I)WSG output to the sensor telescope. A lens svstcui has been procured to facilitate the projection to the full array of a standard ('Cl) with an attached lens svsteni. A demonstration ot operation of the l)WSG through camera optics has been recorded. 'Ihe capability of the l)WSG svsteni to measure' ['PA crosstalk has been exaniined in soiiie (letail.