A major problem encountered in measurement of MTF in sampled-image systems (such as staring or scanning imagers) is that the image modulation depth depends on the position of the deterministic target (typically a point source, line source, or bar target) with respect to the image sampling locations. 1-3 A random transparency test target of known spatial-frequency content allows measurement of a shiftinvariant MTF because the information of the test target has random position with respect to the sampling sites. Random test targets have been used previously for MTF measurements of nonsampled systems such as camera lenses4 and telescopes.5 An alternative technique, the scanning-knife-edge method,6 has been developed to address the issue of shift variance in MTF measurement of imager systems that use focal-plane arrays (FPAs). A tilted knife edge is scanned across a column of the FPA. Our random-target method does not require mechanical scanning and tests the entire image plane at one time. The random-target method creates random test patterns similar to those created using the laser-speckle method,7 but on a broadband basis, without the use of laser radiation. This allows use of blackbody radiation for the source. This method tests both the FPA and the optics together, whereas the speckle MTF tests only the FPA.

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Laser Speckle is the optical phenomena resulting from the random interference of coherent light. This phenomenon can be utilized to measure the Modulation Transfer Function (MTF) of detector arrays. Common devices used for speckle generation, such as integrating spheres and ground glass, suffer from low efficiencies less than 20%. Microlens diffusers are shown to be more efficient alternatives for speckle generation. An analysis of the statistical behavior of microlens diffusers is presented with emphasis on their application to MTF testing of detector arrays in the visible spectrum.

The design and fabrication of an integrating sphere to provide a uniform illumination source was the basis for a student laboratory project. The design process emphasizes several important concepts in radiometry. An integrating sphere is a useful component for other student laboratory experiments, and the design presented is cost-effective when compared with commercially available products.

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