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8 September 1995 Influence of nonideal chopper design on nonuniformity in uncooled pyroelectric staring array systems
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Choppers are inevitable parts of thermal imager or radiometer systems based upon uncooled pyroelectric focal plane arrays, since pyroelectric detectors require the incident radiation to be modulated. In comparison with other chopper techniques such as oscillator or shutter choppers rotating circular disks are considered superior in both mechanical simplicity and electronic control. However, the use of rotating disks introduces two non-ideal circumstances affecting the system's operation quality. Two-dimensional arrays require a bended chopper edge to approximate an ideal straight edge traveling over the array. Since sampling is performed line- sequentially, a local shift in time occurs between the sampling instant and the change of the optical chopper phase within each line. Furthermore, the chopper can only be placed in front of the entrance window of a detector array and, therefore, modulates the incident radiation in the blurred region of the optical path. This flattens the ideal rectangular modulation shape one would obtain if the chopper were able to run in the focal plane. Both effects attenuate the sensor output signal. The article presents a model for designing optimum chopper disks for 2- D arrays in order to achieve minimal possible signal attenuation. The optimization procedure incorporates all interdependencies between chopper layout, array size, chopper position, and readout velocity. The model also considers the unavoidable distance of the chopper plane from the focal plane and provides a chopper performance prediction method where the varying signal attenuation is discussed as contribution to the array's nonuniformity. Finally, a sample design is given, and measurements are presented.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jochen Koepernik, Helmut Budzier, and Guenter Hofmann "Influence of nonideal chopper design on nonuniformity in uncooled pyroelectric staring array systems", Proc. SPIE 2552, Infrared Technology XXI, (8 September 1995);

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