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AssigneeUniversity of Rochester
InventorsRobert Boni, Paul Jaanimagi
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A system for the photometric calibration of streak cameras and similar imaging devices provides a precise knowledge of the camera's flat-field response as well as a mapping of the geometric distortions. The system provides the flat-field response, representing the spatial variations in the sensitivity of the recorded output, with a signal-to-noise ratio (SNR) greater than can be achieved in a single submicrosecond streak record. The measurement of the flat-field response is carried out by illuminating the input slit of the streak camera with a signal that is uniform in space and constant in time. This signal is generated by passing a continuous wave source through an optical homogenizer made up of a light pipe or pipes in which the illumination typically makes several bounces before exiting as a spatially uniform source field. The rectangular cross-section of the homogenizer is matched to the usable photocathode area of the streak tube. The flat-field data set is obtained by using a slow streak ramp that may have a period from one millisecond (ms) to ten seconds (s), but may be nominally one second in duration. The system also provides a mapping of the geometric distortions, by spatially and temporarily modulating the output of the homogenizer and obtaining a data set using the slow streak ramps. All data sets are acquired using a CCD camera and stored on a computer, which is used to calculate all relevant corrections to the signal data sets. The signal and flat-field data sets are both corrected for geometric distortions prior to applying the flat-field correction. Absolute photometric calibration is obtained by measuring the output fluence of the homogenizer with a “standard-traceable” meter and relating that to the CCD pixel values for a self-corrected flat-field data set.
A system for measuring, from a single image produced during a sweep in an optoelectronic imaging device, the spatial variation in the sensitivity of the device, which system comprises means for applying a spatially uniform and constant in time input source field to an input slit of said device for a period including the duration of said sweep, means for producing an output image during a sweep period exceeding 1 ms, and means for deriving a measurement representing said spatial variations during said sweep.
A system for operating optoelectronic imaging devices having a photocathode and an image-forming element from which a signal data set is derived by a photodetector, said system comprising means for illuminating said photocathode uniformly and continuously during calibration operations, means for deriving as a calibrating signal a flat-field data set from said image-forming element during an interval which lasts a period exceeding about 1 ms, and means for combining said flat-field data set and said signal data set for calibrating said devices.
A source of constant illumination comprising a light source, a pipe transmissive of said illumination having an input end and an output end, over which said illumination presented by said light source, is uniformly distributed over said output end, said pipe having an exterior periphery which is reflective and being of sufficient length from said input to output ends to spatially mix and homogenize illumination incident on said input end which reaches said output end, and wherein said pipe is a rectangular slab having rectangular input and output ends, said source of illumination includes a bundle of optical fibers arrayed in space relationship along the length dimension of said rectangular input end which launches said illumination into said input end, said reflective periphery being the sides of said pipe.
A source of constant illumination comprising a light source, a pipe transmissive of said illumination having an input end and an output end, over which said illumination presented by said light source, is uniformly distributed over said output end, said pipe having an exterior periphery which is reflective and being of sufficient length from said input to output ends to spatially mix and homogenize illumination incident on said input end which reaches said output end, and further comprising a grid over said output end of said pipe for spatially modulating the illumination from said output end.
A system for mapping geometric distortion in an optoelectronic imaging device having a photocathode and an image-forming element from which a signal data set is derived by a photodetector, said system comprising means for illuminating said photocathode with spatially and temporally modulated illumination during mapping operations, means for deriving as a mapping signal a geometric correction data set from said image-forming element during an interval which lasts a period exceeding about 1 ms, and means for combining said geometric correction data set and said signal data set for calibrating said devices.
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