ORDER-SORTING FILTER TRANSMITTANCE MEASURED WITH AN ARRAY DETECTOR

The simultaneous measurement of the spectrally and spatially variant t ransmittance of a linear variable order-sorting filter in a manner tha t closely resembles its conditions of actual use is described. The tra nsmittance of a prototype order-sorting filter was measured in the 400 -to 880-nm wavelength region by illuminating it with the output beam o f a spectrophotometer while the filter was attached to the front of a 30 x 32 pixel silicon array detector. The filter was designed to be us ed in the output beam of a grating spectrometer to prevent the dispers al of higher diffracted orders onto an array detector. Areas of the fi lter that were spatially matched to the corresponding detector pixel c olumn had measured peak transmittances of about 90% that were uniform to within +/-1.5% along a given column. Transmittances for incident wa velengths shorter than the desired bandpass, corresponding to the orde r overlap region, were measured in the 3 x 10(-3) range. Line spread f unction measurements made with the array detector indicated no signifi cant beam spreading caused by inserting the filter into the beam.