Non-uniform thermal imaging detector

In a thermal radiation image scanning system which employs means for scanning a thermal radiation image across a focal plane, an integrating detector for receiving said scanned radiation on an exposed surface thereof, wherein said integrating detector is an elongated strip of semiconductor material rendered photoconductive by the generation of electron and hole photocarriers when said radiation image is scanned along said strip, first and second biasing electrodes mounted on opposite ends of said strip and means for applying a D.C. biasing source to said first and second electrodes to produce a generally lengthwise D.C. electric current flow through said strip and thereby cause an ambipolar drift of photocarriers in said strip and at least one read out electrode on said strip located near the end of said strip to which said photocarriers are drifting, an improvement whereby said elongated detector strip is formed to have a constantly variable cross-section along its length of elongation thereby affecting the charge density of said drifting photocarriers along the length of said detector strip by the resultant variations in the electrical bias field density along said length.