Abstract

This paper reviews the major problems plaguing the pyroelectric vidicon from its inception: short tube life, low responsivity and spatial resolution, ineffective temporal modulation of the radiation. The tube life was extended from a few hundred to over two thousand operating hours by abandoning the gassy tube approach, in which negative charges are eliminated by positive ions¹ and going to hard vacuum tubes. The latter required a new readout method to reset the target potential by secondary electron emission.² Special coatings protect the targets against erosion by the electron beam and impose a responsivity that is uniform within about 5 %. The tube performance was increased by reducing the electron beam discharge lag. This was achieved by using a laminar flow electron gun to lower the beam impedance and by replacing the triglycine sulfate target by deuterated triglycine fluoroberyllate to reduce the capacitance.³ These measures improved the performance of the panning camera with a T/1 optics from a minimum detectable temperature difference of 0.5°C at 100 TV lines to 0.5°C at 250 TV lines. Temporal modulation of the input radiation, required to generate video signals in pyroelectric vidicons, restricts the camera operation either to imaging of moving objects or to panning or chopping. These modes will be discussed, and it will be shown that chopping and proper signal processing⁴ remove the thermal streaking characteristic of the panning mode without introducing objectionable flicker. As a result pyroelectric vidicon cameras approach the image quality of a well designed infrared scanner having the equivalent performance.

© 1976 Optical Society of America