Transient temperature response of thin film thermal detectors in infrared imaging systems

The transient temperature response of a continuous thin film two-dimensional thermal detector array to a step function temperature change in an observed scene is analyzed for representative thermal imaging configurations. The temperature pattern in the scene consists of a single strip or a large number of equally spaced strips above a uniform temperature background. The effects of lateral heat conductivity in the thermal detector film, the atmosphere, and losses in the imaging system are taken into account. Curves are calculated which give the temperature sensitivity and resolution as a function of time for physical parameters that are representative of short and long range thermal imaging applications. It is shown that substantial improvements in the resolution can be realized if a readout is performed before the temperature rise in the thermal detector film reaches the steady state value. An analysis is also made of the steady state temperature response of a detector film to a circular temperature pattern in the scene. Some preliminary experimental results on a thermal imaging system employing heat quenched phosphors as the thermal detector material are discussed briefly.