Time Resolution Limitations in Single-stage Image Converter Photography

Abstract

This chapter discusses the time-resolution limitations in single-stage image-converter photography. For direct observations of ultrashort optical events the best available time resolution is that afforded by image-converter streak cameras. A laser spark produced by the breakdown of an inert gas by a focused giant-pulse laser beam was used as the light source for the tests. The surface brightness of the laser spark in the visible region of the spectrum is that of a black body at about 10 6 K for several nanoseconds after the instant of breakdown. The emission then decays with a time constant of the order of 200 nsec. This high brightness allows single-shot investigation of the limits of time resolution and dynamic range, while the later steady decay allows easy checking of streak-speed uniformity. The spatial resolution of the image tube in dynamic operation is important in determining the minimum resolving time obtainable in the streak mode. If the slit width is made equal to the spatial resolution limit, then the resolving time is the minimum that can be reached for the streak speed. It is found that the best results were obtained with an S·20 photocathode, which showed no saturation at current densities up to 60 mA/cm 2 , but other photocathodes were not so good.