Evaluation of dynamic range for LLNL streak cameras using high-contrast pulses and "pulse podiatry" on the NOVA laser system

A standard LLNL streak camera has been used to analyze high contrast pulses on the Nova laser facility. These pulses have a plateau at their leading edge (foot) with an amplitude which is approximately 1 of the maximum pulse height. Relying on other features of the pulses and on signal multiplexing we were able to determine how accurately the foot amplitude was being represented by the camera. Results indicate that the useful single channel dynamic range of the instrument approaches 100:1. 1. BACKGROUND Requirements for achieving power balance among the ten Nova beamlines demand that complex pulse shapes be measured with accuracy of better than 10 at all points in time. The standard instrument used to measure pulseshape is the LLNL streak camera. While this streak camera has a well understood sweep rate and flat field response1 its small signal response is less certain. The purpose of this work is to determine the minimum on-line signal level that meets the 10 accuracy specification. As a final " footnote" regarding the background of the title since we are analyzing a (pulse) foot to see how healthy (accurate) it is the colloquialism " pulse podiatry" seemed appropriate. 1. 1. The LLNL streak camera The LLNL streak camera uses a large format streak tube coupled to a 40mm diameter microchannel plate intensifier. The intensifier output is imaged through a lens onto a CCD chip