Quantitative measurements using soft x-ray streak cameras

Abstract

A Soft X‐ray Streak Camera (SXRSC) is a fast timing instrument sensitive to x rays from 100 eV to 30 keV. The instrument has excellent time resolution (∼15 ps) and large dynamic range (∼103) which are well suited for measuring x‐ray pulses produced by laser‐fusion targets. The SXRSC uses a thin transmission photocathode to convert x‐rays to a secondary electron signal which is acelerated, focused, and deflected onto a phosphor producing an image of the x‐ray pulse time history. In the past, such instruments have been used only to make relative measurements of the time history. At LINL we have calibrated the SXRSC in order to make absolute intensity measurements of the soft x‐ray flux from laser fusion targets. Such measurements will assist in understanding the laser plasma processes and conditions needed to attain laser‐produced fusion. Because of the nature of the instrument, we have calibrated it in the dynamic mode using a small laser‐produced pulsed x‐ray source. Details of the calibrations will be given. We have measured the SXRSC response to be linear over more than two orders of magnitude with the range limited by the x‐ray source strength. The dynamic range of similar instruments sensitive to optical light has been demonstrated to be greater than 103. Based on first generation calibrations, flux measurements are accurate to ±30% with the largest uncertainty in the calibrations being in determining the source spectrum and intensity. The uncertainties can possibly be reduced by a factor of two by better source characterization. In that case errors in SXRSC measurements would approach those of other x‐ray pulse detectors, such as x‐ray diodes.