Achromatically filtered diamond photoconductive detectors for high power soft x-ray flux measurements

A 1-mm-square diamond photoconductive detector (PCD) has been installed on the LLNL Nova laser system, for use as a broadband soft x-ray power diagnos tic. The PCD is installed behind an array of pinholes, which cast multiple, overlapping images of the source onto the diamond. This allows reduction o f the x-ray intensity, to avoid saturation problems, while avoiding the spe ctral dependency of thin film filters. The diode current is read out on a 5 GHz bandwidth scope. The system is calibrated by comparison to an absolute ly calibrated array of filtered vacuum x-ray photodiodes ("dante''). The ti me response of the PCD and its bias electronics have been characterized usi ng the 5th harmonic (210 nm) of a short pulse (< 1 ps) Ti: sapphire laser. The data show a fast rise, limited by the 5 GHz scope bandwidth, and a slow er fall off, characterized by an RC time of order 200 ps. (C) 1999 American Institute of Physics. [S0034-6748(99)62701-0].