Determination of the laser intensity applied to a Ta witness plate from the measured x-ray signal using a pulsed micro-channel plate detector

The laser intensity distribution at the surface of a high-Z material, such as Ta, can be deduced from imaging the self-emission of the produced x-ray spot using suitable calibration data. This paper presents a calibration method which uses the measured x-ray emissions from laser spots of different intensities hitting a Ta witness plate. The x-ray emission is measured with a micro-channel plate (MCP) based x-ray framing camera plus filters. Data from different positions on one MCP strip or from different MCP assemblies are normalized to each other using a standard candle laser beam spot at ∼1 × 1014 W/cm2 intensity. The distribution of the resulting dataset agrees with results from a pseudo spectroscopic model for laser intensities between 4 and 15 × 1013 W/cm2 . The model is then used to determine the absolute scaling factor between the experimental results from assemblies using two different x-ray filters. The data and model method also allows unique calibration factors for each MCP system and each MCP gain to be compared. We also present simulation results investigating alternate witness plate materials (Ag, Eu and Au).