Single Hit CCD Spectrometers for X-ray conversion efficiencies (revisited)

Absolute conversion efficiencies from laser energy into X-rays are difficult to obtain given uncertainties in required filters and detector characteristics. A known method for measuring absolute X-ray flux is using a CCD camera that is placed far enough away and filtered well enough such that no more than one photon can be detected per pixel of the detector while maintaining precise knowledge of the attenuation. The image histogram then serves as an X-ray spectrum. However, remaining noise, fluorescence, sky-shine in ultra-intense laser experiments, and charge splitting to neighboring pixels are just a few complications that pose challenges to this diagnostic. We will present recent results with the Z-Petawatt and Z-Beamlet lasers and share observation and attempted explanation for spectral features from detector interactions that were previously unnoticed.