Application of An Avalanche Photodiode in Synchrotron‐Based Ultra‐fast X‐Radiography

A possibility of using avalanche photodiode has been investigated while operated in current or continuous wave mode to accommodate high‐intensity synchrotron x‐ray beams in an ultra‐fast x‐radiography. To achieve a time resolution of 1 μs or better in a time‐resolved x‐radiograhic experiment, the entire time‐sequence of the APD response to the pulsed synchrotron x‐ray beam is recorded with time resolution of 1–2 ns. We have characterized the APD detector in the continuous wave mode to reveal its linearity, signal to noise ratio, and the time response with various circuit configurations. We have demonstrated that signal‐to‐noise ratio better than 1000 can be achieved, which is limited only by Poisson statistics. These detectors, coupled with finely focused x‐rays, have been used to study structure and dynamics of supersonic fuel sprays with 50 μm‐spatial resolution and μs‐temporal resolution in the region close to an injection nozzle.