X-ray detection by direct modulation of an optical probe beam—Radsensor: Progress on development for imaging applications

Abstract

We present a progress report on our new x-ray detection technique based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. The electron–hole pairs create a frequency dependent shift in optical refractive index and absorption. This is sensed by simultaneously directing an optical probe beam through the same volume of semiconducting medium that has experienced an x-ray induced modulation in the electron–hole population. If the wavelength of the optical probe beam is close to the semiconductor band-edge, the optical probe will be modulated significantly in phase and amplitude. We have analyzed the physics of the imaging radsensor, developed modeling tools for device design, and are cautiously optimistic that we will achieve single x-ray photon sensitivity, and picosecond response. These predictions will be tested with Cu Kα xrays at the LLNL USP facility this spring and summer, with a cavity-based radsensor detector suitable for use in x-ray imagers.