Coherent optical ultrasound detection with rare-earth ion dopants

We describe theoretical and experimental demonstration for optical detection of ultrasound using a spectral hole engraved in cryogenically cooled rare-earth ion doped solids. Our method utilizes the dispersion effects due to the spectral hole to perform phase to amplitude modulation conversion. Like previous approaches using spectral holes it has the advantage of detection with large \'etendue. The method also has the benefit that high sensitivity can be obtained with moderate absorption contrast for the spectral holes.