Interferometric detection of acoustic shock waves

We excite high-amplitude longitudinal coherent acoustic strain waves in a chromium film deposited on a thin sapphire slab, by 100-fs pulses from a 1-kHz Ti:sapphire regenerative amplifier. The bipolar strain pulse that is launched into the crystal, gradually transforms into a shock wave when attenuation by thermal phonons is weaker than the nonlinear action. We detect such shock waves at the opposite side of the slab by probing the reflection of a second chromium film in a standard reflection geometry, with a common-path interferometer to resolve both the induced amplitude and phase changes. We first discuss the interferometer and its standard performance. We then present the measurements on propagating shock waves, and analyze the results on a qualitative level.