The Sound of Light: Using optical breakdown to drive extreme mechanical excitations

When a high-power laser is focused to a small spot in a fluid, nonlinear interactions at the focus can excite a plasma that expands explosively and emits a strong mechanical shock wave into the ambient medium. This phenomenon – called optical breakdown – can generate peak pressures exceeding 1 MPa a centimeter from the source, with pressure pulses typically lasting less than 1 microsecond. In liquids, optical breakdown is accompanied by the growth of a vapor bubble that rapidly expands from micron to millimeter scales. Together, the ultrafast shock and subsequent bubble expansion can be used to probe the dynamic mechanical response of materials at short time scales and large stress scales. In this talk, I will demonstrate how I have leveraged optical breakdown to remotely measure the mechanical properties of submerged solids. I will show how the mechanical excitation can be tuned optically, and discuss how this technique can be adapted to measure the mechanical response of soft media.