Ultrafast optical studies of single-bubble sonoluminescence

Single-bubble sonoluminescence (SBSL) is the emission of picosecond flashes of visible light from a gas bubble in water driven by acoustic waves. The bubble undergoes strong nonlinear oscillations in synchrony with the sound field, and light is emitted at the end of each violent runaway collapse.; A complete laboratory was set up to study SBSL. Two ultrafast light scattering techniques are applied to SBSL for the first time to push the temporal resolution of the collapse events leading to light emission. The first, time-stamp light scattering, relies on scattering a laser pulse from the bubble and clocking precisely the time delay between it and the SBSL event. By varying the delay, scattering and timing information is collected simultaneously, yielding an ordered sequence of scattering intensities. We achieve a resolution of 1.5 ns, reflecting the limits imposed by electronic timing jitter in the detection equipment. The excess scattering observed after the SBSL flash is consistent with the picture of an expanding shock wave launched by the bubble implosion into the surrounding water. We estimate that an ultimate jitter-limited resolution of 50 ps is achievable using ultrafast electronics.; To eliminate the jitter problem entirely, a novel ultrafast technique is presented. Differential light scattering (DLS) consists of scattering from the bubble many pairs of ultrashort laser pulses, the pulses in each pair separated by a known time delay. The timing relationship between the pulses is used to reconstruct the collapse dynamics. We introduce an implementation of DLS using polarization and develop the relevant theory of polarized light scattering. This work shows that the time resolution in DLS is independent of jitter in the detection instrumentation but is affected by intensity noise. We map the SBSL dynamics around light emission at a resolution of a few hundred picoseconds. The data show significant departures from the behavior expected in the assumption of a constant and uniform internal refractive index, although the spread in the data prevents a positive identification of the source of such departures. The ultimate resolution achievable with DLS is the laser pulse length used, which could be less than one picosecond.