R. Pecha

Pulse width and shape in single bubble sonoluminescence

To test the different theoretical models describing the light emitting process in SBSL measurements of the width and shape of the emitted light pulses are essential. The light pulses have been characterized by two independent methods: with time‐correlated single photon counting and with a streak camera. Both methods lead to the same results. The pulse width strongly depends on the parameter’s driving pressure, gas and gas concentration and temperature and varies between 60 ps and more than 300 ps, and there is no difference between the red and uv part of the spectrum. The streak camera results additionally show that the pulse shape is slightly asymmetric with a steeper ascent and a slower descent. This asymmetry increases with decreasing temperature.

Single‐bubble sonoluminescence: Acoustic emission measurements with a fiber‐optic probe hydrophone

In single‐bubble sonoluminescence additionally to the short light pulses, the bubble emits in the collapse phase a sound wave which can be measured with a fiber‐optic probe hydrophone [Staudenraus and Eisenmenger, Ultrasonics 31, 267 (1993)]. This type of hydrophone is an absolute ultrasonic wideband reference standard. Compared to piezoelectric hydrophones it allows measurements with higher spatial (0.1 mm) and temporal (10 ns) resolution. The intensity and the width of the emitted sound wave increase with increasing driving pressure, but vary only slightly with water temperature in contrast to the emitted light intensity. The total radiated energy of the sound wave is below 10% of the initial energy of the bubble. The results are compared with earlier measurements on transient cavitation bubbles and with new theoretical results.

Ultrasound, shock waves, and phonons

On Dec. 10, 2016, the brilliant experimental physicist Prof. Wolfgang Eisenmenger passed away completely unexpectedly. His extensive work had influence on many different fields of acoustics. This presentation gives an overview on his remarkable and inspiring life and research.

Single‐bubble sonoluminescence: Investigation of the emitted pressure wave with a streak camera and a fiber‐optic probe hydrophone

In the collapse end phase of single‐bubble sonoluminescence (SBSL), in addition to a short light pulse, a spherical pressure wave is emitted by the bubble into the surrounding liquid. This pressure wave was investigated with two different methods: (1) If the bubble is illuminated by a laser beam, laser light is Mie‐scattered by the bubble itself, but also by the outgoing pressure pulse. The scattered light of both was recorded with a streak camera with a spatial resolution of 8 μm and a temporal resolution of 500 ps. From the time‐dependent radial distance of the pressure pulse r(t) from the bubble, the velocity v(t) can be determined. The speed of sound in the vicinity of the bubble is increased in comparison to normal conditions. This change in the sound velocity was used to estimate the amplitude of the pressure pulse. (2) At a distance of 2.5 mm from the bubble, a fiber‐optic probe hydrophone with a spatial resolution of 100 μm and a rise time of 5 ns was used to measure the pressure wave. Measurement...

The cavitation collapse on a sub‐ns time scale

A single sonoluminescing air bubble trapped in the pressure maximum of a resonant sound field in water is an ideal model system to investigate the end phase of the cavitation collapse. The dynamics of these single bubbles can be characterized with Mie‐scattering. In earlier experiments, the scattered light was detected with photomultiplier tubes (PMT) where the time resolution is limited by the response of the PMT and no spatial resolution is possible. Using a streak camera, the scattered light can be recorded with high spatial and temporal resolution. The streak images show that at the minimum radius the scattered light intensity is not only a function of R(t) anymore, and the changes in the refractive indices inside the bubble and in the highly compressed water surrounding the bubble have to be considered. Together with the width and intensity of the emitted light pulses, the results represent a complete data set for the end phase of the bubble collapse.