Oscillations, Waves, and Interactions - GWDG

The single bubble – a hot microlaboratory 153
Figure 14. Shape dynamics of two elongated femtosecond-laser-induced bubbles. The
height of the frames is 47 µm. Comparison with theory courtesy of N. Pelekasis and K.
Tsiglifis [25].
the shock wave. Figure 16 gives the result of a shock wave pressure measurement
series with different bubble sizes Rmax. The upper and lower boundaries of the shaded
area give the error bounds of the measurements. The pressures obtained at distance
d from the breakdown site have been extrapolated to the minimum bubble radius
by using a 1/r-dependence for the amplitude, where the minimum radius has been
obtained by a numerical fit to the bubble collapse. About 10 kbar are reached for a
bubble collapsing from a radius of 500 µm and about 25 kbar when collapsing from a
radius of 3 mm. Unfortunately the collapse pressure from trapped bubbles cannot be
measured this way as these bubbles are extremely sensitive to a disturbance nearby
and also of lower shock wave strength, because they reach a lower maximum size
of less than about a 100 µm and thus have less total energy. But extrapolating the
pressure values down to smaller radii Rmax gives strong evidence of collapse pressures
in the range of a few 1000 bar for standard sonoluminescing trapped bubbles.
laser pulse
glass fibre
R max
d
Fibre−optic hydrophone
Figure 15. Experimental arrangement with a fibre-optic hydrophone for the measurement
of shock waves from laser-induced breakdown and of bubble collapse shock waves. The
distance d between the fibre tip and the bubble can be varied.