Oscillations, Waves, and Interactions - GWDG

148 W. Lauterborn et al.
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Figure 8. Comparison of the experimental single bubble oscillation (open circles) as shown
in Fig. 7 with numerical simulations based on the Gilmore model (solid line).
3 Single light-induced bubbles
The single bubbles in an acoustic trap must adjust to special conditions to be trapped.
Thus their size goes with the driving frequency, being larger for lower frequency, and
the gas content of the liquid should be low for best stability of the oscillation. Also,
in the course of oscillation the bubble contents alters in adjustment to the outer and
self-produced conditions via diffusion of mass and heat and via chemical reactions
triggered by high temperatures in the inside during collapse [17,18].
A larger variety of single bubbles can be produced by concentrating light energy in
the focus of a laser beam forcing dielectric breakdown of the liquid with concomitant
bubble formation [19]. In analogy to acoustic cavitation this bubble forming process
has been called optic cavitation. As the location of the bubble and its instant
of generation are precisely known, similarly sophisticated measurements with highspeed
optical equipment are possible on bubble oscillation, shock wave radiation and
light emission as in the case of acoustically trapped bubbles. Moreover, additional
measurements are possible on the special dynamics of bubbles near walls.
Bubble dynamics near boundaries or obstacles is outside the scope of trapped bubbles,
as bubble stability cannot be maintained. It is, however, of strong relevance
to hydrodynamic cavitation with its erosion problem and also to ultrasonic cleaning.
Even more so, bubble interaction can be studied with light-induced bubbles by producing
two or more bubbles simultaneously at preselected places and of preselected
sizes or with a time shift between them. Some of the possibilities have already been
explored [20–24], the majority of cases, however, waits to be investigated.