Media 1: Numerical far field simulations with the fast Fourier transformation and Fourier space interpolation

Originally published in Optics Express on 09 February 2015 (oe-23-3-3341

Overview of the analyzed sample media with constant spot separation.

<p>Overview of the analyzed sample media and the applied laser parameters pulse energy E_pulse (also in multiple of the threshold E_th for de-ionized water, the given values lie within the precision of the threshold determination) and spot separation Δr, which are constant here for all media. However, the resulting spatial overlap parameter η_r as well as the observable interaction mechanism vary for different mechanical properties.</p><p>Overview of the analyzed sample media with constant spot separation.</p

Schematic depiction of the adjustment of subsequent generated cavitation bubbles.

<p>The first bubble is induced on the left side at a time defined as t₁ = 0.0 µs. The second cavity is generated at t₂ after a constant delay of 10.0 µs. The bubble size is characterized as its radius R_Cav while the distance between the focal spots amounts to Δr.</p

Overview of the analyzed sample media with adapted spot separation.

<p>Overview of the analyzed sample media and the applied laser parameters pulse energy E_pulse (also in multiple of the threshold E_th for de-ionized water, the given values lie within the precision of the threshold determination) and spot separation Δr. By adapting these for the different media spatial overlap parameters η_r within the same range as for water are achieved. In this case, the observable interaction mechanisms correspond.</p><p>Overview of the analyzed sample media with adapted spot separation.</p

Single snapshots of the cavitation bubble interaction dynamics in a 5% porcine gelatin solution.

<p>The pulse energy is 10.5-times breakdown threshold in water and the focus separation confirms to 30.4 µm; the spatial overlap parameters is η_r = 1.41: (<b>a</b>) Formation of second cavity close to first one, (<b>b</b>) jet formation through first bubble, and (<b>c</b>) jet through right cavitation bubble along the direction of laser scanning.</p

Cavitation bubble dynamics of different observable interaction mechanisms.

<p>The first cavitation bubble occurs at about 0.0 µs for every image series. Its single bubble dynamics is shown in two more frames at 5.0 µs and 9.0 µs. The second cavity with defined temporal and spatial separation appears at 10.0 µs next to the first one. Afterwards the dynamics of the cavitation bubble interaction is shown at selected points in time. A more detailed depiction with equidistant time steps can be seen in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114437#pone.0114437.s002" target="_blank">S2 Figure</a>. Especially, the jet formation of interaction mechanism 7 is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114437#pone-0114437-g004" target="_blank">Fig. 4</a> for the whole duration of oscillation and for the total jet length.</p

Contour depiction of the jet characteristics scaled with the applied laser pulse energy.

<p>Jet length within the parameter space of (<b>a</b>) focus separation and pulse energy (scaling the temporal overlap) as well as (<b>b</b>) spatial overlap parameter η_r and temporal overlap parameter η_t, and jet velocity as a function of (<b>c</b>) focus separation and pulse energy as well as (<b>d</b>) the overlap parameters η_r and η_t. The cross signs the maximum impact on the untreated medium (here water) at a maximum value for jet length and velocity at the same time. The dashed and dotted lines show supposed borders between the previously introduced interaction scenarios for visual assistance.</p

Schematic depiction of the experimental setup of the laser path (red) and the illumination path (orange).

<p>Single pulses of the fs-laser are selected by an acousto-optic modulator (AOM), half-wave plate and polarizing beam-splitter cube allow for laser power adjustment. Subsequent laser pulses are spatially separated via polygon scanner and a Keplerian telescope imaging (see also magnified image detail). The focal region inside the sample medium-filled cuvette is illuminated homogeneously by Koehler illumination and a magnified image of the cavitation bubble is reproduced on the chip of the CCD camera.</p

Detailed bubble dynamics of two cavities in the observable interaction mechanism 7.

<p>The parameters to observe mechanism 7 were here a focus separation of Δr = 71.8 µm and a laser pulse energy of E_pulse = 10.7-times E_th. The image series begins with the occurrence of the second cavity at 10 µs. Afterwards, the dominating jet formation in laser scanning direction is shown with the overall jet length by composing two images covering different imaging regions within the cuvette at the same time delay. A more detailed time evolution of the effects and the whole dynamics in equidistant time steps is shown in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114437#pone.0114437.s003" target="_blank">S3 Figure</a>).</p

Cavitation bubble dynamics after five subsequent laser pulses in water.

<p>Single pictures of the cavitation bubble dynamics due to the application of five subsequent laser pulses using the optimum parameters for water (see Section 3.3). The second and fourth cavities lead to jet formation (see pictures at 15 and 35 µs). Due to the modified overlap by the previous interaction mechanisms the second jet is weaker.</p