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Interaction mechanisms of cavitation bubbles induced by spatially and temporally separated fs-laser pulses.

Tinne N, Kaune B, Krüger A, Ripken T - PLoS ONE (2014)

Bottom Line: The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots.Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components.In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers.

View Article: PubMed Central - PubMed

Affiliation: Laser Zentrum Hannover e.V., Biomedical Optics Department, Hannover, Germany.

ABSTRACT
The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots. In order to get more insight into the dynamics a time-resolved photographic analysis of the interaction of cavitation bubbles is presented. Particularly, we investigated the influence of fs-laser pulses and their resulting bubble dynamics with various spatial as well as temporal separations. Different time courses of characteristic interaction effects between the cavitation bubbles were observed depending on pulse energy and spatio-temporal pulse separation. These ranged from merely no interaction to the phenomena of strong water jet formation. Afterwards, the mechanisms are discussed regarding their impact on the medical application of effective tissue cutting lateral to the laser beam direction with best possible axial precision: the mechanical forces of photodisruption as well as the occurring water jet should have low axial extend and a preferably lateral priority. Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components. In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers.

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Cavitation bubble dynamics of different observable interaction mechanisms.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 S2 Figure. Especially, the jet formation of interaction mechanism 7 is shown in Fig. 4 for the whole duration of oscillation and for the total jet length.
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pone-0114437-g003: Cavitation bubble dynamics of different observable interaction mechanisms.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 S2 Figure. Especially, the jet formation of interaction mechanism 7 is shown in Fig. 4 for the whole duration of oscillation and for the total jet length.

Mentions: Inside water as sample medium, two temporally as well as spatially separated laser pulses showed a very complex interaction and hence different resulting bubble dynamics compared to the single bubble dynamics. For that reason the two-dimensional parameter space was analyzed regarding the various observable effects and mechanisms first. The different cavitation bubble dynamics are shown in Fig. 3 as series of 8 or more single pictures and, additionally, for mechanism 7 in Fig. 4. Here, starting at a time of 10.0 µs the depicted images are composed of two pictures taken at different imaging regions to cover the whole jet length. (A more detailed time evolution of the effects and the whole dynamics in equidistant time steps is shown in the S2 and S3 Figures). Depending on the scanning velocity, which defined the spatial focus separation Δr, and on the pulse energy comparatively to the breakdown threshold (encoding the temporal overlap) a number of characteristic interaction effects was detected (confer to dynamics in Fig. 3). In Fig. 5 a depiction is shown listing the ten different, overall observable interaction effects. The snapshots of characteristic interaction effects shown in Fig. 5 were selected from picture series of the whole oscillation dynamics.


Interaction mechanisms of cavitation bubbles induced by spatially and temporally separated fs-laser pulses.

Tinne N, Kaune B, Krüger A, Ripken T - PLoS ONE (2014)

Cavitation bubble dynamics of different observable interaction mechanisms.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 S2 Figure. Especially, the jet formation of interaction mechanism 7 is shown in Fig. 4 for the whole duration of oscillation and for the total jet length.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263672&req=5

pone-0114437-g003: Cavitation bubble dynamics of different observable interaction mechanisms.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 S2 Figure. Especially, the jet formation of interaction mechanism 7 is shown in Fig. 4 for the whole duration of oscillation and for the total jet length.
Mentions: Inside water as sample medium, two temporally as well as spatially separated laser pulses showed a very complex interaction and hence different resulting bubble dynamics compared to the single bubble dynamics. For that reason the two-dimensional parameter space was analyzed regarding the various observable effects and mechanisms first. The different cavitation bubble dynamics are shown in Fig. 3 as series of 8 or more single pictures and, additionally, for mechanism 7 in Fig. 4. Here, starting at a time of 10.0 µs the depicted images are composed of two pictures taken at different imaging regions to cover the whole jet length. (A more detailed time evolution of the effects and the whole dynamics in equidistant time steps is shown in the S2 and S3 Figures). Depending on the scanning velocity, which defined the spatial focus separation Δr, and on the pulse energy comparatively to the breakdown threshold (encoding the temporal overlap) a number of characteristic interaction effects was detected (confer to dynamics in Fig. 3). In Fig. 5 a depiction is shown listing the ten different, overall observable interaction effects. The snapshots of characteristic interaction effects shown in Fig. 5 were selected from picture series of the whole oscillation dynamics.

Bottom Line: The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots.Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components.In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers.

View Article: PubMed Central - PubMed

Affiliation: Laser Zentrum Hannover e.V., Biomedical Optics Department, Hannover, Germany.

ABSTRACT
The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots. In order to get more insight into the dynamics a time-resolved photographic analysis of the interaction of cavitation bubbles is presented. Particularly, we investigated the influence of fs-laser pulses and their resulting bubble dynamics with various spatial as well as temporal separations. Different time courses of characteristic interaction effects between the cavitation bubbles were observed depending on pulse energy and spatio-temporal pulse separation. These ranged from merely no interaction to the phenomena of strong water jet formation. Afterwards, the mechanisms are discussed regarding their impact on the medical application of effective tissue cutting lateral to the laser beam direction with best possible axial precision: the mechanical forces of photodisruption as well as the occurring water jet should have low axial extend and a preferably lateral priority. Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components. In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers.

Show MeSH
Related in: MedlinePlus