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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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Related in: MedlinePlus

Observable interaction mechanisms of two spatially and temporally separated laser pulses and their cavitation bubbles.(a) Overview of occurring interaction effects A to J as part of the observable mechanisms 1 to 11. The depiction shows, which effects are combined as a superposition within each of the experimentally observable interaction mechanisms. (b) Bar diagram of observable interaction mechanism depending on the stepwise adjusted distance between the two foci Δr and the continuously varied applied pulse energy. Vertical lines mark the measured limit between two significantly different mechanisms. The error bars show the standard deviation resulting from the experimental measured pulse energy over 50 pulses as well as energy losses due to a vignetting of the scanning setup. The selected colors differentiate between weak interaction mechanisms (blue), strong interaction mechanisms within the scanning plane (green) and suppressed or axially medium-affecting interaction mechanisms (red). The dashed horizontal line denotes the applied pulse energy, above which the resulting cavitation bubble had a lifetime>10 µs.
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pone-0114437-g006: Observable interaction mechanisms of two spatially and temporally separated laser pulses and their cavitation bubbles.(a) Overview of occurring interaction effects A to J as part of the observable mechanisms 1 to 11. The depiction shows, which effects are combined as a superposition within each of the experimentally observable interaction mechanisms. (b) Bar diagram of observable interaction mechanism depending on the stepwise adjusted distance between the two foci Δr and the continuously varied applied pulse energy. Vertical lines mark the measured limit between two significantly different mechanisms. The error bars show the standard deviation resulting from the experimental measured pulse energy over 50 pulses as well as energy losses due to a vignetting of the scanning setup. The selected colors differentiate between weak interaction mechanisms (blue), strong interaction mechanisms within the scanning plane (green) and suppressed or axially medium-affecting interaction mechanisms (red). The dashed horizontal line denotes the applied pulse energy, above which the resulting cavitation bubble had a lifetime>10 µs.

Mentions: Applying two laser pulses with a set of parameters for pulse energy and spot separation complex interaction mechanisms could be observed. In most of the cases, more than one of the interaction effects appeared as part of a mechanism (see Figs. 3, 5 and 6a); the concerned effects occurred one after another in the course of time. For example, if interaction mechanism 5 proceeded the effects B (asymmetric bubble collaps), C (flattening of bubble surfaces on allocated sides), D (jet formation through first cavity towards scanning direction), and E (jet formation through second cavity in scanning direction) could be observed (confer to dynamics in Fig. 3). Here, an assumed interaction mechanism corresponds to a significant change in appearing combination of interaction effects. The effects themselves showed a sufficient reproducibility regarding their manifestation for constant laser parameters (2 to 3 times per individual time point). The dependency between the resulting interaction mechanisms and the experimental parameters is shown in Fig. 6b for the 8 different analyzed distances between the two foci. Here, at the border of two mechanisms the standard deviation of pulse energy over 50 pulses as well as energy losses due to a vignetting of the scanning setup were indicated as error bars. As an example, for constant spot separation of 28.9 µm up to 3.7-times the breakdown threshold interaction mechanism 1 was observable. By further increasing the applied pulse energy up to 7.3-times threshold the effects of mechanism 5 appeared. Mechanism 6 occurred until a next significant change of effect combination at 7.5-times Eth. Afterwards, mechanism 7 was observable at the focal volume up to 8.0-times breakdown threshold. A further increase in pulse energy led to mechanism 8 until 8.8-times and mechanism 9 up to 9.2-times threshold, respectively. Following this, mechanism 10 was observable up to 10.0-times Eth. Afterwards, mechanism 11 appeared up to the maximum applied pulse energy of 12.0-times breakdown threshold. In turn, the occurring interaction mechanisms become weaker for larger focal distances as for a constant spot separation of 130.8 µm for example: Here, mechanism 1 was observable up to 5.3-times breakdown threshold. An increase in applied pulse energy led to mechanism 2 until 9.3-times Eth. Afterwards, mechanism 3 appeared until 10.8-times breakdown threshold, while mechanism 4 was observable up to the maximum applied energy of 12.0-times threshold.


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)

Observable interaction mechanisms of two spatially and temporally separated laser pulses and their cavitation bubbles.(a) Overview of occurring interaction effects A to J as part of the observable mechanisms 1 to 11. The depiction shows, which effects are combined as a superposition within each of the experimentally observable interaction mechanisms. (b) Bar diagram of observable interaction mechanism depending on the stepwise adjusted distance between the two foci Δr and the continuously varied applied pulse energy. Vertical lines mark the measured limit between two significantly different mechanisms. The error bars show the standard deviation resulting from the experimental measured pulse energy over 50 pulses as well as energy losses due to a vignetting of the scanning setup. The selected colors differentiate between weak interaction mechanisms (blue), strong interaction mechanisms within the scanning plane (green) and suppressed or axially medium-affecting interaction mechanisms (red). The dashed horizontal line denotes the applied pulse energy, above which the resulting cavitation bubble had a lifetime>10 µs.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0114437-g006: Observable interaction mechanisms of two spatially and temporally separated laser pulses and their cavitation bubbles.(a) Overview of occurring interaction effects A to J as part of the observable mechanisms 1 to 11. The depiction shows, which effects are combined as a superposition within each of the experimentally observable interaction mechanisms. (b) Bar diagram of observable interaction mechanism depending on the stepwise adjusted distance between the two foci Δr and the continuously varied applied pulse energy. Vertical lines mark the measured limit between two significantly different mechanisms. The error bars show the standard deviation resulting from the experimental measured pulse energy over 50 pulses as well as energy losses due to a vignetting of the scanning setup. The selected colors differentiate between weak interaction mechanisms (blue), strong interaction mechanisms within the scanning plane (green) and suppressed or axially medium-affecting interaction mechanisms (red). The dashed horizontal line denotes the applied pulse energy, above which the resulting cavitation bubble had a lifetime>10 µs.
Mentions: Applying two laser pulses with a set of parameters for pulse energy and spot separation complex interaction mechanisms could be observed. In most of the cases, more than one of the interaction effects appeared as part of a mechanism (see Figs. 3, 5 and 6a); the concerned effects occurred one after another in the course of time. For example, if interaction mechanism 5 proceeded the effects B (asymmetric bubble collaps), C (flattening of bubble surfaces on allocated sides), D (jet formation through first cavity towards scanning direction), and E (jet formation through second cavity in scanning direction) could be observed (confer to dynamics in Fig. 3). Here, an assumed interaction mechanism corresponds to a significant change in appearing combination of interaction effects. The effects themselves showed a sufficient reproducibility regarding their manifestation for constant laser parameters (2 to 3 times per individual time point). The dependency between the resulting interaction mechanisms and the experimental parameters is shown in Fig. 6b for the 8 different analyzed distances between the two foci. Here, at the border of two mechanisms the standard deviation of pulse energy over 50 pulses as well as energy losses due to a vignetting of the scanning setup were indicated as error bars. As an example, for constant spot separation of 28.9 µm up to 3.7-times the breakdown threshold interaction mechanism 1 was observable. By further increasing the applied pulse energy up to 7.3-times threshold the effects of mechanism 5 appeared. Mechanism 6 occurred until a next significant change of effect combination at 7.5-times Eth. Afterwards, mechanism 7 was observable at the focal volume up to 8.0-times breakdown threshold. A further increase in pulse energy led to mechanism 8 until 8.8-times and mechanism 9 up to 9.2-times threshold, respectively. Following this, mechanism 10 was observable up to 10.0-times Eth. Afterwards, mechanism 11 appeared up to the maximum applied pulse energy of 12.0-times breakdown threshold. In turn, the occurring interaction mechanisms become weaker for larger focal distances as for a constant spot separation of 130.8 µm for example: Here, mechanism 1 was observable up to 5.3-times breakdown threshold. An increase in applied pulse energy led to mechanism 2 until 9.3-times Eth. Afterwards, mechanism 3 appeared until 10.8-times breakdown threshold, while mechanism 4 was observable up to the maximum applied energy of 12.0-times threshold.

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