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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

Color-coded map of the different interaction mechanisms in the effective parameter space of pulse overlap.The map includes the parameter space of spatial overlap parameter ηr and temporal overlap parameter ηt. The dots mark the experimentally measured limit of different interaction mechanisms. For visual assistance they were connected by lines while the space in between was filled with the color belonging to the prevalent mechanism. The mechanisms are described in Fig. 4 regarding their combination of characteristic interaction effects.
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pone-0114437-g007: Color-coded map of the different interaction mechanisms in the effective parameter space of pulse overlap.The map includes the parameter space of spatial overlap parameter ηr and temporal overlap parameter ηt. The dots mark the experimentally measured limit of different interaction mechanisms. For visual assistance they were connected by lines while the space in between was filled with the color belonging to the prevalent mechanism. The mechanisms are described in Fig. 4 regarding their combination of characteristic interaction effects.

Mentions: Additionally, the temporal as well as spatial overlap parameters associated with each series of measurement were calculated. The representation of interaction mechanisms within this effectively analyzed parameter space is shown in Fig. 7. It can be seen that for a temporal overlap ηt<0.925 (see dotted horizontal line in Fig. 7) there was a dependency of the interaction mechanism only on the spatial overlap parameter ηr. This means that only the distance between the focal spot of the subsequent laser pulse and the first bubble's center of mass was essential for the resulting interaction mechanism: For a large overlap (ηt<1, ηr<1) and impinging an existing cavitation bubble with the subsequent laser pulse a further LIOB was suppressed on the one hand. On the other hand, an axial bubble shift with decreasing energy conversion efficiency appeared. The bubble collapse was asymmetric and there were liquid jets directed in surrounding medium which had an axial amount of mechanical impact. In contrast, for a temporal overlap (ηt<1) combined with an increasing spatial separation between existing cavity and subsequent laser pulse (1<ηr<2.5) effects with strong mechanical impact perpendicular to the optical axis of the laser could be observed. For this reason, the properties of this jet and their dependency on the pulse separation were studied in detail with water as sample medium; the results are shown in the following section.


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)

Color-coded map of the different interaction mechanisms in the effective parameter space of pulse overlap.The map includes the parameter space of spatial overlap parameter ηr and temporal overlap parameter ηt. The dots mark the experimentally measured limit of different interaction mechanisms. For visual assistance they were connected by lines while the space in between was filled with the color belonging to the prevalent mechanism. The mechanisms are described in Fig. 4 regarding their combination of characteristic interaction effects.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0114437-g007: Color-coded map of the different interaction mechanisms in the effective parameter space of pulse overlap.The map includes the parameter space of spatial overlap parameter ηr and temporal overlap parameter ηt. The dots mark the experimentally measured limit of different interaction mechanisms. For visual assistance they were connected by lines while the space in between was filled with the color belonging to the prevalent mechanism. The mechanisms are described in Fig. 4 regarding their combination of characteristic interaction effects.
Mentions: Additionally, the temporal as well as spatial overlap parameters associated with each series of measurement were calculated. The representation of interaction mechanisms within this effectively analyzed parameter space is shown in Fig. 7. It can be seen that for a temporal overlap ηt<0.925 (see dotted horizontal line in Fig. 7) there was a dependency of the interaction mechanism only on the spatial overlap parameter ηr. This means that only the distance between the focal spot of the subsequent laser pulse and the first bubble's center of mass was essential for the resulting interaction mechanism: For a large overlap (ηt<1, ηr<1) and impinging an existing cavitation bubble with the subsequent laser pulse a further LIOB was suppressed on the one hand. On the other hand, an axial bubble shift with decreasing energy conversion efficiency appeared. The bubble collapse was asymmetric and there were liquid jets directed in surrounding medium which had an axial amount of mechanical impact. In contrast, for a temporal overlap (ηt<1) combined with an increasing spatial separation between existing cavity and subsequent laser pulse (1<ηr<2.5) effects with strong mechanical impact perpendicular to the optical axis of the laser could be observed. For this reason, the properties of this jet and their dependency on the pulse separation were studied in detail with water as sample medium; the results are shown in the following section.

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