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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

Contour depiction of the jet characteristics scaled with the applied laser pulse energy.Jet length within the parameter space of (a) focus separation and pulse energy (scaling the temporal overlap) as well as (b) spatial overlap parameter ηr and temporal overlap parameter ηt, and jet velocity as a function of (c) focus separation and pulse energy as well as (d) the overlap parameters ηr and ηt. 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.
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pone-0114437-g008: Contour depiction of the jet characteristics scaled with the applied laser pulse energy.Jet length within the parameter space of (a) focus separation and pulse energy (scaling the temporal overlap) as well as (b) spatial overlap parameter ηr and temporal overlap parameter ηt, and jet velocity as a function of (c) focus separation and pulse energy as well as (d) the overlap parameters ηr and ηt. 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.

Mentions: The strong water jet along the trajectory of laser scanning was observable within the interaction mechanisms 5 to 7 (see Figs. 3–4 and 6). The jet's properties which were affecting its influence on the untreated medium are the maximum jet length, and hence the range of impact, as well as its maximum velocity (regarding its operating momentum). These characteristic values were analyzed regarding their magnitude within the parameter space of pulse energy (coding the temporal overlap) and focus separation. The results of this examination can be seen as a contour plot in Fig. 8a and Fig. 8c. Furthermore, the Figs. 8b and 8d show an analogue depiction as a function of the overlap parameters. The grey-scale value maps the maximal length (Figs. 8a and 8b) and velocity, respectively (Figs. 8c and 8d). The four dashed and dotted lines depict assumed borders between the interaction mechanisms defined in Section 3.2. For a specification of the effective jet impact the dimensions were scaled with the applied laser pulse energy.


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)

Contour depiction of the jet characteristics scaled with the applied laser pulse energy.Jet length within the parameter space of (a) focus separation and pulse energy (scaling the temporal overlap) as well as (b) spatial overlap parameter ηr and temporal overlap parameter ηt, and jet velocity as a function of (c) focus separation and pulse energy as well as (d) the overlap parameters ηr and ηt. 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.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0114437-g008: Contour depiction of the jet characteristics scaled with the applied laser pulse energy.Jet length within the parameter space of (a) focus separation and pulse energy (scaling the temporal overlap) as well as (b) spatial overlap parameter ηr and temporal overlap parameter ηt, and jet velocity as a function of (c) focus separation and pulse energy as well as (d) the overlap parameters ηr and ηt. 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.
Mentions: The strong water jet along the trajectory of laser scanning was observable within the interaction mechanisms 5 to 7 (see Figs. 3–4 and 6). The jet's properties which were affecting its influence on the untreated medium are the maximum jet length, and hence the range of impact, as well as its maximum velocity (regarding its operating momentum). These characteristic values were analyzed regarding their magnitude within the parameter space of pulse energy (coding the temporal overlap) and focus separation. The results of this examination can be seen as a contour plot in Fig. 8a and Fig. 8c. Furthermore, the Figs. 8b and 8d show an analogue depiction as a function of the overlap parameters. The grey-scale value maps the maximal length (Figs. 8a and 8b) and velocity, respectively (Figs. 8c and 8d). The four dashed and dotted lines depict assumed borders between the interaction mechanisms defined in Section 3.2. For a specification of the effective jet impact the dimensions were scaled with the applied laser pulse energy.

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