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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

Single snapshots of the cavitation bubble interaction dynamics in a 5% porcine gelatin solution.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 ηr = 1.41: (a) Formation of second cavity close to first one, (b) jet formation through first bubble, and (c) jet through right cavitation bubble along the direction of laser scanning.
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pone-0114437-g010: Single snapshots of the cavitation bubble interaction dynamics in a 5% porcine gelatin solution.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 ηr = 1.41: (a) Formation of second cavity close to first one, (b) jet formation through first bubble, and (c) jet through right cavitation bubble along the direction of laser scanning.

Mentions: Further confirmation was given by the experimental results presented in Table 2. Here, the range of the spatial overlap parameter ηr of water was specified for the interaction mechanisms 2 (ηr>2.85), 7 (1.05<ηr<1.5) and 8 (0.77<ηr<1.05). For the other four analyzed media the experimentally applied laser parameters pulse energy Epulse and spot separation Δr were adapted relatively to those applied to the sample medium water regarding the spatial overlap (ηt<0.925 in all cases). This led to a compliance in the spatial overlap parameter ηr, and furthermore, in the resulting interaction effects and mechanisms, respectively. For example, as for interaction mechanism 7 in water even in 5% gelatin solution the following effects were observable (e.g. Fig. 10): The generation of a further cavitation bubble close to the existing one (see Fig. 10a) led to jet formation through the latter one towards the laser scanning direction (see Fig. 10b, characteristic effect D). The following jet in scanning direction was clearly visible as well (see Fig. 10c, characteristic interaction effect E). It has to be noticed that the jet length again decreased with increasing gelatin concentration and hence scaled with rheological properties of the sample medium.


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)

Single snapshots of the cavitation bubble interaction dynamics in a 5% porcine gelatin solution.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 ηr = 1.41: (a) Formation of second cavity close to first one, (b) jet formation through first bubble, and (c) jet through right cavitation bubble along the direction of laser scanning.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0114437-g010: Single snapshots of the cavitation bubble interaction dynamics in a 5% porcine gelatin solution.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 ηr = 1.41: (a) Formation of second cavity close to first one, (b) jet formation through first bubble, and (c) jet through right cavitation bubble along the direction of laser scanning.
Mentions: Further confirmation was given by the experimental results presented in Table 2. Here, the range of the spatial overlap parameter ηr of water was specified for the interaction mechanisms 2 (ηr>2.85), 7 (1.05<ηr<1.5) and 8 (0.77<ηr<1.05). For the other four analyzed media the experimentally applied laser parameters pulse energy Epulse and spot separation Δr were adapted relatively to those applied to the sample medium water regarding the spatial overlap (ηt<0.925 in all cases). This led to a compliance in the spatial overlap parameter ηr, and furthermore, in the resulting interaction effects and mechanisms, respectively. For example, as for interaction mechanism 7 in water even in 5% gelatin solution the following effects were observable (e.g. Fig. 10): The generation of a further cavitation bubble close to the existing one (see Fig. 10a) led to jet formation through the latter one towards the laser scanning direction (see Fig. 10b, characteristic effect D). The following jet in scanning direction was clearly visible as well (see Fig. 10c, characteristic interaction effect E). It has to be noticed that the jet length again decreased with increasing gelatin concentration and hence scaled with rheological properties of the sample medium.

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