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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

Cavitation bubble dynamics after five subsequent laser pulses in water.Single pictures of the cavitation bubble dynamics due to the application of five subsequent laser pulses using the optimum parameters for water (see Section 3.3). The second and fourth cavities lead to jet formation (see pictures at 15 and 35 µs). Due to the modified overlap by the previous interaction mechanisms the second jet is weaker.
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pone-0114437-g011: Cavitation bubble dynamics after five subsequent laser pulses in water.Single pictures of the cavitation bubble dynamics due to the application of five subsequent laser pulses using the optimum parameters for water (see Section 3.3). The second and fourth cavities lead to jet formation (see pictures at 15 and 35 µs). Due to the modified overlap by the previous interaction mechanisms the second jet is weaker.

Mentions: In Fig. 11, extracted pictures of the time-resolved analysis of the interaction of five laser pulses in water as sample medium are shown. While the progress shows the former interaction of two laser pulses at the beginning (bubble dynamics shown up to 15 µs), at a time of 20 µs, 30 µs, and 40 µs the third till fifth pulse impinged the medium. Due to the interaction of the first two cavities (applied overlap correlates with the optimum overlap parameters in water, see Section 3.3) there was the strong jet formation to the right (see characteristic effect E). The jet led to a premature cavitation bubble collapse so that the third pulse (after 20 µs) impinged only persistent gas bubbles at the focal volume. This means a first modification of the resulting overlap between a cavitation bubble and the subsequent laser pulse; the temporal separation was constant. In consequence of the persistent liquid flow the third cavitation bubble showed a deformation to the right side but no jet (see picture at 25 µs). The fourth LIOB occurred at about 30 µs. Here, due to the deformation of the previous bubble there was another, but less strong modification in spatial overlap. Hence, another jet formed which was decreased in its propagation length with increased statistical variation. The last and fifth pulse hit again persistent gas bubbles and results in a cavity with the same deformation as the third one.


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 after five subsequent laser pulses in water.Single pictures of the cavitation bubble dynamics due to the application of five subsequent laser pulses using the optimum parameters for water (see Section 3.3). The second and fourth cavities lead to jet formation (see pictures at 15 and 35 µs). Due to the modified overlap by the previous interaction mechanisms the second jet is weaker.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0114437-g011: Cavitation bubble dynamics after five subsequent laser pulses in water.Single pictures of the cavitation bubble dynamics due to the application of five subsequent laser pulses using the optimum parameters for water (see Section 3.3). The second and fourth cavities lead to jet formation (see pictures at 15 and 35 µs). Due to the modified overlap by the previous interaction mechanisms the second jet is weaker.
Mentions: In Fig. 11, extracted pictures of the time-resolved analysis of the interaction of five laser pulses in water as sample medium are shown. While the progress shows the former interaction of two laser pulses at the beginning (bubble dynamics shown up to 15 µs), at a time of 20 µs, 30 µs, and 40 µs the third till fifth pulse impinged the medium. Due to the interaction of the first two cavities (applied overlap correlates with the optimum overlap parameters in water, see Section 3.3) there was the strong jet formation to the right (see characteristic effect E). The jet led to a premature cavitation bubble collapse so that the third pulse (after 20 µs) impinged only persistent gas bubbles at the focal volume. This means a first modification of the resulting overlap between a cavitation bubble and the subsequent laser pulse; the temporal separation was constant. In consequence of the persistent liquid flow the third cavitation bubble showed a deformation to the right side but no jet (see picture at 25 µs). The fourth LIOB occurred at about 30 µs. Here, due to the deformation of the previous bubble there was another, but less strong modification in spatial overlap. Hence, another jet formed which was decreased in its propagation length with increased statistical variation. The last and fifth pulse hit again persistent gas bubbles and results in a cavity with the same deformation as the third one.

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