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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

Snapshots of the bubble-to-bubble interaction within different sample media.Images show representative interactions after application of constant laser parameters in: (a) De-ionized water, (b) porcine vitreous body (increased artefacts due to inhomogeneities inside the biological tissue), (c) 1% gelatin solution, (d) 2% gelatin solution, and (e) 5% gelatin solution. The pulse energy Epulse corresponds to 8.5-times breakdown threshold Eth in water and the focus separation confirms to Δx = 46.1 µm. All pictures are taken at Δt = 13.6 µs. While (a), (b), and (c) show the typical interaction effects of mechanism 7, in (c) and (d) mechanism 2 conveys.
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pone-0114437-g009: Snapshots of the bubble-to-bubble interaction within different sample media.Images show representative interactions after application of constant laser parameters in: (a) De-ionized water, (b) porcine vitreous body (increased artefacts due to inhomogeneities inside the biological tissue), (c) 1% gelatin solution, (d) 2% gelatin solution, and (e) 5% gelatin solution. The pulse energy Epulse corresponds to 8.5-times breakdown threshold Eth in water and the focus separation confirms to Δx = 46.1 µm. All pictures are taken at Δt = 13.6 µs. While (a), (b), and (c) show the typical interaction effects of mechanism 7, in (c) and (d) mechanism 2 conveys.

Mentions: To begin with, for focusing two subsequent fs-laser pulses with constant pulse energy Epulse as well as spot separation Δr inside the different sample media, a change of occurring interaction mechanisms could be observed. For a pulse energy of 8.5-times the breakdown threshold Eth in water and a distance between the foci Δr = 38 µm a similar bubble oscillation appeared in water, vitreous body and the 1% gelatin solution (see Table 1). All interaction effects within these media belonged to mechanism 7: There was the jet through the first cavitation bubble to the left (towards laser scanning, characteristic effect D). Afterwards, the second jet formed in scanning direction (characteristic effect E) which is shown in Fig. 9 for all media at related parameters of Epulse = 8.5-times Eth and Δr = 46.1 µm. While the jet properties in general were very similar for porcine vitreous body compared to de-ionized water, their reproducibility falled slightly due to the inhomogeneities within the biological tissue. This effect was clearly recognizable due to a comparison of the three images at each point of time during the whole bubble dynamics. As can be seen in Fig. 9b there are comparably large tissue structures within the vitreous body. These led to an increased variation of jet length as well as changes of the exact jet direction. In detail, in some single image there could be observed no jet at all. However, for 1% gelatin the maximum bubble radius Rmax of the first cavity as well as the jet length decreased.


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)

Snapshots of the bubble-to-bubble interaction within different sample media.Images show representative interactions after application of constant laser parameters in: (a) De-ionized water, (b) porcine vitreous body (increased artefacts due to inhomogeneities inside the biological tissue), (c) 1% gelatin solution, (d) 2% gelatin solution, and (e) 5% gelatin solution. The pulse energy Epulse corresponds to 8.5-times breakdown threshold Eth in water and the focus separation confirms to Δx = 46.1 µm. All pictures are taken at Δt = 13.6 µs. While (a), (b), and (c) show the typical interaction effects of mechanism 7, in (c) and (d) mechanism 2 conveys.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0114437-g009: Snapshots of the bubble-to-bubble interaction within different sample media.Images show representative interactions after application of constant laser parameters in: (a) De-ionized water, (b) porcine vitreous body (increased artefacts due to inhomogeneities inside the biological tissue), (c) 1% gelatin solution, (d) 2% gelatin solution, and (e) 5% gelatin solution. The pulse energy Epulse corresponds to 8.5-times breakdown threshold Eth in water and the focus separation confirms to Δx = 46.1 µm. All pictures are taken at Δt = 13.6 µs. While (a), (b), and (c) show the typical interaction effects of mechanism 7, in (c) and (d) mechanism 2 conveys.
Mentions: To begin with, for focusing two subsequent fs-laser pulses with constant pulse energy Epulse as well as spot separation Δr inside the different sample media, a change of occurring interaction mechanisms could be observed. For a pulse energy of 8.5-times the breakdown threshold Eth in water and a distance between the foci Δr = 38 µm a similar bubble oscillation appeared in water, vitreous body and the 1% gelatin solution (see Table 1). All interaction effects within these media belonged to mechanism 7: There was the jet through the first cavitation bubble to the left (towards laser scanning, characteristic effect D). Afterwards, the second jet formed in scanning direction (characteristic effect E) which is shown in Fig. 9 for all media at related parameters of Epulse = 8.5-times Eth and Δr = 46.1 µm. While the jet properties in general were very similar for porcine vitreous body compared to de-ionized water, their reproducibility falled slightly due to the inhomogeneities within the biological tissue. This effect was clearly recognizable due to a comparison of the three images at each point of time during the whole bubble dynamics. As can be seen in Fig. 9b there are comparably large tissue structures within the vitreous body. These led to an increased variation of jet length as well as changes of the exact jet direction. In detail, in some single image there could be observed no jet at all. However, for 1% gelatin the maximum bubble radius Rmax of the first cavity as well as the jet length decreased.

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