Interaction mechanisms of cavitation bubbles induced by spatially and temporally separated fs-laser pulses.

Nadine Tinne,Tammo Ripken,Alexander Krüger,Brigitte Kaune,Yingxiao Wang

doi:10.1371/journal.pone.0114437

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.

Highlights

Nowadays, in numerous therapeutic applications of ophthalmic laser surgery the fundamental physical effect of photodisruption is used for tissue dissection
The fundamental interaction effect after focusing a single ultra-short laser pulse into an aqueous medium like transparent biological tissue has already been studied extensively; various former publications deal with its explicit description
Because different target materials were used the laser-induced optical breakdown (LIOB) threshold was determined for water and each material

Summary

Introduction

In numerous therapeutic applications of ophthalmic laser surgery the fundamental physical effect of photodisruption is used for tissue dissection. Interaction of fs-Laser-Induced Separated Cavitation Bubbles the focal volume due to the high intensities [1,2,3]. As a consequence of this pressure rise a shock wave propagates into the surrounding medium; its tensile stress component results in cavitation bubble formation by exceeding the spinodal limit far below the critical point of water [3,4]. The fundamental interaction effect after focusing a single ultra-short laser pulse into an aqueous medium like transparent biological tissue has already been studied extensively; various former publications deal with its explicit description (see for example [1, 3, 5,6,7,8,9,10,11])

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Conclusion