Study of the pulse-to-pulse interaction optimizing the cutting of high-repetition fs-laser systems in medicine

• Applicant: Dr. Tammo Ripken
• Subject Area: Medical Physics, Biomedical Technology
• Term: from 2010 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 184423677

The pulse-to-pulse interaction of fs-laser inside biological tissue is only almost completely understood: if temporal pulse separations are large compared to the effects induced (plasma formation, shock wave, cavitation bubble), and if the biological tissue without any restrictions, can be assumed to consist of water or at least an aqueous liquid. Thus, predictions of average quality, efficiency and side effects of cuts in e.g. crystalline lens tissue and especially corneal tissue are not really predictable and often simply determined empirically for each individual application. The challenge is to describe and compare these very fast processes in not completely regenerating media and tissue while applying several subsequent and in their mechanical effects temporally overlapping laser pluses. So far, the necessary reproducibility to create a series of pictures from single images is not given.Currently, such investigations are performed by means of shadow-photography in water or aqueous media, in this context, to avoid inconvenient spatial dimensions and time scales often ns-laser-pulses are used. The dynamics of a single cavitation bubble in the vitreous, lens or cornea is not yet published. Conclusions are not drawn from basic experiments, but only from actual cutting tests, e.g. performed on porcine eyes or in animal studies. Sporadically pump-probe experiments or expensive drum or high-speed cameras are used as an alternative.With an extension of the existing experiment, for the first time, the dynamics of two or more interacting laser-induced optical breakdowns will be shown in tissue with time scales in the nanosecond range. For this, a chromatically coded exposure sequence is realized with LED flashes and mapped to different spatial regions of a sCMOS sensor, by this recording a series of images from a single event. With the simultaneous elimination of system-induced aberrations by an adaptive optics system a high degree of comparability for different tissues and tissue samples is achieved, which in turn allows the deduction of a more general statement.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Holger Lubatschowski