Since the beginning of the investigation of laser-material interaction using pulsed lasers, it is of interest to learn about the potential transport of surface-material by laser-induced processes. Liquid jets, induced by the collapse of a laser-induced vapor bubble near a boundary to a soft material, may pierce such interfaces, resulting in the injection of superficial material into the underlying material. Jets can be classified into three different regimes according to their stand-off distance and their temporal evolution e.g. standard jet, intermediate jet and bullet jet.

The present manuscript describes investigations of the “bullet-jet”-technique to pierce soft materials, e.g gelatine, as surrogate of biological tissue. The dynamics and depth of the injection is studied by using laser pulses (1064 nm, 850 μJ/pulse, 4 ns) and high speed imaging techniques on a water-gelatine interface in dependency of the elasticity of the media (solid and liquid) and of repetitive successive applications at the same spot. The experiments suggest that the limit depth is a function of the media properties. Compared to other jets, it looks that a “bullet-jet” induces less deformation of the surrounding media and the amount of liquid retained into the depth is highest. The presented technique sounds simple and it looks that the injection depth of the jet can be controlled.

Prior to industrial and medical application, like needle-free drug or ink delivery into the skin, further investigations should be performed including preparation of e.g. drug eluting stents or the transport of living material into the tissue depth retaining its biological activity, as observed earlier [Frenz M et al. Transport of biological active material in laser cutting. Las Surg Med 8:562-566 (1988)].

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