Photodisruption in biological samples using femtosecond laser pulses

Tightly focused femtosecond laser pulses can be absorbed nonlinearly inside biological materials, vaporizing tissue in the focal volume. High intensity is achieved at the focus with relatively low energy, minimizing collateral damage and unwanted heat deposition. We focus 100-fs laser pulses using a high numerical aperture microscope objective in the bulk of the skin tissue, disrupting micrometer-sized regions up to 100 mm beneath the sample surface. When the laser beam is focused even deeper into the sample, we observe the formation of filaments in the skin bulk rather than spherical sub-surface cavities, indicating that critical self-focusing occurs. The small scale of the photodisruption suggests the possibility for precise ablation of sub-cellular organelles in single cells. We investigate the potential of disrupting mitochondria and cutting actin fibers in the cytoskeleton of a living cell. When using a 1.4 N. A. microscope objective, the energy required for single cell photodisruption is only a few nanojoules, well within the range of a Ti:Sapphire laser oscillator. This greatly simplifies the laser system needed. The high repetition rate of the laser oscillator also makes possible real-time imaging of the sample using multiphoton fluorescence techniques while simultaneously inducing photodisruption with the same laser system.