Three-dimensional subsurface microprocessing of collagen by ultrashort laser pulses

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Abstract
Submicron sized damage spots were created by multiphoton absorption of ultrashort 775 nm laser pulses in collagen gel stained with fluorescent dye. Submicron nodules were formed in the collagen both near the surface and at a depth of up to 30 μm. We have shown that large numbers of pulses at low pulse energy provide well-controlled sample damage restricted to a small focal volume. The damage threshold was dependent on dye concentration but not significantly dependent on the depth. This will be useful for experiments that study laser-induced damage in living biological samples on a cellular scale and deep within the specimen.