Abstract: The Vanderbilt free-electron laser provides a continuously tunable ($lambda equals 2 - 10 micrometer) source of pulsed IR radiation with a pulse structure unlike those of conventional lasers (a macropulse of 4.5 ms consisting of a micropulse train of 1 ps pulses separated by 350 ps). Tuned to the vibrational mode of the amide-II band ($lambda equals 6.45 micrometer), the laser is well suited for precise tissue ablation with reported minimal thermal and collateral tissue damage. However, the relative influences of the pulse structure and wavelength on tissue ablation is still not clear. The effects of different wavelengths ($lambda equals 2.94, 3.36, and 6.45 micrometer) on tissue ablation were compared using pump-probe imaging of tissue phantoms while simultaneously laser-induced pressures were measured with a piezoelectric needle hydrophone. Bovine heart tissue was ablated in vitro using clinically relevant parameters and laser induced damage was examined histologically. The results of these experiments, and their implications will be discussed. !1
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