Infrared laser ablation dynamics using light scattering

The dynamics of infrared laser ablation at atmospheric pressure was studied employing continuous visible laser light scattering in the expanding plume. A pulsed infrared optical parametric oscillator at 2940 nm wavelength and 5 ns pulse width was used to irradiate samples comprising liquid glycerol or 50 mu m thick sections of rat liver tissue. The scattered light from the expanding laser ablation plume was measured using a 532 nm continuous laser parallel to the target and several millimeters above the ablated spot. The scattered light was recorded using a photomultiplier detector and the signal used to estimate the time at which the plume front passed through the continuous laser beam. The velocity of the ablation plume was obtained from consecutive time and distance measurements and the fraction of the laser energy transferred to the expanding shock wave was determined using the Taylor shock wave model. Plume modeling calculations indicate that the ablation is driven by phase explosion that is thermally confined and near the stress confinement regime.