Planar and spherical shock wave generation during infrared laser ablation of calcium carbonate

Laser ablation of calcium carbonate was studied at wavelengths of 1.064, 4.0 and 7.0 mm using a time-resolved surface plasmon probe, plume photography and scanning electron microscopy. The surface plasmon measurements make it possible to correlate surface morphology with shock wave velocities. Planar shock wave production, either on the front or rear side of the ablated sample, is highly correlated with uniform material removal all across the irradiated spot on the sample surface. While rear-side ablation was not observed at longer wavelengths, front-side ablation with uniform material removal and planar shock waves are produced by excitation of calcium carbonate at its fundamental vibrational mode at 7 mm using a free-electron laser. At 1.064 mm, the mechanism of ablation appears to be related to absorption by surface defects, while at 7 mm, material appears to be removed by evaporation triggered by the resonant excitation of a fundamental vibrational mode. q1998 Elsevier Science B.V.