Laser-induced expansion and ablation mechanisms of organic materials

Time-resolved interferometry, surface light scattering imaging, and optical microscopic imaging have been developed and applied to amorphous and multicrystalline films upon intense pulsed excitation. Nanosecond interferometry of neat polystyrene film gives interesting expansion dynamics followed by complete recovery. Femtosecond surface light scattering imaging reveals the roughing processes of Copper phthalocyanine (CuPc) films. Femtosecond optical microscopic imaging of a single anthracene microcrystal shows dynamics of its laser-induced fracture and destruction. All the morphological behaviors have been directly measured in the time domain by these newly developed pump-probe methods. Ablation of CuPc crystalline and amorphous films show novel dependence of etch profile on excitation pulse width; fs etch depth increases stepwise with laser fluence, while ns etch depth becomes gradually deep as fluence does. The results are discussed in view of how electronic excitation energy evolves to morphological change.