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 research on 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 roughening 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 a time domain by these newly developed pump-probe methods. Ablation of CuPc crystalline and amorphous films shows a novel dependence of the etch profile on the excitation pulse width; fs etch depth increases stepwise with laser fluence, while ns etch depth gradually increases as fluence increases. The results are discussed in view of how electronic excitation energy evolves to morphological change.