Use of coincident ultraviolet laser pulses of two different wavelengths to ablate organic polymers

Abstract

A scheme for up-pumping the chromophores in a polymer is investigated experimentally. It is based on the assumption that ultraviolet (UV) ablation takes place principally from excited states higher than the first excited state. Energies that correspond to UV photons lead to electronic transitions in organic molecules. The excitations that result can promote bonding electrons to antibonding states or to Rydberg states. Since the density of such states rises rapidly with increasing excitation energy, it is possible to achieve successive absorption of two or more photons, leading to high electronic states, by the use of two coincident UV laser pulses of different wavelengths. One photon must be absorbed resonantly, whereas the other can be a longer wavelength at which there is no one-photon absorption. Results for polymethyl methacrylate and polyethylene terephthalate are presented and discussed.