Picosecond pulsed laser deposition at high vibrational excitation density: the case of poly(tetrafluoroethylene)

The availability of tunable, picosecond free-electron lasers operating with high efficiency in the mid-infrared opens a materials-processing regime qualitatively distinct from that accessed by femtosecond Ti:sapphire lasers, one which is characterized by a high spatio-temporal density of vibrational, rather than electronic, excitation. As an example of this novel materials-processing regime, we present new results on pulsed laser deposition of thin poly(tetrafluoroethylene) films. Films of poly(tetrafluoroethylene) were deposited by resonant (4.2 and 8.26 μm) and non-resonant (7.1 μm) infrared picosecond laser ablation from either a pressed powder target or a commercial bulk target. The films were smooth and crystalline and largely free of particulates without annealing. Infrared and X-ray photoelectron spectra indicated that the films retained the chemical properties of the starting material. Observations of the film properties are consistent with a steady-state ablation mechanism, possibly enhanced by non-linear absorption due to the high photon flux in the free-electron laser micropulses.