Based on the normal pulsed laser ablation method, femtosecond pulsed laser deposition (fs-PLD) is adopted in vacuum for the production of TiO₂nanoparticle-assembled films. We study the morphology and electronic characteristics of TiO₂nanoparticle-assembled films deposited at different oxygen background gas pressures from high vacuum (~10^-4 Pa) to 100 Pa and different deposition time. Our results show that TiO₂nanoparticle-assembled films obtained in high vacuum present both a mixture with rutile phase and anatase phase and a pure rutile phase. At the same time, there are more mesoporous structures in the film after annealing, which is beneficial for the enhancement of photocatalytic activity. In water splitting experiment, part of the TiO₂nanoparticle-assembled films embedded with a small mass fraction of CdS nanoparticles (~5%) present an interesting photocurrent enhancement with a maximum value of ~0.2 mA/cm² under a solar simulator.

We investigate the angular distribution and average kinetic energy of ions produced during ultrafast laser ablation (ULA) of a copper target in high vacuum. Laser produced plasma (LPP) is induced by irradiating the target with Ti:Sapphire laser pulses of ～50 fs and 800 nm at an angle of incidence of 45o. An ion probe is moved along a circular path around the ablation spot, thereby allowing characterization of the time-of-flight (TOF) of ions at different angles relative to the normal target. The angular distribution of the ion flux is well-described by an adiabatic and isentropic expansion model of a plume produced by solid-target laser ablation (LA). The angular width of the ion flux becomes narrower with increasing laser fluence. Moreover, the ion average kinetic energy is forward-peaked and shows a stronger dependence on the laser pulse fluence than on the ion flux. Such results can be ascribed to space charge effects that occur during the early stages of LPP formation.