Reactive pulsed laser ablation deposition of thin films is a technique which has already given good results for the formation of metal and semiconductor oxide and nitride films. To improve the quality of the deposited films it is important to understand the ablation process and the materials transport phenomena from the target to the collecting substrate. Optical emission spectroscopy of the plasma plume, formed by the interaction of the laser pulse with the target is generally used to try to understand the reaction mechanisms during the transport process. An eight speed camera was also used to determine plasma plume expansion velocity and the total duration of luminous emission of the plume. The effect of ambient pressure in the ablation chamber on the plasma composition was observed.
Ultrafine alumina powder was produced by aluminum target ablation with a Nd:YAG laser beam (1064 nm wavelength; 340 mJ/pulse energy; 7 ns pulse duration; 10 pps repetition rate), in a 120 Torr O2 atmosphere. A theoretical approach for the ablation process, based on laser energy absorption and energy balance in the target, is used for comparison with the experimental production rate. Three experimental irradiation conditions were chosen: (1) energy density of 5 J/cm2, considered reference (RDE), (2) lower energy density of 2.5 J/cm2 (LDE) and (3) RDE with auxiliary discharge between an auxiliary electrode and target, triggered by the ablation plume (RDA). Calculated and experimental data of target weight loss show good agreement (135 ng/pulse, calculated, and 100, 110, 120 ng/pulse, experimentally, for RDE, LDE, RDA conditions, respectively). The X-Ray Diffraction spectra of alumina show formation of (gamma) -alumina particles only, especially in LDE and RDA conditions. From Scanning Electron Microscopy size analysis, a decrease of particle size, in LDE and RDA irradiating conditions, is observed. The decrease of laser beam fluence or aiding of ablation using an auxiliary discharge is both favorable for the production of high quality powder, without diminishing the production rate. This can be a good basis for future improvement of the ultrafine powder production process.
CO2 reduction to CH4, by H2, can be achieved at room temperature over a NiO catalyst under laser irradiation. The H2 adsorption states on NiO surface, pre-irradiated and non-irradiated, were put in evidence by Temperature Programmed Desorption. A 248 nm KrF* excimer laser radiation was used to stimulate the filling of the room temperature H2 adsorption state, considered as the first step of the CO2 methanation mechanism.
Laser radiation interaction with materials is a complex process in which creation of acoustic waves or stress waves is a part of it. As a function of the laser radiation energy and intensity incident on steel target surface ultrasound signals were registered and studied. Thermoelastic, ablation and breakdown mechanisms of generation of acoustic waves were analyzed.
Structured modifications are produced by interaction of solid state media with high intensity laser beams. The most useful beams for such purposes are generated by CO2-TE lasers in IR field, and excimer lasers in UV field. The paper describes laser pumping circuits for both lasers with significant temporal decays that occurs between trigger and laser pulses. Also, temporal behavior of above mentioned lasers: pulse duration, delays and jitters, in various operation conditions, i.e., gases mixture, pressure and pumping energy, is made by temporal determination of pulses and delays involved. Finally, synchronization methods, electrical or optical are recommended in relation with necessary conditions of synchronization between beams.