Tomokazu Sano

Optimization of laser-induced forward transfer process of metal thin films

The optimization of laser-induced forward transfer (LIFT) process using laser ablation of thin film and the evaluation of the dependence in laser spot size on the resolution of deposited material are reported. Ni thin film of several hundred of nanometer thickness, which is deposited on fused silica substrate, was irradiated by single pulse of KrF excimer laser (wavelength: 248 nm, pulse width: 30 ns), and transferred to a Si acceptor substrate. Images of the plume, which were photographed using image intensified CCD camera, indicated the cause of transfer of particles. The deposited material with clear contour was obtained under the condition that thin film was in contact with an acceptor substrate to inhibit the transfer of particles which were generated by laser irradiation. The resolution of a deposited material tended to be improved as the size of laser spot became smaller.

Direct Welding between Copper and Glass Substrates with Femtosecond Laser Pulses

We demonstrate direct microwelding between glass and copper substrates by use of femtosecond (fs) pulses. The joint strength is as high as >16 MPa. A scanning electron microscopy cross-sectional image of the sample proves successful joining without voids or cracks. Furthermore, we show that, compared with ns-pulses, the use of fs-pulses can reduce the pulse energy required for welding by two orders of magnitude, leading to the suppressed effect of heat and to the precise control of the welded region.

Shock Hugoniot and temperature data for polystyrene obtained with quartz standard

Equation-of-state data, not only pressure and density but also temperature, for polystyrene (CH) are obtained up to 510 GPa. The region investigated in this work corresponds to an intermediate region, bridging a large gap between available gas-gun data below 60 GPa and laser shock data above 500 GPa. The Hugoniot parameters and shock temperature were simultaneously determined by using optical velocimeters and pyrometers as the diagnostic tools and the α-quartz as a new standard material. The CH Hugoniot obtained tends to become stiffer than a semiempirical chemical theoretical model predictions at ultrahigh pressures but is consistent with other models and available experimental data.

Femtosecond laser quenching of the ε phase of iron

The quenching of the e phase of iron, which has not been observed under a conventional shock compression, was attained using a femtosecond laser. The crystalline structure in a recovered iron sample was determined using an electron backscatter diffraction pattern system. The femtosecond laser driven shock may have the potential to quench high-pressure phases of other materials.

Laser-shock compression and Hugoniot measurements of liquid hydrogen to 55 GPa

KYOKUGEN, Center for Quantum Science and Technology under Extreme Conditions,Osaka University, Toyonaka, Osaka 560-8531, Japan(Dated: January 7, 2011)The principal Hugoniot for liquid hydrogen was obtained up to 55 GPa under laser-driven shockloading. Pressure and density of compressed hydrogen were determined by impedance-matching toa quartz standard. The shock temperature was independently measured from the brightness of theshock front. Hugoniot data of hydrogen provide a good benchmark to modern theories of condensedmatter. The initial number density of liquid hydrogen is lower than that for liquid deuterium, andthis results in shock compressed hydrogen having a higher compression and higher temperature thandeuterium at the same shock pressure.

Femtosecond laser-driven shock synthesis of hexagonal diamond from highly oriented pyrolytic graphite

We synthesized hexagonal diamond directly from highly oriented pyrolytic graphite (HOPG) using a femtosecond laser pulse without catalyst. A femtosecond laser pulse with wavelength of 800 nm, pulse width of 130 fs, the intensity of 2×1015 W/cm2 was irradiated onto the HOPG surface in air. Crystalline structures of the fs laser-affected region in the HOPG were analyzed using grazing-incidence XRD method. We found that the hexagonal diamond which is the metastable high-pressure phase of carbon appeared in the HOPG which was irradiated by the femtosecond laser normal to the basal plane. We suggest that the femtosecond laser-driven shock wave induces the graphite – hexagonal diamond transformation and that the hexagonal diamond is synthesized due to the rapidly cooling in the shock heated region.

Sputtering and thermal effect during ion microbeam patterning of polymeric films

The purpose of this article is to investigate the machinability of polymers and the main parameters involved during ion microbeam processing of polymers. Investigations were made for the case of ion microbeam patterning of polyethyleneterephthalate and nylon-6 using a focused ion beam system with a needle type ion source. The extracted beam diameter was 0.2 μm, the current density on the target was 1.0 A/cm2, and the beam energy was 30 keV. The removal rate, which shows the number of atoms removed when an ion impinges on the surface, was obtained experimentally. By comparing the removal rate and the theoretical sputtering yield, it became clear that effects other than sputtering have a great influence on the machinability of polymers. Two-dimensional unsteady heat conduction equations were computed using the finite difference method in order to estimate the temperature increment within and around the beam irradiated area. The results show that localized heating and a change of chemical bonding state durin...

Formation of High-Density Dislocations and Hardening in Femtosecond-Laser-Shocked Silicon

High-density dislocations are formed in silicon by a femtosecond-laser-driven shock wave. The silicon is hardened to around 6.4 times harder than the matrix material as measured by micro-indentation hardness test using nanoindentation. Because the depth, size, and inhomogeneity of the area where the high-density dislocations exist are the same as those of the hardened area, we conclude that the hardening is caused by the high density of dislocations. We suggest that the femtosecond laser shock compression plays an important role in creating high-energy-density states in materials.

Thermally stabilized photoinduced Bragg gratings

Bragg gratings were printed in Ge–SiO2 and Ge–B–SiO2 thin glass films by KrF excimer laser irradiation through a phase mask. The diffraction efficiency of the grating printed in the Ge–B–SiO2 film was approximately one order of magnitude greater than that of the Ge–SiO2 film. Although the gratings were almost erased upon annealing at temperatures lower than 500 °C, a grating with much higher diffraction efficiency than before annealing was formed exclusively in the Ge–B–SiO2 film after annealing at 600 °C. The diffraction efficiency of the grating was unchanged upon repeated heating between room temperature and 600 °C.

Hugoniot and mean ionization of laser-shocked Ge-doped plastic

Pressure, density, temperature, and reflectivity measurements along the principal Hugoniot of Ge-doped plastics used in Inertial Confinement Fusion capsules surrogates were obtained to pressures reaching up to 7 Mbar and compared to Quotidian Equation of State models. The experiment was performed using the GEKKO XII laser at the Institute of Laser Engineering at Osaka University in Japan. High precision measurements of pressure and density were obtained using a quartz standard and found to be in good agreement with theoretical Hugoniot curves. Modeling of reflectivity measurements show that shocked samples can be described as poor metals and that mean ionization calculated within the frame of QEOS is overestimated. Similarly, shock temperatures were found to be below theoretical Hugoniot curves.