Kou Kurosawa

X-ray emission spectroscopic studies of silicon precipitation in surface layer of SiO2 induced by argon excimer laser irradiation

Abstract The ultra-soft X-ray emission spectra were taken from surfaces of bulk silica glass and silica glass films exposed to an argon excimer laser ( λ =126 nm) and compared with the spectra taken from the virgin surfaces. The precipitation of crystalline silicon is found to take place in thin surface layers of the irradiated bulk silica glass and 15 nm film. An estimation of concentration of crystalline silicon precipitation with the depth is given on the basis of the measurements of Si L 2,3 X-ray emission spectra obtained at different accelerating voltages of the electron beam on the X-ray tube. Based upon the precipitation conditions for these samples, we discuss the crystalline silicon precipitation mechanism: the electronic excitation induces the bond-breaking between Si and O atoms, although there is a critical density of photons for the bond-breaking and temperature rise enhances the crystalline silicon precipitation.

X-ray radiation effects on second-harmonic generation in thermally poled silica glass

We observed a strong second-order optical nonlinearity in a fused silica glass poled under the condition of a static electric field of 4 kV/mm at 260 °C. The nonlinearity layer was localized in the surface region contacted on the positive electrode during poling in a thickness comparable to or thinner than the interaction length of 22 µm. The second-order nonlinearity was not observed in synthetic silica glass under the same poling condition. However, when the synthetic glass was first exposed to x-ray radiation, the poling induced a nonlinearity of almost the same value as that in the fused silica glass, which we attribute to the x-ray formation of defects. The values were found to depend on water contents in the synthetic silica glass.

Development of Laser Turning Using Femtosecond Laser Ablation

Ablation using femtosecond-lasers has taken much attention for micromachining with the advantages of efficient ultra-thin layer peeling without undesirable thermal effects for both opaque and transparent materials. In this work, we have proposed the femtosecond-laser turning based on the fact that femtosecond-laser ablation is a promising technique for excellent surface finishing techniques. The effect of the machining conditions such as focusing condition, energy of laser pulse and plural scanning, on the thickness of peeling layer for various kinds of materials (PMMA, silica glass, silicon, copper and aluminum) have been investigated. As a result, the important information for the laser turning as a practical application of the femtosecond lasers were obtained.

Generation of tunable intense coherent radiation around 126nm with an argon excimer laser

Generation of intense coherent radiation with an electron beam pumped argon excimer laser is presented. A tunable oscillation was established in the wavelength range from 124nm to 127.5nm, and the maximum output power of 2.2MW was obtained at the line center. The spectral region is extended using stimulated Raman scattering in hydrogen molecules. The conversion efficiency is as high as about 50% in 8atm hydrogen gas.

Photochemical reactions in silicon nitride with ArF excimer laser

Exposure of silicon nitride to above-bandgap 6.5-eV photons from an ArF excimer laser drives both the dissociation of silicon-nitrogen bonds and the desorption of nitrogen atoms and/or molecules over a wide fluence range. Crystalline silicon precipitates are also generated on laser exposed surfaces, however, only for fluences exceeding 0.2 J/cm2. The rates of nitrogen desorption and the concentration of silicon precipitation were found to depend strongly on laser fluence, rising rapidly above 0.2 J/cm2, and saturating at approximately 0.5 J/cm2. This saturation was also observed in the thickness of the silicon precipitate layer, which peaked at 35 nm depth for fluences greater than 0.5 J/cm2. Such saturation phenomena can be explained by the onset of laser ablation at approximately 0.5 J/cm2 fluence which removes material in the laser affected zone. The formation of silicon precipitates is discussed in the context of photochemical reactions that follow band-to-band electronic transitions.

Stimulated Raman scattering experiments of hydrogen molecules in the VUV region around 126nm

High power tunable argon excimer laser was used for a pumping source of stimulated Raman scattering in molecular hydrogen. Intense Stokes radiations up to second order were observed. The threshold power of the stimulated scattering and the conversion efficiency of the first Stokes radiation were measured. An effect of the dispersion of the refractive index of H2 on stimulated Raman scattering and feasibility of generation of the anti‐Stokes radiation are discussed.