Ablation rate dependence on laser fluence for copper subjected to oblique femtosecond laser irradiation has been determined experimentally in order to investigate processing induced by oblique irradiation. A difference of ablation rate between p-polarized and s-polarized oblique irradiation is clearly observed. Effective penetration depth is defined to explain the ablation rate dependence instead of using optical penetration depth, which is treated as a key value for determining the ablation rate in conventional theory. The effective penetration depth for copper is presented in simple formulas as a function of laser incidence angle for each polarization. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4905353]Femtosecond lasers are candidates for high value-added processing of metals, particularly when minimal thermal metamorphism, 1,2 self-construction of characteristic surface morphology, 3-6 micromachining, 7 or extremely shallow ablation 8,9 is desired. Ablation rate is a fundamental parameter for controlling laser processing, such as drilling, scraping, and cutting, and for estimating the damage threshold of optical components. Additionally, recent research has demonstrated that the ablation rate is related to the formation of laser-induced surface structures. 10,11 For normal laser incidence, the dependence of ablation rate on laser fluence has been investigated for various metals, pulse widths, wavelengths, and atmospheric pressures. 12-24 Three fluence ranges (high, middle, and low) with distinct ablation rates have been reported for all metals. 12 In the conventional theory derived from a one-dimensional two-temperature model, 25 ablation rates in high and middle fluence ranges are expressed by the following equation: 14

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. Ks, 64.70.Kb, 81.05.Dz High-pressure X-ray diffraction studies of Co x Zn 1-x O (x = 0, 0.05, 0.10) were carried out with a synchrotron radiation source. The crystal parameters for three samples under pressure were refined by the Rietveld method. The bulk moduli for Co x Zn 1-x O (x = 0, 0.05, 0.10) were determined by Birch's equation of state to be 144.9 ± 0.6, 143.4 ± 4.2, and 138.5 ± 1.9 GPa, and also the transition pressure from the wurtzite structure to the rocksalt structure were determined to be 8.2, 7.7, and 6.1 GPa, respectively. On increasing the Co-doping into the ZnO, both the bulk moduli and transition pressures decrease, but the rates are quite different. The bulk modulus decreases by 4.8% with 10% Co-doping but the transition pressure decreases by 25%.

A high-pressure synchrotron X-ray diffraction study of zintl phase BaSi 2 semiconductor has been performed up to 45 GPa. The pressure-induced amorphization occurred at 13 GPa. In the amorphous phase, the Ba -Si bond distance decreased with increasing pressure, while the Ba -Ba bond distances were almost unchanged. The Rietveld refinement revealed that these distances in the crystal phase decreased with increasing pressure. By combining these results, the Ba -Si bond compressibility in both phases is almost identical.

The emerging fabrication techniques for transparent materials such as glass and crystal that use focused ultra-short laser pulses will be reviewed from the viewpoint of functionalities of the products to be integrated into a future photonic system. The devices include waveguide and waveguide couplers, mirrors and lenses, filters and holograms. The future photonic system may consist of many functional subsystems which are connected through transparent gates or windows. Welding technique may play an important role for this system integration. The welding technique for transparent materials using ultra-short laser pulses will also be reviewed along with applications to hermetic sealing. The author presents experimental results on the temperature dynamics. The author will also discuss on an idea connecting the relaxation of internal stress and the high index change and a role of the void and its motion in the fabrication process. The bright near future and challenges of the glass processing techniques with ultrafast lasers will briefly be touched on.