Kiyotaka Miura

Diffraction of a plane wave by a thick strip grating

The diffraction of a plane electromagnetic wave by a thick strip grating is solved rigorously by the Wiener-Hopf technique. The solution contains an infinite number of unknowns, which are shown to satisfy a certain infinite set of equations. By applying the modified residue calculus technique, this set of equations is solved and the approximate solution is derived. Representative numerical examples are given and the transmission characteristics of the grating are discussed. >

Nanowire formation under femtosecond laser radiation in liquid

The size and shape of nanoscale materials provide excellent control over many of the physical and chemical properties, including electrical and thermal conductivity, magnetic properties, luminescence, and catalytic activity (Lieber, 1998). In particular, the synthesis and morphological control of nanosized particles, which exhibit surprising and novel phenomena based on the unique property called the quantum size effect, are attractive to chemists and physicists (Alivisatos, 1996). In recent years, nanoparticles are widely used in many applications ranging from biosensing (Anker et al., 2008; Elghanian et al., 1997; Lin et al., 2006), plasmonic devices (Ferry et al., 2008; Maier et al., 2003), and multifunctional catalysts (Hu et al., 1999; Lu et al., 2004). There are a wide variety of techniques that are capable of creating nanoparticles with various morphology and production yield. These nanoparticle formation approaches are typically grouped into two categories: ‘top-down’ and ‘bottom-up’. The first involves the breaking down of large pieces of bulk material into the required nanostructures. The second involves the building of nanostructures, atom-byatom or molecule-by-molecule in a gas phase or solution. These two approaches have evolved separately and reached the limits in terms of feature size and quality, in recent years, leading to exploring novel hybrid approaches in combining the top-down and bottom-up methods. Colloidal chemists have gained excellent controlled nanosized particles for several spherical metal and semiconductor compositions, which has led to the discovery of quantum size effect in colloidal nanocrystals (Alivisatos, 1996). However, various bottomup approaches for making morphologically controlled nanoparticles have been found; most of these solution methods are based on thermal process. On the other hand, top-down approaches have been developed for producing metal and semiconductor nanowires, nanobelts, and nanoprisms (Hu et al., 1999; Pan et al., 2001; Jin et al., 2001). In particular, the laser-induced ablation method has become an increasingly popular approach for making nanoparticles due to the applicability to various target materials in an ambient atmosphere (Jia et al., 2006a; Kawasaki & Masuda, 2005; Link et al., 1999; Sylvestre et al., 2004; Tamaki et al., 2002; Tull et al., 2006). Recently, various shape-controlled nanoparticles, such as nanowires (Morales & Lieber, 2008), nanotubes (Rao et al., 1997), and composite nanostructures (Zhang et al., 1998), have been fabricated by this technique. More recently, pulsed laser ablation in liquid has become profoundly intrigued for preparing nanoparticles from the viewpoint of the concise procedure and the ease of handling (Kawasaki & Masuda, 2005; Tamaki et al., 2002; Shimotsuma et al., 2007).

Space-selective microscopic modifications of glass structure by a femtosecond laser

Femtosecond laser is a perfect laser source for materials processing when high accuracy and small structure size are required. Due to the ultra short interaction time and the high peak power, the process is generally characterized by the absence of heat diffusion and, consequently molten layers. Various induced structures have been observed in glasses after the femtosecond laser irradiation. Here, we report on space-selective valence state manipulation of active ions, long-lasting phosphorescence and photostimulated long-lasting phosphorescence phenomena in the femtosecond laser-irradiated glasses, and recent development of direct writing of optical waveguide in glasses with femtosecond laser pulses.

Strain and stress dynamics of femtosecond laser bulk processing of transparent fcc crystals

Strain and stress dynamics after photoexcitation by a focused femtosecond laser pulse inside various transparent solids (sodalime glass, MgO, LiF, NaCl and CaF2 single crystals) were observed by a pump-probe polarization microscopy. The observation showed that a stress wave was generated from the photoexcited region and the shape of the stress wave depended on materials. The shapes of the stress waves could be explained by the anisotropic velocity of elastic waves calculated using elastic constants. In addition, the observation showed that the strain distribution was changed by crack generation. The origins of the differences in the observed strain distributions were discussed based on the anisotropies of elastic properties of crystals.