Mika Horiike

Diffraction Measurement of Grating Structure Induced by Irradiation of Femtosecond Laser Pulse in Acrylate Block Copolymers

Diffraction measurement was carried out for the evaluation of grating structures induced by irradiation of near-infrared (NIR) femtosecond laser pulse in block copolymers of methyl methacrylate and (ethyl acrylate and butyl acrylate) {p-(MMA/EA-BA) block copolymer}. Line irradiation, performed by scanning these copolymer bulks with a laser spot, produced the aggregated deposits of sub-micron scale. Stripe-shaped grating structures of approximately 3–5 µm width and approximately 30–220 µm thickness were induced at an interval of 7 to 15 µm. The total number of gratings was between 10 and 50. The grating structure obtained was evaluated by means of diffraction measurement. Raman–Nath type and Bragg type transmission diffraction patterns with diffraction efficiencies of approximately 1–13% and Q values of approximately 0.1–9 were observed depending on the grating interval and thickness. Refractive index changes evaluated using the Bessel function were approximately 0.20-3.0×10-3. A Bragg type diffraction pattern was observed in the sample with a Q value of approximately 9 and a refractive index change of 0.30×10-3 was obtained by optimization using the Robust design (Taguchi Method). Relative grating intensity linearly increased with increasing photo-crosslinker content in the acrylate block copolymer. Multiple scanning of line irradiation increased the refractive index from 0.30×10-3 for a single scan to 1.1×10-3 for three scans.

Femtosecond laser induced crystallization and permanent relief grating structures in amorphous inorganic (In2O3+1 wt % TiO2) films

This letter presents an investigation of crystalline relief grating structures induced by irradiation of near-infrared femtosecond laser pulses on an amorphous inorganic (In2O3+1 wt % TiO2) film. The shapes of crystallized relief structures were sensitive to the scanning rate and the focused point height of irradiation, and the optimized irradiation condition gave cone-shaped cross section structures. Selective wet etching on unirradiated amorphous regions using a 3% hydrochloric acid solution could make sharper relief grating structures of crystalline regions. Diffraction efficiency of the relief grating structures with Au coating was measured, and it was confirmed that first-order diffraction, efficiencies were approximately 40% and 20% for etched and nonetched samples, respectively.

Structures induced in polysilane and thin polysilane layer coated polymer films by irradiation of femto-second laser pulse

Abstract We investigated the structures induced in polysilane and polysilane coated thermoplastic bis-phenol A type epoxy (Epoxy) and poly(methyl methacrylate) (PMMA) films by irradiation of near-infrared (NIR) femto-second laser pulse. Long stripe-shaped structures with approximately 200–400 μm length was induced in polysilane bulk. Thin polysilane layer coated Epoxy and PMMA films showed photo-sensitive effect on the formation of stripe-shaped structures in PMMA and Epoxy, whereas no structures were induced in uncoated PMMA and Epoxy films. An ensemble of stripe-shaped structures worked as a diffraction grating. This photo-sensitive effect has potential application to grating structures in optical polymeric fiber (OPF).

Periodic Bell-shaped Upheaval Structure on Surface of Polycarbonate by Irradiation of Femtosecond Laser Pulse

A periodic bell-shaped upheaval structure was formed on the surface of polycarbonate (PC) by line irradiation of a near-infrared (NIR) femtosecond laser pulse onto PC bulks. The upheaval structures were controlled by the irradiation depth and irradiation energy in PC. For example, the increase in irradiation energy at a constant target depth (50 µm) induced the discontinuous change in structures: a small periodic bell-shaped upheaval structure, an intermediate continuous band-shaped structure without a clear upheaval structure and a final large periodic bell-shaped upheaval structure. The size of the bell-shaped upheaval structure varied from approximately 15 µm to 45 µm in diameter of a basal plane upon changing the irradiation conditions. Using the cross-sectional images of the irradiated PC bulk samples observed using an optical microscope, a scanning electron microscope (SEM) and a differential interference laser scanning microscope, we confirmed the position of cracks and voids, and the structure with refractive index modulation formed in PC bulk. The mechanism of the formation of the upheaval structures in PC was investigated by changing the irradiation conditions. We proposed a mechanism of the formation of the upheaval structure in PC on the basis of multiphoton absorption, anisotropic thermal gradient, growth of microcracks by microexplosion at the focused point and movement of the grown cracks toward the surface along the anisotropic thermal gradient.