Kenji Kamada

Laser micromachining for Ag ion exchanged glasses

Machining properties of Ag containing glasses (ACG) using KrF excimer laser and femtosecond laser are reported. Ag ions in the ACG are effective to prevent cracking and chipping during the laser machining. A 4x4 hole array fabricated by KrF excimer laser onto an ACG has good uniformity of hole diameter, d(ave) equals 129.9um and (sigma) equals 0.8um. V- and U- grooves are fabricated on ACG using a Ti:Al2O3 laser irradiation. The cross- sectional shape is controlled by Ag ion concentration in ACG.

Transient light-induced refractive index change made by laser microfabrication in nitroaniline-doped PMMA film

We report the observation of high light-induced change in refractive index (recognizable by observation in conventional microscope) in PMMA film doped with an optically non-linear dye 2-nitroaniline (NO2(C6H4)NH2 abbreviated as 2NA). The optically altered micrometer-sized regions were fabricated by single-shot radiation of 120 fs laser pulses into doped PMMA film using high numerical aperture 1.3 and high magnification x100 objective lens. The doping of films can be achieved in a wide range of 2NA concentrations (up to 40 wt%) without precipitation. This allows to control a storage time of an optically altered region up to one month by the adjusting the energy of the femtosecond (fs) recording pulse at 800 nm. Typical recording energy was 10-80 nJ/pulse at the point of irradiation. Total recovery of transmission of the PMMA2NA film was confirmed by optical transmission measurements in a microscope. The light induced damage threshold (LIDT) (for permanent damage) was increased more than by four times (up to 40 nJ/pulse) when 2NA doping were ca.1e wt%. While the LIDT for transient damage was decreased by 1.5-2 times. Total optical recovery was observed single exponential with decay time of ca. 0.5-1 minute for moderate irradiation intensities (0.1xLIDT of permanent damage). The damage induced with at the higher intensities lasts up to a month, but the recovery was not total (residual transmission changes were observable). The phenomenon can be applied for the optical memory, photonic crystal, and micro-mechanical applications. The underlying mechanism of the phenomenon is discussed in terms of anelastic (alpha) and (beta) -relaxation (polymer backbone and side chain relaxation, respectively).

Theoretical and experimental approaches to enhanced two-photon absorption

A selection rule for two-photon transition is considered based on the alternancy symmetry and the result is adopted to explain the experimental and calculation results of two-photon absorption (TPA) properties of two diacetylene derivatives with neutral and charged peripheral groups. The discussion successfully explains the difference in strength of the TPA bands and the existence of the higher-lying TPA states that is strongly allowed and plays a main role to the resonance enhancement of TPA.

Polarized light-induced anisotropy of azo dyes studied by polarized FTIR spectroscopy

The anisotropy induced in the poly(methyl methacrylate) (PMMA) films doped with Disperse Orange 3 (DO3, NO2-phenyl-N=N-phenyl-NH2) was investigated by polarized FTIR spectroscopy. Observed infrared absorption bands of DO3 in the polymers were assigned to symmetric (NO2s, 1341 cm−1) and antisymmetric (NO2as, 1523 cm−1) stretching modes of NO2, and the C-N stretching mode of C-NH2 (C-N, 1303 cm−1). By measuring the polarized IR spectra of DO3/PMMA, the infrared dichroism was observed in NO2s and C-N bands. From these results, the orientation factors, KZfn (f=x,y,z), for each isomer were determined. The factors indicate that it is difficult for NO2 group to move in the PMMA during trans-cis-trans isomerization and that phenyl group with NH2 mainly moves in PMMA on isomerization. This study clarified that the anisotropy of DO3 in PMMA is induced by photoselection with the irradiation of linearly polarized light and is not induced by reorientation of DO3 molecules, since the entire DO3 molecule cannot rotate i...