Yusuke Ozaki

Intracavity second‐harmonic generation using a deuterated organic ionic crystal

A large organic ionic crystal (10×28×15 mm3):4‐nitrophenol sodium(:Na) salt dihydrate (NPNa) crystal, which had good optical, mechanical, and thermal properties, was grown for the second‐harmonic generation (SHG) device. Its effective nonlinear constant was found to be 5.0 pm/V at 1064 nm. The Vickers hardness and thermal conductivity were about two times larger than those of molecular crystals. The SHG device made of DNPNa, in which the water of crystallization of NPNa was deuterated, was used for the intracavity SHG of a diode‐pumped cw Nd:YVO4 laser. High SHG power of 4.4 mW at 532 nm was obtained for the first time with an organic nonlinear material.

Crystal growth and the nonlinear optical properties of 4‐nitrophenol sodium salt dihydrate and its deuterated material

Large organic ionic crystals on the order of a few centimeters of 4‐nitrophenol sodium(:Na) salt dihydrate (NPNa) and DNPNa, in which the water of crystallization of NPNa was deuterated, were grown for second‐harmonic generation (SHG). The Vickers hardness and thermal conductivities of NPNa were about two times larger than those of conventional organic molecular crystals. The effective nonlinear optical constants of NPNa and DNPNa were estimated to be 5.0 and 5.5 pm/V, respectively. The optical loss coefficients, measured by spectrophotometry, of NPNa and DNPNa were 1.8 and 0.6 dB/cm at 1064 nm, respectively. The substitution of D2O for H2O in NPNa crystal is very effective in reducing the optical loss coefficient. High power of 4.4 mW green SH light was obtained using a 1.5‐mm‐thick DNPNa crystal as the intracavity SHG device of a diode‐pumped Nd:YVO4 laser.

Influence of cation off-stoichiometry on structural and transport properties of (Ba,La)SnO3 epitaxial thin films grown by pulsed laser deposition

We investigate the influences of cation off-stoichiometry on structural and transport properties of 3% La-doped BaSnO3 (BLSO) epitaxial thin films grown on SrTiO3 substrates by pulsed laser deposition. We show that cation off-stoichiometry, namely, Sn excess and Sn deficiency, is introduced by variations in either laser fluence or the cation composition of the target used for the film growth and that the cation off-stoichiometry influences the properties of the grown films. While all films investigated in this study undergo relaxations from the substrate-induced strain, the out-of-plane lattice constant decreases with the increase in the Sn content in the film. The electrical conductivity, carrier concentration, and mobility are strongly dependent on the type of the cation off-stoichiometry (Sn excess and Sn deficiency). The highest room-temperature mobility, 35 cm2/V−1s−1, is seen for a film grown by ablating the stoichiometric target with a fluence of 1.6 J/cm2, which keeps the cation ratio in the film ...

Intracavity Second-Harmonic Generation and Influence of Optical Loss of Organic Nonlinear Optical Materials

We propose two different methods to estimate the optical loss of organic nonlinear optical (NLO) materials, which significantly reduces the efficiency of intracavity second-harmonic generation. One method is the estimation of the optical loss from the intracavity optical power at 1064 nm. The optical loss of the 4-nitrophenol sodium (:Na) salt dihydrate (NPNa) crystal was 1.3 dB/cm, and that of the DNPNa crystal, in which the water of crystallization of NPNa was deuterated, was 0.15 dB/cm. Another method is the estimation of the optical absorption loss from a liquid, the molecular structure of which has the same particular structural groups as those of the organic NLO materials. This latter method is very useful when new organic NLO materials are designed. The optical absorption losses at 1064 nm for the particular structural groups of the benzene ring were found to increase in the following order: -Cl<-NO2<-CH3=-OCH3<-OC2H5<-NH2.

Melting of Oxygen Vacancy Order at Oxide–Heterostructure Interface

Modifications in oxygen coordination environments in heterostructures consisting of dissimilar oxides often emerge and lead to unusual properties of the constituent materials. Although lots of attention has been paid to slight modifications in the rigid oxygen octahedra of perovskite-based heterointerfaces, revealing the modification behaviors of the oxygen coordination environments in the heterostructures containing oxides with oxygen vacancies have been challenging. Here, we show that a significant modification in the oxygen coordination environments-melting of oxygen vacancy order-is induced at the heterointerface between SrFeO2.5 (SFO) and DyScO3 (DSO). When an oxygen-deficient perovskite (brownmillerite structure) SrFeO2.5 film grows epitaxially on a perovskite DyScO3 substrate, both FeO6 octahedra and FeO4 tetrahedra in the (101)-oriented SrFeO2.5 thin film connect to ScO6 octahedra in DyScO3. As a consequence of accommodating a structural mismatch, the alternately ordered arrangement of oxygen vacancies is significantly disturbed and reconstructed in the 2 nm thick heterointerface region. The stabilized heterointerface structure consists of Fe3+ octahedra with an oxygen vacancy disorder. The melting of the oxygen vacancy order, which in bulk SrFeO2.5 occurs at 1103 K, is induced at the present heterointerface at ambient temperatures.