Akihiro Mito

Second harmonic generation in electrically poled Li2ONb2O5TeO2 glasses

Abstract Optical second harmonic generation has been observed in electrically poled Li 2 ONb 2 O 5 TeO 2 glasses. Electrical poling was performed at 250°C for 30 min under an applied dc potential of 3–4 kV. Second harmonic generation takes place in binary Li 2 OTeO 2 and Nb 2 O 5 TeO 2 glasses as well as ternary 10Li 2 O · 10Nb 2 O 5 · 80TeO 2 and 15Li 2 O · 15Nb 2 O 5 · 70TeO 2 glasses as previously reported. The observation of second harmonic generation in tellurite glasses which do not contain Li + ions leads to speculation that the second harmonic generation is not attributed to the Li + ion migration but is presumably ascribed to a long-range orientation of electric dipoles due to asymmetrical structural units, i.e., TeO 4 trigonal bipyramids and TeO 3 trigonal pyramids.

Second Harmonic Generation in Poled Tellurite Glasses

Second harmonic generation has been observed in electrically poled tellurite glasses with 80TeO210Li2O10Nb2O5 and 70TeO215Li2O15Nb2O5 compositions. The poling was carried out at 200 to 300°C for 30 min under applied dc field of 4 to 5 kV. To explain the mechanism generating the second-order nonlinearity in the poled tellurite glasses, it is proposed that strong local polarization is caused by migration of lithium ions and/or periodic orientation of lone pairs of electrons in the tellurium ions.

Influence of the OH Content on Second Harmonic Generation from Electrically Polarized SiO2 Glasses

The influence of the OH content in the SiO2 glasses on the intensity of second harmonic generation was investigated. The SiO2 glasses containing various amounts of OH were electrically polarized by applying 3 kV at 300°C. The intensity of the second harmonic generation was dependent on the OH content, and the largest χ33(2), which was nearly 2% of the χ33(2) value of LiNbO3, was obtained for sol-gel-derived SiO2 glass containing the largest amount of OH.

Second-harmonic generation from electrically poled SiO 2 glasses: effects of OH concentration, defects, and poling conditions

To clarify the origin of second-harmonic generation (SHG) from electrically polarized SiO2 glasses, we have investigated the influence of the OH concentration and structural defects in the SiO2 glasses and that of the poling conditions on the intensity of SHG. The SHG intensity was increased with increased OH concentration, and the most intense SHG was observed from the solgel-derived SiO2 glasses containing 2500 parts in 106 OH. On the other hand, the intensity of SHG was not clearly related to the specific defects observable by electron spin resonance and vacuum-ultraviolet absorption spectra. With respect to the poling conditions, the intensity of SHG was the largest when the glasses were poled by 3 kV at 200 °C for 4 h, and χ33(2) was evaluated as 0.37 pm/V, which was ∼8% of χ22(2) for LiNbO3.

Second harmonic generation from an electrically polarized TiO2-containing silicate glass

Abstract Second harmonic generation was observed in electrically polarized TiO 2 -containing silicate glasses. Poling at near 250°C and with at least 1 kV was necessary to give rise to the phenomenon. Dielectric breakdown disturbed the application of the dc voltage higher than 3 kV and temperature above 300°C. The largest χ (2) value corresponded to nearly 2% of χ (2) 22 of LiNbO 3 .

Nonlinear Optical Susceptibility of Fe2O3 Thin Film Synthesized by a Modified Sol-Gel Method

The homogeneous transition metal oxide Fe2O3 thin films are synthesized in a modified sol-gel process by spin coating. The third order nonlinear optical susceptibility of the film is about 2 × 10−9 esu at 488 nm wavelength by the z-scan method with a 180 femtosecond pulse laser beam. The film is expected to be useful for the application of nonlinear optical devices.

PREPARATION AND FEMTOSECOND THIRD-ORDER NONLINEAR OPTICAL PROPERTIES OF CU/SIO2 COMPOSITE THIN FILMS

A multitarget sputtering method was applied to embed Cu particles in SiO2 glass thin films (Cu/SiO2 films) with a high concentration of Cu particles (18 at.%). In the optical-absorption spectra of the as-deposited Cu/SiO2 films, the absorption peak due to the surface plasmon resonance of Cu particles was observed around 580 nm. The imaginary part of the third-order nonlinear susceptibility, | Im [χ(3)]|, exhibited a peak at the absorption peak, and the maximum value was estimated to be 1.8×10-10 esu in the femtosecond time region. The nonlinear response time derived from the recovery time of the nonlinear absorption of the film was estimated to be 1.4 ps at the absorption peak of the surface plasmon.

A compact seawater pCO2 measurement system with membrane equilibrator and nondispersive infrared gas analyzer

A compact measurement system for partial pressure of CO2 in seawater (pCO2) with a membrane tube and a nondispersive infrared gas analyzer (NDIR) has been developed. Gaseous CO2 in seawater diffuses through the membrane into flowing air inside the tube, and the concentration of CO2 in the air is measured by NDIR. Equilibrium between the water and the air is achieved with a time constant of 2 minutes.pCO2 changes in seawater are monitored automatically and continuously with an uncertainty of ±5 μatm. Since the membrane equilibrator can be deployed directly in sea water, the system is small and requires only a small power supply. The system has wide application, not only in coastal zones but also in the open ocean or in incubators.

Second harmonic generation in electrically poled TeO2-based glasses

Optical second harmonic intensity has been measured for electrically poled several TeO2- based glasses in order to discuss relation between second harmonic intensity and glass structure. The glass systems, ZnO-TeO2, BaO-TeO2, WO3-TeO2 and ZnO- BaO-TeO2, have been chosen because these systems possess relatively extended glass- forming region. The second harmonic intensity increases with an increase in the concentration of ZnO in the binary ZnO-TeO2 system. It is known that an addition of ZnO to TeO2 glass converts TeO4 trigonal bipyramids to TeO3 trigonal pyramids and leads to creation of non-bridging oxygens. We presume that these tellurite glass structural units, which are lacking in center of symmetry, are oriented to the direction of external dc electric field and that the orientation takes place more easily in the ZnO-rich glass because the glass-network structure is more flexible owing to the presence of trigonal pyramids and non-bridging oxygens. While the second harmonic generation is clearly observed in ZnO-TeO2 and WO3-TeO2 glasses, it does not occur in BaO-TeO2 glasses under the present poling conditions. We speculate that the orientation of structural units scarcely occurs in the BaO-TeO2 glasses because the external field mainly causes the electron polarization of Ba2+ ions.

High nonlinear optical coefficient (χ3=10−7 esu) of cyanine dye J aggregates doped silica film synthesized by a simple sol–gel method

Abstract We have synthesized, for the first time, a thin silica film doped with condensed J aggregates of 1,1′-diethyl-2,2′-cyanine bromide dye using a simple sol–gel method. The film is homogeneous in thickness and stable at room temperature. The J band formed in the spin coating process is independent of polarizer angle and the film is isotropic without any dichroism. The high optical nonlinearity ( χ 3 =5.0×10 −7 esu) of the film at the resonance wavelength (=577 nm) of the J aggregates was first observed by Z -scan using a 180 fs pulse laser at 77 K under a vacuum ( −5 torr). The doping ratio of J aggregates in silica film suggests that the net ∣ χ (3) ∣ value of pure J aggregates is 4.0×10 −6 esu. Preliminary experiments using a pump-probe showed the film to have a response time τ of 0.5 ps under 575 nm excitation at room temperature. Since the J aggregates are incorporated into the silica film, further research is likely to lead to improved stability.