Aiko Narazaki

Induction and relaxation of optical second-order nonlinearity in tellurite glasses

Second harmonic generation has been examined for 30ZnO⋅70TeO2 glass with a two-step poling procedure in order to understand the poling temperature dependence of second harmonic intensity. When the poling temperature increases, the second harmonic intensity increases, manifests a maximum at the temperature which we call an optimum poling temperature, and decreases drastically just below the glass transition temperature. The glass treated with two-step poling, which includes poling at 300u200a°C and subsequent poling at the optimum poling temperature, i.e., 280u200a°C, exhibits much smaller second harmonic intensity and more unambiguous Maker fringe pattern than that poled only at 280u200a°C. This fact suggests that the decrease in second harmonic intensity with an increase in poling temperature cannot be attributed to a reversible process like a thermal fluctuation of dipoles, but is governed by an irreversible one. Based on a linear relation between the optimum poling temperature and glass transition temperature, the...

Large optical second-order nonlinearity of poled WO 3 –TeO 2 glass

Second-harmonic generation, one of the second-order nonlinear optical properties of thermally and electrically poled WO>(3)-TeO>(2) glasses, has been examined. We poled glass samples with two thicknesses (0.60 and 0.86 mm) at various temperatures to explore the effects of external electric field strength and poling temperature on second-order nonlinearity. The dependence of second-harmonic intensity on the poling temperature is maximum at a specific poling temperature. A second-order nonlinear susceptibility of 2.1 pm/V was attained for the 0.60-mm-thick glass poled at 250 degrees C. This value is fairly large compared with those for poled silica and tellurite glasses reported thus far. We speculate that the large third-order nonlinear susceptibility of WO>(3)- TeO>(2) glasses gives rise to the large second-order nonlinearity by means of a X((2)) = 3X((3)) E(dc) process.

Optical second harmonic generation in poled MgOZnOTeO2 and B2O3TeO2 glasses

Optical second harmonic generation has been observed in electrically poled MgO-ZnO-TeO 2 and B 2 O 3 -TeO 2 glasses. The theoretical Maker fringe curve fitted to the experimental data leads to the fact that the poled region is almost identical with the sample thickness. In other words, the poled region is not restricted to the surface of the sample. For the MgO-ZnO-TeO 2 glasses, the second harmonic intensity is higher in the glass with lower glass transition temperature when the poling temperature is constant. It is thought that the orientation of asymmetrical tellurite structural units which possess electric dipole moments causes the optical second harmonic generation and that the orientation takes place as a result of the structural relaxation of the tellurite network around the glass transition temperature. The second harmonic intensity and the second-order non-linear coefficient are larger for the MgO-ZnO-TeO 2 glasses than for the B 2 O 3 -TeO 2 glasses. This phenomenon is explainable in terms of the difference in the glass network structure between these two systems.

Second-harmonic generation in Ge-As-S glasses by electron beam irradiation and analysis of the poling mechanism

Abstract With the method of Maker fringe, second-harmonic generation (SHG) was observed in Ge–As–S glasses irradiated by electron beam. It is related to the space–charge electrostatic field which makes the glasses poled and breaks the centrosymmetry of the glasses. So one new ministructure is formed and can keep constant for a long time, which makes the glasses difficult to restore relaxationally to its origin state and induces SHG. Second-order nonlinearity χ(2) as high as 0.8 pm/V was obtained. The results of thermally stimulated depolarization current measurements indicated that the poled regions were located at the superficial layers of the glass surfaces (several micrometers), which were the same as the calculated result in theory. The nonlinearities in Ge–As–S glasses are stable.

Second-harmonic generation in Ge 20 As 25 S 55 glass irradiated by an electron beam

Second-harmonic generation was observed in Ge(20)As(25)S(55) chalcogenide glass irradiated by an electron beam. The second-harmonic intensity increased with increasing electron-beam current and accelerating voltage. The second-harmonic generation in Ge(20)As(25)S(55) glass was caused by the space-charge electrostatic field that was generated by irradiation of an electron beam. Second-order nonlinearity X((2)) as great as 0.8 pm/V was obtained. The results of measurements of thermally stimulated depolarization current indicated that the glass was poled in the thin layers of its surface (several micrometers) and that the nonlinearity was stable.

Effect of poling temperature on optical second harmonic intensity of sodium zinc tellurite glasses

Poling temperature dependence of optical second harmonic intensity has been examined for Na2O–ZnO–TeO2 glasses. All the glasses exhibit such a tendency that the second harmonic intensity increases, experiences a maximum, and decreases as the poling temperature increases. The poling temperature giving rise to the maximum second harmonic intensity, which we call an optimum poling temperature, correlates with glass transition temperature; there exists a linear relation between them. This phenomenon indicates that the structural change of glass network near the glass transition temperature affects the orientation of electric dipoles with a long range order which induces the second harmonic generation. We suggest that some electrochemical reactions take place on the anode-side surface of glass at around the glass transition temperature where viscous flow is allowed and disturb the orientation of electric dipoles.

POLING-INDUCED CRYSTALLIZATION OF TETRAGONAL BATIO3 AND ENHANCEMENT OF OPTICAL SECOND-HARMONIC INTENSITY IN BAO-TIO2-TEO2 GLASS SYSTEM

Effect of poling on surface crystallization behavior of BaTiO3 in 15BaO–15TiO2–70TeO2 glass and on second-harmonic generation of the resultant glass ceramics has been examined. A direct current voltage in a range of 0.3–1 kV was applied to the original glass at around 400u200a°C, which is above its glass transition temperature, followed by cooling of the sample to room temperature with the voltage kept constant. X-ray diffraction patterns indicate that the poling increased the fraction of crystalline phases precipitated at the glass surface and that BaTiO3 crystallites were precipitated preferentially with (101)- or (110)-orientation. It is also observable that the x-ray diffraction line assigned to BaTiO3 shifted from the position corresponding to bulk cubic crystal to that of ferroelectric tetragonal one when the applied voltage was increased. In other words, the poling treatment stabilizes the tetragonal BaTiO3 phase, leading to a larger optical second-order nonlinear susceptibility. In fact, the second-ha...

Poling temperature dependence of optical second‐harmonic intensity of MgO–ZnO–TeO2 glasses

Poling temperature variation of optical second‐harmonic intensity induced by electrical poling has been examined for 30ZnO⋅70TeO2, 5MgO⋅25ZnO⋅70TeO2, and 10MgO⋅20ZnO⋅70TeO2 glasses. The Maker fringe pattern of these glasses indicates that the orientation of electric dipoles presumably due to TeO4 trigonal bipyramids and TeO3 trigonal pyramids is not restricted within the glass surface but extends into the inside of bulk glass. The poling temperature dependence of second‐harmonic intensity manifests a maximum in all the glasses. There exists a tendency that the poling temperature which corresponds to the maximum of second‐harmonic intensity is higher in the glass with higher glass transition temperature. This fact suggests that the orientation of tellurite structural units occurs as a result of the structural relaxation of tellurite network at around the glass transition temperature.

Optical second-order nonlinearity of transparent glass-ceramics containing BaTiO3 precipitated via surface crystallization

Second-harmonic generation of transparent glass-ceramics containing BaTiO 3 crystalline phase was investigated using Maker fringe method. When 15BaO · 15TiO 2 · 70TeO 2 glass was heat-treated at 415 °C for 0.5–12 h, (101)- or (110)-oriented BaTiO 3 crystals precipitated in the near-surface region. The resultant glass-ceramics exhibit second-harmonic generation. Variation of second-harmonic intensity with angle of incidence, i.e., the Maker fringe pattern changes drastically with an increase in heat treatment time and temperature. No second-harmonic signal was detected in glass-ceramics derived from 15SrO · 15TiO 2 · 70TeO 2 glass. These facts suggest that BaTiO 3 crystal is responsible for the second-order nonlinear phenomenon, although its structure is closer to cubic than tetragonal according to x-ray diffraction measurements. In order to estimate second-order nonlinear optical coefficient d (2) , Maker fringe patterns of the BaTiO 3 -containing glass-ceramics were analyzed. For the glass-ceramic after heat treatment for 0.5 h, d 33 and thickness of BaTiO 3 -crystallized layer, L , are 3.65 pm/V and 3.43 μm, respectively. The value of second-order nonlinear optical coefficient is comparable to those of BaTiO 3 films prepared via metalorganic chemical vapor deposition and pulsed-laser deposition. On the other hand, the glass-ceramic heat-treated for 12 h exhibits d 15 = 0.31 pm/V and L = 300 μm. The thickness of the layer active in second-order nonlinearity evaluated from the Maker fringe pattern is coincident with the observation by scanning electron microscopy.

Poling-induced structural change and second-order nonlinearity of Na+-doped Nb2O5-TeO2 glass

The effect of thermal/electrical poling on surface structure and poling-induced second-harmonic generation have been examined for 15Nb2O5·85TeO2 glass. Since the poling was carried out with the 15Nb2O5·85TeO2 glass sandwiched in between two commercial borosilicate glasses containing Na+, penetration of Na+ into the anode-side surface of 15Nb2O5·85TeO2 glass took place, as revealed by x-ray photoelectron spectroscopy (XPS). XPS studies also suggest that Nb5+ migrates from the anode-side surface into the bulk by the poling. It is thought that the migration of Na+ and Nb5+ forms an internal dc electric field, leading to the second-harmonic generation.