Yoshihiro Takahashi

Large second-order optical nonlinearities of fresnoite-type crystals in transparent surface-crystallized glasses

Second-order optical nonlinearities, d33 values, of fresnoite-type crystals, Ba2TiSi2O8 (BTS), Sr2TiSi2O8 (STS), and Ba2TiGe2O8 (BTG), have been evaluated by measurements on transparent surface-crystallized glasses consisting of fresnoite-type crystals with the Maker fringe technique. It is found that all these crystals show large d33 values, i.e., d33=13±2 pm/V for BTS, d33=7.2±0.4 pm/V for STS, and d33=22±3 pm/V for BTG. In particular, it is emphasized that BTG has an extremely large d33 value, comparable to LiNbO3 single crystal. It is clarified that the d33 value of fresnoite-type crystals increases with increasing c/a ratio in the lattice parameters of their structures. It is suggested that the increase in the c/a ratio results in the elongation of TiO5 pyramidal units along the c axis, consequently enhancing spontaneous polarizations in the fresnoite-type structure. Transparent surface-crystallized glasses consisting of fresnoite-type crystals are candidates for nonlinear optical materials.

Second harmonic generation in transparent surface crystallized glasses with stillwellite-type LaBGeO5

Transparent optical nonlinear crystallized glasses with the composition of 25La2O3 25B2O3 50GeO2, stoichiometric to ferroelectric stillwellite-type LaBGeO5 crystalline phase, have been prepared by a two-step heat-treatment (first heat treatment: T1=670 °C, t1=10 h, second heat-treatment: T2, t2), and their second harmonic (SH) intensities have been examined using the Maker fringe method. The samples obtained by heat treatments at T2=720∼725 °C for t2=3 h show only surface crystallization and exhibit clear and fine (narrow) fringe patterns. The samples heat treated at T2=740 and 750 °C exhibit relatively strong SH intensities, but the fringe patterns in such samples are broad. It is proposed that SH waves generated from surface LaBGeO5 crystalline layers scatter at LaBGeO5 crystals formed in the interior of glass, causing the disappearance of fine fringe patterns.

Nonlinear-optic and ferroelectric behavior of lithium borate–strontium bismuth tantalate glass–ceramic composite

Transparent glasses in the system (100–x)

Optical second order nonlinearity of transparent Ba2TiGe2O8 crystallized glasses

Li_2B_4O_7 –xSrBi-2Ta_2O_9 (0 \leq x \leq 20)

Transparent surface crystallized glasses with optical non-linear LaBGeO5 crystals

were fabricated via a splat-quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity (40 nm) in the heat-treated (glass-ceramic) samples. The dielectric constant (\epsilon r) of the glass–ceramic composite (x = 20, heat treated at 773 K/8 h) was in between that of the parent host glass

Second-Order Optical Nonlinearity of LaBGeO5, LiBGeO4 and Ba2TiGe2O8 Crystals in Corresponding Crystallized Glasses

(Li_2B_4O_7)

Second-harmonic generation in transparent surface crystallized glasses in the BaO-B2O3-TeO2 system

and strontium bismuth tantalate ceramics in the frequency range 100 Hz–40 MHz at 300 K. These exhibited intense second-harmonic generation and a ferroelectric hysteritic behavior (P vs E loops) at 300 K. The coercive field

Ferroelectric properties and second harmonic intensities of stillwellite-type (La,Ln)BGeO5 crystallized glasses

(E_c)

Formation mechanism of ferroelastic Ba2TiGe2O8 and second order optical non-linearity in transparent crystallized glasses

and the remnant polarization

Crystalline phases and second harmonic intensities in potassium niobium silicate crystallized glasses

(P_r)