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Metal-semiconductor-metal solar blind ultraviolet photodetectors have been fabricated using both BGaN-GaN and BGaN-AlN superlattices as active layers. A high internal gain (up to 3 × 104for optical power in the nW range) is obtained with a highly reduced dark current thanks to the boron incorporation. In the high optical power regime (W range), the time response is in the nanosecond range, which is much smaller than that of GaNand ZnO-based ultraviolet photodetectors. Moreover, the boron incorporation in GaN material allows the tuning of the cutoff wavelength.

The electro-optic (EO) coefficients r22of a congruent LiTaO3bulk crystal, with dimensions of 6 × 5 × 20 mm3, have been measured over a wide frequency range (from dc up to 150 MHz) using the novel and elaborate step-voltage time-response method (TRM). At low frequencies, these results are compared with those obtained with the frequency-doubling EO-modulation (FDEOM) method. From these measurements, the clamped and unclamped EO coefficients, r22Sand r22T, respectively, have been derived and the acoustic contribution r22ato the EO effect has been deduced and compared with theoretically calculated values. Also, using the values of acoustic contribution, ra, the true value of the EO coefficient r22has been extracted. Lastly, the above results are compared with those obtained for a pure congruent LiNbO3crystal in the framework of a typical intensity-modulation (IM) EO system.

The frequency dispersion of the large electro-optic effect in rubidium hydrogen selenate is measured from 300 Hz to 200 kHz as a function of the direction of propagation. It is shown that the major coefficient is r_42 (750 pm/V at 1 kHz). Both dielectric and electro-optic responses exhibit strong, perfectly correlated dispersions in this frequency range. The experimental results confirm the major contribution of domain dynamics in the huge electro-optic effect and are in perfect agreement with calculations based on the tilting of the optical indicatrix. The possible use of rubidium hydrogen selenate in low-frequency electro-optic modulators is briefly discussed.

The deflection of light in ferroelastic crystals results from refraction and reflection at domain walls. When the tilt angle of the principal axes in neighboring domains is small, simple relationships between the crystal birefringences and the angles of the deflected beams can be deduced from Snell’s law of refraction. As a rule, this condition is satisfied at W-domain walls in ferroelastic species that have a biaxial prototype phase. In this case, measurement of the deflection angles permits one to determine the birefringences easily. This method has as its main advantages independence of the sample thickness and the need for only rough sample preparation. It is absolutely insensitive to temperature fluctuations. We have applied the method to crystals of rubidium hydrogen selenate and dihydrated barium chloride as illustrative examples.

The electro-optic and dielectric properties of organic–inorganic 2-amino-5-nitropyridium dihydrogen phosphate crystals were measured near room temperature at a wavelength of 632.8 nm and as a function of an electric-field frequency that varied from 1 kHz to 40 MHz. The frequency dispersion of the electro-optic coefficients and their comparison with the second-harmonic generation coefficients showed that the largest part of the electro-optic properties is electronic in origin (whereas the piezo-optic contribution is small). Results reveal a large anisotropy of the ionic and electronic contributions that is related to the contributions of the organic molecule to nonlinear polarizability.

The refractive indices of rubidium hydrogen selenate are measured for several wavelengths at room temperature, and the transmission spectrum is measured from the UV (240 nm) to the near IR (2000 nm). The orientation of the optical indicatrix with respect to the crystal axes is also determined at several wavelengths in the visible range. Using a new method based on the deflection of light by the ferroelastic domain structure, we also determine refined values for birefringence at several wavelengths. Finally, the dispersion of the three birefringences in the range 450–900 nm is deduced from polarimetric measurements. This set of results yields complete knowledge of the linear optical characteristics required for interpretation of the electro-optical and nonlinear optical properties of this compound.

Rubidium hydrogen selenate (RbHSeO_4) was recently reported as exhibiting one of the largest electro-optic coefficients ever measured in any material. We report on the dependence of the electro-optic properties on the dc electric field. This behavior can be interpreted by the change in the birefringence that is due to the domain reversal. This particular electro-optic effect also explains the large sensitivity of the electro-optical properties to the orientation of the laser beam-propagation direction with respect to the domain walls.