L. Guilbert

Birefringence measurements by means of light deflection at domain walls in ferroelastic crystals

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.

Optical characteristics of triclinic rubidium hydrogen selenate

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.

Electrooptical properties of rubidium hydrogen selenate : influence of the DC electric field and origin of the large electrooptic coefficient

Rubidium hydrogen selenate ( RbHSeO4) 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.

Origin of light-deflection in lithium niobate and lithium tantalate under electric field.

The deflection of light reported by Müller et al. in lithium niobate [Appl. Phys. B 78, 367-370] and lithium tantalate [Appl. Optics 43 (34), 6344-6347] under electric field originates from refraction at domain-walls, like in ferroelastics. In ferroelectrics the optical discontinuity takes place at domain-walls as a consequence of the electro-optic effect. The theoretical deflection angle calculated from Snells law is proportional to the square root of the electric field and matches the experimental results reported by Müller et al. for lithium niobate. The finite domain-wall thickness mentioned by the authors is not involved in the deflection phenomenon.

Raman probing of proton exchange waveguides in lithium niobate

We report Raman scattering spectroscopy in proton exchanged LiNbO 3 wave guides. Large differences have been observed according to the fabrication processes, and it is shown that. the soft proton exchange technique does not induce structural change in the crystal. Raman spectroscopy is pointed out to be an efficient technique to control the quality of the guides.

On the succesive phase transitions in RbHSeO4 and NH4HSeO4 crystals

Abstract Effect of external electric field and external mechanical stress influence on domain structure of RbHSeO4(RHSe) and NH4HSeO4 (AHSe) crystals was studied. Taking into account microscopic observations of domain structure in particular phases we consider the succesive changes of symmetry in this family as 222→2→1. It is in accordance with predictions of Aizu and Sapriel and the 222 is a symmetry of nonexisting prototype phase. The monoclinic phases are potentially ferroelectric and fully ferroelastic and the triclinic phases are fully ferroelastic and fully ferroelectric.

Indirect Pockels effect in rubidium hydrogen selenate: measurement of the larger r 42 coefficient

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 r42 (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.

Electrooptic investigations in ammonium hydrogen selenate NH4 HSeO4

Within a simple model, a connection can be established between the frequency dependences of the EO coefficient and the dielectric permittivity in a wide frequency range

Temperature Dependence of Polaron Photoluminescence in Congruent Lithium Niobate

Photoluminescence attributed to small polarons Nb Li 4+ is recorded as function of temperature from 80 K to 290 K in nominally-pure congruent LiNbO 3 . It is found that the integrated area of the main peaks remains nearly constant at low temperature and then decreases sharply with activation energy of about 0.12 eV above 200 K. The limit between the two regimes is thought to correspond to the crossing point between the radiative and non-radiative lifetimes of the polaron excited state.