The effect of the ferroelectric domain walls in the scanning near field optical microscopy response of periodically poled Ba(2)NaNb(5)O(15) and LiNbO(3) crystals

A study of Ba(2)NaNb(5)O(15) and LiNbO(3) crystals with periodic ferroelectric domain structures using the scanning near field optical microscopy technique is reported. Optical contrast is observed in the regions of ferroelectric domain boundaries and it is analysed using beam propagation method modelling. This reveals that the optical contrast, a consequence of changes in the refractive index, is not due to variation of the waveguide-coupling efficiency, and supports the hypothesis that it is associated with the domain array, which is related to the size of the domain.

Vacuum ultraviolet spectroscopy of Ce(3+)-doped SrMgF(4) with superlattice structure

X-ray diffraction of Ce(3+)-doped SrMgF(4) (SMF:Ce) crystals shows a superlattice structure, reflecting the distribution of Ce(3+) polyhedra centres observed in optical experiments. Optical absorption bands and fluorescence bands from the Ce(3+) polyhedra centres overlap in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions, respectively, so that wide pumping and tuning ranges are expected for laser operation. The SMF:Ce crystals, as well as the isomorphous BaMgF(4), are candidates for a tunable laser gain material with nonlinear properties. The optical absorption, excitation, and fluorescence bands observed in the SMF:Ce crystals at low temperatures are ascribed to five distinct fluorescent centres. Three centres have well-known Ce(3+) optical characters, for example, fluorescence with double peaks separated by 2000 cm(-1) and five resolved absorption/excitation bands. These centres are assigned to Ce(3+)-polyhedra classified by weak and strong crystal fields as a consequence of the superlattice structure. The other two fluorescence bands observed in the visible region have 1.5-2 times larger linewidths than those of the former three bands. These bands are interpreted as optical transitions from complexes consisting of Ce(3+) and one or two electrons trapped at a vacancy of the nearest neighbour F(-) ligand ions.

Femtosecond pump-probe measurements of non-radiative relaxation in LiAlO(2):V(3+)

We report on time-resolved studies of non-radiative relaxation of V(3+) ions in LiAlO(2) by means of a two-beam, pump-probe saturation experiment performed with the 150 fs pulsed output of a Ti-sapphire laser. Exciting into the vibronically broadened [Formula: see text] transition at 800 nm, a (3)T(1) relaxation time of 199 ps has been measured at 4 K. This value decreases to 82 ps at room temperature, representing a reduction in the lifetime of a factor of 2.5 due to internal-conversion processes. The relative probabilities for non-radiative, phonon-assisted barrier hopping and quantum mechanical tunnelling through the potential barrier to the (3)A(2) ground state have been obtained using Mott's expression, yielding best-fit parameters of W(0) = (5.2 ± 1) × 10(9) Hz and W(1) = (7.5 ± 1) × 10(10) Hz for a potential barrier of E(nr) = 530 ± 50 cm(-1).