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The Raman spectra of Ba2NaNb5O15 single crystals were recorded for various scattering configurations from 77°K to 843°K. Splittings of the vibrational modes due to electrostatic and anisotropic forces were found to be small. The line-widths of the 650 cm-1 and the 280 cm-1 modes were found to increase with increasing temperature. The 'soft' A1(z) mode at 723°K was fitted by means of a graphical interpolation to an overdamped lineshape with an undamped mode frequency of 40 cm-1 and a damping constant of 2.

We have measured the Raman spectra of Ba2 NaNb5 O15 at temperatures from liquid nitrogen to 570°C. In the x(zzy scattering configuration a heavily damped mode was identified; and, its temperature dependence was sufficient to account for the dielectric anomaly found in this material. It is concluded that Ba2 NaNb5 O15 has a 'soft' A, vibrational mode as expected, but in contrast with the E mode which is 'soft' in BaTiO3.

A novel sensor that uses tapered single-mode fibers is discussed. The tapered single-mode fiber is bent in a simple fixture to increase its sensitivity. Pressure sensors have been fabricated utilizing the bend-sensitive property of the biconically tapered single-mode fibers.

The modal power distribution technique is applied to a multimode optical fiber embedded in a three-dimensional composite material for real-time characterization and monitoring of the structure. The measurements on the modal power distribution within these fibers, and the subsequent redistribution induced by external perturbation, indicate that the modal power distribution technique is more sensitive than the intensity-modulation technique for smart-structure characterization.