Strontium barium niobate is a tungsten-bronze ferroelectric crystal having a tetragonal unit cell. Low-temperature x-ray diffraction studies were performed on a single crystal of Sr0.75Ba0.25Nb2O6 to determine the thermal expansivity along the a- and c-axes. Negative thermal expansion was observed along the c direction while a positive thermal expansion was measured along the a axis. The anisotropic thermal expansion behavior is explained as arising due to the geometry of the crystal structure.

A prototype weakly interacting massive particle (WIMP) detector system is described. The detection efficiency is much larger when the incident neutral particle flux is perpendicular to the detector plane than when it is parallel to the plane. A greatly scaled-up system based on this device would therefore be sensitive to the diurnal rotation of the "WIMP wind" produced by the solar system's rapid motion through the galactic halo. Experimental results are reported which exhibit the detection efficiency anisotropy when neutrons were used to simulate the interactions of WIMPS.

New versatile and linear optical sensor based on electro-optical modulation and compensation Rev.

Electro-optic (EO) sensors, used for the nonperturbative detection of electric fields, are typically configured to modulate an optical probe beam along a crystal direction in which the EO tensor coefficient is largest. However in fiber optic EO sensors, such configurations can be strongly limited by phase noise and cumbersome compensation optics. Our results demonstrate that a greater signal to noise ratio can be achieved by modulating along a crystal direction of low static birefringence, even when the active EO tensor coefficient is several times smaller.

Strontium barium niobate has the tungsten-bronze structure with a tetragonal unit cell, and it exhibits negative thermal expansion along the c axis between −120°C and room temperature while having a positive thermal expansion along the a axis for the same temperature range. At higher temperatures, close to the Curie temperature and above, the negative thermal expansion along the c axis changes to positive thermal expansion. The a axis lattice parameter as a function of temperature shows a change in slope at the Curie temperature. These results indicate the presence of a second-order phase transition near the Curie temperature.