No abstract

We have measured length change vs time for several low thermal expansion materials maintained in evacuated environments at constant temperature (near 300 K). Materials were two types of fused silica, Cer-Vit, ULE, Zerodur, Invar, and Super Invar. tsL/L was measured over a period of 170 days to a precision of two to three parts in 10 s » In addition, we have measured time-dependent changes in optical contact interfaces and have placed an upper limit on drift of optical phaseshift on reflection from multilayer dielectric coatings.

We have measured the pressure response of a high temperature pressure transducer fabricated from a super alloy. This transducer contains a microbend fiber-optic sensor to measure diaphragm deflection and a reference fiber to help reduce light source fluctuations caused by perturbations in the fiber leads. The transducer was characterized at pressures up to 22.8 MPa and temperatures to 430°C. The experimental data taken at constant temperature shows a 0.58 percent (of full scale pressure) minimum deviation between the fiber-optic pressure transducer output and output of a calibrated gage pressure transducer. Over the entire temperature range of 2O-43O0C, the fiberoptic pressure transducer output exhibits a 1.2-percent (of full scale pressure) maximum deviation from calibrated pressure.

A novel method for determining thermal expansion coefficients has been devised. It is based on the dependence of Fabry-Perot resonances on the mirror separation. The expansion sample is formed into an etalon spacer, with highly reflecting endplates optically contacted to each end. The Fabry-Perot resonances are probed by variable radiofrequency sidebands derived from a frequency stabilized 633-nm He-Ne laser. A change in sample temperature DeltaT causes a change in interferometer length DeltaL, which shifts the resonance frequencies by Deltanu. Then alpha = (1/DeltaT)(DeltaL/L) = (1/DeltaT)(Deltanu/nu). alpha can be measured with precision limited ultimately by the stability of the stabilized laser (1:10(9) with presently available commercial lasers). alpha vs temperature has been measured for samples of Owens-Illinois Cer-Vit, Corning ULE silica, and Schott low expansion glass-ceramic.