We report ultraslow group velocities of light in an optically dense crystal of Pr doped Y2SiO5. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 micros. Deceleration and "stopping" or trapping of the light pulse was also observed. These reductions of the group velocity are accomplished by using a sharp spectral feature in absorption and dispersion that is produced by resonance Raman excitation of a ground-state spin coherence.
A new technique that provides linear measurement of dynamic phase change in a no-feedback, no-phase-bias fiber-optic interferometer is described. The phase measurement is unaffected by random changes in phase, source intensity, and fringe visibility. A minimum detectable phase shift of 0.1 rad has been measured for the configuration reported.
The minimum detectable phase shift indicated in recent experimental reports of new linear spectrumanalysis techniques of optical interferometric vibration detection is established as the direct consequence of the 1/f noise voltage in the system components. The dynamic range and inaccuracy predicted by the simple theoretical model presented is in good agreement with experimental measurements. The conclusions of the analysis are compared with experimental reports of heterodyne shot-noise-limited optical systems. With this effective tool the generic class of spectrum-analysis techniques can be analyzed and relatively weighed to assess the effect of noise. This analysis is applicable to optical interferometry in general, although the experiments specifically involved fiber-optic modulators.
Delamination detection is important in ensuring the safety and timely repair of structures. In this paper, a novel technique for detecting delamination is proposed. By embedding an optical fiber inside a structural component, the integrated strain along the fiber can be determined. With a load moving along the component, a plot of integrated strain vs load position can be obtained. By correlating changes in the plot with the presence of delaminations, a simple loading test can be employed for delamination detection. The objective of the present investigation is to assess the feasibility of the proposed technique. Experimentally, to ensure the measurement of small length changes as a result of delamination, a highly sensitive interferometer is developed. Laboratory tests are carried out on simply supported beams and beams on elastic foundation. To compare with experimental measurements, finite element analysis is carried out to obtain numerical results. The experimental and numerical results correlate reasonably well with one another. The findings of this investigation demonstrate the potential of the technique and warrant further developments for practical applications.
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