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A new interferometric scheme for measuring mode conversion distributed locally along a polarizationmaintaining fiber is presented. Using this technique the power coupling coefficient, varying with magnitude and angle of external pressure transversely applied to a fiber, was evaluated both theoretically and experimentally. The coupling point location is determined with +/- 1.5-cm accuracy and resolution of better than 10 cm for a 220-m long fiber having modal birefringence of 4.4 x 10 (- 4). The coupling coefficient was proportional to the external force in the range from 5 x 10 (- 3) to 0.1 kg/mm. The relationships determined experimentally reflected those predicted by theory.

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Accurate X-ray intensities of a PtP2 crystal were measured with the multiple-diffraction effect avoided by using the ~b rotation of the crystal around the scattering vector. The results were compared with those of a measurement made without avoiding the effect. The extinction parameters were more isotropic and the peaks of the deformation density were significantly smaller when multiple diffraction was avoided. In the measurement made without avoiding the effect, the number of structure factors affected by * To whom correspondence should be addressed.© 1994 International Union of Crystallography Printed in Great Britain -all rights reserved more than 1% was 403 from 936 reflections measured. Of 272 strong reflections with sin0/A < 0.6 A-1 and Fob s > 200, 27 reflections were affected by more than 1%. These facts, as well as the smaller R values, indicate that the multiple-diffraction effect cannot be neglected in electron-density studies of crystals including heavy atoms. To assess the intensity fluctuation calculated in the present study, the intensities of 200 reflections were measured at intervals of 0.5 c from 0 to 180 ° in ~0 and compared with the calculated values. The variations of the measured and calculated intensities with ~ correspond to each other, which indicates that the present method can Acta Crystallographica Section A ISSN 0108-7673 © 1994KIYOAKI TANAKA et al. 247be used effectively to identify the reflections affected significantly by multiple diffraction.

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