Biomedical subjects

Mike Melnichuk

Publications and source records attributed to Mike Melnichuk.

4 recordsLinked to original sources

PubMed2006

Determining selected quadratic coefficients in noncentrosymmetric crystals.

We present a systematic theoretical examination concerning the practical possibility of measuring components of the quadratic symmetry tensors for solid materials lacking inversion symmetry. We show that information concerning the quadratic effects in noncentrosymmetrical crystals can be obtained directly by methods that allow for the bypassing of the coexisting dominant linear effects. Here, we deal only with the particular case of the electro-optic effect; however, the results and conclusions are also valid for the elasto-optic effects.

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PubMed2005

Method for measuring off-diagonal Kerr coefficients by using polarized light transmission.

We report a method for measuring the off-diagonal coefficients of the quadratic electro-optic (Kerr) tensor by using polarized light transmission. The method relies on designing an experimental configuration in which the linear electro-optic (Pockels) effect does not contribute to the data. Our method can be used to obtain off-diagonal Kerr coefficients for all but two of the 20 crystal point groups for which the Pockels effect and the Kerr effect coexist. Our theoretical model includes effects from transmission, multiple reflections, and electrostriction but neglects absorption in the crystal. To verify the method, we used it to measure the R12 and R13 Kerr coefficients for a (100)-type single crystal of ferroelectric barium titanate (BaTiO3) at room temperature (23.5 degrees). To our knowledge, this is the first time this method has been used and the first time these coefficients have been measured for the unclamped crystal in the tetragonal state. The mean values obtained with this method are R12 = -3.5+/-0.3 x 10(-17) m2/V2 and R13 = -8.0+/-0.7 x 10(-17) m2/V2.

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PubMed2005

Time-resolved optical transients in tetragonal BaTiO3.

We present and analyze the room temperature (T= 23.5 degrees C) time behavior of the transmitted intensities of polarized light passing through an unclamped (100)-type single crystal of barium titanate (BaTiO3) when subject to a time-dependent, externally applied electric field. To the authors' knowledge, this is the first reported observation and analysis of such time-resolved optical transients. According to a previous [J. Opt. Soc. Am. A 22, 377 (2005)] observation by the authors, this original optical technique can, in principle, be used on 18 out of 20 noncentrosymmetric crystal point groups where the first-order (Pockels) and second-order (Kerr) electrooptic effects coexist. Because of its nondestructive nature, this novel optical method would be a useful tool in other fields of condensed-matter physics in which time-behavior observation and characterization of certain physical parameters of crystals are important.

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PubMed2003

Fraunhofer diffraction to determine the twin angle in single-crystal BaTiO3.

We present a new method for determining the electrically induced twin angle alpha of a (100) bulk single crystal of barium titanate (BaTiO3) using a nondestructive optical technique based on Fraunhofer diffraction. The technique required two steps that were performed simultaneously. First, we analyzed the diffracted light intensity captured with a line camera. Second, we measured the size of the diffracting element by analyzing images of crystal's surface taken with a CCD camera. The value obtained for the twin angle is 0.67 degrees +/- 0.05 degrees, which compares favorably with the theoretical value of 0.63 degrees.

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