Spectroscopic dielectric tensor of monoclinic crystals: CdWO4
ABSTRACT Generalized ellipsometry measurements were made using 12 orientations of a monoclinic CdWO4 crystal. Using these measurements and the associated analytical methods presented here, it is shown that the four independent complex elements of the dielectric tensor can be determined at each wavelength. Below the band edge (similar to 4 eV), the dielectric tensor is real, and, therefore, it is possible to uniquely diagonalize the dielectric tensor and determine the birefringence for light passing along the unique axis, but the orientation of the dielectric tensor axes will be a function of wavelength. Above the band edge, unique diagonalization is not possible. The generalized ellipsometric spectra show some symmetry in the cross-polarization coefficients. When the unique axis is perpendicular to the sample surface, the condition rho(ps) = -rho(sp) is valid. If the unique axis is perpendicular to the plane of incidence, rho(sp) = rho(ps) = 0, and if the unique axis is in the plane of incidence, parallel to the sample surface, then rho(ps) = rho(sp) not equal 0. The combined experimental and analytical methods described here are applicable to the determination of the spectroscopic dielectric tensors of monoclinic crystals in general.
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ABSTRACT: The properties of CdWO4 (CWO) crystals in gamma spectrometry were studied. Several small samples of 10×10×3 mm size, typically used in CT X-ray detectors, were tested and then compared to the performance of a larger crystal of 20 mm in diameter and 20 mm in height. The light output, energy resolution, and non-proportionality of the CWO response versus gamma-ray energy, were measured and compared with those of a small BGO to discuss further the origin of the intrinsic resolution of pure undoped scintillating crystals. A high light output of 6500 ± 200 phe/MeV and a good energy resolution of 6.6 ± 0.2% for 662 keV gamma rays from a 137Cs source were measured for the small samples coupled to an XP3212 photomultiplier. Common non-proportionality curves and consequently common intrinsic resolutions of small CWO and BGO suggest that they represent fundamental characteristics of the heavy oxide scintillating material themselves.IEEE Transactions on Nuclear Science 01/2004; 2. · 1.22 Impact Factor
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ABSTRACT: The optical functions of uniaxial ZnO have been determined using two-modulator generalized ellipsometry, where a single measurement is sufficient to determine the optical functions from appropriately aligned uniaxial crystals. Above the direct band edge (∼3.3eV), this technique produces the most accurate values of the optical functions of ZnO presently available, while the refractive indices determined below the direct band edge agree with minimum-deviation methods. Near the direct band edge, the optical functions are modified by the excitonic interaction with a three-dimensional critical point. The optical dielectric response functions are fit to a recent formulation by Holden et al. [Phys. Rev. B 56, 4037 (1997)]. One isotropic point in the spectrum was observed at 3.114 eV, and a near-isotropic point near 3.31–3.34 eV.Physical review. B, Condensed matter 01/1998; 58(7). · 3.77 Impact Factor
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ABSTRACT: We present a unified theoretical approach to electromagnetic plane waves reflected or transmitted at arbitrarily anisotropic and homogeneous layered systems. Analytic expressions for the eigenvalues for the four-wave components inside a randomly oriented anisotropic medium are reported explicitly. As well, the partial transfer matrix for a slab of a continuously twisted biaxial material at normal incidence is described. Transition matrices for the incident and exit media are presented. Hence, a complete analytical 4×4 matrix algorithm is obtained using Berreman's 4×4 differential matrices [D. W. Berreman, J. Opt. Soc. Am. 62, 502 (1972)]. The algorithm has a general approach for materials with linear optical response behavior and can be used immediately, for example, to analyze ellipsometric investigations.Physical review. B, Condensed matter 03/1996; 53(8):4265-4274. · 3.77 Impact Factor