Quantitative evaluation of two-dimensional dynamic deformations using digital holography

An optical system for the parallel evaluation of in- and out-of-plane dynamical deformations will be described. A double pulse laser with pulse separation in the microsecond range is used for the investigations. Two separate interferograms of an object under test, in its undeformed and deformed state, are recorded in a few microseconds. The object is illuminated from two different directions and imaged onto a CCD sensor. This produces two sensitivity vectors. The reference beams have different directions in order to produce two directional spatial carriers. The Fourier method is used for quantitative evaluation, and the measurements along different sensitivity vectors are separated in the Fourier domain. The phases of the two interferograms are obtained from the complex amplitudes and the two dimensional deformation is calculated from the phases. Experimental results are presented.     

Applications of fractional transforms to object reconstruction from in-line holograms

We propose a method for the digital reconstruction of an object whose diffraction pattern has been recorded on a hologram. The fractional Fourier transform is used for the object reconstruction. To determine the position of the object, the fractional order is scanned. The fractional cosine and fractional Hartley transforms are also employed for object reconstruction. These two transforms are real valued and allow the reconstruction to be done with lower computing complexity. Simulations and experimental results are presented.     

Quenching of the Haldane gap in LiVSi<Subscript>2</Subscript>O<Subscript>6</Subscript> and related compounds

We report results of susceptibility χ and ⁷Li NMR measurements on LiVSi₂O₆. The temperature dependence of the magnetic susceptibility χ(T) exhibits a broad maximum, typical for low-dimensional magnetic systems. Quantitatively it is in agreement with the expectation for an S=1 spin chain, represented by the structural arrangement of V ions. The NMR results indicate antiferromagnetic ordering below T_N=24 K. The intra- and interchain coupling J and J_p for LiVSi₂O₆, and also for its sister compounds LiVGe₂O₆, NaVSi₂O₆ and NaVGe₂O₆, are obtained via a modified random phase approximation which takes into account results of quantum Monte Carlo calculations. While J_p is almost constant across the series, J varies by a factor of 5, decreasing with increasing lattice constant along the chain direction. The comparison between experimental and theoretical susceptibility data suggests the presence of an easy-axis magnetic anisotropy, which explains the formation of an energy gap in the magnetic excitation spectrum below T_N, indicated by the variation of the NMR spin-lattice relaxation rate at T≪T_N.     

Bridgman growth and site occupation in LuAG:Ce scintillator crystals

LuAG:Ce single crystals with various activator concentrations were grown by the vertical Bridgman technique. Characterization of crystals was done in terms of actual doping level, macroscopic defects and degree of non-equivalent substitutions by Lu for Al in octahedral lattice sites. Scintillation measurements were performed using 2×2×8 mm³ shaped samples with Ce concentration in the range 0.05–0.55 at%. Essential improvement of performance was demonstrated in samples containing ≥0.2 at% of Ce; the light yield measured in LuAG:Ce (0.55 at%) was about 26000 ph/MeV, or close to that of LSO.     

Aperture synthesis in phase retrieval using a volume-speckle field

The resolution of the reconstructed wave by a phase-retrieval method using a volume-speckle field depends on the aperture defined by the size of the CCD array. The use of a larger aperture is introduced by measuring the speckle field at two different positions in the transverse plane and stitching the measurements together. Improvements in the quality of reconstructions are demonstrated experimentally and by computer simulations. Undesirable effects of camera tilt on the quality of reconstructions from synthetic aperture intensity measurements are experimentally observed and corrected.