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We discuss a method to record and reconstruct color holograms by using a stack of photodiode sensors associated to a one-way reference beam. The reconstruction algorithm follows a convolution strategy in which a transverse magnification leads to the full reconstruction of the object in the reconstructed horizon. The transverse magnification of the object depends on the curvature of the reference wave. Analysis of the spatial resolution indicates that it is linked to the transversal magnification but that no extra information is gained or lost in the process. Experimental results confirm the validity of the proposed approach for two-color digital holography. The error due to spectral mixing is investigated and found to be quite irrelevant compared to the range of the phase measurement. [c] 2010 Optical Society of America OCIS codes: 090.0090, 090.1995, 090.4220, 090.1705, 090.2880, 100.2000.

Features offered by the combination of time averaging and digital Fresnel holography are investigated. In particular, we introduce the concept of the zero-crossing phase of Bessel fringes, which allows a highly contrasted determination of the dark fringes in the hologram. We discuss some particularities of the digital reconstruction and show how time-averaged digital holography can be used to study vibration drifts. Experiment results are presented in the ease of a loudspeaker under a sinusoidal excitation; digital and analogical holography are also compared. OCIS codes: 090.0090, 090.2880, 100.2000, 120.3180, 120.0120, 120.4630.

We present an all-numeric multiplexing/demultiplexing technique for digitally recorded holograms that allow the simultaneous determination of the in-plane and the out-of-plane components of the displacement vector of an object submitted to some loading. The twin-sensitivity measurement is obtained from two different illumination directions that give two sensitivity vectors. The spatial multiplexing is achieved by an incoherent mixing of two duplets of coherent waves that produce holograms carried with orthogonal polarized reference waves. The spatial demultiplexing uses the autocorrelation function of the multiplexed holograms as a position estimator. The estimator then enables the determination of the pixel-to-pixel correspondence between the holograms for the double component determination. Results of the experiment are presented. OCIS codes: 090.0090, 090.2880, 100.0100, 100.2000, 120.3180, 120.0120.

The detailed theoretical description of how picosecond plane shear acoustic fronts can be excited by ultrafast lasers at the interface of two isotropic media, a transparent medium and an opaque medium, is presented. The processes leading to the emission of inhomogeneous plane bulk shear acoustic modes from the interaction at the interface of plane inhomogeneous compression/dilatation modes thermoelastically generated by laser interference gratings are analyzed. The theory describes the basic features of the spectral transformation function of the laser light conversion into shear modes and predicts an interval of frequencies where it is possible to achieve the emission into the transparent medium of propagating shear inhomogeneous modes only, while the compression/dilatation inhomogeneous modes will be evanescent and will be localized at the interface. The guidelines for optimal choice of the materials, with the goal of improving the amplitude of the photoexcited picosecond shear acoustic fronts are proposed. All-optical monitoring, i.e., excitation and detection, by fs-ps laser pulses of picosecond plane inhomogeneous shear acoustic fronts propagating in thin films and substrates can be applied for the noncontact determination of shear rigidity of materials. [ABSTRACT FROM AUTHOR]

The structure of the Ruddlesden-Popper layered perovskite Li2CaTa2O7, known for its high photocatalytic water activity since its discovery in 2008, is reinvestigated. This oxide has been characterized by powder X-ray and neutron thermodiffraction, TEM, second harmonic generation (SHG), and Raman experiments on powders and single crystals. It is shown that it undergoes two structural phase transitions (i) around 220 °C, mainly characterized by the progressive emergence of SHG signal at low temperatures, and (ii) at 660 °C, mainly characterized by changes of the temperature behavior of lattice parameters and by the emergence of Raman signals that linearly increase on decreasing temperature. It is shown by powder neutron diffraction profile refinements at RT, 400, and 800 °C that the space groups of the successive phases of Li2CaTa2O7 are the acentric Pna21 (RT = T = 220 °C), Pnma (220 °C = T = 660 °C), and Cmcm (T = 660 °C). A soft mode associated with the transition to the highest symmetry for this structural arrangement (I4/mmm) is also found in the Raman spectra. All these transitions appear continuous: the high temperature ones can be attributed to progressive vanishings of the octahedra tiltings (displacives) while the transition in the vicinity of 220 °C from Pna21 to Pnma exhibits order-disorder character. [ABSTRACT FROM AUTHOR]

The present work concerns the thermal structural characterization of the acentric Ruddlesden-Popper LiHSrTa2O7. A previous study, performed with powder neutron diffraction data, has revealed that at room temperature, LiHSrTa2O7 crystallizes in the Ama2 space group and that the acentric character is mainly due to the unequal distribution of the Li+ and H+ cations on their sites. In this new paper, the thermal behaviour has been studied by several techniques: powder X-ray and neutron diffraction, SHG experiments and Raman spectroscopy. All of them have revealed that LiHSrTa2O7 undergoes a reversible structural transition from an orthorhombic to a tetragonal symmetry around 200 °C. This transition is associated with the progressive vanishing of the TaO6 octahedra tilting, becoming completely straight in the high temperature form (S.G. I4/mmm), and with a variation of the Li+ and H+ distribution in the interlayer spacing. [ABSTRACT FROM AUTHOR]

The electromagnetic properties of scroll microcoils are investigated with finite element modelling (FEM) and the design of experiment (DOE) approach. The design of scroll microcoils was optimized for nuclear magnetic resonance (NMR) spectroscopy of nanoliter and subnanoliter sample volumes. The unusual proximity effect favours optimised scroll microcoils with a large number of turns rolled up in close proximity. Scroll microcoils have many advantages over microsolenoids: such as ease of fabrication and better B 1 -homogeneity for comparable intrinsic signal-to-noise ratio (SNR). Scroll coils are suitable for broadband multinuclei NMR spectroscopy of subnanoliter sample. [ABSTRACT FROM AUTHOR]