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Under coherent plane wave illumination, the classical Talbot effect yields exact replica of the periodic input pattern in planes periodically distributed in the free propagation direction (paraxial regime). But when the period of the object is comparable with the wavelength, the Talbot phenomenon is considered to enter its non-paraxial regime(non-paraxial Talbot effect). In this contribution an experimental and theoretical report of this phenomenon is presented at non-paraxial regime with a amplitude grating of period 1μm, using a plane wave with wavelength of 616nm. The experimental self-images are registered by a confocal microscope and these self-images are contrasted with those obtained by the theory of diffraction in representation of plane waves. Contrary to what was expected, the remarkable results obtained is that it does not present quasi-self-images phenomenon and a detailed discussion of this behavior is included. [ABSTRACT FROM AUTHOR]

An alternative object positioning technique based on digital moire´ is presented. The moire´ pattern is obtained by the digital subtraction of different self-images under predetermined conditions including a grating rotation. The principle of the method relies on the fringe visibility matching in the moire´ process while moving from one self-image plane to another. The motion produces both loose of fringe contrast and rotation of the moire´ fringes. The theoretical model of this matching is provided. It applies the concept of measuring a global maximum contrast to each image, which allows to obtain both the best contrast and the adequate rotation. This allows a precise identification of each Talbot plane associated to an object to be positioned. [Copyright &y& Elsevier]

A digital collimation technique based on the self-imaging phenomenon is proposed. Basically, a moire´ pattern is observed by viewing the Fresnel image of an original self-imaged grating through a second grating. Decollimation of the laser beam causes a variation in the self-image period. In our method, the moire´ beating is produced through a digital subtraction operation of a replica of the original grating and the self-images provided by a decollimated beam. The variation of the moire´ period is related to the amount of decollimation of the illuminating beam. Lenses of different focal lengths were used in the collimation procedure, as well as gratings with different periods. The validity of the approach is experimentally demonstrated and setting sensitivities are compared. [Copyright &y& Elsevier]

Abstract: In this paper, a one-dimensional image distribution is stored as modulation of birefringence in a BSO photorefractive crystal in an incoherent to coherent converter arrangement. The features of the read-out image under different write-in image magnifications of an input object are analyzed. In particular, characteristic parameters are introduced to assess the feasibility of an adequate recognition of the converted image. Experimental results under extinction configuration obtained by using intensity-normalized images are described. [Copyright &y& Elsevier]