An approach is proposed for removing the wavefront curvature introduced by the microscope imaging objective in digital holography, which otherwise hinders the phase contrast imaging at reconstruction planes. The unwanted curvature is compensated by evaluating a correcting wave front at the hologram plane with no need for knowledge of the optial parameters, focal length of the imaging lens, or distances in the setup. Most importantly it is shown that a correction effect can be obtained at all reconstruction planes. Three different methods have been applied to evaluate the correction wave front and the methods are discussed in detail. The proposed approach is demonstrated by applying digital holography as a method of coherent microscopy for imaging amplitude and phase contrast of microstructures.

The emission properties of a new phosphor based on LiTaO3:Tb3+ are described. It is shown to be a storage phosphor, i.e., after previous x-ray exposure, Tb3+ emission in green-red region of spectrum can be photostimulated by light in 400–800 nm spectral range. Emission centers (Tb3+ ions), electron storage centers (oxygen vacancies) and competing nonradiative recombination centers (oxygen ion and Li vacancy couples), are recognized as the key elements in the energy transfer processes and overall emission efficiency of LiTaO3:Tb3+.

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We propose the use of digital holography (DH) as a metrological tool for inspection and characterization of MEMS structures. We show that DH can be efficiently employed to assess the fabrication process of micro structures as well as to test their behaviour in operative conditions. DH allows reconstructing both the amplitude and phase of microscopic objects and, compared to traditional microscopy, it provides quantitative phase determination. We demonstrate that DH allows determination of full field deformation maps that can be compared with analytical and/or numerical models of the deformed microstructure. Application of DH on structures with several different geometries and shapes, like cantilever beams, bridges and membranes is reported and result will be discussed. Dimensions of the inspected microstructures ranging from 1 to 50µm. Examples of application are presented were DH allows determination with high accuracy out of plane deformations due to the residual stress introduced by the fabrication process. An optical setup for recording digital holograms based on a Mach-Zehnder interferometer was adopted and a laser source which wavelength is λ=532nm was employed. The light reflected by the object under investigation was made to interfere with a plane wave front. Holograms were recorded by a CCD array with 1024 x 1280 square pixels with 6.7 µm size. A mirror mounted on a piezo-actuator was inserted along the reference arm of the interferometric in order to introduce controlled phase steps and to employ phase shifting technique. This technique allows suppressing both the zeroth-order and the conjugate wave-front in the numerical holographic reconstruction process. A method for compensating numerically curvature of the wave front and introduced by the microscopic objective lens is proposed and discussed.

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