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We present a new approach for the fabrication of volume holograms in an optical nonlinear material with voxel sizes on the order of 1µm i.e., with increased degrees of freedom and thus improved multiplexing functionality.

In this work digital speckle photography is applied to measure changes in length and curvature of a stepped steel shaft during a gas quenching process with sub-pixel accuracy. Changes in the length of the workpiece were measured and compared to the results from a coordinate tactile machine, which were taken at room temperature. Measurements were undertaken in an industrial environment, i.e. without vibration isolation, in order to gain insight on the sensitivity of this method to the vibrations inherent to the process. The motivation behind this study is the measurement of three dimensional deformations of the object in order to facilitate minimization and/or compensation of distortions in steel quenching processes, which is crucial for quality and product assurance. From the preliminary results presented in this work it is clear to see that speckle photography enables a non-invasive, time resolved and accurate online measurement of these defomations. Furthermore, it is apparent that the method is insensitive to different interfering effects, e.g. the gas field and black body radiation of the hot object, within the quenching stand. The well reproducible results attained here will help to better monitor quenching in flexible gas fields and thereby play an important role in facilitating distortionless quenching.keywords Digital speckle photography Á Sub-pixel accuracy Á Quenching Á Distortion engineering Á In-plane displacements 1 Introduction

We propose a new application of broad band lasers for digital holography. The aim is to capture the shape of objects by a single hologram using multiple wavelengths. Our approach is to separate the reference wave spectrally by a grating while the object wave remains unaffected. This leads to many lamellar holograms in one hologram. As consequence different restrictions like aperture and wavelength dependency of the reconstruction algorithm have to be taken into account. In experiments we have successfully demonstrate that lamellar holograms can be generated, reconstructed and that all necessary steps for shape measurement are accomplishable.

We present a least-squares solution for the inverse problem in in-line digital holography which is based on a point source model. We demonstrate that by reformulating the reconstruction problem as an inverse problem and by integrating a contour gradient based auto-focus search algorithm into the reconstruction routine, a more fundamental solution for the inversion of a hologram can be attained. With this approach the inversion can be calculated without any prior knowledge of the object’s shape/size and without imposing any constraints on the imaging system. In a proof-of-concept study we show that our method facilitates a more accurate reconstruction, as compared to conventional methods, and that it facilitates object localization with an accuracy on the order of the optical wavelength.