7 March 2006 Resolution improvements of the digital light-in-flight recording by holography method
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Abstract
An electronic 3D-shape measurement method has been developed by combining light-in-flight recording by holography (lif) with digital holography. Lif is a technique for direct visualization of the propagation of a short light pulse when it is e.g. intersecting a 3D-shaped object resulting in contour lines of the object. This is achieved by letting the reference beam be delayed in comparison to the object beam along a CCD-sensor. A Fourier-Fresnel algorithm numerically reconstructs the hologram. A Littrow mounted reflection grating in a Twyman-Green type interferometer set-up creates the optical delay between the object and the reference beam. The 3D-shape and the position of the object can be determined by combining the contour lines of the object together to a depth map. The recorded hologram from one point will be confined to a rectangular area on the CCD-sensor, where the delay between the reference and the object beam is within the pulse length of the laser. Due to diffraction limitation will the resolution be poor in the direction of the delay since the recorded rectangle area will have its shortest side there. The resolution can however be improved by making two recordings in two perpendicular directions. The two holographic images can then be combined keeping the best resolution of the two holograms. Increase of the resolution makes the lif method useful for more applications for shape and deformation measurements.
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Bengt J.L. Nilsson, Torgny E. Carlsson, "Resolution improvements of the digital light-in-flight recording by holography method", Proc. SPIE 4101, Laser Interferometry X: Techniques and Analysis, (7 March 2006); doi: 10.1117/12.498443; https://doi.org/10.1117/12.498443
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