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60   Chapter Two



                                                                   CCD
                                           Rotation
                                            axis

                Insertion
                 device
                                                     0.001 - 1 m
                              Multilayer                       High resolution
                             monochromator           Near field  detector
                                           Sample  Fresnel diffraction
                                            stage

               FIGURE 2.3 Scheme of the setup for X-ray holotomography operated on
               the ID19 beamline of the ESRF (Grenoble, France). The X-ray beam is
               monochromatized by a crystal monochromator or a multilayer, the energy
               used being typically around 15 keV (wavelength around 0.08 nm). The
               sample is mounted on a rotating table. The detector ensemble is a scintillator
               screen coupled by light optics to a CCD camera. This dectector can be moved
               to record images close to the object or at different distances from it.


               applied to a large variety of objects of interest in biological or material
               sciences.



          2.9 Conclusion
               The AF shares with the WDF the ability to describe the propagation
               of a partially coherent beam in free space and through a paraxial opti-
               cal system in a simple and elegant way. The AF is a generalization of
               the intensity spectra which are the basis of important phase retrieval
               methods. The images given by a space-invariant system are conve-
               niently described in terms of AF of the object and of the pupil AF,
               which is a generalization of the OTF and has important applications
               in the design of phase apodizers. Phase-space tomography is a grow-
               ing field of research, in which the AF reconstruction may be more
               practical than the WDF tomographic reconstruction.



          References

                1. P. M. Woodward, Probability and Information Theory with Application to Radar,
                  Pergamon, New York, 1953.
                2. A. Papoulis, “Ambiguity function in Fourier optics,” J. Opt. Soc. Am. 64: 779–788
                  (1974).
                3. M. J. Bastiaans, “The Wigner distribution function applied to optical signals
                  and systems,” Opt. Comm. 25(1): 274–278 (1978).
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