Abstract
We have implemented a modified Young's double slit experiment using pinholes with tunable separation distance coupled with compound refractive lens for hard X-ray spatial coherence characterization. Varying distance between the apertures provides a high sensitivity to the determination of spatial coherence across a wide range of experimental parameters. The use of refractive lenses as a Fourier transformer ensures far field registration conditions and allows the realization of a very compact experimental setup in comparison with the classical Young technique and its derivatives. The tunable double aperture interferometer was experimentally tested at the ESRF ID06 beamline in the energy range from 8 to 25 keV. The spatial coherence and the source size were measured by evaluating the visibility of the interference fringes at various separation distances between the apertures and this value agrees very well with the data obtained by other techniques. The proposed scheme can be used for comprehensive characterization of the coherence properties of the source on low emittance synchrotrons in the hard X-ray region.
Highlights
In recent years, continuous development of synchrotron sources, such as 3rd generation synchrotrons and free electron lasers, has resulted in a dramatic increase of coherence properties of a photon beam especially in the hard X-ray region
Varying distance between the apertures provides a high sensitivity to the determination of spatial coherence across a wide range of experimental parameters
The tunable double aperture interferometer was experimentally tested at the ESRF ID06 beamline in the energy range from 8 to 25 keV
Summary
Continuous development of synchrotron sources, such as 3rd generation synchrotrons and free electron lasers, has resulted in a dramatic increase of coherence properties of a photon beam especially in the hard X-ray region. One classical way to characterize the coherence is the Young’s double slit experiment where interference of two coherent beams created by two narrow slits occurs This is a direct and straightforward technique to measure the spatial coherence and is widely used in the soft X-ray region [18,19]. In classical optics the Fraunhofer diffraction pattern can be observed at distances much closer than implied by mentioned above relation if lenses are used It is well known attribute of a convergent lens, in the case of a plane wave illumination, at the back focal plane of the lens the Fourier transform occurs and this image is considered as a far field image [26]. We would like to stress that refractive lenses have been already used to perform Fourier transform for high resolution X-ray diffraction [29,30]
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