Hard X-ray in-line interferometers fabricated by Si planar technologies.
The modern microfabrication technologies allowed profiling of Si crystals to a significant depth with a high quality of vertical sidewalls offering unique opportunities such manufacturing of X-ray optical elements like planar compound refractive lenses (CRL) and bilens interferometers [1, 2]. The CRL based bilens interferometer consists of two parallel lens arrays which under coherent illumination produces the interference pattern i.e. standing wave with a variable period ranging from tens of nanometers to tens of micrometers, depending on the observation distance.
Recently, in order to expand bilens beam acceptance, we have proposed a multilens system . The interference field produced by the multilens system, in comparison with the bilens, has a more rich longitudinal structure and may be described by the Talbot imaging formalism. The increase of the beam acceptance raises an intensity and a contrast of the interference pattern leading interference maxima narrowing which is confirmed by the experimental studies . The large interferometer “aperture” gives higher sensitivity and precision for characterization of the beamline optics.
Another promising option offered by the microfabrication technologies is the ability to create reflection-based systems, where sidewalls of the etched structures can be used as reflecting mirrors: two parallel mirrors represent a micro-mirror interferometer . Experimental tests showed that the interference pattern produced by such interferometers is sensitive to a roughness of the etched surface.
The proposed interferometers can be applied for coherence and optics characterisation, surface metrology in the energy range 5-100 keV. Finally, high contrast of the tunable interference pattern can be used for new type of moiré radiography and standing wave techniques. The strong advantage of Si planar technologies is the ability to create integrated optical systems on one chip consisting of refractive lenses, lens- and mirror-based interferometers. A scanning electron microscope (SEM) image of such chip is disposed in Fig. 1.
Fig. 1. SEM image of a Si chip containing different X-ray optical elements.
 A. Snigirev, I. Snigireva, V. Kohn, V. Yunkin, S. Kuznetsov, M. B. Grigoriev, T. Roth, G. Vaughan, and C. Detlefs, Phys. Rev. Lett. 103 (2009) 064801.
 A. Snigirev, I. Snigireva, M. Lyubomirskiy, V. Kohn, V. Yunkin, and S. Kuznetsov, Opt. Express 22 (2014) 25842.
 M. Lyubomirskiy, I. Snigireva, S. Kuznetsov, V. Yunkin, and A. Snigirev, Opt. Lett. 40 (2015) 2205.