High-efficiency multilevel zone plates for keV X-rays

Abstract

The development of high brilliance X-ray sources coupled with advances in manufacturing technologies has led to significant improvements in submicrometre probes for spectroscopy, diffraction and imaging applications. The generation of a small beam spot size is commonly based on three principles(1) total reflection las used in optical elements involving mirrors or capillaries), refraction (such as in refractive lenses(2)) and diffraction. The latter effect is employed in Bragg-Fresnel or Soret lenses, commonly known as Fresnel zone plate lenses. These lenses currently give the best spatial resolution, but are traditionally limited to rather soft X-rays-at high energies, their use is still limited by their efficiency. Here we report the fabrication of high-efficiency, high-contrast gold and nickel multistep (quaternary) Fresnel zone plates using electron beam lithography. We achieve a maximum efficiency of 55% for the nickel plate at 7 keV. In addition to their high efficiency, the lenses offer the advantages of low background signal and effective reduction of unwanted diffraction orders. We anticipate that these lenses should have a significant impact on techniques such as microscopy(3), micro-fluorescence(4) and micro-diffraction(5), which require medium resolution (500-100 nm) and high flux at fixed energies

Homodyne and heterodyne X-ray photon correlation spectroscopy: latex particles and elastomers

“…This size can be further reduced with the new X-ray focusing elements (Schroer et al, 2003;Di Fabrizio et al, 1999).…”

Double-Exposure Grayscale Photolithography

“…Three-dimensional photolithography techniques alleviate this restriction by enabling enhanced control over the photoresist profile. This method has been demonstrated in optics [10][11][12], where 3D lenses exhibit greater performance. For example, the phase Fresnel lens in [12] can be realized as a phase zone plate using only planar technology, but it will have a diminished efficiency compared to a 3D phase Fresnel lens.…”

High-efficiency zone-plate optics for multi-keV X-ray focusing

“…In these terms, the binary zone plates represent the most basic two-level approximations and, once the phase shift is reached, the approximation can only be improved by adding additional levels. Such multilevel zone plates have been previously demonstrated (DiFabrizio et al, 1999) to reach diffraction efficiencies up to 55%, but this required the compromise of 1 mm effective smallest zone width (the smallest zone width of multilevel zone plates is the half-pitch).…”