Hard X-ray nano-focusing with Montel mirror optics Wenjun Liu a,n , Gene E. Ice b , Lahsen Assoufid a , Chian Liu a , Bing Shi a , Paul Zschack a , Jon Tischler b , Jun Qian a , Ruben Khachartryan a , Deming Shu a a Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA b Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA article info Keywords: Montel mirrors Hard X-ray nano-focusing Achromatic abstract Kirkpatrick–Baez mirrors in the Montel (or nested) configuration were tested for hard X-ray nanoscale focusing at a third generation synchrotron beamline. In this scheme, two mirrors, mounted side-by-side and perpendicular to each other, provide for a more compact focusing system and a much higher demagnification and flux than the traditional sequential K–B mirror arrangement. They can accept up to a 120 mm  120 mm incident X-ray beam with a long working distance of 40 mm and broad-bandpass of energies up to 30 keV. Initial test demonstrated a focal spot of about 150 nm in both horizontal and vertical directions with either polychromatic or monochromatic beam. Montel mirror optics is important and very appealing for achromatic X-ray nanoscale focusing in conventional non-extra-long synchrotron beamlines. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Although traditional Kirkpatrick–Baez (K–B) mirrors [1] are widely used for synchrotron micro/nanofocusing, Montel (or nested K–B) mirror optics [2] are very appealing because of their compact design with stronger demagnification and the ability to collect larger divergences. Recent papers have described their advantages for neutron microfocusing [3] and for possible syn- chrotron applications [4,5]. With traditional K–B optics, X-rays are focused by sequential elliptical surfaces. Fabrication of ultra- precise mirror surfaces has been achieved to create the smallest doubly and singly focused beams to date [6,7]. With nested K–B optics however the two elliptical mirrors are positioned side-by- side and perpendicular to each other, as illustrated in Fig. 1. Some rays strike one mirror first while others strike the other mirror first. This geometry has important advantages compared with tradi- tional sequential arrangement: the focal distance of the mirrors is much shorter than that for the primary mirror of a comparable sequential K–B system, which creates a greater geometrical demagnification of the source and reduces the effect of figure errors (in one direction), and the larger divergence allows for greater flux and/or a lower diffraction limit; the mirrors can be easily aligned to be orthogonal, which is critical for nanofocusing, and the mirror system is much more compact. 2. Optical design and mirror fabrication Many efforts have been made in recent years to use multilayer mirrors to increase the numerical aperture for lowering the diffraction limit [7–9]. However multilayer mirror optics typically has a restricted energy bandpass. To preserve achromatic focusing perfor- mance, total-external-reflection X-ray mirrors are still essential for applications such as diffraction experiments and extended X-ray absorption fine structure measurements. The prototype hard X-ray nanofocusing Montel system has been designed for Laue diffraction microscopy at the 34-ID-E station of the Advanced Photon Source (APS) [10]. The experimental station is located about 60 m from the source. A horizontal slit at 28 m was placed to control the total power in the beam and to reduce the horizontal source size to o100 mm; thus the slit also acts as a new effective object. In the vertical plane, the APS type-A undulator source, with FWHM of about 40 mm serves directly as the object [11]. In a Montel system, the mirror surfaces must come together at the corner of the mirror pair. Instead of cutting a prefigured mirror into two parts at a 451 angle to the surface at edges, we cut the edge of one mirror at slightly less than 901 at edge to ‘‘nest’’ against the companion mirror. The advantage of this approach is that only the edge of one mirror must be used, and the alignment is primarily one-dimensional at each end of the mirror pair. The two elliptical mirrors are both 40 mm long and coated with Pt to produce an identical focal length of 60 mm at 3 mrad incident angles. They can accept up to a 120 mm  120 mm incident X-ray beam with a broad- bandpass of energies up to 30 keV. The main challenge of nested mirror fabrication and assembly is to preserve the mirror surface quality at the reflecting edge. Two Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.11.080 n Corresponding author. E-mail address: wjliu@anl.gov (W. Liu). Please cite this article as: W. Liu, et al., Nucl. Instr. and Meth. A (2010), doi:10.1016/j.nima.2010.11.080 Nuclear Instruments and Methods in Physics Research A ] (]]]]) ]]]–]]]