X-ray refractive lenses were pioneered at the European Synchrotron Radiation Facility in 1996 [1]. Soon after the first experimental demonstration of X-ray focusing by refractive lenses, it became immediately clear that the refraction-based methods traditionally used in the visible light regime can be successfully applied for X-rays. The use of X-ray refractive optics has rapidly expanded and they are now in common use on various beamlines at 15 synchrotrons in 10 countries. Firstly, this dramatic progress was driven by the unprecedented properties of X-ray beams delivered by third generation synchrotron sources such as very low emittance coupled with high brilliance. Secondly, refractive optics offers number of advantages over the existing optics taking into account applicability, tunability and diversity in terms of energy range, focal distance and focal spot.
This development has intensified after the successful implementation of transfocators [2], which are tuneable devices based on refractive lenses. A large variety of transfocators and lens changers has been widely deployed in many Phase I Upgrade Programme ESRF beamlines. They offer high efficiency and high mechanical and radiation stability, making them ideal for beam transport (condensing, focusing, divergence and convergence control) in high-energy experiments requiring versatility and robustness. The use of the strong dispersion properties of refractive lenses in combination with an energy-selecting aperture placed at the focal point may offer an effective method to create a high-throughput broadband monochromator [3]. These optics might also play an important role in filtering out high harmonics [4] and the unwanted power developed by the source in order to reduce thermal deformation or radiation damage of downstream optical components such as mirrors and crystals. In addition, as being pure imaging lenses, transfocators in hand might offer microscopy-like options for high resolution imaging of the source, beamline components and samples. To extend these capabilities we have developed a compact transfocator suitable for complex imaging and microscopy experiments at sub-100 nm resolution, which is sufficiently more powerful, more compact, and lighter than the current transfocators used for beam conditioning.
Recently a new project based on refractive optics has been started at the ESRF to develop a dedicated Hard X-Ray Microscopy (HXRM) instrument. HRXM will include 3 major modes of operations: bright field microscopy for in situ studies of growth in solidification experiments [5], dark field microscopy for mapping individual crystallographic domains and their stress states and coherent diffraction microscopy for mesoscopic and photonic structures [6,7]. An integral part of this project is the development of the required refractive lenses, in particular for the objective lens. An investigation of alternative X-ray homogeneous or amorphous materials like nano-Be and single-crystal diamond is under way.
References
[1] A. Snigirev A., V. Kohn, I. Snigireva, B. Lengeler, Nature, 384, 49-51 (1996)
[2] A. Snigirev et al, Journal of Physics: Conference Series 186, 012073 (2009).
[3] G. Vaughan et al, J. Synchrotron Rad., 18, 125-133 (2011)
[4] M. Polikarpov, I. Snigireva, A. Snigirev, J. Synchrotron Rad., 21, 484-487 (2014).
[5] R.H Mathiesen et al, Met Mat Trans A, 42, 1770-180 (2011).
[6] A. Bosak, I. Snigireva, K. Napolskii, A. Snigirev, Adv. Mater., 22, 3256-3259 (2010).
[7] D. Byelov et al, RSC Advances, 3, 15670 (2013).