DIAMOND REFRACTIVE LENSES FOR DIFFRACTION-LIMITED X-RAY SOURCES
- Mr. Maxim POLIKARPOV
- Mr. Maxim POLIKARPOV (IKBFU)
An intensive development of X-ray refractive optics’ instrumentation and tools has given birth to X-ray refractive lenses  which are now standard elements at third-generation synchrotron radiation sources. In view of the global switch to the fourth generation of synchrotron sources and X-ray Free Electron Lasers, there is a growing need for x-ray optical elements fabricated from materials that can withstand extreme heat and radiation loads while still providing effective focusing and imaging. Diamond can satisfy all the requirements provided that a suitable lens manufacturing technology is available.
In our research , for the first time single crystal diamond planar refractive lenses were fabricated by laser micromachining in up to 1.2 mm thick diamond plates which were grown by CVD and HPHT. Various linear lenses with apertures up to 1mm and radii of the parabola apex up to 500µm were manufactured and investigated with SEM, AFM, Raman spectroscopy and, of course, X-ray tests at the ESRF ID06 beamline. X-ray focusing showed the high quality of the lens’s side walls and profile allowing to focus the X-radiation in accordance with the lens demagnification factor. Planar lenses were followed by 2D parabolic X-ray refractive half lenses, which were also manufactured by laser micro-machining of single-crystal diamond. A single 2D lens had an aperture of 1 mm and parabola apex radii of 200 µm. Forming a compound refractive lens with 24 single lenses within, it has been successfully tested in the focusing and imaging modes both at the APS source  and at the laboratory setups using Cu Kα X-radiation from the rotating anode generator and microfocus MetalJet X-ray tube with a liquid-gallium jet as the anode using Ga Ka line. The lens has successfully reproduced the triangular object with the theoretical demagnification while the focusing of the 20 µm source was performed with the small deviation from the theoretical value.
The present study demonstrated that laser micro-fabrication technology provides a straight forward method for the fabrication of single-crystal diamond refractive lenses with large acceptance and high shape and surface (peak-to-valley roughness ~ 1µm) quality. Unique optical properties of diamond single-crystal lenses (the refractive index decrement, δ, in diamond is double that of beryllium) coupled with its excellent thermal qualities (high thermal conductivity and shock resistance; low thermal expansion coefficient; high temperature stability) allow them to be applied as focusing, imaging and beam-conditioning elements at high-heat flux beams of today and future X-ray sources.
- Snigirev, A., et al., A compound refractive lens for focusing high-energy X-rays. Nature, 1996. 384(6604): p. 49-51.
- Polikarpov, M., et al., Large-acceptance diamond planar refractive lenses manufactured by laser cutting. Journal of Synchrotron Radiation, 2015. 22(1): p. 23-28.
- Terentyev, S., et al., Parabolic single-crystal diamond lenses for coherent x-ray imaging. Applied Physics Letters, 2015. 107(11): p. 111108.