Multilayer X-ray imaging optics in IPM RAS
Owing to the high peak and integral reflection coefficients, multilayer interference mirrors (MIMs) have unique X-ray optical characteristics in the extreme ultraviolet (EUV) and X-ray wavelength range of 0.01-60 nm. On their basis, experimental a new generation nanolithographs for a wavelength of 13.5 nm, microscopes for the transparency windows of silicon (13 nm region), carbon (5-6 nm) and water (2.8-4 nm) have been manufactured. The greatest amount of information about the physical processes occurring on the Sun is obtained from investigations of the solar corona in the EUV and X-ray ranges. Recently, in connection with the advent of super-power femtosecond lasers, great interest arose in aperiodic MIMs, which allows transporting, focusing, and spectral analysis of atto- and even sub-atto- second pulses of electromagnetic radiation. The wide bandwidth of such MIMs allows one to control these beams without "blurring" the wave packet, or even to shorten it in time. The short wavelength and pulse duration allow to increase by 3-5 orders of magnitude the power density of the radiation in the focusing spot and to come close to reaching the "vacuum breakdown" values of 1028-1030 W/cm2. MIMs are widely used in synchrotron centers both in the EUV and in the hard x-ray range, up to 100 keV. By providing collimation and focusing of X-ray radiation, due to the large operating angles and the controlled spectral bandwidth of the MIMs, they outperform the traditional grazing incidence mirrors, both in terms of the aperture and in the diffraction distortions of the reflected wave fronts. The latter is especially important for synchrotrons of the third and fourth generation. On the basis of the MIM’s technology, recently a new X-ray optical element has appeared: a free-standing (without substrate) multilayer structure. It can be used as a polarizer, phase shifter, beam splitter and spectral filter with a given bandwidth. The use of this element on synchrotrons makes it possible to carry out interference experiments, to certify the polarization composition of the probe and secondary (scattered, reflected, X-ray luminescence) X-ray beams. To use the potential of the MIMs for imaging, focusing, collimating and transportation of the beams without distortion of the wave fronts in full, diffraction quality optics for the X-ray range is required. In comparison with traditional optics, its accuracy should be at least 2 orders of magnitude higher: subnanometric shape accuracy and angstrom roughness are required. Traditional methods of manufacturing and examination the mirrors do not meet these requirements. The report describes the main scientific and technological directions and methods developed in the Institute for Physics of Microstructures of the Russian Academy of Sciences for solving the problems noted above, and the main results obtained in recent times are given. Considerable attention will be paid to the works on the development of diffractive quality optics for the EUV and X-ray ranges. Research includes metrology of shape and roughness, ion-beam polishing and the substrates surface shape correction techniques, deformation-free fixing substrates in frames, searching for new materials and deposition of "stress-free" MIMs, and other aspects.