Aleksandr V. Vinogradov

High-reflectivity multilayer mirrors for a vacuum-ultraviolet interval of 35–50??nm

Sc-Si multilayers are suggested as high-reflectivity coatings for a VUV interval of 35-50 nm. Fabricated mirrors show normal-incidence reflectivity of 30-54%, which is high enough for effective manipulation of the beams of compact-discharge, laser-driven x-ray lasers. The values obtained are not, however, limits for Sc-Si coatings. Theoretical estimations as well as electron microscopy studies of Sc-Si interfaces indicate a large potential for a further increase in their reflectivity.

On the reflectivity of surfaces with thin transition or contaminated layers

The spatial profile of the dielectric pemittivity of any bulk sample is always to some extent smoothed or modified by various factors including interaction with atmospheric and environmental gases. This fact hinders optical measurements and should be taken into account in the interpretation of experimental data. The modification of the Fresnel reflectivity formula for the case where the spatial permittivity distribution deviates from an abrupt stepwise profile is considered. A correction in terms of the integral characteristics of this deviation is obtained and it is valid ifa sin δ<λ, wherea is the depth of the contaminated layer, and λ and δ are the wavelength and grazing angle of the incident beam, respectively.

On the explicit parametric description of waves in periodic media

A method for the parameterization of the one-dimensional wave equation is proposed that makes it possible to find its solution by quadratures under an arbitrary dependence of the refraction index on the current wave phase. The form of the solution found is used to investigate the structure of the wave function for a periodic refraction index. Explicit expressions for the fundamental system of solutions and for the Floquet index are obtained. Examples of applying the proposed method to the optimal synthesis of multilayer interference mirrors and Bragg waveguides are discussed.

New methods of X-ray reflectometry of solids and solid thin films

X-ray reflectometry makes it possible to determine optical constants of materials in the corresponding range of wavelengths and the thickness of thin films on the basis of measurements of reflection coefficients in relation to the grazing angle. New reflectometry methods based on measurements of either the derivatives with respect to the grazing angle or the ratios of reflection coefficients for two characteristic wavelengths are suggested. Calculations and measurements indicate that the method suggested makes it possible to enhance the sensitivity of reflectometry and the accuracy of measuring the optical constants. Practical implementation of the method is based on an unconventional system of selecting monochromatic beams with the use of semitransparent crystals. The results of reflectometry studies of GaAs single crystals and a Ga0.25Si0.75−Si multilayer structure on a Si substrate are reported.

Soft X-ray microscopy in the spectral region of “carbon window” with the use of multilayer optics and a laser-plasma source

This paper reports on the fabrication and testing of multilayer mirrors for X-ray optical systems operating in the “carbon window” region (at wavelengths from 4.5 to 5.0 nm) and the results of their application in soft X-ray imaging of the internal structure of organic objects. The developed approaches to the fabrication and control of graded Co/C multilayer coatings have made it possible to create an X-ray multimirror system with a maximum known entrance aperture and throughput. The use of the developed high-spatial-resolution X-ray optics can significantly extend the field of practical application of soft X-ray absorption microscopy based on compact laser-plasma sources.

Theory Of Multilayer X-Ray Mirrors With Slowly Varying Period

Broadening of multilayer-mirror reflection band is achieved by slow variation of its period. The paper is devoted to the theory of such optical elements based on a general theory of wave propagation through a quasi-periodic medium. The calculation results are presented for the reflection coefficient of broadband mirrors in the 1 to 50 Å range. A statement of the inverse problem is also considered, namely, creation of a multilayer structure possessing the prescribed reflection coefficient.

Concentrators of soft x-rays

The properties of axisymmetric and cylindrical optical concentrators in the wavelength region where all the substances possess low reflectivity are considered. The losses related to radiation leaving the system through side faces and reflective walls are found, and the ultimate efficiency of the concentrator is determined. On the basis of available data on optical constants the dependence of the efficiency on the choice of the reflective coating material is analyzed. The role of the roughness of the reflective surface is discussed and the principal requirements on the accuracy of concentrator fabrication are stated.

Residual infrared absorption in metal mirrors

An analysis is made of the physical factors that limit the reflectivity of mirrors in the infrared range. It is shown that the mechanism responsible for the finite residual absorption is the electron–phonon interaction in the presence of a photon (Holstein–Gurzhi effect). A study is also made of the influence of the surface roughness on the absorptivity of mirrors.