V. A. Bushuev

Enhancement of second-harmonic generation with femtosecond laser pulses near the photonic band edge for different polarizations of incident light

We present experimental evidence of enhancement of second-harmonic generation as a result of an increase of the fundamental-field energy density within a multilayer structure near the photonic band edge.

Diffraction of X-ray free-electron laser femtosecond pulses on single crystals in the Bragg and Laue geometry.

A solution of the problem of dynamical diffraction for X-ray pulses with arbitrary dimensions in the Bragg and Laue cases in a crystal of any thickness and asymmetry coefficient of reflection is presented. Analysis of pulse form and duration transformation in the process of diffraction and propagation in a vacuum is conducted. It is shown that only the symmetrical Bragg case can be used to avoid smearing of reflected pulses.

Dynamical Bragg diffraction of optical pulses in photonic crystals in the Laue geometry: Diffraction-induced splitting, selective compression, and focusing of pulses

A theory for the dynamical Bragg diffraction of a spatially confined laser pulse in a linear photonic crystal with a significant modulation of the refractive index in the Laue geometry has been developed. The diffraction-induced splitting of a spatially confined pulse into the Borrmann and anti-Borrmann pulses localized in different regions of the photonic crystal and characterized by different dispersion laws is predicted. The selective compression or focusing of one of these pulses with the simultaneous broadening or defocusing of the other pulse is shown to be possible.

Wave-optical description of X-ray phase contrast images of weakly absorbing non-crystalline objects

SummaryThe work deals with the theoretical wave-optical diffraction description of X-ray phase image peculiarities of non-crystalline objects in the Phase Dispersion Imaging technique. The equation for diffracted beam arnplitudeEh(x) coincides with the ones obtained by other authors. The equation for transmitted beam amplitudeE0(x) contains the additional term with the field derivative∂E0/∂x. The comparison of computer simulation of the X-ray intensity distribution in the image plane of the test object with the experimental results demonstrates that the theory is satisfactory.

Polarization effects in diffraction-induced laser pulse splitting in one-dimensional photonic crystals

The polarization effects in the diffraction-induced pulse splitting (DIPS) observed under the dynamical Bragg diffraction in the Laue geometry in linear one-dimensional photonic crystals (PCs) are studied theoretically and experimentally. It is demonstrated that the characteristic length of the laser pulse path in a PC, or splitting length, used to describe the temporal pulse splitting, as well as the number of the outgoing femtosecond pulses, are influenced significantly by the polarization of the incident laser pulse. We have observed that the characteristic splitting time in porous quartz PCs for the s-polarized probe pulse is approximately 1.5 times smaller as compared with that measured for the p-polarized radiation. These results are supported by the theoretical description and ensure that the polarization sensitivity of the DIPS effect is due to a large lattice-induced dispersion of the PC. It is also shown that the number of output pulses can be varied from two up to four in both transmission and diffraction directions depending on the polarization of incident femtosecond pulses.

Calculating the extended defect contrast for the X-ray-beam-induced current method

The contrast of extended defects representing dislocations and grain boundaries has been calculated for the X-ray-beam-induced current (XBIC) method. It is established that the maximum contrast increases with the diffusion length of excess charge and decreases with increasing X-ray beam width. The simulated XBIC profile contrasts are compared to experimentally measured patterns.

Raman and X-ray studies of nanocrystals in porous stain-etched germanium

Abstract Using a combination of stain-etching with subsequent annealing in hydrogen, porous germanium films with a high concentration of germanium nanocrystals (NCs) were prepared for the first time. Structural studies of the films were performed by X-ray reflectometry and high-resolution triple-crystal diffractometry and Raman light spectroscopy methods. From a thorough analysis of the experimental data obtained by both methods, it was revealed that the films consist of germanium NCs with average sizes approximately 8–10 nm in annealed films. Other basic information about thickness, porosity, roughness, and lateral coherence length of the films is also presented.

Characterization of the structure of porous germanium layers by high-resolution X-ray diffractometry

The surface morphology and the structure of porous germanium layers obtained by chemical etching of n-type single-crystal Ge(111) substrates with their subsequent annealing in hydrogen atmosphere are studied by high-resolution X-ray diffractometry. It is established that upon etching a 1.5 to 2.0-μm-thick porous germanium layer is formed, which contains quasi-ordered microinhomogeneities in the form of elongated pits with characteristic dimensions of 1 μm and an average distance between them of 3–4 μm. The layer bulk has pores with radii ranging within 25–30 nm and nanocrystallites with an average size of 10 nm, with the average porosity being 56%.

Temporal and coherence properties of hard x-ray FEL radiation following Bragg diffraction by crystals

At XFEL sources, coherent and time-resolved experiments will strongly depend on the properties of the incoming radiation passed through beamline optical elements to experimental stations. We investigate analytically and make numerical modeling of SASE pulse propagation through optical transport systems of hard X-ray FEL beamlines. The results on evolution of SASE XFEL pulses and its statistical properties during propagation through a double crystal monochromator in Bragg and Laue diffraction geometry are presented.

Diffraction-induced laser pulse splitting in a linear photonic crystal

We demonstrate analytically a linear optical property of photonic crystals--diffraction-induced incident optical pulse splitting in two pulses propagating with different group velocities in a linear photonic crystal. The reason of this phenomenon is in spatially inhomogeneous field localization within the photonic crystal in case of the Bragg diffraction at the Laue scheme. The field of the fast first pulse is mainly localized within low refractive index layers, whereas the slow second pulse field is mostly in high refractive index layers. Changing optical properties of either high-index or low-index layers of periodical multilayer structure, it is possible to control parameters of each propagating pulse separately. The distance between two transmitted and two diffractively reflected output pulses can be controlled by varying the crystal thickness and modulation depth of the refractive index.