Krassimir Nedialkov Stoev

Optimization of curved x‐ray multilayer mirrors for total reflection x‐ray fluorescence spectrometry

Various x-ray optical configurations combining focusing and monochromatizing mirrors for application in total reflection x-ray fluorescence (TXRF) spectrometry were numerically modelled for the case of extended x-ray sources. The influence of the system parameters, such as mirror shape, the extension of the source, the angular divergence and the nature of the multilayer (uniform or graded ML), on the detection limits (DL) of TXRF were studied for two excitation energies of practical interest: 9.67 keV (W Lβ) and 17.48 keV (Mo Kα). No significant dependence of the DL on the mirror shape was observed. For smaller anode sizes the use of curved x-ray mirrors leads to a more significant improvement in the DL compared with a flat mirror. The use of graded ML mirrors does not bring significant advantages to TXRF because of the very short section of the ML used and the corresponding very low gradient in the d-spacing over this section. A combination of focusing x-ray mirrors with flat ML monochromators is of advantage only for anode–sample distances longer than 20 cm. Optimum DLs can be achieved with a circular Pt mirror and a flat double ML for 9.67 keV and a circular ML mirror for 17.48 keV.

Phase-stepping automatic fringe analysis in holographic moiré

The phase-stepping technique is used to analyze holographic moiré patterns. This new application permits the instantaneous determination of phase functions in both moiré and carrier fringes. Two modified phase-stepping self-calibrating techniques are proposed and demonstrated on computergenerated noisy moiré patterns. The techniques do not complicate the holographic moiré arrangement and do not need auxiliary carrier fringes. A holographic moiré interferometer that has been adapted for these phase-stepping techniques is proposed.

Automated Fourier transform fringe-pattern analysis in holographic moiré

Fourier transform fringe-pattern analysis is a wide-spread technique with many applications to optical metrology. Introducing a spatial carrier into a holographic moire pattern is also a well-known technique to obtain observable moire fringes. Preprocessing of the holographic moire pattern includes optical or digital Fourier filtering to remove the carrier. The pattern is then processed by employing time-consuming and less accurate fringe-counting algorithms. This work presents a new application of the Fourier transform method to automated analysis of holographic moire fringe patterns. The method has the advantage of instantaneous determination of both phase functions in the fringe pattern. Investigations are carried out on the frequency limitation imposed on the spatial carrier. The technique is demonstrated on computer-generated noisy holographic moire patterns. The technique does not complicate the conventional holographic moire arrangement.

Phase-stepping holographic moiré: simultaneous in-plane and out-of-plane displacement measurement.

A new use for the phase-stepping technique in holographic moiré is demonstrated. The method has the advantage of providing instantaneous determination of in-plane and out-of-plane displacements without the necessity for auxiliary carrier fringes.

An algorithm for artificial resolution enhancement of X-ray fluorescence spectra

Abstract Theoretical expressions for resolution enhancement procedure proposed by Betin and Zavgorodni have been derived and tested on synthetic and experimental X-ray spectra. A formula for transformed spectrum is obtained without changing the total peak area and peak positions. The main advantage of the procedure is the lack of negative regions in the processed spectrum. Empirical criteria for evaluation and control of the processing parameters are proposed. The influence of the processing parameters (peak separation, peak dispersion, relative peaks intensities, number of iteration and resolution parameter) on the accuracy of the method has been studied. A computational algorithm has been developed and incorporated in a PC based computer program for routine analysis of X-ray spectra.

Wavelength demultiplexing by chirped waveguide gratings

The spectral response of a chirped sinusoidal surface relief grating in an optical waveguide has been studied by means of Local Normal Mode Expansion theory. A matrix technique has been applied to account for the varying grating period. The grating is divided into segments with constant periods and coupling coefficients. Nonslanted grating is considered in a first-order diffraction. Also, contradirectional coupling between guided modes in phase synchronism at an arbitrary angle of incidence is considered. Performance considerations include TE-TE, TE- TM, and TM-TM mode coupling for different grating geometry and waveguide parameters. We show the effect of geometry and waveguide parameters on the performance of the chirped grating as a wavelength demultiplexer. Also, we demonstrate how the filtering and demultiplexing characteristics and the spectral shift between different polarization modes can be controlled.

Holographic moire patterns processed by the Fourier transform method

Spatial-carrier fringe pattern analysis is a wide-spread technique and has found a lot of applications to optical metrology. Introducing a spatial-carrier into a holographic moire pattern is also a well-known technique to obtain observable moire fringes. Preprocessing of the holographic moire pattern includes optical or digital Fourier filtering to remove the carrier. The fringe pattern is then processed by using time-consuming fringe-counting algorithms. The current work presents a new application of the Fourier transform method to automated analysis of holographic moire fringe patterns. The method owns the advantage of instantaneous determination of both phase functions in the pattern. Investigations are carried out on the frequency restrictions imposed on the phase functions. The technique is demonstrated on computer generated noisy holographic moire patterns. The technique does not complicate the conventional experimental holographic moire arrangement.