V. Mocella - Academia.edu (original) (raw)

Papers by V. Mocella

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001

The aim of this work is to generate the rocking curves of monochromators exposed to heat load in ... more The aim of this work is to generate the rocking curves of monochromators exposed to heat load in synchrotron radiation beams with a computer code performing diffraction calculations based on the theory of Takagi and Taupin. The model study starts with the calculation of deformation by finite element analysis and from an accurate characterization of the incident wave and includes the simulation of the wavefront propagation between the first and the second crystal (analyzer) of a double crystal monochromator. A monochromatic plane wave as well as a polychromatic spherical wave approach is described. The theoretical predictions of both methods are compared with experimental data measured in Bragg geometry and critically discussed. #

Proceedings of the 2nd International Workshop onAdvanced Ground Penetrating Radar, 2003., 2003

ABSTRACT

Journal of the European Optical Society: Rapid Publications, 2014

In this paper, experimental evidences about the resonance phenomena in a negative 2D photonic cry... more In this paper, experimental evidences about the resonance phenomena in a negative 2D photonic crystal are shown. Localized plasmon-like modes and guided mode resonances are detected in the reflectivity spectrum of a photonic crystal slab irradiated with out-of-plane incident radiation. The strong confinement of the radiation, in addition to the field enhancement, make photonic crystals a very appealing alternative to plasmonic substrates, avoiding the limits of absorption losses in metals.

Optics Express, 2007

An advanced wave-optical approach for simulating a monochromator-analyzer set-up in Bragg geometr... more An advanced wave-optical approach for simulating a monochromator-analyzer set-up in Bragg geometry with high accuracy is presented. The polychromaticity of the incident wave on the monochromator is accounted for by using a distribution of incoherent point sources along the surface of the crystal. The resulting diffracted amplitude is modified by the sample and can be well represented by a scalar representation of the optical field where the limitations of the usual 'weak object' approximation are removed. The subsequent diffraction mechanism on the analyzer is described by the convolution of the incoming wave with the Green-Riemann function of the analyzer. The free space propagation up to the detector position is well reproduced by a classical Fresnel-Kirchhoff integral. The preliminary results of this innovative approach show an excellent agreement with experimental data.

Optics Express, 2008

An analytical approach has been developed to derive aberration effects in parabolic and elliptic ... more An analytical approach has been developed to derive aberration effects in parabolic and elliptic multilayer optics with weak interaction between photons and matter. The method is based on geometrical ray tracing including refraction effects up to the first order of the refractive index decrement δ . In the parabolic case, the derivation leads to simple parametric equations for the caustic shape. In the elliptic case, the analytical results more involved, but can be well approximated by the parabolic solution. Both geometries are compared with regard to the fundamental impact on their focusing properties.

Journal of Synchrotron Radiation, 2006

Among the several available X-ray optics for synchrotron radiation producing micrometre and submi... more Among the several available X-ray optics for synchrotron radiation producing micrometre and submicrometre beams with high intensity, the X-ray waveguide (WG) can provide the smallest hard X-ray beam in one direction. A drawback of this optics is that, owing to the divergence at the exit, a nanometre-sized spot on the sample can only be obtained if this is within a few micrometres of the WG exit. Another limitation is that in planar WGs the beam is compressed in only one direction. Here, using a dynamically bent elliptical Si/Pt mirror, the guided X-ray beam has been refocused at $ 1 m from the waveguide exit. The large working distance between the device and the submicrometre focus leaves some space for sample environment (vacuum chamber, furnace, cryostat, magnets, high-pressure device etc.) and allows cross-coupled geometries with two WGs for efficient compression in two directions.

Journal of Applied Crystallography, 2008

Recent X-ray optical experiments have validated previous theoretical work on focusing by bent cry... more Recent X-ray optical experiments have validated previous theoretical work on focusing by bent crystals in Laue geometry. It was shown that a suitable choice of the crystal thickness significantly improves the focusing performance of the crystal by combining the dynamical focusing of the Borrmann triangle with the geometrical focusing obtained by the crystal bending. The best focus size achieved during the experiments was less than 5 mm and is in practice limited by the source demagnification for the considered setup. research papers J. Appl. Cryst. (2008). 41, 695-700 V. Mocella et al. Focusing by bent crystals in Laue geometry 697 Figure 3

Crystal Research and Technology, 2002

The x-ray waveguides are a novel optical component for hard x-rays able to produce submicrometer ... more The x-ray waveguides are a novel optical component for hard x-rays able to produce submicrometer beams. In this article we review the operating principle and describe the characteristics of the exiting beam. We will give two significant examples of applications in microdiffraction obtained with an unprecedented spatial resolution of 100 nm.

Journal of Physics D: Applied Physics, 1999

We investigate dynamical diffraction phenomena of a quasi-monochromatic x-ray beam emitted by a s... more We investigate dynamical diffraction phenomena of a quasi-monochromatic x-ray beam emitted by a small source at a large distance from the sample. Under certain conditions of coherence the diffraction intensity profile in a recording plane reproduces the angular profile of the rocking curve of the crystal. The coherence requirements are stronger for thicker crystals. This has been verified in experiments

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001

The aim of this work is to generate the rocking curves of monochromators exposed to heat load in ... more The aim of this work is to generate the rocking curves of monochromators exposed to heat load in synchrotron radiation beams with a computer code performing diffraction calculations based on the theory of Takagi and Taupin. The model study starts with the calculation of deformation by finite element analysis and from an accurate characterization of the incident wave and includes the simulation of the wavefront propagation between the first and the second crystal (analyzer) of a double crystal monochromator. A monochromatic plane wave as well as a polychromatic spherical wave approach is described. The theoretical predictions of both methods are compared with experimental data measured in Bragg geometry and critically discussed. #

Proceedings of the 2nd International Workshop onAdvanced Ground Penetrating Radar, 2003., 2003

ABSTRACT

Journal of the European Optical Society: Rapid Publications, 2014

In this paper, experimental evidences about the resonance phenomena in a negative 2D photonic cry... more In this paper, experimental evidences about the resonance phenomena in a negative 2D photonic crystal are shown. Localized plasmon-like modes and guided mode resonances are detected in the reflectivity spectrum of a photonic crystal slab irradiated with out-of-plane incident radiation. The strong confinement of the radiation, in addition to the field enhancement, make photonic crystals a very appealing alternative to plasmonic substrates, avoiding the limits of absorption losses in metals.

Optics Express, 2007

An advanced wave-optical approach for simulating a monochromator-analyzer set-up in Bragg geometr... more An advanced wave-optical approach for simulating a monochromator-analyzer set-up in Bragg geometry with high accuracy is presented. The polychromaticity of the incident wave on the monochromator is accounted for by using a distribution of incoherent point sources along the surface of the crystal. The resulting diffracted amplitude is modified by the sample and can be well represented by a scalar representation of the optical field where the limitations of the usual 'weak object' approximation are removed. The subsequent diffraction mechanism on the analyzer is described by the convolution of the incoming wave with the Green-Riemann function of the analyzer. The free space propagation up to the detector position is well reproduced by a classical Fresnel-Kirchhoff integral. The preliminary results of this innovative approach show an excellent agreement with experimental data.

Optics Express, 2008

An analytical approach has been developed to derive aberration effects in parabolic and elliptic ... more An analytical approach has been developed to derive aberration effects in parabolic and elliptic multilayer optics with weak interaction between photons and matter. The method is based on geometrical ray tracing including refraction effects up to the first order of the refractive index decrement δ . In the parabolic case, the derivation leads to simple parametric equations for the caustic shape. In the elliptic case, the analytical results more involved, but can be well approximated by the parabolic solution. Both geometries are compared with regard to the fundamental impact on their focusing properties.

Journal of Synchrotron Radiation, 2006

Among the several available X-ray optics for synchrotron radiation producing micrometre and submi... more Among the several available X-ray optics for synchrotron radiation producing micrometre and submicrometre beams with high intensity, the X-ray waveguide (WG) can provide the smallest hard X-ray beam in one direction. A drawback of this optics is that, owing to the divergence at the exit, a nanometre-sized spot on the sample can only be obtained if this is within a few micrometres of the WG exit. Another limitation is that in planar WGs the beam is compressed in only one direction. Here, using a dynamically bent elliptical Si/Pt mirror, the guided X-ray beam has been refocused at $ 1 m from the waveguide exit. The large working distance between the device and the submicrometre focus leaves some space for sample environment (vacuum chamber, furnace, cryostat, magnets, high-pressure device etc.) and allows cross-coupled geometries with two WGs for efficient compression in two directions.

Journal of Applied Crystallography, 2008

Recent X-ray optical experiments have validated previous theoretical work on focusing by bent cry... more Recent X-ray optical experiments have validated previous theoretical work on focusing by bent crystals in Laue geometry. It was shown that a suitable choice of the crystal thickness significantly improves the focusing performance of the crystal by combining the dynamical focusing of the Borrmann triangle with the geometrical focusing obtained by the crystal bending. The best focus size achieved during the experiments was less than 5 mm and is in practice limited by the source demagnification for the considered setup. research papers J. Appl. Cryst. (2008). 41, 695-700 V. Mocella et al. Focusing by bent crystals in Laue geometry 697 Figure 3

Crystal Research and Technology, 2002

The x-ray waveguides are a novel optical component for hard x-rays able to produce submicrometer ... more The x-ray waveguides are a novel optical component for hard x-rays able to produce submicrometer beams. In this article we review the operating principle and describe the characteristics of the exiting beam. We will give two significant examples of applications in microdiffraction obtained with an unprecedented spatial resolution of 100 nm.

Journal of Physics D: Applied Physics, 1999

We investigate dynamical diffraction phenomena of a quasi-monochromatic x-ray beam emitted by a s... more We investigate dynamical diffraction phenomena of a quasi-monochromatic x-ray beam emitted by a small source at a large distance from the sample. Under certain conditions of coherence the diffraction intensity profile in a recording plane reproduces the angular profile of the rocking curve of the crystal. The coherence requirements are stronger for thicker crystals. This has been verified in experiments