Photon-matter Interaction Research Articles

3D extension of the Monte Carlo code MCSHAPE for photon–matter interactions in heterogeneous media

MCSHAPE is a Monte Carlo code for the simulation of gamma and X-ray diffusion in matter which gives a general description of the evolution of the polarisation state of the photons. The model is derived from the so-called ‘vector’ transport equation. The three-dimensional (3D) version of the code can accurately simulate the propagation of photons in heterogeneous media originating from either polarised (i.e. synchrotron) or unpolarised sources, such as X-ray tubes. Photoelectric effect, Rayleigh and Compton scattering, the three most important interaction types for photons in the considered energy range (1–1000keV), are included in the simulation with the state-of-art extent of detail. In this paper, the 3D version of the code MCSHAPE is presented. The sample is described using the so-called voxel model. Results from the validation studies and applications of the code to scanning XRF and XRF tomography experiments are discussed.

Coherent Rayleigh-Brillouin scattering in molecular gases

We present an experimental and theoretical study of the coherent Rayleigh-Brillouin scattering in gases in the kinetic regime. Gas density perturbation waves were generated by two crossing pump laser beams through optical dipole forces. A probe laser beam was then coherently scattered from the perturbation waves. The line shape of the scattered light was modeled using kinetic theory. The model takes into account the internal energy modes of the gas particles and is applicable to both molecular and atomic gases. We discuss the implication of coherent Rayleigh-Brillouin scattering on kinetic theory and photon matter interaction.

Origin of absorption enhancement in a tungsten, three-dimensional photonic crystal

A three-dimensional, metallic photonic crystal is realized and its absorption measured at infrared wavelengths. The metallic absorption rate is found to be suppressed in the photonic bandgap regime (λ∼8–20 μm). On the other hand, order-of-magnitude absorption enhancement is observed at the photonic band edge (λ∼5.8 μm). The enhancement is attributed to the slower group velocity of light at the photonic band edge, a longer photon–matter interaction length, and a finite intrinsic absorption of tungsten.

Photon assisted CVD

Various aspects of photon-matter interactions are discussed in the frame of applications to chemical vapor deposition processes. Based on the examples of carbon and tungsten deposition, the influences of photon sources like lamps, pulsed- or cw-lasers on the deposition mechanisms are outlined. Peculiarities arising from the different interactions of photons with the gas phase and/or the substrate surface and their effect on the compositional or structural characteristics of the deposited material are described.

Characterization of soil’s structural crust by spectral reflectance in the SWIR region (1.2–2.5 μm)

Structural crust is a thin layer formed on the soil surface after a rainstorm. The crust is the result of a physical segregation and rearrangement of soil particles in a way that affects some of the soil properties, such as infiltration, runoff and soil erosion. In practice, there is no rapid, in situ method for monitoring, assessing and mapping crust intensity and quality. In this study, a controlled spectral investigation of the structural crust across the NIR–SWIR spectral region was conducted on three selected Israeli soils, to study the potential of reflectance radiation to detect structural crust in soils. Two major factors served as the driving forces for this study: (1) there is no valid method for in situ assessment of the crust’s characteristics in the agriculture field, and (2) the crust might bias thematic remote sensing of soils, because the thin layer of crust blocks photon–matter interaction, which represents the relevant soil body. Through the use of a laboratory rainfall simulator and a sensitive spectrometer, it was revealed that for three selected soils, significant spectral differences occurred between the crust and its bulk soil. The spectral information was found to be related to changes in particle size distribution and texture at the surface of the soil. This conclusion was based on indications of absorption of OH in clay lattice, OH in adsorbed water and CO3 in carbonates. It was concluded that the structural crust is a phenomenon that should not be ignored by remote‐sensing users. In fact, in the field of agriculture, the spectral properties of crust can be used as tools for estimating the crust’s intensity.

Configuration-space quantum-soliton model including loss and gain

We examine the effects of loss and gain on a quantum soliton using a configuration-space approach. A simple microscopic model of local photon-matter interaction is applied to solitons with arbitrary quantum superpositions of momentum. Such a theory is needed in the analysis and design of systems that manipulate the wave function of soliton center-of-mass coordinates. The formalism is tested by calculating the momentum noise induced by loss and gain, and by comparison with the well-known Gordon-Haus calculation [J. P. Gordon and H. A. Haus, Opt. Lett. 11, 665 (1986)]. The comparison provides physical insight and reproduces the old result as a special case.

A general Monte Carlo simulation of energy-dispersive X-ray fluorescence spectrometers. Part 3. Polarized polychromatic radiation, homogeneous samples

A general Monte Carlo (MC) code, capable of simulating photon-matter interactions in the energy range of 1–80 keV, has been adapted to model the behavior of synchrotron radiation X-ray fluorescence (SR-XRF) spectrometers using polarized, polychromatic radiation as means of excitation. A brief description of the simulation method specific for polychromatic excitation is presented for homogeneous, multi-element samples. The code has been verified by comparing calculated spectral distributions of samples of various nature with experimentally collected data, taken at the bending magnet source based X26A SR-XRF beamline installed at the National Synchrotron Light Source (NSLS). Simulated results have also been compared with previously developed analytical calculations. Applications of the program in the field of quantitative analysis of biological and glass materials are presented and the use of the software to study the influence of the changes in the excitation-detection geometry on the predicted spectral distributions is demonstrated. Depending on the thickness and matrix type of the samples, the average deviations of the predicted fluorescent line and scatter background intensities relative to the experimentally obtained values are in the 3–12% range for homogeneous samples.

A general Monte Carlo simulation of ED-XRF spectrometers. II: Polarized monochromatic radiation, homogeneous samples

A general Monte Carlo code for the simulation of X-ray fluorescence spectrometers, described in a previous paper is extended to predict the spectral response of instruments employing polarized exciting radiation. Details of the calculation method specific for the correct simulation of photon-matter scatter interactions in case of polarized X-ray beams are presented. Comparisons are made with experimentally collected spectral data obtained from a monochromatic X-ray fluorescence setup installed at a synchrotron radiation source. The use of the simulation code for quantitative analysis of intermediate and massive samples is also demonstrated.

Tailoring of surface properties by removal and deposition with laser radiation

The tailoring of chemical, morphological, and mechanical surface properties with laser radiation is described on the basis of the understanding and control of photon-matter interaction. The removal of matter by thermal and non-thermal processes including etching, the deposition of multilayer thin films, and the photoresistless patterning by direct and indirect processing techniques are illustrated by examples.

Plasma in photon matter interaction during laser material processing

Plasma state is always present in several processes which require very high densities of energy : this is the case in pulse processing mode where, for nanoseconds pulse durations, intensities of several G W / C ~ ~ are required. For CW processing, these phenomena occurs for intensities in the MW/cm2 range. This is the case of the welding process. Even if this process has been used for industrial application quite since the begining of the laser, the precise role of this plasma is not completely understood during this process. We propose in this paper to give some new insigths in this field. In a first part, we will recall basic principles of plasma generation ; a second part is devoted to some experimental results on its characterization in the plume and inside the keyhole.

A particle picture of ?tunneling? and the nature of ?photon?-matter interaction

Brownian motion is employed as a model to formulate a probabilistic statement of the Heisenberg uncertainty relationship. By means of the latter, a tunneling formula identical to that obtained from the WBK method is derived from the particle picture. The nature of photon-matter interaction is discussed in the light of the quantal Brownian motion.