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Femtosecond laser pulses are currently regarded as an emerging and promising tool for processing wide bandgap dielectric materials across a variety of high-end applications, although the associated physical phenomena are not yet fully understood. To address these challenges, we propose an original, fully analytical model combined with Two Temperatures Model (TTM) formalism. The model is applied to describe the interaction of fs laser pulses with a typical dielectric target (e.g., Sapphire). It describes the heating of dielectrics, such as Sapphire, under irradiation by fs laser pulses in the range of (1012–1014) W/cm2. The proposed formalism was implemented to calculate the free electron density, while numerical simulations of temperature field evolution within the dielectrics were conducted using the TTM. Mathematical models have rarely been used to solve the TTM in the context of laser–dielectric interactions. Unlike the TTM applied to metals, which requires solving two heat equations, for dielectrics the free electron density must first be determined. We propose an analytical model to solve the TTM equations using this parameter. A new simulation model was developed, combining the equations for non-equilibrium electron density determination with the TTM equations. Our analyses revealed the non-linear nature of the physical phenomena involved and the inapplicability of the Beer–Lambert law for fs laser pulse interactions with dielectric targets at incident laser fluences ranging from 6 to 20 J/cm2. [ABSTRACT FROM AUTHOR]

An atomistic simulation of silicon dioxide thin films deposited using oxide targets is performed. The influence of the oxide target on the deposition process is taken into account by introducing O=Si=O molecules into the flow of particles moving from the target to the substrate. The fraction of these molecules varied from 0 to 50%. It was found that the presence of O=Si=O molecules leads to film densification during a normal deposition. With a low-energy deposition, the increase in density was twice as high as with a high-energy deposition. The absolute value of the compressive stress increased with an increasing fraction of O=Si=O molecules in the flow of deposited particles at a normal, high-energy deposition. The influence of O=Si=O molecules on the structure of the glancing angle deposited films depends on the deposition angle. [ABSTRACT FROM AUTHOR]

The signal source of synthetic aperture radar (SAR) usually adopts the linear frequency modulation (LFM) signal, which exhibits the characteristics of a wide pulse. Hence, in the case of usage of the LFM signal by time-domain shooting and bouncing ray (TDSBR) to simulate the SAR echo signal, numerous time sampling points are generated, resulting in huge computational efforts; thereby, it is hard to exploit the TDSBR algorithm for simulating the SAR echo. In order to unlock this dilemma, the hybrid approach, the transfer function in conjunction with the range frequency-domain pulse coherence, is developed, in which the transfer function is stated by the radar cross-section. The proposed methodology is capable of enhancing the computational efficiency through avoiding the massive time sampling, so that the suggested TDSBR approach could be more conveniently applied to the SAR echo simulations. Furthermore, because of the efficiency advantage of the TDSBR in the calculation of wideband scattering field, the proposed methodology exhibits higher computational efficiency than the frequency-domain shooting and bouncing ray in the SAR image simulation. Finally, the key equation of the TDSBR for the transient scattering field of dielectric targets based on a closed-form integration formula is analytically derived, which is the basis of SAR imaging simulation for the composite scene of ships above the sea surface.

Computing the Radar Cross-Section (RCS) of a given object is a topic of major importance for many applications, e.g., target detection and stealth technology. In this context, high-frequency asymptotic methods are widely used. In this article, we derive a Gaussian Beam Summation (GBS) method for both metallic and dielectric targets. The basic idea is to use the GBS method to compute the scattering far fields generated by the equivalent currents flowing on the surfaces. The validity of the proposed method is then investigated in the X-band. To accomplish this, the results obtained using this technique were compared to those obtained using other sufficiently accurate methods such as the ray tracing of FEKO and the ray asymptotic solution. As an example of the method's accuracy, the GBS method was used to obtain the wave field in a homogeneous medium by fitting the results to a point source. In the same way, the method was used to compute the RCS of dielectric cuboids. [ABSTRACT FROM AUTHOR]

Galerkin testing in method-of-moments procedures is defined as the use of the same set of functions as both basis functions and testing functions to construct a linear system from a continuous equation. There is a widespread belief that Galerkin testing enhances the accuracy of numerical results, and this has been shown to be true under certain conditions for surface integral equation formulations. This property is investigated for the volume electric field integral equation (EFIE) applied to dielectric bodies. The relative accuracy obtained in internal fields and scattering cross section for Galerkin and for point testing schemes is compared for a variety of target sizes and materials. In many cases, the point-tested results converge at the same rate as the Galerkin results and are more accurate. [ABSTRACT FROM AUTHOR]

A previously developed simulation platform for localization purposes has been extended and customized to accurately analyze and simulate ultra wideband (UWB) through-wall imaging (TWI) synthetic aperture radar (SAR) systems as well. The newly added features/modules include electromagnetic simulator to account for wall presence and target scattering, a wideband backprojection imaging algorithm, and different transceiver architectures and antenna array configurations. The developed platform is capable of time gating to suppress early wall reflections and simulates various discrete components and functions of the UWB SAR system using both linear and nonlinear analysis. The simulator has been experimentally validated for both dielectric and metallic targets. The developed simulator can also be used to study various effects related to operation frequency, pulse width, pulse shape, wall dispersion, and carrier leakage. It predicts UWB system performance such as detection range, image resolution, and receiver dynamic range. The system's components can be re-optimized for high performance 3-D imaging based on our developed models. The simulation platform is also suitable for designing the optimal signal waveform that could improve the recovered image quality for TWI applications. [ABSTRACT FROM AUTHOR]

The composite electromagnetic scattering from dielectric targets above and below the dielectric rough surface using the method of moments (MOM) and the Extended Propagation-Inside-Layer Expansion (EPILE) combined with the Forward-Backward method (FBM) is studied. The established integral equations are validated by comparing with the related theory. The efficiency and exactness of the EPILE+FBM are verified by comparing with the MOM. The influences from the target size, the target height/depth, the target horizontal distance, the relative permittivity, the rms height, as well as the correlation length to the bistatic scattering coefficient are also investigated. The presented scheme is of generality for the targets and rough surface composite scattering problems. [ABSTRACT FROM PUBLISHER]

The present work is devoted to the precise spatiotemporal mapping of the absolute density of Ar(1s5) in a ns‐pulsed argon plasma jet. The plasma impinges on glass and alumina targets at floating potential placed 5 mm away from the reactor's nozzle. Under these conditions, diffuse discharges are established in the small gas gap. As so, the line‐of‐sight absolute density of Ar(1s5) is effectively evaluated via laser absorption spectroscopy. The application of the Abel‐inversion is also demonstrated for different operating conditions leading to the precise radial mapping of the Ar(1s5) absolute density. The influence of each target is studied for two gas flow rates, 0.3 and 0.4 l min−1. The temporal density profiles over a voltage pulse period reveal two maxima related with the Ar(1s5) production in the streamer head and in the residual diffuse plasma channel. Furthermore, the maximum Ar(1s5) axial/radial density (∼1013 − 3.5 × 1014 cm−3) depends on the target material and gas flow rate. Finally, the plasma is proved to be very effective for the fast desorption of organic molecules (bibenzyl) deposited on both targets. The results obtained suggest that the desorption of bibenzyl is due to the production of high Ar(1s5) densities at the close vicinity of the targets. Argon plasma jets (APJs) have been poorly studied for the detection of weakly volatile substances (of interest for different applications). Hereby, an APJ is optimized for the desorption of organic molecules (bibenzyl) deposited on different dielectric plates. The experiments are focused on the accurate quantification of argon metastables spatial (axial‐radial) and temporal densities, suggesting their implication on the desorption process. [ABSTRACT FROM AUTHOR]