arXiv subjects

Zh. Gevorkian

Publications and source records attributed to Zh. Gevorkian.

4 recordsLinked to original sources

arXiv2025

Strong Energy Dependent Transition Radiation in a Photonic Crystal

Radiation of a charged particle crossing an alternating stack of slabs in the optical region is considered. Both disordered and periodic stacks are investigated. It is shown that for special type of alternating disordered and periodic stacks the radiation problem can be solved exactly for backward and forward Brewster observation angles. Strong $N^2$ dependence of radiation intensity on slab number is re-established in special case of the disordered stack. This leads to strong directivity either on forward or on backward Brewster angles depending on the type of stack randomness. In certain type of periodic photonic crystal, a strong energy dependence $E^4$ for relativistic particles of the radiation intensity, observed at Brewster's angle is found. Further increment of particle energy leads to saturation. The band structure of the corresponding photonic crystal (PhC) has a behavior, analogous to the Dirac cones in graphene. We suggest this special type $1D$ photonic crystal for application as a detector of relativistic particles.

physics.acc-ph↗

arXiv2024

Nanoroughness induced anti-reflection and haze effects in opaque systems

How to make a material anti-reflective without changing its high refraction index? Achieving anti-reflection in high-refractive-index materials poses challenges due to their high reflectivity (Fresnel equations). Based on theory with new boundary conditions, we propose modifying surface properties on a nanoscale to tackle this. Our study on weakly rough opaque surfaces reveals significant changes in specular and diffuse scattering, predicting anti-reflection where roughness matches light penetration depth for the first time. Experimental validation on nano-roughened Si films (at wavelengths 300-400 nm) supports our findings. We also analyze angular and polarization dependences of nanoroughness-induced haze, showing predominant p-polarization and minimal haze at nanoscale, yet impactful specular reflection reduction.

physics.optics↗

arXiv2024

Impact of Surface Roughness on Light Absorption

We study oblique incident light absorption in opaque media with rough surfaces. An analytical approach with modified boundary conditions taking into account the surface roughness in metallic or dielectric films has been discussed. Our approach reveals interference-linked terms that modify the absorption dependence on different characteristics. We have discussed the limits of our approach that hold valid from the visible to the microwave region. Polarization and angular dependences of roughness-induced absorption are revealed. The existence of an incident angle or a wavelength for which the absorptance of a rough surface becomes equal to that of a flat surface is predicted. Based on this phenomenon a method of determining roughness correlation length is suggested.

physics.optics↗

arXiv2015

Localization length calculations in alternating metamaterial-birefringent disordered layered stacks

A detailed theoretical and numerical analysis of the localization length in alternating metamaterial-birefringent random layered stacks, under uncorrelated thickness-disorder, has been performed. Similar structures have recently been reported to suppress the Brewster delocalization for $\it{p}$-polarized light, when "standard" isotropic layers (with positive index of refraction) are considered instead of metamaterial layers, providing a generic means to produce polarization-insensitive, broadband reflections. However, this enhancement of localization is valid for short wavelengths $λ$ compared to the mean layer thickness $a_0$. At higher wavelengths, we recover the Brewster anomalies for $\it{p}$-polarized states impeding a remarkable localization of light. To achieve a better localization for a wider range of wavelengths, we replaced the conventional isotropic layers by negative-index metamaterials presenting low losses and constant index of refraction over the near-infrared range. As a result, our numerical calculations exhibit a linear dependence of the localization length with $λ$ (in the region $5 <λ/a_0 < 60$) reducing the Brewster anomalies in more than two orders of magnitude with respect to the standard isotropic scheme at oblique incidence. This enhancement of localization is practically independent of the thickness disorder kind and is also held under weak refractive-index disorder.

physics.optics↗