Showing 4 results for Karimi
A. Gharavi, H. Karimi-Alavijeh, E. Sarailou, M.–a. Baghban, G.–m. Parsanasab,
Volume 2, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol. 2, No. 1, Winter 2008)
Abstract
In this paper, we have reported the fabrication of two-dimensional photonic crystals, using a direct writing method in azo polymers. Periodic structures have been fabricated using the interference patterns of two coherent laser beams. The frequency response of the initial one-dimensional structure shows an attenuation of 19.3dB at 1554nm. The twodimensional structure shows 8.3dB and 11.3dB of attenuation at 1554nm in two perpendicular main axes of the structure. The diffraction pattern shows the characteristic rectangular pattern.
F Karimi, S Khorasani,
Volume 5, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 5, No 1, Winter-Spring 2011)
Abstract
Here, we investigate the possible optical anisotropy of vacuum due to gravitational field. In doing this, we provide sufficient evidence from direct coordinate integration of the null-geodesic equations obtained from the Lagrangian method, as well as ray-tracing equations obtained from the Plebanski’s equivalent medium theory. All calculations are done for the Schwarzschild geometry, which results in an anisotropic (pseudo-isotropic) optical equivalent medium when Cartesian coordinates are taken. We confirm that the results of ray-tracing in the equivalent medium and null geodesics are exactly the same, while they are in disagreement with the results of integration in the conventional isotropic equivalent medium of Schwarzschild geometry.Based on the principle invariance of physical due to coordinate transformation, there exists just one result. This Contradiction will be solved by tensor algebra and it will be shown that the conventional isotropic approach is wrong, and even by transforming the metric into isotropic form, the optical behavior of vacuum will remain anisotropic. Hence, we conclude that the true optical behavior of curved spacetime must be anisotropic, and it is an intrinsic property of vacuum in the presence of gravitational field. We provide further discussions on how to detect this possible anisotropy, and what further consequences might be expected in the interpretation of gravitational lensing data.
Nayyereh Daroogheh, Elham Karimi, S.m. Bagher Ghorashi,
Volume 13, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 13, No 2, Summer-Fall 2019)
Abstract
In this study, a sol-gel peroxotungstic acid sol was employed to deposit tungsten oxide (WO3) films by the spin-coating technique. In view of smart window applications, electrochromic windows were then designed and fabricated using a thin tungsten oxide film. For this purpose, Glass/ FTO/ WO3/ electrolyte/ FTO/Glass could be of use due to its special structure that consists of an electrochromic layer (WO3) on a transparent conductor (FTO), an electrolyte containing Li+ cations, and a transparent conductor layer. A voltage was applied on the fabricated sample, which was later assesed for its transmission, switching speed, and coloration efficiency. An increase in the coloration efficiency from 87 cm2/C-1 to 99.1 cm2/C-1 was found associated with an increase in the deposition speed. Moreover, the increase in the deposition speed led to a decrease in the coloration and bleaching time duration from 11.4 s to 6.2 s and from 12.8 s to 5.2 s respectively. The results obtained on the thin film WO3 can be useful for electrochromic applications.
Elham Karimi, Seyed Mohamad Bagher Ghorashi, Maryam Hashemi,
Volume 14, Issue 1 (Winter-Spring 2020)
Abstract
Recently, organo–metal halide perovskites have attracted much attention of the scientific community relating to their successful application in the absorber layer of low-cost solar cells. However, enough is known about the material and device properties, to realize that much remains to be learned.
In this paper, the electrical and optical properties of perovskite solar cells are investigated
using the COMSOL Multiphysics simulation program. It is a study of the influences
of carrier diffusion length (L), dielectric constant (ε
r), the valence band offset (VBO) of absorber/hole transport materials (HTM) and illumination intensity on fill factor (FF), short-circuit current density(J
SC), performance (PCE), and open-circuit voltage(V
OC). Also, J-V characteristics are calculated for diff
erent ε
r values. The simulation results point to the great dependence of efficiency on the carrier diffusion length of absorber layers. It is shown that, to obtain a high rate of efficiency, the relative permittivity should not be higher than 45.
