Showing 5 results for Yousefi
H. Ghomi, M. Yousefi, Sh. Rostami, Y. Hayashi, E. Hotta,
Volume 4, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 4, No. 2, Summer-Fall 2010)
Abstract
A capillary plasma z-pinch as an alternative active medium of soft X-Ray lasers was studied experimentally and theoretically. The theoretical analysis was based on the self consistent solution of the so called “snow plow” model. The dynamics of pinched plasma is determined by the capillary parameters and by the time dependence of electrical current passing through it. The current time dependence is strongly influenced by the electrical circuit connected to the capillary. In order to optimize the pinch dynamics from the point of view of laser pumping, the effects of the electrical circuit parameters on plasma evolution are studied in this paper
Dr. Mohsen Hatami, Ms. Elham Yousefi,
Volume 7, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 7, No 2, Summer-Fall 2013)
Abstract
In this study, a new numerical method is introduced to obtain the exact shape of output pulse in the chalcogenide fiber Bragg grating (FBG). A Gaussian pulse shape with 173 ps width is used as an input pulse for lunching to a 6.6 mm nonlinear FBG. Because of bistable and hysteresis nature of nonlinear FBG the time sequence of each portion of pulse is affected the shape of output pulse. So we divide the pulse to leading and trailing portion in time. By using bistability curve and Fourier transformation, the exact shape of output pulse is simulated. In comparison of non-unique solution for output pulse in the previous papers, the results of this study have an optional merit.
Elham Yousefi, Mohsen Hatami, Sajjad Dehghani,
Volume 11, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 11, No 1, Winter-Spring 2017 2017)
Abstract
We solve the coupled mode equations governing the chalcogenide nonlinear fiber Bragg gratings (FBGs) numerically, and obtain the bistability characteristics. The characteristics of the chalcogenide nonlinear FBGs such as: switching threshold intensity, bistability interval and on-off switching ratio are studied. The effects of FBG length and its third order nonlinear refractive index on FBG characteristics are investigated. We obtain an interesting result that independent of the third order nonlinear refractive index; there exists an optimum FBG length of about 6 mm at which the on-off switching ratio becomes maximized. It is also found that by increasing the nonlinearity, the maximum value of on-off switching ratio decreases. The results of this paper can be mainly used for designing all-optical switches and memories.
Elham Yousefi, Mohsen Hatami, Amin Torabi Jahromi, Sajjad Dehghani,
Volume 13, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 13, No 2, Summer-Fall 2019)
Abstract
In recent decades, fiber Bragg gratings (FBGs) have been very much considered for their many applications in optical communication systems, as well as due to their bistability and multi stability properties. In this paper, the formation of ternary stability (TS) in nonlinear chalcogenide fiber Bragg gratings (NCFBGs) is investigated via numerical simulations. Effective parameters on TS such as the FBG length, input wavelength and nonlinear property (or nonlinearity) on TS formation are introduced and studied. It is found that there exists a minimum length for each third order nonlinear coefficient that TS phenomena can be observed. Also, the threshold intensity for TS formation is calculated with respect to the length, input wavelength and third order nonlinearity. In addition, the relevance between the minimum length for TS formation and the third order nonlinearity in the range of chalcogenide nonlinearities are looked into. It is numerically confirmed that increasing the input wavelength (in a valid FBG input wavelength range) increases the TS formation threshold intensity, while decreases the needed FBG length. Because of using experimental values in this paper, it has valuable information about designing the all-optical device with three - level stability which makes NCFBG a suitable option for all-optical ternary switching and all-optical memory in the integrated optical circuits.
Vahideh Rezaie Kahkhaie, Mohammad Hassan Yousefi, Seyyed Mohammad Reza Darbany, Abolhassan Mobashery,
Volume 13, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 13, No 2, Summer-Fall 2019)
Abstract
stabilized Ag Nanoparticles (NPs) were synthesized using Lee-Meisel method under three different conditions in an oil bath. UV-Vis spectroscopy of the Ag NPs showed a Localized Surface Plasmon (LSP) band around 430 nm, indicating Ag NPs had a size range around 40 nm. To fabricate a surface Enhanced Raman Spectroscopy (SERS) substrate, LSP properties of Ag NPs was employed with the goal of detecting Rhodamine 6G dye. SERS spectrum was recorded by using 180 degrees, back-scatter Raman configuration in a custom-made mount. The results showed that ideal Ag NPs agglomeration condition had been achieved by applying centrifuging process and due to this, adding NaCl salt to the SERS substrate was found to be unnecessary. The optimum rate of tri-sodium citrate versus silver nitrate and its influence on UV-Vis and SERS spectra was determined. It was understood that in order to obtain a uniform SERS intensity profile, employing a heater-stirrer instead of an oil bath alongside controlling the atmospheric condition and also drying the substrate in the Argon gas medium are the most necessary conditions for Ag NPs synthesize. The novelty point is obtained when SERS of R6G on a certain substrate, immediately after fabrication and after one month, were compared with a bare R6G dye substrate which, have revealed exceptional performance.
