Showing 11 results for Scattering
H. Pakarzadeh, A. Zakery,
Volume 4, Issue 1 (1-2010)
Abstract
In this paper, by including Raman scattering in the coupled-mode equations, the scalar modulation instability in photonic crystal fibers is investigated. The evolution of the pump, Stokes and anti-Stokes waves along the fiber as well as the conversion efficiency for two cases, with and without Raman effect, are studied. The effect of anti-Stokes seed and the pump depletion on the evolution of Stokes wave is also considered. Moreover, the parametric gain when it is affected by Raman gain is dealt with. The results show that it is important to take into account Raman scattering, especially for wide-bandwidth parametric amplifiers which results in an asymmetric spectrum and more amplification of the Stokes wave.
Mohammad Ali Ansari,
Volume 6, Issue 2 (10-2012)
Abstract
In this paper, the evaluation of time profile of a femtosecond pulse laser propagated through biological tissues is studied. The majority of the biological tissues with a high scattering anisotropy must be considered as turbid media, that their optical responses are complicated. To study the propagation of ultra-short pulse in turbid media, the diffuse equation is used. In this study, the analytical and numerical solution for diffuse equation is investigated. The numerical method is based on Boundary Integral method (BIM), and also, the time evaluation of propagating pulse is studied.
Dr. Roghaieh Parvizi,
Volume 6, Issue 2 (10-2012)
Abstract
we investigate the temperature-dependences of the Brillouin frequency shift in three different kind of single-mode fibers using a heterodyne method for sensing temperature. Positive dependences coefficients of 0.77, 0.56 and 1.45MHz/0C are demonstrated for 25 km long single-mode fiber, 10 km long non-zero dispersion shifted fiber and 100 m photonic crystal fiber, respectively. The results indicate that microstructure fibers with a partially Ge-doped small core have great potential for fiber Brillouin distributed sensing.
Dr Roghaieh Parvizi,
Volume 7, Issue 1 (6-2013)
Abstract
We have investigated and developed a theoretical approach to explore stimulated Brillouin scattering (SBS) phenomena in single mode fiber. SBS happening threshold power condition has been studied in terms of fiber parameters and input pump power. To assess threshold power precisely, the pump depletion effect and fiber loss has been included by employing 1% criterion. The threshold exponential gain Gth can be anticipated by this simulation which strongly depends on the fiber length Brillouin gain content and effective area. The value of Gth is not a constant as usually assumed in the literature and its value is 4 for the longer lengths and between 10 and 18 is for relatively shorter lengths. This simulation can anticipate the optimum length of fiber against the every launched pump power to generate SBS effect.
Prof. Rasoul Malekfar, Mr. Akbar Cheraghi,
Volume 8, Issue 1 (1-2014)
Abstract
Nanocrystallite α-cordierite glass-ceramics are synthesized using a modified Pechini method. The structural and lattice modes of the products are investigated via XRD and Micro Raman back-scattering spectroscopy. The Debye-Scherrer formula is used to confirm the grain sizes estimated by the SEM slides. Dielectric coefficients calculation and DTA analysis are used to study the synthesized nanocrystallites properties.
Prof. Rasoul Malekfar, Ms. Marziye Parishani, Mr. Akbar Cheraghi,
Volume 9, Issue 2 (11-2015)
Abstract
Ni ferrite crystalline material is synthesized using a sol-gel method at two different temperatures. The vibrational and stretching modes, crystalline phase, size distribution and morphology of the products are investigated via Raman back-scattering and Fourier transform infrared (FTIR) spectroscopy, XRD and FESEM, respectively. Vibrational modes of spinel ferrite are observed at Raman and FTIR spectra. Group theory phonon analysis reveals five Raman active modes for the molecular system. However, in the present investigation, four Raman modes are identified in the inelastic Stokes region of the recorded Raman scattering spectra. Also, the results of the present study reveals that the sizes of the synthesized particles were increased and crystalline structures were completed by increasing the temperature.
Mahmoud Zolfaghari,
Volume 13, Issue 2 (12-2019)
Abstract
A comparative study of anti-resonance effects in InSe and InSe doped with GaS, using the resonant Raman spectroscopy is presented. The nonpolar optical phonon of

symmetry in InSe exhibits a pronounced decrease in the Raman cross-section at excitation energy 2.585 eV. In InSe doped with GaS samples, it is found that the anti-resonance behavior decreases as doping contents are increased. To account these observations, a model is applied to explain and interpret the Raman intensity evolution versus incident photon energy. The agreement between theory and experiment is good.
Peymaneh Rafieipour, Abbas Ghasempour Ardakani,
Volume 14, Issue 2 (12-2020)
Abstract
The random laser (RL) emission characteristics can be improved by many different routes including either the material processing or optimizing the concentration of the relevant constituents. These routes can be very hard and even not practical in many cases, leaving us with the search of new schemes for the externally improvement of the random laser performance. In this paper, we suggest a simple approach for the externally enhancement of the random laser emission properties that can be applied in any designed transparent random lasing structures with single mode or multi-mode emission. This approach is based on using an adhesive tape in order to introduce an external scattering medium to the lasing structure and also return back the amplified leaking photons. For our investigated sample with nonresonant feedback, it is demonstrated that the emission intensity can be increased by a factor of 4.2 and the random laser threshold can be decreased by a factor of 1.8.
Parisa Khajegi, Majid Rashidi-Huyeh,
Volume 15, Issue 1 (1-2021)
Abstract
Nobel metal nanoparticles (NPs) are widely used in various applications including optical and biological sensors, biomedicine, photocatalysts, electronics, and photovoltaic cells. The optical properties of gold NPs are surveyed in this paper under the Localized Surface Plasmon Resonance (LSPR) effect, which increases the light absorption and scattering at the LSPR wavelength. This LSPR frequency depends on various factors, including the shape and size of the particles as well as incident electromagnetic polarization. Here, the optical response of gold NPs with different shapes and sizes are investigated using the finite element method (FEM). The results show that the bandwidth, amplitude, and LSPR wavelength depend on the shape and dimensions of the NPs as well as the polarization of the incident light. The LSPR wavelength changes from 500 to 650 nm for different shapes of the gold NPs including sphere, octahedral, cube, ellipsoid, triangle, and with identical volume. To study the NP size effect on the optical properties, the absorption and scattering cross-sections (CSs) are also investigated for different sizes of NPs. The results show a redshift in the LSPR wavelength by increasing the NP size.
Dr. Morteza Janfaza, Dr. Hamed Moradi, Mr. Morteza Maleki,
Volume 15, Issue 2 (7-2021)
Abstract
Graphene and molybdenum disulfide (MoS2), as two of the most attractive two-dimensional (2D) materials, are used to improve the temperature and strain sensing responses of the few-mode fibers (FMFs). The temperature and strain effects are detected based on distributed optical fiber sensors equations, where the Brillouin scattering (BS) is investigated for the FMF tapered region. For this purpose, the 2D materials were assumed as cover layers on the tapered FMF to enhance its sensitivity. Graphene and MoS2 are used as the cover layer on the FMF cladding at a distance of 10 μm from the core, and the impact of the number of material layers is investigated. By increasing the graphene layers, the temperature and strain sensitivities increase (3% and 16%, respectively) due to the rise of the inter-modal interference of the FMF. Moreover, the increasing of the MoS2 layer number improves the temperature sensitivity by 28% but shows a lower impact on strain sensitivity (about 13%). The advantage of MoS2 with respect to graphene originates from the imaginary part of the refractive index of graphene (assumed with chemical potential of 0.4 eV at the working wavelength of 1550 nm), which leads to a lower effective index of the tapered region, hence lower sensitivities. This sensitivity enhancement can improve the performance of the BS-based sensors for local detection of the parameters under-investigation in multi-parameter sensors.
Zoha Ameri, Fazel Jahangiri,
Volume 16, Issue 2 (7-2022)
Abstract
Using terahertz waves for intra-body communications between nanomachines is associated with dissipation during propagation, of which scattering is one of the most important effects. In this paper, scattering path loss with two different assumptions of air-enclosed and tissue-enclosed in subcutaneous fat is calculated and compared. The results show that for TM polarization, air-enclosed assumption gives smaller and greater scattering loss for frequencies less and bigger than 0.26 THz. The greatest difference between air-enclosed and tissue-enclosed results is observed for TE polarization at the approximate frequency of 0.4 THz.