Showing 8 results for Malekfar
Mrs. Hajar Ghanbari, Dr. Rasoul Sarraf-Mamoory, Prof. Jamshid Sabbagh Zadeh, Mr. Ali Chehrghani, Dr. Rasoul Malekfar,
Volume 7, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 7, No 2, Summer-Fall 2013)
Abstract
In this study, Highly Oriented Pyrolytic Graphite was ablated in various polar and nonpolar solvents by Q-switched neodymium: yttrium-aluminum-garnet laser (wavelength=1064 nm, frequency=2 kHz, pulse duration=240 ns). Then, the products were examined using Scanning Electron Microscopy and UV-Vis spectroscopy. The images showed that different carbon structures such as cauliflower-like structures in benzene, spiral integrated forms in toluene, organic integrated networks in hexane, and nanoparticles in ethanol were formed. In n-methyl-2-pyrrolidone (NMP), sheets and bulk deformed structures were seen. Also, in Dimethylacetamide, particles in different stages of growth could be detected. The nonlinear optical absorption (NLA) behaviors of the products were investigated by exposing them to a 532 nm nanosecond laser using the Z-scan technique. The saturated NLA coefficient, obtained from structures of NMP and hexane-based synthesized samples, are 1.1×10-8 and 2.4×10-8 cm W-1, respectively. The saturable absorption responses of these samples were switched to the reverse saturable absorption responses in the other synthesis mediums. The maximum nonlinear absorption coefficient of 10.2×10-8 cm W 1 was measured for spiral integrated superstructures, produced in the toluene medium.
Prof. Rasoul Malekfar, Mr. Akbar Cheraghi,
Volume 8, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 8, No 1, Winter-Spring 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.
Mrs Marzieh Nadafan, Prof. Rasoul Malekfar, Mrs. Zahra Dehghani,
Volume 8, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 8, No 2, Summer-Fall 2014)
Abstract
Polyurethane closed cell (PUCC)/SiO2 nanocomposites have been prepared by using in situ polymerization approach. The third-order optical nonlinearities of PUCC/SiO2 nanocomposites, dissolved in DMF are characterized by Z-scan technique at the measurement wavelength of 532 nm. The nonlinear refractive (NLR) indices and nonlinear absorption (NLA) coefficients of samples were calculated from closed and open aperture Z-scan in the order of 10-8 with negative sign and 10-5 , respectively. The origin of optical nonlinearity in this case may be attributed due to the presence of two photon absorption (TPA) effect. The synthesized samples were examined by optical microscopy, SEM imaging and Raman spectroscopy. All the results related to NLO properties, suggest that PUCC/SiO2 may be a promising candidate for the application to optical limiting in the visible region.
Prof. Rasoul Malekfar, Ms. Marziye Parishani, Mr. Akbar Cheraghi,
Volume 9, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 9, No 2, Summer-Fall 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.
Ms Fatemeh Kazemizadeh, Prof. Rasoul Malekfar, Dr. Fatemeh Shahshahani,
Volume 10, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 10, No 2, Summer-Fall 2016)
Abstract
The present article is concerned with an analytical solution for some parts of rare earth doped fiber laser equations. The presented model is valid for both four and three-level fiber lasers consisting high reflectivity mirrors. A typical method to obtain initial value in the numerical solutions of fiber laser equations is shooting method, which is based on an iteration process. Whereas this standard method needs to repeat computational loops to correct an initial guess value in order to satisfy the boundary conditions, which is a time consuming task.
The model and its analytical solution, presented in this article, and the accuracy of the obtained values reveals that the method significantly reduces the time computation. The proposed method has been used for an erbium doped fiber laser and it shows that when the reflectivity of mirrors is more than 0.6 (60%), the calculated results are in agreement with the results of standard numerical methods and the error is less than 10 percent.
Hadi Zarei, Rasoul Malekfar,
Volume 12, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 12, No 1, Winter-Spring 2018)
Abstract
In this paper, tetragonal chalcopyrite (CIGS) Cu(InxGa1-x)Se2 with x=0, 0.5, 0.8, 1 are synthesized by heating-up method. These nanoparticle structures differ in morphology and absorption properties due to the synthesis temperatures of 250, 255, 260, 265, 270 and 280 ºC, and gallium molar ratio over the total gallium and indium contents. These features are studied using scanning electron microscope, X-ray diffraction and absorption spectroscopy in visible, ultra-violet and near-infrared wavelengths. Results indicate that by increasing gallium content, absorption edge rises toward the visible light. Any modification in the absorption edge changes the band gap and as a result the energy gap and the absorption of cell increases considerably. Also in the heating-up method, increasing the reaction temperature improves nanoparticles crystallites. This leads the absorption improvement and higher cells efficiency. Produced nanoparticles are spherical shape with are varying the diameter around 30-80 nm.
Hamid Motahari, Rasoul Malekfar,
Volume 13, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 13, No 1, Winter-Spring 2019)
Abstract
Laser micro-Raman spectroscopy is an ideal tool for assessment and characterization of various types of carbon-based materials. Due to its special optical properties (CrN) coated stainless steel substrates. NCD films have been investigated by laser micro-Raman spectroscopy. The fingerprint of diamond based materials is in the spectral region of 1000-1600 cm-1 in the first order of Raman scattering spectrum. By using of Gaussian peak fitting, characteristic peaks in the micro-Raman spectrum of NCD films including diamond peak (D), NCD features, a vibrational density of states (VDOS) in the ultra-nanocrystalline diamond (UNCD) clusters, graphitic (G) band and disordered (D) band can be assigned. These peaks and bands can be broadened, shifted in the spectral region or may be eliminated from the spectra due to NCD films grain sizes, synthesis conditions and other surface effects on the crystals. The increasing grain sizes to about 100 nm and faceted grains as the most important parameters can promote the diamond Raman signal, eliminate the VDOS, UNCD and even NCD features in the Raman spectrum.
Bahareh Morovvati , Rasoul Malekfar,
Volume 13, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 13, No 2, Summer-Fall 2019)
Abstract
The active substrates in surface enhanced Raman scattering (SERS) spectroscopy were prepared through self-assembly of nanoparticles on functionalized glasses. Colloidal silver nanoparticles (Ag NPs) were prepared chemically in two different sizes by reduction of AgNO3 using trisodium citrate and sodium borohydride. Gold–silver core–shell nanoparticles were also prepared to compare between the optical behaviors of their silver shell and Ag NPs. Absorption spectra of nanoparticles were measured by ultraviolet–visible (UV–Vis.) spectroscopy, and their approximate sizes were determined by dynamic light scattering (DLS). The core–shell nanoparticles were approximately the same size as the largest Ag NPs (35 nm) and had the same maximum absorption wavelength. The potential of these substrates for detection applications was investigated with 1 M and 0.1 mM solutions of Raman-active molecule of crystal violet (CV) dye. The Raman enhancement signal was recorded for 0.1 mM solution with 532 nm laser wavelength, and the obtained spectra enhancement factor (EF) was calculated. EF values indicated that although the silver and gold–silver core–shell nanoparticles had the same surface plasmon resonance, the substrate with smaller Ag NPs had the highest enhancement factor compared to other substrates, which was 9.5´103, and the core–shell substrate even had a slightly lower enhancement factor in compare with the large Ag NPs.
