Arashmid Nahal

Bio: Arashmid Nahal is an academic researcher from University of Tehran. The author has contributed to research in topics: Grating & Polarization (waves). The author has an hindex of 10, co-authored 29 publications receiving 246 citations. Previous affiliations of Arashmid Nahal include International Centre for Theoretical Physics & Institute for Advanced Studies in Basic Sciences.

High precision refractometry based on Fresnel diffraction from phase plates

Abstract: When a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic parallel beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The visibility of the diffraction fringes varies periodically with changes in incident angle. The visibility period depends on the plate thickness and the refractive indices of the plate and the surrounding medium. Plotting the phase change versus incident angle or counting the visibility repetition in an incident-angle interval provides, for a given plate thickness, the refractive index of the plate very accurately. It is shown here that the refractive index of a plate can be determined without knowing the plate thickness. Therefore, the technique can be utilized for measuring plate thickness with high precision. In addition, by installing a plate with known refractive index in a rectangular cell filled with a liquid and following the described procedures, the refractive index of the liquid is obtained. The technique is applied to measure the refractive indices of a glass slide, distilled water, and ethanol. The potential and merits of the technique are also discussed.

Photothermal-induced dichroism and micro-cluster formation in Ag + -doped glasses

Abstract: In this paper, we report the observation of an induced dichroism in an ionic silver cluster-doped glass, under the interaction of a CW high-power (Pmax∼8 W) Ar+ laser beam. It is found that, as a result of the photo-thermal interaction, a dichroism due to the formation of chain-like silver clusters is induced. Because of the electromagnetic interaction, the orientation of these chain-like structures is related, in general, to the direction of the laser beam polarization. The effect is seen in the regime, where the laser beam power is increased rapidly. In this regime micrometer size (d∼2 μm) clusters are generated on the surface of the sample. In this report, we discuss the production of such large silver clusters as a result of changing of the initial ionic clusters to the neutral ones and then aggregation of the generated small neutral clusters under the supersaturation condition.

Laser-induced dendritic microstructures on the surface of Ag+-doped glass

Abstract: Fractal dendritic silver microstructures are observed on the surface of the Ag+-doped glasses as a result of a photothermal interaction with a focused multiline cw high-power (Pmax=8 W) Ag+ laser beam. It is found that evolution of the structures depends on the exposure time and also on the concentration of the silver ions in the sample. The fractal dimension of the generated dendritic microstructures increases with the exposure time. Instability of the contact line of the molten silver flow toward the periphery of the interaction area is discussed as a result of the temperature gradient, due to the Gaussian intensity distribution across the laser beam.

Study of spontaneous grating formation in photosensitive films by means of small-angle scattering

Abstract: The formation of spontaneous gratings induced by a polarized laser beam in thin photosensitive AgCl waveguide films, doped by Ag, was studied by means of small-angle scattering. It is shown that small-angle scattering is determined by the domain structure of the spontaneous gratings and arises because of the re-emission of waveguide modes by neighbouring domains. The instability and reorganization of the gratings have been found and studied upon the change of the azimuth of the laser beam polarization.

Integrated optics

Abstract: In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Abstract: Integrated OpticsIntegrated Optics and Optical SwitchingIntegrated Optics: Theory and TechnologyIntroduction to Integrated OpticsElements of Photonics, Volume IIEncyclopedic Handbook of Integrated OpticsOptical Fiber Communication Conference and Sixth International Conference on Integrated Optics and Optical Fiber CommunicationIntegrated Optical Circuits and ComponentsIntegrated OpticsAdvances in Integrated OpticsFundamentals of Fibre Optics in Telecommunication and Sensor SystemsIntegrated OpticsIntegrated Optics, Microstructures, and SensorsMulti-Photon Quantum Information Science and Technology in Integrated OpticsIntegrated Optics, Microstructures, and SensorsIntegrated PhotonicsOptics and LasersA Consideration of Possibilities and Difficulties in Passive Circuits in Integrated OpticsSemiconductor Integrated Optics for Switching LightIntegrated OpticsIntegrated OpticsAdvanced Materials for Integrated Optical WaveguidesIntroduction to Semiconductor Integrated OpticsCommercial Integrated OpticsIntegrated OpticsIntegrated Optics and MicrostructuresElectromagnetic Principles of Integrated OpticsIntegrated Optics and Micro-Optics with PolymersIntroduction to Integrated OpticsIntegrated Optics SuppliersIntegrated Optics: Theory and TechnologyDiffractive Optics and Optical MicrosystemsIntegrated Optics and OptoelectronicsFiber and Integrated OpticsEncyclopedic Handbook of Integrated OpticsFirst International Conference on Integrated Optical Circuit EngineeringIntegrated OpticsIon Exchange in Single Crystals for Integrated Optics and OptoelectronicsOptics and LasersIntegrated Optics: Devices, Materials, and Technologies

Synthesis of silver/montmorillonite nanocomposites using γ-irradiation

Abstract: Silver nanoparticles (Ag-NPs) were synthesized into the interlamellar space of montmorillonite (MMT) by using the γ-irradiation technique in the absence of any reducing agent or heat treatment. Silver nitrate and γ-irradiation were used as the silver precursor and physical reducing agent in MMT as a solid support. The MMT was suspended in the aqueous AgNO3 solution, and after the absorption of silver ions, Ag+ was reduced using the γ-irradiation technique. The properties of Ag/MMT nanocomposites and the diameters of Ag-NPs were studied as a function of γ-irradiation doses. The interlamellar space limited particle growth (d-spacing [ds] = 1.24–1.42 nm); powder X-ray diffraction and transmission electron microscopy (TEM) measurements showed the production of face-centered cubic Ag-NPs with a mean diameter of about 21.57–30.63 nm. Scanning electron microscopy images indicated that there were structure changes between the initial MMT and Ag/MMT nanocomposites under the increased doses of γ-irradiation. Furthermore, energy dispersive X-ray fluorescence spectra for the MMT and Ag/ MMT nanocomposites confirmed the presence of elemental compounds in MMT and Ag-NPs. The results from ultraviolet-visible spectroscopy and TEM demonstrated that increasing the γ-irradiation dose enhanced the concentration of Ag-NPs. In addition, the particle size of the Ag-NPs gradually increased from 1 to 20 kGy. When the γ-irradiation dose increased from 20 to 40 kGy, the particle diameters decreased suddenly as a result of the induced fragmentation of Ag-NPs. Thus, Fourier transform infrared spectroscopy suggested that the interactions between Ag-NPs with the surface of MMT were weak due to the presence of van der Waals interactions. The synthesized Ag/MMT suspension was found to be stable over a long period of time (ie, more than 3 months) without any sign of precipitation.

Optical trapping and light-induced agglomeration of gold nanoparticle aggregates

Abstract: This paper demonstrates the optical trapping of micron-sized gold nanoparticle aggregates (GNAs) with a ${\mathrm{TEM}}_{00}$ mode laser at $532\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and reports the observation of an unusual light-induced agglomeration phenomenon that occurs besides the trapping of the GNAs. The observed agglomerate has a $60--100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ donut-shaped metal microstructure with the rate of formation dependent on the laser power used. Citrate capped gold nanoparticles also show light-induced agglomeration, yielding different sized microstructures from those produced with GNAs. While the observed trapping can be explained by a model including the optical radiation and radiometric forces, the light-induced agglomeration cannot be explained by these two forces alone as the size of the agglomerate is much greater than the waist of the Gaussian beam used in the optical trapping. We attribute the additional cause of the light-induced agglomeration to ion detachment from the surface of the nanoparticles (aggregates) due to light illumination or heating. This is supported by the observation of reversible electrical conductivity changes of the solution of the nanoparticles (aggregates) upon laser illumination or direct heating. Light-induced agglomeration can be useful in the design and fabrication of microstructures from nanomaterials for various device applications.