نشریه اپتوالکترونیک
سال سوم شماره 2 (پیاپی 9، بهار و تابستان 1400)

In the framework of the nanoplasma model, the interaction of intense femtosecond laser pulses with the nanometer sized neon clusters is studied. In this simulation, the expansion of a neon cluster irradiated by an intense femtosecond laser pulse with respect to ionization and heating process is investigated. The effects of laser intensity, pulse duration time on the evolution of ion and electron density, average state charge, and radius of cluster, electron temperature and  hydrodynamic pressure are studied. The simulation results show that as laser intensity and pulse duration increase, ion density in the cluster is decreased while cluster radius and average charge state are increased. Also, by increasing laser intensity, the electron density, temperature, and electron hydrodynamic pressure increase.

In the present work, by using the first-princilpes calculations within the density functional theory framework, the structural, electronic and magnetic properties of AlCu2Mn and CuHg2Ti crystal structures of the full-Heusler compound Co2TaGa were studied. The results indicate that the ground state of this compound is AlCu2Mn-Type with ferromagnetic order and a magnetic moment of 2.00µB. The results of electronic structure calculations show that the ground state has a half-metallic nature with an energy gap of 0.48eV and 100% spin polarization. According to the results of this study, the Co2TaGa Heusler compound can be recommended as a novel material for future aims in spintronic applications.

In this study, at first, reduced graphene oxide (RGO) has been synthesized by Hummers’ method and then RGO/SiO2 binary compound and finally RGO/SiO2/Fe3O4 ternary compound were synthesized by co-precipitation method. Magnetic properties of nanoparticles were investigated by VSM and their morphology was studied by SEM. Crystalline structure and functional groups and bonds analyzed by XRD and FTIR, respectively. The size of nanoparticles of iron-oxide, reduced graphene oxide/silicon dioxide, and iron-oxide/reduced graphene oxide/silicon-dioxide was respectively estimated as 11.9, 10.44, and 11.17 nm. Saturation magnetization of iron-oxide and ternary nanocomposite are obtained as 72 emu/g and 31.2 emu/g respectively that shows that by covering iron-oxide nanoparticles with non-magnetic materials, the obtained saturation magnetization decreases. Photocatalytic activity of the synthesized RGO/SiO2/Fe3O4 was evaluated in the degradation of methyl orange dye (MO) as a pollutant under irradiation of ultraviolet light. Photocatalytic efficiency 51.59% was obtained. RGO/SiO2/Fe3O4 composite with capable of photocatalytic activity with efficiency of 51.59 % , was evaluated as a pollutant in the degradation of methyl orange (MO).

The aim of this experimental study is investigating the interactional effects of molecular surrounding environment on its third order nonlinear optical properties. In this case, the nonlinear behavior of an azo dye in different concentrations of three various groups of solvents with strong hydrogen bond donor and acceptor ability and weak tendency for formation of hydrogen bonds  was investigated. Therefore, azo dye solutions with different polarity and concentrations were placed in open aperture Z-scan setup. According to the results, value of nonlinear absorption coefficients and type of involved third order nonlinear absorption phenomena depend on the concentration and intractional properties of molecular surrounding environment. In this case, the opposite behavior of azo dye solutions in two different concentrations are related to different molecular interactions.Under this condition, in low concentrations, the nonlinear absorption coefficients indicate high value in environments with strong hydrogen bond donor ability such as methanol. In high concentrations, environments with strong hydrogen bond acceptor ability such as DMF lead to increasing the nonlinear absorption coefficients. Therefore, by changing the concentration and molecular interactions, controlling the nonlinear behavior of optical material is possible. Therfore, the investigated azo dye with controllable saturable and reverse saturable absorption properties can play an important role in designing optical devices.

In this study, hydrothermal method was used to synthesize Pure molybdenum disulfide and doped molybdenum disulfide with copper. XRD, FTIR, UV-VIS, TEM analysis was used to identify the structural and morphological properties of the samples. The Fourier transform infrared spectrum well showed the formation of MoS2 bonds as well as doped MoS2. The results of X-ray diffraction patterns confirmed the crystalline structure and the single phase of synthesized samples, and also the boradening of the XRD peaks and TEM images indicated the formation of nano layerd structure of MoS2 and doped MoS2. It can be concluded that by placing copper in the crystal structure (Which is located in the interstitial site), the location of the peaks has been moved only to a small extent .The photocatalytic activity of nanostructures in methylene blue color degradation by stimulating ultraviolet light was investigated, which is about 95 percent  by doped sample with copper.

Plasmonic science has been noticed by researchers, with the increasing development of knowledge and technology in nanometer dimensions. Gold and silver ellipsoidal metal nanoparticles can exhibit unique optical properties due to their ellipsoidal structure with special symmetry and are therefore very suitable options for use in the new generation of optical sensors. Therefore, in this work, the optical properties of gold and silver metal ellipsoidal nanoparticles were simulated in different dielectric environments as well as in different sizes with using the MATLAB program. The results show that with increasing the diameter of the ellipsoidal nanoparticles (flattened state) of gold, the peak of the absorption, scattering and extinction spectra increases, which can be a good option for plasmonic applications and optical devices. Also, compared to ellipsoidal nanoparticles (elongated state), the absorption and extinction efficiencies intensity are higher and the scattering peak appears at higher wavelengths, while for the elongated state, ellipsoidal nanoparticles do not show such a case. Due to the small number of conducting electrons in nanoparticles and the homogeneous displacement of free charges within the nanoparticle, it is only the bipolar distribution of free charges that causes single peaks in the extinction and absorption spectrum of ellipsoidal gold and silver nanoparticles.

In this paper, a complete study has been done in the field of optical crystal logic gates. Also, several gates have been designed and simulated in the ultraviolet and infrared wavelengths (wavelength range of 1500 nm). In all cases, the boundary conditions of the complete absorber are considered. First, the method of constructing a waveguide is presented, which is used to construct a divider. Then, with the help of this waveguide, an amplifier loop is designed. In this simulation, an attempt has been made to reduce the gate operator time. For this purpose, we have used dividers as a combination of wave generators in the center of the gate. These gates respond in a very short time, about 0.3 femtoseconds, to incoming light. In the telecommunication area, silicon has been used to build gates. Also, in the center of the gate, the Mach Zander interferometer is used instead of the power combiner, which increases the response time; In this range, the dispersion of silicon material is considered. Another advantage of these gates is the input and output on one side, which can be used in integrated circuits. Powerful RSOFT software has been used to simulate the gate and to observe and analyze the results. Also, the band gap calculations of the PWE flat wave expansion method have been performed with the same software, and in the gate output wavelength calculations, the time domain finite difference method of FDTD has been used.

The operation principle of calorimeters used for dosimetry of ionizing radiations is based on measuring the induced temperature difference in the adsorbent due to thermal energy deposition of the ionization radiation. In recent years, one of these methods has been the holographic optical calorimetry by laser beams. One of the problems that affect the response accuracy of the calorimeters is the heat transfer phenomenon in the adsorbent material. This phenomenon affects the measurement accuracy of the absorbed dose. In this work, using numerical coding in the FORTRAN environment, the dose profile change due to heat transfer effects in the PMMA tissue-equivalent material inside a holographic interferometry calorimeter has been investigated and the results have been compared with the finite element method results.

on density functional theory the electronic, magnetic and optical properties of the Cr2ScSb full-Heusler compound have been investigated. This compound has half-metallic gap of 0.07 eV at equilibrium lattice constant, but there is no band gap in the band structure.Cr2ScSb is stable in ferromagnet state. The total magnetic moment of Cr2ScSb is 4 μ_B and following the Slater-Pauling rule. Results of the investigation of optical properties showed that this compound is a good choice for use as an electromagnetic waves absorbent.

In this study, iron-oxide (magnetite) synthesized by co-precipitation method and binary TiO2-Fe3O4 and ternary rGO-TiO2-Fe3O4 nanocomposites (called GTF) prepared by hydrothermal method. Crystal structure and bonds, studied by X-ray diffraction (XRD) and FTIR analysis respectively. The morphology of samples was studied by SEM. The average size of nanoparticles estimated ~12.3 nm and saturation magnetization of nanocomposites obtained by VSM, was 40.26 emu/g. The photocatalytic activity of synthesized nanocomposites determined by degradation of methyl orange under UV light irradiation. The ternary nanocomposites showed ~98.7 % degradation of methyl orange which has a remarkable improvement compared to TiO2-Fe3O4 binary nanocomposites with 84 % degradation.

We predicted that half-Heusler alloy PtFeBi is a potential candidate for using in spintronic and optoelectronic devices. By using first principle calculations based on density functional theory (DFT) within generalized gradient approximation (GGA), we studied the structural, electronic, magnetic and optical properties of PtFeBi half-Heusler alloy in bulk state and (001) surfaces and for FeBi and PtPt terminations. Spin polarization at Fermi level is -77.7% for bulk and -70.5% and -70.2% for FeBi and PtPt terminatins, respectively. The real part of the dielectric function for the incident light in both the xx and zz directions for energies greater than 8eV for all three terminations is the same, and for energies greater than 15eV they converge to one, indicating that they act as an isotropic insulator. Also, the refractive index for energies greater than 7.5 eV is less than one, indicating super-luminance.

In this paper, we investigate a 1-D ternary photonic crystal (1-DTPC), with symmetric geometry. The defect modes for both TE and TM polarization are investigated by variation of wavelength. In this case, there are two resonant peaks within the photonic bandgap (PBG) which corresponds to the so-called defect mode. In the TE polarization, by increasing the incident angles the defect modes are shifted toward the shorter wavelength, and in the TM polarization shifted toward the larger wavelength. The height of defect modes is not related to the incident angles. By increasing the number of unit cells, the width of the defect modes is decreased and this increase doesn’t influence the position of defect mode. Furthermore, by increasing the refractive index of the defect layer, the defect modes are shifted toward the center of the bandgap for TE and TM polarizations. The defect mode with a shorter wavelength is shifted faster than the defect mode with a larger wavelength. By increasing the thickness of the defect layer, the defect modes are shifted toward the larger wavelength.