International Journal of

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In this article, the impact of input pump profile on the gain spectrum as well as the saturation behavior of one-pump fiber optical parametric amplifiers (FOPAs) is investigated. Since in practical circumstances, pump sources used for FOPAs have Lorentz-Gaussian profile instead of Gaussian, a more realistic case is considered for simulating FOPAs in this article. The results of simulations for the Gaussian and the Lorentz-Gaussian profiles show that a higher gain and a faster saturation are obtained for a pump with a Lorentz-Gaussian profile than a Gaussian pump. The results of this article provide a more realistic model for FOPAs.

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One concern in using photonic band-gap fiber (PBGF) as a gas sensor is the response time. In this type of the gas sensors, response time is the time required for gas to diffuse into the hollow-core. So considering a large hollow-core PBGF (HC-PBGF), the response time can be significantly reduced. But in the large HC-PBGF, the fundamental issue is the presence of higher order modes (HOMs). Sometimes the leakage loss of the HOMs is comparable to those of the fundamental mode. So in order to suppression of the HOMs, six small-cores with reasonable radius were incorporated in the cladding of the proposed fiber. In other words, due to resonant-coupling mechanism of HOMs in central core with fundamental mode of outer cores, the leakage loss of the HOMs can be enhanced. Considering optimum parameters such as hollow-core radius, air filling factor, and the distance between the center-to-center of two adjacent air holes, the small-cores are surface-mode-free and proposed structure can be considered effectively single mode. So at the wavelength of 1550nm the relative sensitivity of the gas sensor was improved to 97%. The results proved the ability of proposed design as a sensitive gas sensor with low response time.

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In this paper, the gain spectrum and the saturation behavior of one-pump fiber optical parametric amplifiers (1-P FOPAs) are investigated by taking into account the fourth-order dispersion coefficient b₄ in the analysis. The results show that it is necessary to consider b₄ in the analysis when the wavelength difference between the signal and pump waves is large enough and/or whenever the pump wavelength approaches to the zero-dispersion wavelength (ZDW) of the fiber. Also, it is shown that by increasing the value of b₄, the gain value is increased and the saturation power is decreased. Finally, the simulation results are compared with the available experimental data and a very good agreement is obtained.

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Experimental and theoretical absorption spectra of [2-[2-[4-(dimethylamino) phenyl]ethenyl]-6-methyl-4H- pyran-4-ylidene]-propanedinitrile (DCM) have been studied. UV-Visible (UV-Vis.) absorption spectrum of DCM has been reported after its synthesis. Two relatively intense peaks appeared at 473 and 362 nm respectively. A theoretical investigation on the electronic structure of DCM is presented in an effort to rationalize our experimental results. Theoretical results have been obtained with a polarizable continuum model time-dependent density functional theory (PCM-TD-DFT) approach. At first, a vast functional benchmark has been performed to determine a suitable approach for determination of electronic structure and UV-Vis. absorption spectrum of DCM. In a second step, we evaluated the impact of the atomic basis set on the electronic transition energies using a large panel of Pople’s basis sets ,up to the 6-31+G(3df,2p) and also a correlation consistent basis set, cc-pVTZ. It turns out that the selected basis set has a relatively finite influence on the calculated electronic transition energies as well as the topology of the absorption shape, but both are significantly affected by the chosen functional. In the present case, no single functional simultaneously provides highly accurate positions and intensities of the different bands, but mPW1PBE and mPW1LYP appear to be a good compromise. The mPW1PBE along with medium basis sets produced both absorption bands with maximum peaks about 463 and 346 nm. At all stages, ethanol has been chosen as a solvent environment. To improve the accuracy of first electronic excitation, a complete analysis of the origin of the band shape using TD-DFT vibrational couplings was performed. Finally the computed transition energy was corrected to 472 nm which was in excellent agreement with experiments.

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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.

 

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This paper describes the second-order coherence degree of photons produced in SPDC. First, the nonlinear BBO crystal generates the twin correlated signal and idler photons in the experimental setup. Then, g² (0) is obtained experimentally via Hanbury Brown-Twiss set-up for investigation of the light source nature. The results show this value is less than 1 which verifies the generated photons are in the heralded single photon (HSP) regime.

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Background: Multiple Sclerosis (MS) is a chronic immune-mediated disease affecting the central nervous system, leading to various disturbances, including visual impairment. Early and accurate diagnosis of MS is critical for effective treatment and management. Scanning Laser Ophthalmoscopy (SLO) is a non-invasive technique that provides high-quality retinal images, serving as a promising resource for the early detection of MS. This research investigates a vessel-based approach for MS detection in SLO images using Long Short-Term Memory (LSTM) networks.
Material and Methods: A total of 106 Healthy Controls (HCs) and 39 MS patients (78 eyes) were enrolled. After implementing quality control measures and removing poor-quality or damaged images, the research utilized a total of 265 photos (73 MS and 192 HC). An approach for the early detection of MS in SLO images using LSTM network is introduced. This approach involves two steps: 1.It involves pre-processing and extracting vessels and then pre-training a deep neural network using the source dataset, and 2. tuning the network on the target dataset of SLO images.
The significance of vessel segmentation in MS detection is examined, and the application of the proposed method in improving diagnostic models is explored. The proposed approach achieves an accuracy rate of 97.44% when evaluated on a test dataset consisting of SLO pictures.
Through experiments on SLO datasets and employing the proposed vessel-based approach with LSTM, empirical results demonstrate that this approach contributes to the early detection of MS with high accuracy. These models exhibit the capability to accurately detect the disease with high precision and appropriate sensitivity.
 

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The spatial self-phase modulation (SSPM) method was used to study the nonlinear optical responses of hydraulic oil containing dispersed nanosheets of reduced graphene oxide (rGO), hydroxylated rGO (rGO-OH), and carboxylated rGO (rGO-COOH). The intensity-dependent number of observed symmetric diffraction rings was analyzed to estimate the samples' thermally induced nonlinear refractive indexes and lead to estimated thermo-optical coefficients. Based on the observed symmetric diffraction rings, the nonlinear refraction coefficient and thermo-optical coefficient of samples were estimated to be in the order of magnitude of 10^-6 cm²/W and 10^-2 K^-1, respectively. The results indicated that the presence of rGO derivatives significantly enhanced the optical nonlinearity of hydraulic oil.

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In this research, palladium nanoparticles (Pd NPs) were first synthesized using laser ablation in the deionized (DI) water environment. Also, metal-organic framework (MOF) was produced using the solvothermal method at a temperature of 150°C. To accumulate Pd NPs on the synthesized MOF, ultrasonic and magnetic stirring methods were used. Different analytical methods were used to investigate the structure and morphology of the synthesized nanocomposite. Also, the sensitivity of the synthesized nanocomposite to ethanol and methanol organic vapors was investigated. The results showed an increase in the response of the MOF in the presence of nanoparticles.