In this paper, the theory of the open-aperture (OA) Z-scan experiment was revisited and the classical relationships were developed to achieve a simpler method. As we know, the OA Z-scan method is a common method for calculating the nonlinear absorption coefficient of materials, and it is not only used in nonlinear optics, but has also recently used in chemistry and materials science. However, the use of classical Z-scan relations requires minimal knowledge of coding and numerical fitting, which is usually not possible for many experimenters. The goal of the paper is to achieve a simple but accurate method for calculating the absorption coefficient with the help of a simple flowchart and a few steps using simple formulas. In this article, while revealing new aspects of Z-scan theory, a method was introduced that make the use of Z-scan technique simple and friendly for experimenters in different fields.

In this study, two types of epoxy networks based on diglycidyl ether of bisphenol A (DGEBA) were prepared using 4,4 '-diaminodiphenyl sulfone (DDS) and isophorone diamine (IPD) as curing agents. The modified epoxy networks were subjected to thermal treatment to improve their hardness and structural integrity. Various characterization techniques, including absorption spectroscopy, photoluminescence (PL), infrared spectroscopy (IR), open-aperture Z-scan measurements, field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD), were employed to evaluate the effects of GO-NH incorporation. Open aperture Z-scan experiment was carried out using a violet semiconductor laser with continues wave (CW) beam and the wavelength of 405 nm. Also, the incorporation of piperazine-functionalized graphene oxide (GO-NH) at 0.5 wt% into the DGEBA/IPD system was investigated in order to study the effect of GO-NH on optical properties. The results showed that reverse saturable absorption (RSA) is the dominant nonlinear optical mechanism in the systems. DGEBA/DDS shows stronger RSA in comparison of DGEBA/IPD system. Notably, the addition of GO-NH led to a significant increase in the nonlinear absorption of DGEBA/IPD, indicating enhanced polarization and improved electronic interactions within the epoxy matrix. These findings suggest epoxy systems as suitable materials in optical and photonic applications.

Investigating the effect of laser irradiation during synthesis offers a powerful method for precisely engineering the properties of nanomaterials. In this study, we synthesized carbon quantum dots (CQDs) using a thermal decomposition method under the irradiation of green and blue lasers separately and comprehensively investigated the effect of this approach on their structural, surface chemistry, and linear and nonlinear optical properties. Transmission electron microscopy (TEM) observations clearly revealed that this process leads to the synthesis of anisotropic structures, including elongated nanorods alongside spherical particles. Fourier transform infrared spectroscopy (FTIR) analysis revealed subtle changes in surface hydroxyl groups, indicating surface chemical engineering by laser. In terms of optical properties, ultraviolet–visible (UV–Vis) spectroscopy evaluation showed an increase in absorption. At the same time photoluminescence (PL) analysis indicated a significant increase in emission intensity without a substantial spectral shift after laser irradiation, highlighting improved optical performance. Notably, a new method was used to accurately determine the Cauchy scattering coefficients of CQDs, which accurately characterized the colloidal dispersion behavior. Furthermore, in exploring their nonlinear optical properties, phenomena such as inverse saturable absorption and nonlinear diffraction rings were observed, underscoring the high potential of laser-synthesized CQDs in this domain. This work not only provides an advanced approach to tune the optical properties of CQDs through laser-assisted synthesis but also introduces a unique method for determining their dispersion characteristics, paving the way for their advanced applications in nonlinear optics and photonics.

In this study, carbon quantum dots (CQDs) were synthesized using pyrolysis method and monochromatic LED light sources were used to control the chemical reaction during the synthetic time. Four monochromatic LEDs with different wavelengths (violet, blue, green and red) were used in these synthetic routes. CQDs were characterized using different methods such as visible-ultraviolet spectroscopy (UV–Vis), dynamic light scattering (DLS), photoluminescence spectroscopy (PL), Fourier transform infrared (FTIR), and Transmission electron spectroscopy (TEM). According to different optical properties of the synthesized CQDs, third order nonlinear absorption coefficients of CQDs have been measured using the open aperture Z-scan technique. Experiments with close aperture Z-scan setup led only to dense patterns of diffraction rings. There was a perfect correlation between the data of all experiments where indicates the effect of monochromatic light radiation on the synthesis process is mainly on the loading of surface agents of the CQDs. With the increase in the wavelength of the irradiated light, it has been witnessed the decrease of surface agents as surface agents, the decrease of hydrodynamic diameter, increase of absorption in the visible region, increase of luminescence and its red shift, the granularity of the particles in the TEM images and increase of the nonlinear properties of the resulting nanocolloids. The present study can be a new window towards control and engineering in the synthesis of CQDs with the help of only a monochromatic light source.

In this study, numerical processing is used to simulate the drift velocity of a single charged particle. Based on the fourth-order Runge–Kutta method, a general method was applied for the equations of motion of an ion in perpendicular electric and magnetic fields which computes the particle’s trajectory and drift velocity with high accuracy. This method can be used to obtain any kinds of drift and can be utilized for any variable electric and magnetic fields and predict instable or nonlinear behavior of particles trajectories. Also, the effect of initial position and velocity direction of ions on the trajectories and drifts was studied. Guiding center drifts caused by radial magnetic fields were studied in different conditions and it was found that it induced an extra magnetic field at the field center. As a new result obtained from this method, it was shown that the phase difference between oscillating orthogonal electric and magnetic fields can determine the direction of drift velocity. We also developed this model to simulate the trajectory of an alumina nanoparticle in the colloid in the presence of a magnetic field, for the first time and the effects of gravitational drift on nanoparticles and aggregated particles were studied. Considering that the concepts of particle drift in the magnetic field are used for nanoparticles for the first time, it can open new sights in numerical simulation of magnetic field-nanoparticles interactions.

In this paper, a numerical study has been carried out on the effects of the type of solvent and polydispersity of gold nanoparticles (Au NPs) on the absorption and dispersion spectra of its colloidal solution. A theoretical model has been used in which, in addition to considering surface agents, the effect of solvent and polydispersity of the particles can be applied. Different cases were simulated in which the effect of ethylene and methanol alcohol added to the aqueous solution of Au NPs was studied. The refractive index of the mixed solvent was investigated at different percentages of alcohol and at different temperatures. The effect of these factors on the absorption peak which is a result of localized surface plasmon resonance (LSPR) was investigated and it was observed that increasing the refractive index of the solvent (by adding alcohol) can lead to red-shift of the plasmonic peak and the overall increase in the refractive index. Also, effects of polydispersity on the absorption and dispersion curves were studied. To study the optical scattering of Au nano-colloid, the angular dispersion distribution profiles for different hydrodynamic diameters were calculated using the Discrete Dipole Approximation (DDA) model that clearly showed the effect of the hydrodynamic diameter of the target particles on the scattering patterns. The results of this investigation are very important in the interpretation of the absorption spectra of Au NPs, especially the wavelength and width of the plasmonic peak, and through the study of these spectral characteristics, useful information can be obtained about the surface agents and the solvent, which can open a new aperture to sensor applications of Au NPs, such as optical sensors, biomedical imaging and optical communication technologies. These results can be of interest to experimental researchers working in the field of Au NPs and help to interpret spectral data.

Thermoluminescence dosimeters (TLDs) are widely used for radiation dose measurement in various applications, including radiation protection, radiotherapy, and diagnostic radiology. Therefore, efforts to improve TLD response and reduce uncertainty in measurements are highly valuable. This study aims to evaluate the effect of adding silver (Ag) nanoparticles to LiF:Mg,Ti TLD in terms of their structural characteristics, thermoluminescence (TL) properties, and dosimetric performance. The TLD samples were first synthesized, and Ag nanoparticles were subsequently incorporated as a third impurity. Both prepared samples (with and without Ag nanoparticles) were irradiated with predefined dose levels of 6 MV photons and corresponding glow curves and dose-response curves were compared. XRD, FESEM, and EDS analyses confirmed the proper formation of the LiF TLD structure. The presence of Ag nanoparticles was verified without any alteration in the overall crystalline structure of LiF. The obtained elemental correction coefficient (ECC) values were close to unity, indicating a nearly uniform distribution of impurities in the LiF structure. TLD glow curve at the same dose level enhanced when Ag nanoparticles were added to the TLD. Furthermore, the dose-response curve improved in the presence of Ag nanoparticles. Based on the results, it can be concluded that incorporating Ag nanoparticles into LiF:Mg,Ti enhances its thermoluminescence response and sensitivity.

In this study, lithium fluoride doped with magnesium and titanium (LiF:Mg,Ti) powders were synthesized chemically and where used as thermoluminescence dosimeter (TLD) applications. In order to improve thermoluminescence (TL) properties of powders, different percentages of titanium were used in the structures. Different methods were used to characterization of the synthesized powders, such as X-ray diffraction (XRD) method, SEM, FTIR and UV-Visible spectroscopy. Band gap energy of the powders was obtained about 5.4-5.7 eV. It was observed that by increasing the amount of titanium up to a certain amount, the number of electron traps and as a result, the intensity of TL light increases. With the further increase of titanium dopant, the radiation intensity decreases, which can be due to the saturation and destruction of the structure of traps by creating excess traps. Results of this study can be important in the engineering and design of TLDs with higher TL efficiency.

In this study, optical re-orientation of titanium dioxide (TiO2) nanorods (NRs) was studied using Z-scan method. TiO2 NRs have been synthesized using solvothermal synthesis method and were characterized by UV–Vis spectroscopy, X-ray diffraction and transmission electron microscopy methods which indicate formation of TiO2 NRs in anatase phase with dimensions below 50 nm. Z-scan setup containing a He–Ne laser and a laser power meter was used for open and close aperture Z-scan measurements. A uniform electric field was applied perpendicular to the laser beam to orient the NRs and third order nonlinear absorption and refraction indexes were measured in different applied voltages. It was found that the sign of the nonlinear refraction index switched from negative to positive, indicating the dominance of the re-orientation effect over the thermal-lensing effect as voltage increased. Also, the effect of the needle shape of TiO2 NRs on the threshold value of the switch voltage was investigated. In addition to experiments on NRs, nonlinear optical phase change equations resulting from the recirculation effect were developed and used to confirm the experimental results. The results of this investigation can be very important in adjusting the threshold voltage in changing the sign of nonlinear refractive index in laser switches and modulators.

Carbon quantum dots (CQDs) have attracted significant attention due to their potential in various industrial applications. Extensive research has been dedicated to uncovering the complex and enigmatic nature of CQDs from a physicochemical perspective. In the present study, CQDs were synthesized from horsetail plant extract using the hydrothermal method. Iron and cobalt were then loaded onto the CQDs to investigate their adsorption potential. Transmission electron microscopy (TEM), Dynamic Light Scattering (DLS), Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), photoluminescence (PL) spectroscopy, and Z-scan aperture were used to investigate the physical, chemical, and structural properties of the synthesized CQDs. The results revealed changes in the FT-IR spectra of CQDs compared to the metals loaded CQDs. TEM imaging showed that the CQDs had an average size of 5.27 nm. Furthermore, reversed saturation absorption (RSA) and dense diffraction rings patterns were observed in Z-scan experiments, indicating a high nonlinear optical response of CQDs.

The main interaction of laser beam with materials is to create a temperature distribution, which is the introduction to investigating effects such as thermal-lensing, nonlinear absorption and refraction, and laser-induced damage effects. The correct prediction of this temperature profile can be important in the accurate calculation of thermal expansion volumetric stresses that cause optical aberrations in optical devices and photonic and laser materials. In this letter, new approach has been used to solve the heat equation of laser beam radiation to a thin sample and an exact solution for the time-independent heat equation in a laser-irradiated sample was obtained. Considering appropriate boundary conditions, the steady-state temperature distribution without any approximation was obtained which includes the lower incomplete gamma function. Based on the temperature distribution, the nonlinear changes of absorption and refractive indexes resulting from thermal effects can be accurately calculated. This model was extended for both Gaussian and top-hat beams.

In this study, a simple formula has been proposed to calculate the refractive index of surface agents of silver nanoparticles (Ag NPs) by using the plasmonic peak of the absorption spectra of dispersed Ag nano-colloids. The basis of the study is the shift in the localized surface plasmon resonance (LSPR) of Ag NPs upon alteration of surface agents. The color changes in a typical metal nano-colloid are mainly due to the shift in the LSPR, which is caused because of electrical interactions of surface agents on the particles. There are some theoretical models to simulate the absorption spectrum, but using these methods to evaluate the plasmonic peak is not facile for a wide range of users. Here, the required simulations were performed for different values of the refractive index of surface agents and particle sizes, and the absorption spectrum and dispersive curves were accordingly plotted. A simple formula was obtained between the wavelength of the plasmonic peak, the refractive index of the shell of surface agents, and the ratio of the hydrodynamic diameter to Feret size of the particles (R0). The refractive index of the surface agents can be calculated by n2=λmax−(202.3R02−748.6R0+947.4)−152.2R02+561.3R0−405.1, where λmax (in nanometer) is the wavelength of the absorption peak due to LSPR. This method can pave the way for experimenters to obtain the refractive index and consequently the type of surface agents around Ag NPs without the need for numerical or mathematical operations. It can also be useful in analyzing the spectral diagnosis of biological agents such as viral antibodies and antigens.

The distance between conduction and valence bands which is known as bandgap energy is an important factor for semiconductors and is different in various materials. The bandgap energy determines the electrical and optical properties of semiconductors and has a direct effect on the performance of diodes and transistors. In this article, the effect of bandgap energy of the channel region of a npn transistor has been investigated and its effects on capacitance and conductivity, threshold voltage, and the Ion-Ioff ratio were studied. An npn transistor is designed and then the bandgap energy is changed between 0.8 eV and 2.2 eV with a step of 0.2 eV, and subthreshold slope and other electrical quantities have been obtained numerically. By comparing the results, the best performance of the transistor can be obtained. This simulation was done with Silvaco Atlas software. This study can open new windows in design of transistor devices.

Undoubtedly, optical choppers are one of the oldest and most common light modulation tools, which still have many applications in optoelectronic devices such as guidance systems, opto-mechanical mouses, and photoacoustic systems. In this study, transmission function of a chopper with circular shape apertures was studied whereas the distribution of the incident beam was considered Gaussian. A mathematical model was obtained for transmitted signals through the circular chopper. Studies were done for different ratios of apertures diameter to the beam cross section and the effect of this ratio on the profile of output pulses were studied. Finally, this model was validated by a simple optical experiment. This model can be easily extended for any laser beam profiles such as top hat beams and can be a leading method in optical devices and techniques based on the use of chopper wheels.

In this study, silver nanoparticles have been synthesized using green synthesis from Echium amoenum Fisch. &C.A.Mey. extract. The extract of this flower was used to reduction of silver nitrate solution and stabilization of formed silver nanoparticles. The extract of this flower contains different anthocyanin compounds, polyphenols, and vegetable stearic fatty acids that can contribute in reduction and stabilization of silver nanoparticles. Characterization of the nanoparticles was performed using X-ray diffraction method (XRD), dynamic light scattering (DLS), UV–Visible spectrum, and open aperture Z-scan method. The measurements showed that stable nanoparticles with an average size of about 54 nm were synthesized and the use of this extract was successful. Adding a few droplets of the extract to the nano-colloid made the peak of localized surface plasmon resonance (LSPR) clearer. Also, the trend of absorption spectrum changes with the addition of droplets and their nonlinear absorption changes were investigated. Nonlinear optical measurements also showed that silver nanoparticles synthesized by this method exhibit reversed saturation absorption which is due to multi-photon absorption and electrostriction effects. This green synthesis method can lead to the synthesis of stable and high-performance silver nanoparticles with high potential in electro-optic devices and can be considered as an environmentally friendly and low-cost synthesize method.

Carbon quantum dots (CQDs), the newest member of carbonaceous nanomaterials, have drawn many considerations since the past two decades. A vast number of researchers made their efforts to demystify optical behavior of these materials despite being demanding. Nevertheless, their emission origin is still a controversial issue and this area suffers from a lack of hypothesis to explain the radiative transitions of these materials. White emissive CQDs are more prized among the other ones since it has provided an affordable warm white light source for many applications. In this paper, white emissive CQDs samples were prepared through a one-step hydrothermal synthesis approach. By using the advantage of possessing cellulosic networks in the Aloe Vera gel an in-situ matrix was created to encase CQDs particles. During the formation of CQDs particles, they were entrapped and created RGB nanoemitters in the cellulosic units. The leakage of the emitted photons during the radiative transitions followed by inner-filter effect (IFE) and self-/re-absorption acted as white light emissive sources. To scrutinize the validity and possibility of the hypothesis given in this paper, a series of spectroscopic analyses, including transmission electron microscopy (TEM), surface-enhanced Raman scattering (SERS), Fourier Transform Infrared (FT-IR), ultraviolet–visible (UV–Vis), and photoluminescence (PL) were conducted.

Severe respiratory syndrome COVID-19 (SARS-CoV-2) outbreak has became the most important global health issue, and simultaneous efforts to fast and low-cost diagnosis of this virus were performed by researchers. One of the most usual tests was colorimetric methods based on the change of color of gold nanoparticles in the presence of viral antibodies, antigens, and other biological agents. This spectral change can be due to the aggregation of the particles or the shift of localized surface plasmon resonance due to the electrical interactions of surface agents. It is known that surface agents could easily shift the absorption peak of metallic nanocolloids which is attributed to the localized surface plasmon resonance. Experimental diagnosis assays for colorimetric detection of SARS-CoV-2 using Au NPs were reviewed, and the shift of absorption peak was studied from the viewpoint of numerical analysis. Using the numerical method, the refractive index and real and imaginary parts of the effective relative permittivity of the viral biological shell around Au NPs were obtained. This model gives a quantitative description of colorimetric assays of the detection of SARS-CoV-2 using Au NPs.

We study the Fraunhofer diffraction from a single slit as well as a circular aperture in a situation where the light source is monochromatic but partially coherent. In this paper, we try to bring the problem closer to reality and do not fix the coherence length and consider a Gaussian distribution function for it. Numerical study of the effects of coherence parameters with Gaussian distribution on a far field diffraction pattern is performed. In the case of a single slit, as the coherence length decreases, no significant deviation occurs at its central peak, but at higher diffraction levels, a decrease is apparent, depending on the Gaussian distribution of the coherence length. For circular apertures, the parameters of the coherence length distribution function affect the shape of the light intensity distribution and the first-order diffraction pattern decreases, and with a relative decrease in coherence length, the first-order circular diffraction pattern gradually disappears.

This work was done to synthesize tetrazole dye and Z-scan measurement of the synthesized tetrazole compounds has been carried out and interesting results about the origin of positive nonlinear absorption coefficients of dye molecules were obtained. Investigation of linear optical properties of synthesized dyes was done with the help of visible UV absorption, and fluorescence emission spectrum. Also, the electronic characteristics and molecular geometry of the sensitizers were optimized using density functional theory (DFT), and the influence of dye structure on their nonlinear optical performances was studied. Four new dyes with D–π–A architecture were discussed, in which diphenylamine and carbazole units act as donors, methine groups act as conjugated bridge units, and tetrazole derivatives act as acceptor units. Diphenylamine, carbazole, methine, and tetrazole derivatives are, respectively, donor, conjugate, and bridge acceptor units in the structure of these dyes. Moreover, nonlinear absorption and refractive indexes of the synthesized tetrazole components were measured using the Z-scan technique equipped with a 50 mW CW Nd-Yag laser. The nonlinear absorption coefficient of tetrazole derivations was obtained and was positive, and it was demonstrated that the origin of the so-called reverse saturation absorption of dye molecules in low intensities is the electrostriction effect which is due to polarization of the molecules which has an inverse relation with the Homo–Lumo energy gap of the components.

In this article, we propose a simple method to calculate electrical permittivity and refractive index of surface agents of gold nanoparticles (Au NPs), in which it is possible to find the refractive index of surface agents shell by using the absorption peak of the gold nano-colloid. One of the usual tests for detection of surface agents is colorimetric methods based on the change of color of Au NPs. The color change is mainly due to the shift of localized surface plasmon resonance which is related to electrical interactions of surface agents. Although there are many mathematical models for simulating the absorption spectrum and calculating the plasmonic peak, using them is not simple and possible for everyone due to the need for programming. Here, the necessary simulations have been performed for different values ​​of refractive index of surface agents and particle size, and absorption peaks have been obtained. Using numerical methods, a simple formula is obtained between the wavelength of plasmonic peak, the ratio of hydrodynamic diameter to Feret size of the particles, and the refractive index of the surface agents. This method can help researchers to obtain the refractive index and consequently the type or concentration of surface agents around Au NPs without the need for programming or complex mathematical operations. It can also open new horizons in analyzing colorimetric diagnosis of biological agents such as viral antibodies, antigens, and other biological agents.