Changes In Absorption Coefficient Research Articles

A new look at an explanation of band gap of PECVD grown a-Si:H thin films using absorption spectra, spectroscopic ellipsometry, Raman, and FTIR spectrosopy

Amorphous silicon is seen to be among the most promising materials for solar cell applications because of its higher temperature coefficient of resistance, adjustable forbidden-band gap, enhanced optical absorption, and capacity to reduce solar module costs. Changes in deposition rate, absorption coefficient and optical band gap of a-Si:H films with varying silane flow rate show that SiH4 molecules density influence the plasma growth process. Silane flow rate affects the percentage of silicon atoms during processing. The deposition rate of a-Si: H films increased from 14.36 nm/min to 15.97 nm/min by increasing silane flow rate from 25 sccm to 45 sccm. Broadening of optical band is observed. Films deposited at 35 sccm of silane flow rate shows the higher absorption coefficient. All films are characterized by FTIR, Raman spectroscopy, spectroscopic ellipsometry and optical absorption to understand the changes in band gap. The band gap Eg of all films is correlated with microstructure factor, Q factor, bond angle deviation Δθ and width of Si–H2 mode to analyse the effect of defects, disorders and microvoids.

Role of alkyl chain length on aggregation enhanced two-photon absorption and thermal diffusivity of Carbazole-Barbituric acid D-π-A systems

Aggregation Induced Emission (AIE) luminogens exhibit no or faint emission in dilute solution and are induced to emit when aggregated with restriction of intramolecular motion as the principle mechanism. We investigated the role of hydrophobic interaction in AIE effect by varying the alkyl chain length of Carbazole-Barbituric acid (CBA) D-π-A system. We synthesized six CBA conjugates, studied their photophysical properties and morphological changes upon aggregation by varying water: tetrahydrofuran ratio. We performed thermal lens experiment in all CBA conjugates to understand the variation in radiative and non-radiative decays upon aggregation. Both aggregation and hydrophobic interaction is found to play significant role in tuning thermal diffusivity of CBA conjugates. The knowledge about their energy levels was gained by using DFT in Gaussian 09 program package. Perturbation of energy levels associated with molecular aggregation open up the possibility of such D-π-A system in nonlinear optics. The open aperture Z-scan technique with Nd:YAG laser at 1064 nm was utilized to measure the change in two-photon absorption (TPA) coefficient at different stages of aggregation and as a function of alkyl chain lengths. We observed an aggregation enhanced TPA and could tune the TPA in aqueous solution by changing the alkyl chain length. Experimentally observed TPA coefficient showed the same trend as obtained in DFT calculation for hyperpolarizability. Furthermore, for practical utility we fabricated CBA conjugate doped PMMA thin films for low threshold optical limiting applications.

Tunability of the nonlinear optical absorption in a GaAs/Ga0.7 Al0.3 As spherical quantum dots under external factors

We theoretically studied the linear, third-order nonlinear and total optical absorption coefficient changes of a typical GaAs/Al0.3Ga0.7As quantum dot system under the influence of hydrostatic pressure and temperature. The influence of hydrostatic pressure and temperature on the system is treated within the framework of effective mass. In this method, the relative changes of linear and nonlinear absorption coefficients are obtained by using density matrix method and iterative method. In addition, we also reveal the mechanism of the influence of hydrostatic pressure and temperature on the nonlinear optical properties, which is of great significance for us to better understand the causes. We have shown that hydrostatic pressure and temperature change the effective mass, resulting in significant changes in the linear and nonlinear optical properties of the system. In addition, we also reveal the mechanism of the influence of effective mass on the nonlinear optical properties, which is of great significance for us to better understand the causes.

Effect of spin-orbit coupling and impurities on the optical properties of double quantum rings under magnetic fields

In this paper, the energy spectrum of concentric double quantum rings (CDQRs) with double well confinement under the influence of spin-orbit interactions (SOIs), magnetic fields, and hydrogen donor impurities is studied by using diagonalization. The light absorption coefficient is then calculated in the form of a compactness density-matrix. Key findings from this study include the ability to manipulate fine energy level splitting and optical absorption coefficients by tuning the magnetic field, impurity position, spin-orbit coupling, and inner rings size. Furthermore, this study reveals the bleaching effect of the optical absorption coefficient under certain conditions and demonstrates the anisotropic nature of the system through changes in the optical absorption coefficients (OACs) for different incident light polarization angles.

Laser-induced transverse voltage effect in c-axis inclined La x Sr1−x TiO3 thin films prepared by MOCVD

Light and thermal detectors based on the laser-induced transverse voltage (LITV) effect have garnered significant interest for their rapid and broad spectral response. In this study, we prepared the La-doped SrTiO3 (STO) epitaxial thin films on the 12° inclined single crystal LaAlO3 (LAO) (100) substrates using our home-designed metal–organic chemical vapor deposition system. Under the illumination of a 248 nm laser, the LITV signals of La x Sr1−x TiO3 films were observed and showed dependence on the La doping level, which can be explained by the changes in the light absorption coefficient, thermal conductivity, and optical penetration depth. The optimized LITV signal was observed with a peak voltage of 23.25 V and a decay time of 106 ns under the laser power density of 1.0 mJ mm−2. The high peak voltage and fast response time of La x Sr1−x TiO3 show great potential in the field of light and thermal detection.

Modeling of the process of retaining the concentration of aggressive gases during the operation of deaerators

In this article, in the process of deaeration of feed water in thermal deaerators in the saturation temperature range of 20-105 °C, a method is proposed for determining changes in partial pressure, absorption coefficient and concentration values of aggressive gases such as carbon dioxide, oxygen and nitrogen in the gas phase and dissolved in water is modeled according to Henry’s law, and the results obtained are graphically depicted; conclusions are given on how the correspondence of the saturation temperature to an increase in pressure affects the change in the concentration of aggressive gases.

A Study on The Optical Properties of Long-Infrared Intraband Transitions of Quadruple Gaas/Alxga1-Xas Quantum Well Under Applied Electric Field

Semiconductor-emitting/absorbing infrared devices are in the common interest of the scientific and industrial community due to their broad application in these fields. GaAs/AlGaAs based devices are one of the most studied semiconductor heterostructures. In this study, I have aimed to design GaAs/AlGaAs quantum well (QW) semiconductor heterostructures to emit/absorb in the long infrared region and studied the optical properties. To do that, I have designed a quadruple QW, which is composed of GaAs/Al0.44Ga0.56As QW and quantum barriers (QB). I have solved the time-independent Schrödinger equation using the finite element method-based matlab code under effective mass approximation. The wave functions and corresponding energy eigenvalues are obtained for varied electric field (EF) intensities. I have shown that our design can operate up to 80 kV/cm, which is the limit for first bounded energy eigenstates. It is observed that E_32 transition provides long-infrared emission/absorption corresponding to the 0.12-0.14 eV transition energy and it is constant with increased EF intensity. In addition, it is seen that the overlap of the wave functions is increasing with EF intensity which enhances radiative transition in the structure. I have calculated the linear absorption coefficient and refractive index change. I have observed that the absorption coefficient of E_32 transition is increasing with EF intensity while E_31 is decreasing and E_21 is constant. As a last, I have shown that EF intensity has a minor effect on refractive index change.

A Discolorable Flexible Synaptic Transistor for Wearable Health Monitoring.

Multifunctional intelligent wearable electronics, providing integrated physiological signal analysis, storage, and display for real-time and on-site health status diagnosis, have great potential to revolutionize health monitoring technologies. Advanced wearable systems combine isolated digital processor, memory, and display modules for function integration; however, they suffer from compatibility and reliability issues. Here, we introduce a flexible multifunctional electrolyte-gated transistor (EGT) that integrates synaptic learning, memory, and autonomous discoloration functionalities for intelligent wearable application. This device exhibits synergistic light absorption coefficient changes during voltage-gated ion doping that modulate the electrical conductance changes for synaptic function implementation. By adaptively changing color, the EGT can differentiate voltage pulse inputs with different frequency, amplitude, and duration parameters, exhibiting excellent reversibility and reliability. We developed a smart wearable monitoring system that incorporates EGT devices and sensors for respiratory and electrocardiogram signal analysis, providing health warnings through real-time and on-site discoloration. This study represents a significant step toward smart wearable technologies for health management, offering health evaluation through intelligent displays.

Implemantation of firefly algorithm on Arduino Uno

Not only getting the optimal solution of a problem, embedding the algorithm on the microcontroller is also expected to work optimally without burdening the system and fast response. Getting a microcontroller specification that matches the complexity of an algorithm is necessary so that the system can execute the algorithm perfectly. Values for the basic parameters of optimization algorithms inspired by nature such as the firefly algorithm (FFA) which are interpreted into variables greatly affect the performance of the microcontroller in obtaining the expected optimal solution. The observed performance of the Arduino Uno microcontroller in running the FFA includes execution time and memory capacity required to obtain optimal values based on changes in absorption coefficient, random parameters, iterations, and population. Changes in the absorption coefficient and random parameters affect the optimal value but do not significantly affect the execution time and memory capacity of Arduino Uno. Iteration changes greatly affect execution time and population changes most affect the performance of Arduino Uno. With a dynamic memory capacity of 2 Kb, the FFA can be run with a maximum range of 50 populations and up to 20 iterations.

Impact of intense laser Bessel beam on excitonic complexes in ellipsoidal quantum dot

This theoretical study investigates the response of a strongly oblate GaAs ellipsoidal quantum dot to an intense laser field with a Bessel intensity profile at non-resonant extreme violet and simultaneously resonant mid-infrared laser irradiation. Mainly, the linear and nonlinear optical properties of biexcitons in quantum dot are observed. Due to the complexity of the considered particle, all calculations are performed in the framework of the variational method. Biexciton variational function is constructed on the one-particle wave functions, which are correlated with each other by exponents with variational parameters. The biexciton energies for different values of applied intense laser field magnitude on the small geometrical parameter of ellipsoidal quantum dot are calculated. The nonlinear optical properties, including the oscillator strength, third-order nonlinear susceptibility, absorption coefficient, and refractive index change, are evaluated. Numerical results reveal the dependence of the exciton and biexciton energies on the intensity of the laser field and the geometrical parameters of the quantum dot. Additionally, the dependencies of the third-order susceptibility, absorption coefficient, and induced refractive index change on photon energy near the one-photon resonance and two-photon resonance are analyzed. The two-photon absorption coefficient of the biexciton in GaAs ellipsoidal quantum dot is computed, and the spectra of refractive index changes induced by biexciton transitions between ground states are analyzed for different magnitudes of the intense laser field. Biexciton recombination radiative lifetime on the small semiaxis of the ellipsoidal quantum dot for the different values of the laser field influence is estimated. Finally, the visualization of the localization region of biexciton in the ellipsoidal quantum dot is performed.

First steps in the development of next-generation chirped volume Bragg gratings by means of fs laser inscription in fused silica.

The first steps towards the development and characterization of next-generation chirped volume Bragg gratings (CVBGs) by means of fs laser inscription were made. Based on the phase mask inscription technique we realized CVBGs in fused silica with a 3 × 3 mm2 aperture and a length of almost 12 mm with a chirp rate of ∼190 ps/nm around a central wavelength of 1030.5 nm. Strong mechanical stresses induced serious polarization and phase distortions of the radiation. We show a possible approach to solution of this problem. The change in the linear absorption coefficient associated with local modification of fused silica is quite small, enabling utilization of this type of gratings in high average power lasers.

Nonlinear absorption coefficient and relative refractive index change for Konwent potential quantum well as a function of intense laser field effect

Nonlinear absorption coefficient and relative refractive index change for Konwent potential quantum well as a function of intense laser field effect

Optical Absorption Coefficient and Refractive-Index Change in a Coupled Quantum Dot-Metallic Nanoparticle Structure

In the present work, we investigate the problem of the optical absorption coefficient (OAC) and refractive-index change (RIC) in a semiconductor quantum dot placed in the vicinity of a spherical metallic nanoparticle. We derive the total OAC and RIC from the density-matrix equations through different approaches, one without approximations and the other keeping only linear and third-order nonlinear terms. The derived formulae are then applied in a specific hybrid nanostructure to calculate the OAC and RIC. The results obtained from the derived formulae are used to compare cases of various interparticle distance values and applied light intensities and find that, although for specific distances and intensities the formulae may give similar results, in general, they give different results. Moreover, it becomes clear that the distance between the quantum dot and the metallic nanoparticle, in combination with the polarisation of the light field, plays a significant role in the OAC and RIC of the quantum dot. Expressly, conditional on the polarisation of the applied electric field, the OAC and RIC of the quantum dot can be either enhanced or suppressed close to the metallic nanoparticle compared to their values in the absence of the metallic nanoparticle.

Effect of electron beam improved dielectric function on optical properties of sol-gel derived CuIn1-XGaXSe2 thin-film

Electron beam has been applied as a practical posttreatment process for the surface modification at the CuIn1-XGaXSe2 thin film. The rise of the film thickness indicated the advantages of the modified surface-related properties (such as the optical parameters to develop an optimum optical model) via enriching the microstructure with the negative charged beta particles by using Sr-90 radioisotope. The effect of negatively charged beta particles on dielectric constants was examined at two different dose levels (3 and 9.1 Gy) by using Sr-90 radioisotope. The application of the electron beam to the thin film surface caused the slight changes in refractive index (n), extinction coefficient (k) and optical absorption coefficient. The increase of refractive index and the improvement of absorption coefficient provided to distinguish clearly the decrease in extinction coefficient and the decline in energy band gap as the result of the rise of the beta dose at the thin-film. The slight variations in dielectric constants were performed by encouraging more dense structure to form the optimum crystalline network at the thin film (applied beta dose). The application of beta dose favoured inventive variations in the refractive index. The applied two different beta dose levels were below ∼3.1 Gy and above ∼9 Gy. The beta dose level at ∼9 Gy was ∼3 times dose value of 3.1 Gy (applied as a security value for the utilization of this thin film at the extreme environments such as international space station orbit). The refractive index stated its importance specifying the rise of the bending of light in the thin film structure.

The total absorption coefficient and refractive index change of a spherical quantum dot in the confinement radial potential

We have systematically investigated the linear, third-order nonlinear, total absorption coefficients and refractive index change of the spherical quantum dot in the confinement potential family V(r)=Ar2−Br+Crκ by solving the radial Schrödinger equation with the Numerov method in case of the effective mass approximation for the allowed transition of the ground state (1s) to first excited state (2p). We examine the dependencies of the total absorption coefficient and refractive index change on the confinement potential parameters for varying incident photon energy and relaxation times. Our results demonstrate that the absorption coefficients and the change in refractive index strongly depend on the confining potential parameters non-linearly representing various intersubband transitions of quantum dots. We find that increasing the parameter B in the Coulomb plus harmonic oscillator potential or decreasing the parameter A in the Kratzer plus harmonic oscillator potential, the total absorption coefficient and refractive index change shift to higher photon energies.

Nonlinear optical absorption and refractive index change in realistic [formula omitted] V-groove quantum wires

The intersubband optical absorption coefficient and refractive index change of a realistic single-electron GaAs/Ga1−xAlx V-groove quantum wire are calculated. Finite confinement potentials and analytic models capable of adapting to many V-groove quantum wire shapes reported in the literature are used in the calculations. This scheme allows analyzing the effect of the inter-sidewall angle and crescent thickness on the optical response. Additionally, the effects of external fields such as hydrostatic pressure and temperature are taken into account. The results show that the geometrical parameters have a principal role compared to the temperature and hydrostatic pressure. In addition, optical activity within the Terahertz band using the parameter values that fit the typically V-groove quantum wires reported in the literature was found.

Fast noniterative data analysis method for frequency-domain near-infrared spectroscopy with the microscopic Beer–Lambert law

By using the microscopic Beer–Lambert law (MBL), we propose a fast and effective analysis method for retrieving the absorption coefficient changes of a sample from broadband frequency-domain diffuse optical spectroscopy (FD-DOS) or frequency-domain near-infrared spectroscopy (FD-NIRS) data. To verify the advantages of our proposed method, we built a broadband frequency-domain single-distance diffuse optical imaging (DOI) system for measuring the amplitude and the phase of transmitted light. Fifteen liquid phantoms with different absorption and scattering coefficients are prepared, and the changes in the absorption coefficient Δμa are retrieved by using the conventional nonlinear least-squares fitting (NLSF) and the proposed MBL methods. Results show that the computation time and the precision of the MBL method are much better than those of the NLSF method, respectively.

Wavelength and frequency optimization in spatial frequency domain imaging for two-layer tissue

Spatial frequency domain imaging is a non-contact, wide-field, fast-diffusion optical imaging technique, which in principle uses steady-state spatially modulated light to irradiate biological tissue, reconstruct two-dimensional or three-dimensional tissue optical characteristic map through optical transmission model, and further quantify the spatial distribution of tissue physiological parameters by multispectral imaging technique. The selection of light source wavelength and light field spatial modulation frequency is directly related to the accuracy of tissue optical properties and tissue physiological parameters extraction. For improvement of the measurement accuracy of optical properties and physiological parameters in the two-layer tissue, a multispectral spatial frequency domain imaging system is built based on liquid crystal tunable filter, and a data mapping table of spatially resolved diffuse reflectance and optical properties of two-layer tissue is established based on scaling Monte Carlo method. Combined with the dispersion effect and window effect of light-tissue interaction, the study applies numerical simulation to optimize the wavelength in the 650-850 nm range with spectral resolution of 10 nm. In order to minimize the uncertainty of the optical properties, Cramér-Rao bound is used to optimize the optical field spatial modulation frequency by transmitting the uncertainty of optical properties. The results showed that in order to realize the detection of melanin, oxyhemoglobin, deoxyhemoglobin, water and other physiological parameters in two-layer tissue, the best wavelength combination was determined as 720, 730, 760 and 810 nm according to the condition number. The findings of the Cramér-Rao bound analysis reveal that the uncertainty of optical characteristics for the frequency combinations [0, 0.3] mm-1, [0, 0.2] mm-1, and [0, 0.1] mm-1 increases successively. Under the optimal combination of wavelength and frequency, the diffuse reflectance of the gradient gray-scale plate measured by the multi-spectral spatial frequency domain imaging system is linearly correlated with the calibration value. The error between the measured liquid phantom absorption coefficient and the collimation projection system based on colorimetric dish is less than 2%. The experimental results of human brachial artery occlusion indicate that under the optimal wavelength combination, the change of the second layer absorption coefficient captured by the three frequency combinations decreases in turn, so as the change of oxygen saturation.

Linear and nonlinear optical properties in single CuIn1−xGaxSe2 nanowire: Effects of size, incident intensity, relaxation time and Ga concentration

The linear and nonlinear optical properties of CuIn1−xGaxSe2 free standing nanowire have been studied by employing the compact-density matrix formalism and the effective mass approximation. Considering the system under the effect of the polarization vector of the incident light in both cases perpendicular and parallel to the axis of the nanowire, the systematic theoretical investigation contains results with all possible combinations of the involved parameters, such as incident light intensity, relaxation time, nanowire radius and Ga concentration. Our results show that in the case of the polarization vector perpendicular to the nanowire axis, the linear and nonlinear absorption coefficient and refractive index changes can be controlled by changing the nanowire radius, and the effect of Ga concentration is clearly apparent. In contrast, polarization along the nanowire axis allows for a very large absorption coefficient and control of the optical properties through the height, but minimal effect on the transition energy. The increase of the relaxation time as well as the intensity of the incident light has a major role in the nonlinearity effects, while the Ga concentration and the size of the structure influence the amplitude and the transition energy shift.

An investigation of the changes in mass attenuation and energy absorption coefficients at K, L and M photoelectric absorption thresholds

An analysis of photoelectric attenuation and absorption data at the threshold energies for the K, L and M shell absorption discontinuities.