Changes In Absorption Coefficient Research Articles

The synthesis and dielectric characterization of a low temperature smectic a liquid crystal

In the present paper, we have been synthesized a new salicylaldimine-based rod-like liquid crystal 4-((S)-3,7-Dimethyloctyloxy)-2-[[[4-(S)-2-methylbutoxyphenyl]imino]methyl]phenol (DMIP) exhibiting an enantiotropic Smectic A mesophase in the narrow temperature range. We have also evaluated the dielectric parameters of this liquid crystal DMIP as a function of temperature from 25 °C–50 °C and frequency range from 1 Hz to 1 MHz. It is observed that dielectric constant (ε′) and dielectric loss factor (ε″) depends on frequency and temperature. Relative dielectric parameters, such as the dielectric strength, relaxation times and absorption coefficient change at phase transition temperature of the DMIP have been analyzed from the dielectric data of the Cole-Cole equation. Molecular reorientation mechanism has been investigated in the Smectic A mesophase temperature range by Debye type relaxation behaviour.

Non-linear optical properties of nanoscale elliptical ring-shaped at the presence of Rashba spin–orbit interaction and magnetic field

The significant information about the properties of matter can be described with the interaction between light and matter. On this subject, the effect of the applied magnetic field and structural variation on the optical properties of elliptical and circular GaAs quantum rings at the existence of Rashba spin–orbit interaction (RSOI) have been investigated. The effective mass equation for the system containing RSOI and magnetic flux has been solved in cylindrical coordinate with Matrix Diagonalization method for circular quantum ring and with finite difference method for elliptical quantum ring. Also, the linear and third-order nonlinear optical absorption coefficient (AC) and refractive index changes (RIC) are calculated by density matrix. According to the consequence, the geometry of quantum structure plays a significant role in specifying the AC and RIC which provide the methods for fabricating effective application.

Nonlinear absorption coefficient and refractive index changes of two-dimensional two-electron quantum dot in rigid confinement

The Hamiltonian and wavefunctions describing two-dimensional (2D) two-electron ZnO quantum dot in rigid confinement are developed. Then the Schrödinger equation is solved analytically and numerically for determining the ground and excited state energies. The ground state energy of 2D two-electron ZnO quantum dot (QD) in rigid confinement is studied using perturbation and variational methods. The obtained result show that our trial wavefunction is good enough to describe the 2D two-electron QD in rigid confinement. The wavefunction describing the ground state is the combination of symmetric spatial wavefunction and antisymmetric spin wavefunction which is a para-state. The ground state energy eigenvalue obtained by variational technique is a little above that of a perturbation technique. Based on this; the trial wavefunction for the excited state is developed. The excited state energy of 2D two-electron ZnO QD in rigid confinement is studied computationally using variational method. The wavefunction describing the excited state is the combination of symmetric spatial wavefunction with antisymmetric spin wavefunction (para-state) or vice versa (ortho-state). The para and ortho-state energies of the first excited state are calculated and their difference is twice of the exchange energy. Based on the obtained energy eigenvalues of the ground and the first excited state at the value of the coupling constant [Formula: see text] [Formula: see text] 1, the third-order nonlinear absorption coefficient and refractive index changes are investigated. The optical transition is only considered between the two lowest para states.

Strain effects in the absorption coefficient and relative refractive index change in double asymmetric AlxGa1−xN/GaN quantum wells

We theoretically investigate the optical absorption and the relative change in the index of refraction in asymmetric double zinc-blende AlxGa1−xN/GaN quantum wells. Particular emphasis is put in revealing the influence of lattice strain on these properties. For that purpose, the electronic energy structure is determined in the framework of the effective mass and parabolic band approximations whilst the strain effects are incorporated with the use of the model solid theory. The corresponding optical coefficients are then computed through the expressions obtained within the compact matrix density formulation. Linear and nonlinear contributions are reported as functions of the widths of both the separating central potential barrier and the left-hand quantum well.

Rural development and land use land cover change in a rapidly developing agrarian South Asian landscape

It is a general belief that agricultural area, particularly in developing countries, is decreasing with rapid urbanization. This is an important phenomenon in the form of land use land cover change (LULCC) as these countries depend on agriculture to a great extent for food and economic growth. Using Landsat data our investigation in the rural area of Varanasi district revealed that agricultural area, which constituted about 50% of land cover, increased by 37% in the 1993–2013 period and built area increased by 236%. A Relative Rural Development Index (RRDI) was formulated to find out the comparative development in rural blocks of the district. RRDI was based on built, green and agriculture land use, and the number of agricultural workers, LAC and LCR. Kashi Vidyapeeth (KV) and Chiragaon (CG) rural blocks present in close proximity of the urban core had the highest RRDI score and change in Land Absorption Coefficient (LAC) and Land Consumption Ratio (LCR). Proximity to the urban area influenced rural development in the form of agricultural and built area increase. The study can be helpful for focussing development and policymaking efforts to a rural area according to its RRDI score.

Effect of UV wavelength on humic acid degradation and disinfection by-product formation during the UV/chlorine process

The efficiency of the ultraviolet (UV)/chlorine process strongly depends on UV wavelength because chlorine photolysis and its subsequent radical formation are highly wavelength-dependent. This study compared the degradation of humic acid (HA) during the UV/chlorine process by low pressure mercury lamp (LPUV, 254 nm) and ultraviolet light-emitting diode (UV-LED, 275 and 310 nm). The results indicated that HA degradation followed the pseudo-first-order kinetics, and the fluence-based degradation rate constants (kobs) were significantly affected by UV wavelength and solution pH. HA degradation decreased greatly with increasing solution pH during the UV/chlorine process at 254 nm, while the opposite trend was observed at 275 and 310 nm. In the meantime, kobs decreased in the order of 275 nm > 254 nm > 310 nm at pH > 7.0. The changes of chlorine molar absorption coefficients at different UV wavelengths resulted in the variation of chlorine photodecay rates (kobs, chlorine), and the synergistic effects of kobs, chlorine and chlorine quantum yields (Φchlorine) affected HA reduction. The formation of disinfection by-products (DBPs) during the UV/chlorine process was also evaluated. A significant suppression on DBP formation and DBP-associated calculated theoretical cytotoxicity were observed at 275 nm high UV fluence and alkaline pHs. These findings in this study demonstrate that UV wavelength at 275 nm is more suitable for HA degradation by the UV/chlorine advanced oxidation process in practical applications.

Linear and Nonlinear Intersubband Optical Properties of Direct Band Gap GeSn Quantum Dots.

Intersubband optical transitions, refractive index changes, and absorption coefficients are numerically driven for direct bandgap strained GeSn/Ge quantum dots. The linear, third-order nonlinear and total, absorption coefficients and refractive index changes are evaluated over useful dot sizes’ range ensuring p-like Γ-electron energy state to be lower than s-like L-electron energy state. The results show strong dependence of the total absorption coefficient and refractive index changes on the quantum dot sizes. The third order nonlinear contribution is found to be sensitive to the incident light intensity affecting both total absorption coefficient and refractive index changes, especially for larger dot sizes.

Experimental investigation of frost induced damage of cement mortar

Questions connected to influence of frost degradation on microstructure and physical properties of water saturated cement mortars and their resistance to cyclic water freezing are the objectives of research. The main aim of the investigation is to analyze the ice-induced deterioration of cement mortars with different water/cement ratios (w/c=0.50 and 0.40) in a accelerated durability tests. The changes of pore size distribution and water absorption coefficient are investigated by means of mercury intrusion porosimetry and capillary absorption test. Additionally, the analysis of the impact of drying temperature (40°C, 60°C, 80°C and 105°C) on the microstructure is introduced.The performed tests enabled to estimate that the destruction of the cement matrix and the range of observed changes depend on the initial pore size distribution and their volume in the cement matrix. It is also established that the increase of transport properties is correlated with the change of pore size distribution. The obtained results allow to conclude a decrease of content of small pores (up to 150nm) and increase of larger pores for mortar with w/c=0.50. Application of superplasticizer, which resulting in reduction of water to cement ratio up to 0.40, allows to obtained resistant to 150 frost cycles cement mortar.

Stimulated Brillouin scattering in dispersed graphene.

We explored the Stimulated Brillouin scattering (SBS) behavior of a transparent liquid containing a low concentration of strongly absorbing nanoparticles. We measured SBS energies in N-methyl-2-pyrrolidone (NMP) and water at 532 nm-wavelength. The previously unknown NMP Brillouin gain factor is gB = 18.6 ± 1.8 cm⋅GW-1. Graphene nanoflakes suspended in liquids strongly quench SBS. Linear dependence of the SBS-threshold on the graphene absorption coefficient (concentration) makes it suitable for the detection of small nanoparticles quantities in water, with a minimal detectable concentration of 5⋅10-8 g⋅cm-3. The effect is interpreted as an antagonism between electrostriction and thermal expansion, which is induced by the formation of carbon vapor bubbles. It is very sensitive to changes in density, refractive index and acoustic absorption coefficient, which parameters can be determined in the SBS method, including access to the bubbling nanosecond dynamics. SBS suppression may find applications in laser technologies and optical telecommunication networks.

Non-destructive inspection of food and technical oils by terahertz spectroscopy

Quality control and non-destructive monitoring are of notable interest of food and pharmaceutical industries. It relies on the ability of non-invasive inspection which can be employed for manufacturing process control. We hereby apply terahertz (THz) time-domain spectroscopy as non-destructive technique to monitor pure and degraded oils as well as hydrocarbon chemicals. Significant differences in the spectra of refractive index (RI) and absorption coefficient arising from the presence of ester linkages in the edible and technical oils were obtained. Explicit increase from 1.38 to 1.5 of the RI in all THz spectrum range was observed in hydrocarbons and mono-functional esters with the increase of molar mass. This fact is in contrast of RI dependence on molar mass in multi-functional esters, such as Adipate or vegetable oils, where it is around 1.54. Degradation products, Oleic Acid (OA) and water in particular, lead only to some changes in absorption coefficient and RI spectra of vegetable oils. We demonstrate that complex colloidal and supramolecular processes, such as dynamics of inverse micelles and oil hydrolysis, take part during oil degradation and are responsible for non-uniform dependence of optical properties on extent of degradation.

Stability of the light-induced hidden charge density wave state within the phase diagram of 1T−TaS2−xSex

The femtosecond transient optical spectroscopy is employed to study the relaxation dynamics of the equilibrium and hidden metastable charge-density-wave states in single crystals of $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}$ as a function of the Se doping $x$. Similar to pristine $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, the transition to a hidden phase is observed at low temperature after a quench with a single 50 fs laser pulse, in the commensurate Mott phase up to $x=0.6$. The photo-induced hidden-phase formation is accompanied by a notable change in the coherent phonon spectra, and particularly the collective amplitude mode. While the temperature stability of the hidden phase is only slightly dependent on the Se content, the creation-threshold fluence strongly increases with Se content from 1 to $\ensuremath{\sim}4$ mJ/${\mathrm{cm}}^{2}$, which is attributed predominantly to the change in optical absorption coefficient at the laser excitation wavelength, and not an increased barrier of the hidden state with increasing Se.

The quantum-confined Stark effect in layered hybrid perovskites mediated by orientational polarizability of confined dipoles

The quantum-confined Stark effect (QCSE) is an established optical modulation mechanism, yet top-performing modulators harnessing it rely on costly fabrication processes. Here, we present large modulation amplitudes for solution-processed layered hybrid perovskites and a modulation mechanism related to the orientational polarizability of dipolar cations confined within these self-assembled quantum wells. We report an anomalous (blue-shifting) QCSE for layers that contain methylammonium cations, in contrast with cesium-containing layers that show normal (red-shifting) behavior. We attribute the blue-shifts to an extraordinary diminution in the exciton binding energy that arises from an augmented separation of the electron and hole wavefunctions caused by the orientational response of the dipolar cations. The absorption coefficient changes, realized by either the red- or blue-shifts, are the strongest among solution-processed materials at room temperature and are comparable to those exhibited in the highest-performing epitaxial compound semiconductor heterostructures.

Study of electron-related optical responses in the Tietz-Hua quantum well: Role of applied external fields

In the present study, we theoretically reported the effects of applied external fields, such as intense laser field and electric and magnetic fields, on the optical absorption coefficient and refractive index changes in the Tietz-Hua potential quantum well by the compact density-matrix approach. For this, we first calculated the subband energy levels and their corresponding electronic wave functions of the structure by solving the one-dimensional Schrödinger equation within the framework of the effective mass and envelope wave function approximations. Our theoretical results show that the optical absorption coefficient and refractive index changes in the Tietz-Hua potential quantum well are sensitive to the applied external fields. The absorption spectra in the structure can be adjusted depending on the purpose by changing the strength of the applied external fields, and these results can be used to tune and control the electronic and optical properties of the Tietz-Hua potential quantum well.

Influence of hydrostatic pressure and spin orbit interaction on optical properties in quantum wire

The role of hydrostatic pressure and temperature on the optical properties of a two dimensional electron gas confined in a quantum wire having Rashba spin orbit interaction is studied in this work. The energy band gap and thus the effective mass of the charge carriers are found to have strong dependence of the hydrostatic pressure on the quantum wire and its absolute temperature. This in turn affects the linear as well as the nonlinear optical properties of the quantum wire. The external magnetic field, temperature, hydrostatic pressure and the Rashba spin orbit interaction are found to interplay in determining the linear and nonlinear absorption coefficient and refractive change in the quantum wire as a response to incident electromagnetic radiation.

Light-induced absorption and optical damage in Sc-, Mg-, and Zn-doped near-stoichiometric LiNbO3

By measuring the ultraviolet-light-induced absorption in Sc-, Mg- and Zn-doped near-stoichiometric lithium niobate (LiNbO[Formula: see text], we find that the steady-state ultraviolet-light-induced absorption coefficient changes with respect to the doping concentration. There is a strong ultraviolet-light-induced absorption when doping concentration is below its photorefractive threshold and a really weak absorption when the crystal is highly doped. We also use OH[Formula: see text] infrared absorption spectra and the transmitted light spot distortion method to verify the result. Thus, we can determine if the doping level in these doped near-stoichiometric LiNbO3 crystals is above or below their photorefractive threshold by measuring the ultraviolet-light-induced absorption.

Optical properties of a single quantum well under electric and tilted magnetic fields

In this study, the effects of electric and tilted magnetic fields on changes in the total absorption coefficient and the refractive index, including the linear and third-order nonlinear terms for transition between the ground and first excited level of an electron confined within the GaAs/GaAlAs quantum well, have been investigated. Furthermore, the effects of the magnetic field direction (i.e., different tilt angles) and the well parameters as well as the electric field strength on the optical properties are taken into consideration. The energy levels and wave functions of the system are calculated by using the effective mass approximation and the compact density-matrix approach is used for optical transitions. The obtained results show that the optical properties of the system are sensitive to the applied external fields and well dimensions.

Optical properties of parabolic quantum wires in the presence of electron-electron interactions: An Euler-Lagrange variational application

In this work, we investigate the absorption coefficient and refractive index changes of a parabolic quantum well in the presence of electron-electron interactions. We use a nonlinear term in our Schrödinger equation to simulate the electron-electron interaction effect. We solve the resulting nonlinear Schrödinger equation through an Euler-Lagrange variational method. We study the effects of interaction strength and geometrical potential on energy levels, eigenfunctions, absorption coefficient and refractive index changes. We show that, Electron-electron interaction strength tries to delocalize the wavefunction while geometrical parabolic potential parameter tries to localize it. Thus, by means of these parameters we are able to control the electron confinement and wave function localization. In the literatures, it is usually stated that the electron-electron instructions can be neglected in optical properties investigations. But, when we increase the electron-electron interaction strength from 0 to 1 eV (from null to full electron-electron interaction), the absorption coefficient increases up to 20%, thus it cannot be neglected.

Optical properties of phosphate glass with CdSe quantum dots in terahertz frequency range

Optical properties and spectral characteristics of phosphate glasses with CdSe QDs were studied using time-domain terahertz spectroscopy in transmission mode in the frequency range of 0.2 - 1.0 THz. Concentration and size of QDs were varied by changing heat treatment conditions of initial glass samples containing components of the semiconductor phase. The change of refractive index and absorption coefficient at the high frequency edge of the investigated range at variation of secondary processing parameters was observed.

Optimizing the thermal annealing temperature: technological route for tuning the photo-detecting property of p-CuO thin films grown by chemical bath deposition method

In the current work, CuO thin films (~ 110 nm) are grown by employing chemical bath deposition (CBD) method on Si substrate for fabricating the p-CuO/n-Si heterojunction photodetectors. The as-grown films are annealed at 250, 550 and 850 °C for 10 min in Ar ambient for tuning optoelectronic properties of the as-grown CuO thin films. Comparative study on systematic annealing of the film within 250–550 °C indicates a morphological change of the as-grown CuO film to nano-fiber type with its chemical composition remaining unchanged. A variation of refractive index and dielectric constant in the range of 2.65–2.93 and 7.2–9.7, and a change of absorption coefficient and bandgap from 1.33 × 105 to 6.06 × 105 cm− 1 and 1.5 to 2.16 eV have been observed. The current–voltage characteristics both in dark and illuminated conditions suggest that the annealing of CuO film at 550 °C provides the best performance in terms of photo-to-dark current ratio and photoresponsivity. A respective enhancement of 5.07 and 10% for the photo-to-dark ratio and photoresponsivity has been observed for the 550 °C annealed sample.

Tunability of the optical absorption and refractive index changes in step-like and parabolic quantum wells under external electric field

In this paper, the effects of an external electric field on the energy transitions and optical absorption lineshape in step and parabolic GaAs quantum wells are theoretically investigated. The energy separations between the three lowest energy levels E1, E2 and E3 and their corresponding wavefunctions are calculated by solving the Schrödinger equation. Our theoretical findings show that the intersubband transitions and the optical absorption in the step-like quantum well can be tuned and controlled by an applied electric field (F). Especially the optical absorption coefficient α12(ω) presents a blue shift by increasing the intensity of F. Contrary to the case of step-like quantum well, the energy transition and the optical absorption coefficient α12(ω) are less sensitive to the applied electric field F in the case of parabolic quantum well. In the latter case α12(ω) presents a small red-shift variation. The obtained behavior in the optical absorption coefficient and refractive index changes can be used to design and fabricate new optical devices such as optical modulators.