Linear Absorption Coefficient Research Articles

Plasmon enhancement of third-order nonlinear optical absorption of gold nanoparticles dispersed in planar oriented nematic liquid crystals

We report structural and nonlinear optical properties of 20 nm gold (Au) nanoparticles (NPs) that are dispersed in planar degenerate (non-oriented) and planar oriented nematic liquid crystals (LCs) (4′-Pentyl-4-biphenylcarbonitrile-5CB). Taking advantage of elastic forces in the planar oriented nematic LC, we aligned AuNPs parallel to the 5CB director axis. In the case of planar degenerate, 5CB is not aligned and has no preferred orientation, forcing the AuNPs to disperse randomly. Results show that the linear optical absorption coefficient for the planar oriented 5CB/AuNPs mixture is larger than the corresponding planar degenerate sample. The nonlinear absorption coefficients are greatly enhanced in planar oriented samples at relatively high concentrations which can be attributed to plasmon coupling between the aligned AuNPs. This study demonstrates the utility of LCs for developing the assembly of NPs with enhanced optical properties which may offer important insight and technological advancement for novel applications, including photonic nanomaterials and optoelectronic devices.

Influence of a Non-Resonant Intense Laser and Structural Defect on the Electronic and Optical Properties of a GaAs Quantum Ring under Inversely Quadratic Potential

We investigated the impact of a non-resonant intense laser, structural defects, and magnetic fields on the electronic and optical properties of a simple GaAs quantum ring under the inverse quadratic Hellmann potential, using the effective mass and parabolic band approximations. We obtained the energies and wavefunctions by solving the 2D Schrodinger’s equation using the finite-element numerical technique to analyze this. We considered circular polarization to calculate the dipole matrix elements, which were influenced by the laser field and structural defects in the system. This enabled us to study the linear absorption coefficients. Our results demonstrated that the presence of a laser field and a structural defect disrupt the axial symmetry of the problem. When only the non-resonant laser was present, a pattern of excited states appeared in pairs, which oscillated with the magnetic field. However, the amplitude of the oscillation decreased as the magnetic field strength increased, and these oscillations disappeared when the structural defect was introduced. It was also noted that the intensity and position of the linear optical absorption peaks exhibited a non-monotonic behavior with the magnetic field in the absence of a structural defect. However, this behavior changed when the structural defect was present, depending on the type of polarization (right or left circular). Finally, a clear improvement in the absorption peaks with an increase in the laser parameter is reported.

Dispersion of optical constants of Si:PbGeO crystal in the terahertz range

Objectives. Advances in laser physics over the last decade have led to the creation of sources of single-period electromagnetic pulses having a duration of about 1 ps, corresponding to the terahertz (THz) frequency range and a field amplitude of several tens of MV/cm. This allows the electrode-free application of an electric field to a ferroelectric for observing not only the excitation of coherent phonons, but also ultrafast (at the sub-picosecond timescale) dynamic polarization switching. To detect polarization switching, a pump-probe technique is used in which a THz pulse is used with an optical probe. Since its intensity is proportional to the square of the polarization, the signal of the optical second harmonic is used to measure polarization switching under the action of a THz pulse. To evaluate switching efficiency, both linear (refractive index and absorption coefficient) and non-linear optical characteristics (quadratic and cubic susceptibilities) are required. For any application of ferroelectric crystals in the THz range, knowledge of the relevant linear optical characteristics is also necessary.Methods. The technique of THz spectroscopy in the time domain was used; here, a picosecond THz pulse transmitted through the crystal is recorded by strobing the detector with a femtosecond optical pulse. The THz-induced dynamics of the order parameter in a ferroelectric was studied by detecting the intensity of a nonlinear optical signal at the frequency of the second optical harmonic.Results. The transmission of a THz wave and the intensity of second harmonic generation on a lead germanate crystal doped with silicon in the time and spectral domains were measured. On this basis, the absorption coefficient dispersion and cubic nonlinear susceptibility were calculated in the range of 0.5-2.0 THz. The presence of a region of fundamental absorption near the phonon modes was confirmed along with a resonant enhancement of the cubic nonlinear susceptibility for two phonon modes Ω1 = 1.3 THz and Ω2 = 2.0 THz.Conclusions. The proposed technique is effective for analyzing the dispersion of the optical characteristics of ferroelectric crystals. The significantly improved spectral resolution (0.1 THz) increases the accuracy of determining nonlinear susceptibility due to the detailed analysis of the linear and nonlinear contributions to the second harmonic intensity.

Preparation and Performance Study of Radiation-Proof Ultra-High-Performance Concrete

With the continuous development of nuclear technology, it is necessary to urgently solve the nuclear safety problem. γ-rays have a strong penetrating power. The γ-ray-shielding performance of ordinary concrete prepared with natural sand is weak and cannot meet the practical application of engineering. The γ-ray shielding performance of concrete can be effectively improved through the use of titaniferous sand with a better γ-ray protection effect. To prepare ultra-high-performance concrete (UHPC) that can provide radiation protection, the influence law of its performance was investigated. The effects of ilmenite sand on the workability, mechanical properties, durability, and radiation-shielding properties of UHPC were investigated via mix testing, compressive strength and flexural strength testing, and a radiation-shielding simulation. The results show that an appropriate amount of ilmenite sand can improve the ultra-high-performance concrete’s work performance; however, ilmenite sand has little effect on its compressive strength. Although it is not conducive to the development of flexural and tensile strength, the γ-ray shielding performance of the UHPC increases with an increase in the addition of ilmenite sand. When the titanite sand admixture is 70%, the γ-ray linear absorption coefficient of the prepared UHPC is 0.158 cm−1, and the γ-ray shielding performance is significantly improved; meanwhile, its durability performance is excellent.

Investigate shielding of standard materials and glass for stopping 662 KeV gamma ray penetrations

Calculations on shielding are required for the building of a gamma ray radiography exposure room to ensure worker exposure to radiation. A measurement used to evaluate the radiation diffusive and absorption characteristics of a medium is the linear attenuation coefficient ( ). Despite the fact that, as radiation moves through a medium, its absorption is influenced by the wavelength of the radiation as well as the thickness and composition of the medium, the linear absorption coefficient is crucial in the interaction of radiation with matter. This research uses a variety of materials as a shield for a gamma radiation source of emitted by Cs-137. The results obtained using a gamma source with a scintillation counter showed that the Half Value Thickness (HVT) of glass and aluminum were 3.57 cm, and 3.39 cm while for standard materials (concrete, iron, and lead) were 2.98 cm, 1.195 cm, and 0.58 cm respectively.

Spin-Orbit and Zeeman Effects on the Electronic Properties of Single Quantum Rings: Applied Magnetic Field and Topological Defects.

Within the framework of effective mass theory, we investigate the effects of spin-orbit interaction (SOI) and Zeeman splitting on the electronic properties of an electron confined in GaAs single quantum rings. Energies and envelope wavefunctions in the system are determined by solving the Schrödinger equation via the finite element method. First, we consider an inversely quadratic model potential to describe electron confining profiles in a single quantum ring. The study also analyzes the influence of applied electric and magnetic fields. Solutions for eigenstates are then used to evaluate the linear inter-state light absorption coefficient through the corresponding resonant transition energies and electric dipole matrix moment elements, assuming circular polarization for the incident radiation. Results show that both SOI effects and Zeeman splitting reduce the absorption intensity for the considered transitions compared to the case when these interactions are absent. In addition, the magnitude and position of the resonant peaks have non-monotonic behavior with external magnetic fields. Secondly, we investigate the electronic and optical properties of the electron confined in the quantum ring with a topological defect in the structure; the results show that the crossings in the energy curves as a function of the magnetic field are eliminated, and, therefore, an improvement in transition energies occurs. In addition, the dipole matrix moments present a non-oscillatory behavior compared to the case when a topological defect is not considered.

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.

Synthesis of tungsten-doped PbI2 nanostructure

Facile synthesis of the microwave was applied to assist in synthesizing pure and tungsten-doped lead iodide (W: PbI2) nanosheets with less than 100 nm thickness. The proposed W-doped PbI2 nanosheets were subjected to various characterization, including structural, morphological, spectral, optical, dielectric, and radiation studies. SEM and EDX investigations confirmed that the tungsten dopants affect the undoped PbI2 matrix. The structural morphology from XRD patterns approved the good crystallinity of the prepared W-doped PbI2 nanostructures. Optical characterizations revealed the energy band structure of the grown materials. The dielectric constant of the W-doped PbI2 nanostructures varied from 23 to 31, confirming the increasing dielectric trend with increasing W doping concentrations. The Gamma linear absorption coefficient value was found to vary between 9.2 and 15 in case Am-241, suggesting various applications in radiation detectors for the prepared W-doped PbI2 nanostructured sheets.

Linear and nonlinear optical absorption coefficients and refractive index changes of GaAs/GaAsSb/GaAs V-shaped quantum wells affected by intense laser fields

Linear and nonlinear optical absorption coefficients and refractive index changes of GaAs/GaAsSb/GaAs V-shaped quantum wells affected by intense laser fields

Investigation of the mechanical properties, shielding parameters and flux distribution in borate - Based glass system using PHITS code; a simulation study

A descriptive method for the attenuation and spatial distribution of flux of photons and fast neutrons for 20Bi2O3 − xPbO − (80 − 2x) B2O3 − xGeO2 (x = 5, 10, 20 and 30 mol %) glass systems (coded as S1, S2, S3, S4 respectively) were performed using PHITS code. The calculated elastic moduli, Young modulus, EM was ranged between 32.58 and 33.81 GPa, while bulk KM and shear GM moduli were in the range of 23.36–30.45 and 12.32–13.15 GPa, respectively. However longitudinal modulus LM was between 40.89 and 46.89 GPa. The spatial distribution of the transmitted photon flux showed a decrease with increasing Pb and Ge concentrations. The mass attenuation coefficients, μm were found to be 70.755–0.042, 76.160–0.043, 83.378–0.046 and 91.895–0.047 cm2/g for S1, S2, S3 and S4 respectively in the energy range of 0.015–15 MeV. The Half Value Layer (HVL) and mean free path (MFP) values were registered in the order of S4 < S3 < S2 < S1. At low energy, the exposure buildup factor EBF of the glasses recorded decrease by the substitution of B2O3 by PbO and GeO2 contents. At energy 0.15 MeV, a crossed behavior was noticed. However, at high energy the inverse behavior of EBF was observed. The neutron transmitted flux percentages, at thickness 10 cm were in the range of 10.26–15.51% at all the selected energies. The linear absorption coefficients ΣT, ranged between 0.220 and 0.278 cm−1 which indicated that S4 represents the best shielding capacity among all. The overall results of this work assessed the selected glasses potential for use as gamma and fast neutron radiation shielding products.

Investigation of the structural, thermal, magnetic and cell viability properties of Ce/Sr co-doped hydroxyapatites

The present study aims to give a more detailed report on the structural, thermal, magnetic and in vitro cell viability properties of the hydroxyapatites (HAps) co-doped with Sr and Ce at different amounts. Besides these experimental analyses, this study also includes the theoretical calculation results obtained from the modeled systems for the as-prepared samples. Diamagnetic behavior was observed for all the samples, as well as their high cell compatibilities. All the samples showed a thermally stable behavior, and the mass change mechanism and specific heat capacity were affected by the amount of the co-dopants. The bandgap value and linear absorption coefficient varied with the amount of both co-dopants.

Harmonic-Gaussian Symmetric and Asymmetric Double Quantum Wells: Magnetic Field Effects

In this study, we considered the linear and non-linear optical properties of an electron in both symmetrical and asymmetrical double quantum wells, which consist of the sum of an internal Gaussian barrier and a harmonic potential under an applied magnetic field. Calculations are in the effective mass and parabolic band approximations. We have used the diagonalization method to find eigenvalues and eigenfunctions of the electron confined within the symmetric and asymmetric double well formed by the sum of a parabolic and Gaussian potential. A two-level approach is used in the density matrix expansion to calculate the linear and third-order non-linear optical absorption and refractive index coefficients. The potential model proposed in this study is useful for simulating and manipulating the optical and electronic properties of symmetric and asymmetric double quantum heterostructures, such as double quantum wells and double quantum dots, with controllable coupling and subjected to externally applied magnetic fields.

Investigation on nonlinear optical properties of symmetric and asymmetric double V-shaped AlxGa1-xAs/GaAs potential wells with structural parameters and external electromagnetic fields

ABSTRACT Linear, nonlinear and total optical absorption coefficients and relative refractive index changes for symmetric and asymmetric double V-shaped quantum well configurations formed within AlxGa1-xAs/GaAs heterostructure have been theoretically investigated. Responses of these coefficients to well widths, barrier widths and aluminium concentrations within the barrier as well as applied external electromagnetic fields were the subject of this study. The electronic spectra of the structures are obtained as a solution to the Schrödinger equation with relevant potential and external agents in the framework of effective mass and envelope wave function approximations. The optical properties are calculated by the analytical expressions obtained by iterative solutions within the compact density matrix approach. Although increasing barrier width and aluminium concentration act similarly significant red shifting on the referred coefficients for both symmetric and asymmetric double V-shaped wells, the varying well widths act differently for each configuration. Strengthening electric and magnetic fields shift the resonance peaks to blue for both symmetric and asymmetric wells. The results show that optical properties can be controlled by structural parameters, external probes and asymmetry of double V-shaped wells.

Facile microwave synthesis of tungsten-doped PbI2 nanostructures for optoelectronic and radiation detection devices

Facile synthesis of the microwave was applied to assist in synthesizing pure and tungsten-doped lead iodide (W: PbI2) nanosheets with less than 100 nm thickness. The proposed W-doped PbI2 nanosheets were subjected to various characterization, including structural, morphological, spectral, optical, dielectric, and radiation studies. SEM and EDX investigations confirmed that the tungsten dopants affect the undoped PbI2 matrix. The structural morphology from XRD patterns approved the good crystallinity of the prepared W-doped PbI2 nanostructures. Optical characterizations revealed the energy band structure of the grown materials. The dielectric constant of the W-doped PbI2 nanostructures varied from 23 to 31, confirming the increasing dielectric trend with increasing W doping concentrations. The Gamma linear absorption coefficient value was found to vary between 9.2 and 15 in case Am-241, suggesting various applications in radiation detectors for the prepared W-doped PbI2 nanostructured sheets.

On-Line Fluorescence Microscopy for Identification and Imaging of Apoptotic Cell with Synchrotron-Based Soft X-ray Tomography.

Synchrotron-based soft X-ray tomography (SXT), providing three-dimensional morphology and quantitative distribution of linear absorption coefficient (LAC) of the imaged objects, is widely used in many fields to obtain ultra-structure images, especially in cellular imaging. Off-line fluorescence microscopies (FMs) are combined to identify the type of organelles and status of cells. However, deformation and displacement usually occur during the transfer and loading process, which decreases the precision of two-modal images' registration. In this paper, we report on an on-line FM, at the SXT station (BL07W) of the National Synchrotron Radiation Laboratory (NSRL), which avoids deformation and displacement. Therefore, researchers can easily find the sample and take the useful data without tedious post-processing. Combining SXT with on-line FM, we achieved the identification and high-resolution imaging of an apoptotic cell. The experiments revealed that the LAC of the nucleus of the apoptotic cell was larger than that of a normal cell, which could be explained by nucleus pyknosis of the apoptotic cell.

First experiments with carbon black pigment dispersion acting as a Janus ultrasound contrast agent

Abstract Background: Theranostic ultrasound contrast agents comprise a therapeutic component whose controlled release is triggered by an ultrasound pulse. However, once the therapeutic component has been released from an ultrasound contrast agent microbubble, its intended uptake cannot be monitored, as its acoustically active host has been destroyed. Acoustic Janus particles, whose hydrophobic and hydrophilic properties depend on the external acoustic regime, are of potential use as contrast agents and drug-delivery tracers. The purpose of this study was to evaluate the hypothesis that submicron particles with Janus properties may act as ultrasound contrast agents whose hydrophobicity changes over time. Methods: Fifty samples of carbon black were subjected to 5-minute sonication with pulses with a center frequency of 10 MHz and a 1% duty cycle, after which the optical absorption coefficients were measured in n-octanol and water. These coefficients were compared with those of unsonicated samples. Results: Our preliminary results show that the difference between the linear absorption coefficients of sonicated and unsonicated samples was Δα = 80 ± 13 m−1 immediately after sonication, indicating that the carbon black particles were less hydrophobic after sonication than prior to it. Forty-eight hours after sonication, the difference in linear optical absorption coefficients had lessened to Δα = 16 ± 9 m−1, indicating that the carbon black particles had become more hydrophobic over time, but not equal to the hydrophobicity situation prior to sonication. Conclusion: The experiments confirmed that submicron carbon black particles have acoustic Janus properties.

Passively Q-switched fiber laser utilizing molybdenum titanium aluminum carbide (Mo2Ti2AlC2) for pulsed laser generation

In this work, Molybdenum Titanium Aluminum Carbide (Mo2Ti2AlC2) was examined to function as a reliable saturable absorber (SA) for stable pulse generation in the 1563 nm wavelength. To create the Mo2Ti2AlC2-PVA film, Mo2Ti2AlC2 powder with > 200 nm particle size was dispersed into polyvinyl alcohol (PVA) and dried to form a film. The Mo2Ti2AlC2-PVA film had a linear absorption coefficient of about 1.5 dB at the Q-switched working wavelength. The Mo2Ti2AlC2-PVA film was sandwiched between fiber ferules and analyzed in the Erbium-Doped Fiber (EDF) ring cavity design. Self-started Q-switching was realized with pump power ranging from 20 mW to 55 mW. The pulse width shrunk from 21.7 µs to 8.9 µs while the repetition rate increased from 20.45 kHz to 40.40 kHz. The fundamental frequency had a signal-to-noise ratio (SNR) of 61 dB, implying good stability of the pulsed laser. The highest output power and pulse energies are 1.1 mW and 27.2 nJ, respectively. These results demonstrate that Mo2Ti2AlC2 can be a good alternative passive SA to produce laser pulsing in the 1.55-micron wavelength.

Effect of Gaussian and Bessel laser beams on linear and nonlinear optical properties of vertically coupled cylindrical quantum dots

Vertically coupled quantum dots are one of the most interesting and promising structures, which find application in a wide range of fields. Particularly, they are noteworthy candidates as a source of single photon and entangled photon pair sources, as qubits and quantum gates in quantum computation, etc. Various external perturbations can act as an instrument for the manipulation of the properties of these structures and an intense laser field is a great example of this. In this work, vertically coupled cylindrical quantum dots made of InAs in a GaAs matrix with a modified Pöschl–Teller potential have been considered under intense laser fields with two laser beam profiles: Gaussian and Bessel. The energy levels and wave functions have been obtained for this structure. Linear and third-order nonlinear absorption coefficients, refractive index changes and second and third harmonic generation susceptibilities have been investigated at different temperatures and for different values of the laser parameters.

Effects of the confinement potential parameters and optical intensity on the linear and nonlinear optical properties of spherical quantum dots

We study the linear and nonlinear optical properties of a spherical GaAs quantum dot with screened modified Kratzer potential (SMKP) by solving the time-independent Schrödinger wave equation using the diagonalization method. The obtained electronic properties of the system alongside the compact density formalism are used to evaluate the linear, third-order nonlinear and total optical absorption coefficients and change in the relative refractive index of the system. We show that the confinement potential parameters and optical intensity significantly affects the behaviour of absorption coefficients and refractive index changes. It is important to note that the findings of this study will find application in optoelectronics and related areas.

Hydrogenic impurity effect on the optical properties of Ga1-xAlxAs quantum wire under terahertz field

In this study, the effect of impurity factor on the optical absorption coefficients, refractive index changes, second harmonic generation, and third-harmonic generation for the intersubband transitions is explored between the electronic states of Ga1-xAlxAs quantum wire initiated by the symmetric parabolic potential. The system is conquered by the presence of an intense electric field, magnetic field, and Rashba spin-orbit interaction. For the linear and non-linear optical absorption coefficients, refractive index, second harmonic generation, and third harmonic generation coefficient, the analytical expressions are obtained with the assistance of the compact density-matrix approach. The arithmetical outcomes illustrate the optical properties are significantly intuitive to the concentration of impurity and can be controlled by this parameter. The variation in the magnitude and position of peaks via impurity factor indicates the opportunity in the mechanism of optical non-linearity in the quantum wire and also, helps in the optical non-linearity tuning which has device application.