Transparent Region Research Articles

Optical transparency and nonlinearity for a five-level tripod system involving a Rydberg state

We demonstrate electromagnetically-induced transparency and giant Kerr nonlinearity in a five-level atomic system where the upper level is a Rydberg-state coupled coherently to a four-level tripod subsystem. Since the high Rydberg states exhibit rather long lifetimes, the system evolves into a dark state that is a superposition of all long-lived states resulting in an optical transparency for the probe field. We solve the relevant density matrix equations for the atomic system in steady-state and utilize the perturbation approach to obtain the expressions for the linear and nonlinear susceptibility. It is shown that depending on the system parameters, the system can exhibit triple, double or single, optical transparency. Therefore, there is a resulting change in the sign of linear dispersion for different parametric situations giving, rise to switching in the group velocity of the probe pulse from superluminal to subluminal or vice versa. We also identify the existence of giant third-order Kerr nonlinearities within regions of optical transparency and under the slow light condition.

Investigation of the effect of mechanical vibration on optical properties when transmitting infrared radiation through sliver halide fibers

The article is devoted to the study of the influence of mechanical vibration on optical properties of polycrystalline two-layer fibers based on solid solutions of silver halides. It is experimentally established that after exposure to vibration for 22 h with a frequency of F = 50 Hz, and an amplitude оf a = 1.1 mm using vibration protection, the transparency range is expanded towards shorter wavelengths. We also observed an increase in optical transparency compared to the initial by 60 - 10% in the range of 3–5 μm, respectively, in the absence of changes in the longer-wavelength region of transparency of the IR fiber 7–20 μm. This effect in the studied IR fibers is explained by the conversion under the action of vibration of a polycrystalline structure into a nano-subcrystalline one.

Beyond Beer's Law: Spectral Mixing Rules.

Based on Beer's law, it is assumed that the absorbance of a mixture is that of the neat materials weighted by their relative amounts (linear mixing rule). In this contribution, we show that this is an assumption that holds only under various approximations for which no change of the chemical interactions is just one among several. To understand these approximations, which lead incrementally to different well known mixing rules, we finally derive the linear mixing rule from the Lorentz-Lorenz relation, with the first approximation that the local electric field is correctly described in this relation. Further levels of approximation are that the local field equals the applied field (Newton-Laplace mixing rule) and that the change of the index of refraction and, equivalently, absorption is weak (Gladstone-Dale/Arago-Biot mixing rule). Even then the linear mixing rule is only strictly valid if the indices of refraction in the transparency region at higher frequency than the absorption have the same value and the mixing is homogeneous relative to the resolving power of the light ("micro-homogeneous"). Under these preconditions, linear mixing of the individual absorbances is established. We illustrate the spectral differences between the different mixing rules, all of which are based on volume and not on mass fractions, with examples. For micro-heterogeneous samples, a different linear mixing rule governs the optical properties, which refers to the experimental quantities, reflectance, and transmittance. As a result, for such samples, mixtures of already comparably high content give only weak signals due to band flattening, which are hard to distinguish from baseline effects.

Sr5Ga8O3S14: A Nonlinear Optical Oxysulfide with Melilite-Derived Structure and Wide Band Gap.

Sr5Ga8O3S14, which is a novel nonlinear optical oxysulfide, was discovered via solid-state reaction. The compound crystallizes in noncentrosymmetric space group P21212 (No. 18) of the orthorhombic system. The crystal structure is derived from the melilite structure and composed of anionic [Formula: see text] layers intercalated by Sr2+ cations. The anionic layers are constructed by [GaOS3]5- and [GaS4]5- tetrahedra via either corner sharing or edge sharing, while typical melilite only features edge-sharing mode. Because of the existence of electronegative O atoms, it possesses a large band gap (3.9 eV) with a wide transparent region of 0.3-13.4 μm. It exhibits second-harmonic-generation response, which is 0.8 times that of the reference AgGaS2 (AGS) in the particle size range of 20-41 μm under laser irradiation at a wavelength of 2.09 μm laser. Density functional theory calculations indicate that the band edges are mainly composed of the Ga-S bond orbitals, with little participation of O 2p near the valence band maximum.

Growth and Structural Characterization of Doped Polymorphic Crystalline MgPc as an Organic Semiconductor

The doping and crystallization of the molecular semiconductor formed from the magnesium phthalocyanine (MgPc) and 1-(4-Methoxyphenyl)-2,2,6,6-tetramethyl-5-phenylhepta-3,4-dienedioic (MTPDA) acid was carried out in this work. The crystals obtained were characterized by using transmission electronic microscopy (TEM), Raman spectroscopy, and X-Ray diffraction (XRD), to later evaluate their optical behavior. Raman, IR, and UV–Vis results indicate that the MgPc has been doped with the MTPDA. A uniform material layer with particles is observed as a result of a two-stage process, nucleation and growth. The polycrystalline films are constituted by a mixture of α and β phases with crystalline sizes of ~7 nm, 14 nm, and 20 nm average sizes. The films exhibit a preferred orientation along the [001]. The MTPDA doping does not have an important effect on the molecule planar distances indicating that the MTPDA molecule is among the equivalent MgPc plane direction. A transparent region with a minimum at 483 nm is observed, also a B-band at 337 nm and a Q-band transition with a high-energy peak around 639 nm, and a low energy peak around 691 nm.

Optimization of Microemulgel for Tizanidine Hydrochloride.

Background: Tizanidine hydrochloride acts centrally as a muscle relaxant. It is used for the treatment of painful muscle spasm, spasticity associated with multiple sclerosis or spinal cord injury and treatment of muscle spasticity in spinal cord disease. Tizanidine hydrochloride belongs to BCS class II. It has low oral bioavailability and short half-life. Incorporating this drug in microemulgel is an excellent way to overcome problems associated with the drug.Objectives: Present research work was aimed to develop and optimize a microemulsion based gel system for tizanidine hydrochloride.Methods: Screening of oil, surfactant and co-surfactant was carried out. Ternary phase diagram was constructed to obtain concentration range of components. The prepared microemulsion was evaluated for pH, globule size, zeta potential, conductivity, density and viscosity. 32 level factorial design was applied to study the effect of concentration of carbopol 934 and HPMC K15M on % cumulative drug release and viscosity of microemulgel using software Design Expert. Microemulgel was evaluated for pH, spreadability, viscosity, syneresis, drug content, bioadhesive strength, in-vitro as well as ex-vivo diffusion study.Results: Microemulsion was prepared by using isopropyl myristate as oil, tween 80 as a surfactant and transcutol P as cosurfactant. Largest transparent microemulsion region was found with Smix ratio of 1:1. FE-SEM showed globule size 28µm for batch B1 and zeta potential was -1.27mV indicating good stability of the microemulsion. Optimised batch was F6 which showed 92% drug release within 8 hours. It followed the Korsmeyer-Peppas model.Conclusion: A stable, effective and elegant microemulgel formulation, exhibiting good in-vitro and ex-vivo drug release was formulated.

Transparent dentin region in the tooth root.

Transparent dentin in the tooth root forms during the aging process. The transparent dentin is weaker than normal opaque dentin, which may explain the occurrence of root dentin fractures in aged individuals. Tooth fractures are caused by the brittleness of the transparent dentin. Clinical procedures in aged persons require modification to accommodate the reduced strength of the dentin tissue.

ZnO Films Obtained by Reactive Magnetron Sputtering: Microstructure, Electrical, and Optical Characteristics

In this study, a technology producing undoped crystalline zinc oxide films with purposefully changed electrical resistance ρ = 3 × 10–4–1 × 107 Ω cm has been developed. The relationship between the electrical characteristics of ZnO layers and the parameters of their deposition has been studied, and the conditions for the formation of high-resistance i-ZnO and low-resistance n-ZnO films with specified values of electrical resistance have been determined. It has been established that the dominant factor determining the conductivity of ZnO films is a change in the concentration of free carriers, controlled by oxygen vacancies. To select the optimal conditions for the formation of highly transparent coatings with a given conductivity, the microstructure and spectral properties (edge absorption and transmission spectra in the transparency region) of n-ZnO films deposited by reactive magnetron sputtering of a zinc target in an argon atmosphere with oxygen (10% Ar, 90% O2) at a pressure of 5 × 10–3 Torr have been studied. It has been shown that the developed method for the discrete formation of ZnO films on amorphous substrates provides stoichiometric crystal structures with a high packing density and spatial orientation of crystallites in the [002] direction. Even in the case of n-ZnO films with ρ = 3 × 10–3 Ω cm, the microstructure causes a high transmittance of the coatings.

Colored Radiative Cooling Coatings with Nanoparticles

Daytime radiative cooling under sunlight can be achieved by reflecting solar irradiation and emitting infrared thermal radiation in the transparency regions of earth atmosphere. For the sake of aes...

KInSi1.32Sn0.68Se6: An Infrared Nonlinear Optical Material Containing Three Types of Tetrahedral Units.

The deficiency of nonlinear optical (NLO) materials in the infrared region pushes continuous exploration of new ones with desired performances. In this work, a novel pentanary selenide KInSi1.32Sn0.68Se6 is discovered by using a high-temperature solid-state reaction. It crystallizes in the monoclinic noncentrosymmetric space group Cc featuring a 3D [(InSi1.32Sn0.68Se6)-]n polyanionic network, and its powder sample presents promising NLO behaviors, namely 1.3-times second-harmonic generation response and close laser-induced damage threshold than those of benchmark AgGaS2. Besides, it is phase-matchable and shows a wide transparent region. Theoretical calculation addressing its electronic structure and optical property is also performed.

SPATIAL STRUCTURE OF AZIMUTHALLY SMALL-SCALE MHD WAVES IN ONE-DIMENSIONALLY INHOMOGENEOUS FINITE PRESSURE PLASMA WITH CURVED FIELD LINES

We have studied propagation of hydromagnetic (MHD) waves in one-dimensionally inhomogeneous finite pressure plasma with curved field lines. Magnetic surfaces are considered to be concentric cylinders, where the cylinder’s radius models the radial coordinate in Earth’s magnetosphere. The waves are supposed to be azimuthally small-scale. In this approximation there are only two MHD modes — Alfvén and slow magnetosonic (SMS). We have derived an ordinary differential equation for the spatial structure of the wave field in this model. We have examined the character of the singularity on the surface of Alfvén and SMS resonances and the influence of field line curvature on them. We have determined wave transparent regions. The SMS transparent region was found to essentially broaden as compared to the straight field line case. The very existence of the Alfvén transparent region is caused by the field line curvature and finite plasma pressure; otherwise, the wave structure is represented by a localized resonance.

Пространственная структура азимутально-мелкомасштабных МГД-волн в одномерно-неоднородной плазме конечного давления с кривыми силовыми линиями

We have studied propagation of hydromagnetic (MHD) waves in one-dimensionally inhomogeneous finite pressure plasma with curved field lines. Magnetic surfaces are considered to be concentric cylinders, where the cylinder’s radius models the radial coordinate in Earth’s magnetosphere. The waves are supposed to be azimuthally small-scale. In this approximation there are only two MHD modes — Alfvén and slow magnetosonic (SMS). We have derived an ordinary differential equation for the spatial structure of the wave field in this model. We have examined the character of the singularity on the surface of Alfvén and SMS resonances and the influence of field line curvature on them. We have determined wave transparent regions. The SMS transparent region was found to essentially broaden as compared to the straight field line case. The very existence of the Alfvén transparent region is caused by the field line curvature and finite plasma pressure; otherwise, the wave structure is represented by a localized resonance.

Beyond Beer's Law: Why the Index of Refraction Depends (Almost) Linearly on Concentration.

Beer's empiric law states that absorbance is linearly proportional to the concentration. Based on electromagnetic theory, an approximately linear dependence can only be confirmed for comparably weak oscillators. For stronger oscillators the proportionality constant, the molar attenuation coefficient, is modulated by the inverse index of refraction, which is itself a function of concentration. For comparably weak oscillators, the index of refraction function depends, like absorbance, linearly on concentration. For stronger oscillators, this linearity is lost, except at wavenumbers considerably lower than the oscillator position. In these transparency regions, linearity between the change of the index of refraction and concentration is preserved to a high degree. This can be shown with help of the Kramers–Kronig relations which connect the integrated absorbance to the index of refraction change at lower wavenumbers than the corresponding band. This finding builds the foundation not only for refractive index sensing, but also for new interferometric approaches in IR spectroscopy, which allow measuring the complex index of refraction function.

Tailoring of electrical properties of Cu2O thin films fabricated by oxygen injection after argon plasma reduction of CuO films

Cu2O thin films with tailored electrical properties were produced by 25 s plasma reduction of CuO films and immediate oxidation under oxygen flows of 0, 3, 6, 9, 12, 15, and 18 sccm. CuO target films were easily prepared by the dip-coating method and annealing at 400 °C. CuO was transformed to Cu2O by employing an argon plasma treatment devised in our laboratory. Cu2O was produced as the only crystalline phase detected, and the films exhibited smooth surfaces with roughness around 5 nm. All films presented high reflectance in the fundamental absorption region (30%) and high transmittance in the transparency region of Cu2O (65%). The good optical behavior permitted the accurate calculation of optical constants by fitting reflectance and transmittance to an optical model designed with the help of Film Wizard™ software. Variations with oxygen injection were detected for the components of the dielectric function, index of refraction, and absorption coefficient. More importantly, the electrical properties of Cu2O showed a clear dependence on O2 injection. Even though resistivity was on average 80 Ω∙cm, hole mobility varied in the span of 0.75–3.2 cm2/V s, and hole density in the range of 1016–1017/cm3. Upon storage in open-air conditions, the mobility of Cu2O films was increased to 3.8 cm2/V s. The Cu2O films produced show similar quality to those obtained by a sputtering deposition method. However, simpler equipment was employed. The plasma method studied is promising for fast mass production of Cu2O thin films.

Physical and numerical study on unsteady shedding behaviors of ventilated partial cavitating flow around an axisymmetric body

The objective is to investigate the unsteady ventilated partial cavitating flow characteristics with focus on the unsteady shedding behaviors via combined experimental and numerical methods. Experimental results are presented for an axisymmetric body in a water tunnel with the flow pattern recorded by a high speed camera. The numerical simulation is performed with a filter-based turbulence model. Good agreement can be obtained between the experimental and numerical results. The ventilated cavity around the axisymmetric body experiences the rapid growth stage, the growth with small pulsation stage and the periodic shedding stage. The typical ventilated cavitating flow patterns at different angles of attack have also been studied to further investigate the effect of the asymmetry on the unsteady shedding behaviors of ventilated partial cavitating flow. With the increase of the angle of attack, the ventilated cavity develops asymmetrically and the non-transparent gas-liquid mixture region is gradually concentrated on the opposing stream surface along with the transparent cavity region increasing on the confronted stream surface.

Secondary electro-optic response induced by VOD875S dye in polymer stabilised liquid crystals

ABSTRACT Polymer stabilised liquid crystal, which has the scattering state and transparent state, is widely used in tunable optic devices. Here, we demonstrate a polymer stabilised liquid crystal device with secondary electro-optic response phenomenon. Doped VOD875S dye into the normal polymer stabilised liquid crystal, the transmittance of the scattering and transparent states is reduced; moreover, the transparent region can be extended beyond the electrode and the transmittance is increased again when the operating voltage is larger than a critical value. The effects of dye concentration, polyimide (PI) layer and surfactant concentration on the secondary electro-optic response phenomenon of PSLC film were studied. It was found that high dye concentration, no PI layer and high surfactant concentration can effectively reduce the critical voltage of the secondary electro-optic response phenomenon. The secondary electro-optic response phenomenon can be used in some smart devices.

Nonlinear Bleaching of InAs Nanowires in the Visible Range

Spectral and nonlinear optical properties of InAs nanowires synthesized via molecular beam epitaxy suspended in isopropanol are studied in this work at room temperature. The absorption spectra with a characteristic maximum at a wavelength of 235 nm, as well as the Raman spectra in a range of 180–280 cm–1, are obtained. The nonlinear transmittance of InAs nanowires with diameters less than the exciton Bohr radius was firstly investigated by a two-photon excitation in the transparent region (λ = 468 nm). The effect of cumulative bleaching, the manifestation of which is associated with the dynamic Stark effect, was discovered.

EIT-based giant self-kerr-nonlinear behavior of multilevel X-scheme

This paper aims at theoretical evaluation of enhanced self-Kerr nonlinear coefficient in multilevel X-conformation of 87Rb atom. The coupled density matrix equations are numerically solved by iterative perturbation method to obtain first- and third-order probe response spectra. It is found that large self Kerr nonlinearity with reduced absorption is obtained at the positions of Electromagnetically induced transparency regions. The maximum value, sign as well as slope of self-Kerr nonlinearity can be manipulated via adjusting detuning parameter corresponding to the strong electromagnetic (e.m.) fields. The controllability of Kerr nonlinear index finds usage in numerous applications like optoelectronic devices, quantum computing and so on. It is also elucidated that Kerr nonlinearity can be escalated by inculcation of Doppler effect.

Laser on erbie glass with diode pumping

The results of studies aimed at the development and creation of an erbium-diode-laser laser with diode pumping and providing an output energy of several millijoules in pulses of 20-30 ns duration at a repetition rate of 0.5-1.0 hertz are presented.The interest around this laser is due to the fact that its radiation falls into the spectral region, which is relatively safe for vision. In this spectral region there is a transparency window in the earth's atmosphere. Thus, half-micron radiance can be used efficiently for location aims and rangefinder. This is facilitated by the presence of highly sensitive uncooled photo detectors. In addition, the spectral region of 1.5-1.6 μm matches with the region of maximum transparency of quartz optical fibers used in fiber-optic communication lines.The experimental sample of ytterbium-erbium laser emitting at a wave length of 1, 54 μm was designed and manufactured. Pumping of active element was done according to the transverse scheme by two laser diode rulers with a power of 100 W each, which has been put in line. The selected pump scheme provides a high excitation power and eliminates the occurrence of a temperature gradient in the active element. To increase the pumping efficiency, a cylindrical active laser element was placed in a sapphire cylinder, the outer surface of which had a reflective coating. During free generation regime, we implemented the optimization of laser characteristics, depending on the Q-factor of resonator and excitation conditions. To obtain a giant impulse, a passive Q-switch based on aluminum-magnesium spinel with cobalt was used in the work. In the Q-switched mode, single pulses with the energy of 6 mJ were obtained with a duration of less than 30 ns at a pulse repetition rate of one hertz.

Нелинейное просветление InAs нитевидных нанокристаллов в видимом диапазоне

The spectral and nonlinear optical properties of InAs nanowires suspensions in isopropanol were studied at room temperature. InAs nanowires were synthesized by molecular beam epitaxy. The absorption spectra of suspensions with a characteristic maximum at a wavelength of 235 nm were obtained, as well as Raman spectra in the range 180–280 cm – 1. The nonlinear transmission of InAs nanowires with a diameter less than the Bohr radius of the exciton upon two-photon excitation in the transparency region in the visible range (λ = 468 nm) was studied firstly. The effect of cumulative bleaching was discovered, the manifestation of which is associated with the dynamic Stark effect.