Refractive Index Nr Research Articles

Vapour transport grown photosensitive GeO2 thin film

GeO2 thin film (TF) was fabricated by vapour deposition technique in a two zone horizontal quartz tube. Field emission-scanning electron microscopy showed the formation of 200 nm TF on the Si (100) substrate. The X-ray diffraction depicted the presence of the polycrystalline GeO2 TF. The UV–vis absorption spectrum showed humps at 3.1 eV, 4.0 eV and 5.4 eV. The band anticrossing (BAC) model is modified using the Urbach equation to understand the different transitions in the optical absorption spectrum. We have theoretically calculated the relative refractive index (r.i.) (nr) of the GeO2 as 1.8. The temperature dependent current (I)–voltage (V) characteristics and photocurrent of the Au/GeO2/p-Si Schottky device predicted the tunnelling of the carriers, presence of oxygen defects at the junction. The device’s temporal response indicated good photosensitivity at all temperatures and a significant increase in photocurrent was obtained as the temperature increased from 303 K to 403 K.

Structural transition and tunable optical, morphological and magnetic properties of Mn-doped BiFeO3 films

The effects of Mn-doping on the structural, optical and magnetic properties of BiFe1-xMnxO3 (x = 0.0, 0.02, 0.05) thin films prepared by spray pyrolysis technique have been investigated. X-ray diffraction patterns of the annealed films show the distorted rhombohedral crystal structure with R-3 m symmetry. The average crystallite size of films was calculated and found to decrease from 36 nm to 18 nm with increasing Mn-doping from x = 0 to x = 0.05. The microstructural strains calculated from Williamson-Hall plots, increases from 0.0134 to 0.07576 with increasing the Mn-doping. FE-SEM images show that the surface has fibre like network for x = 0.05 and EDS confirms the presence of Bi, Fe, Mn and O element in appropriate stoichiometry. The periodic strips like magnetic domain structures were explored by magnetic force microscopy. The large value of the remanent magnetisation (0.125 emu/cm3) and coercivity (208.35 Oe) of the Mn-doped ferrite films from the magnetic (MH) measurements reveals the enhancement of ferromagnetism via the release of the latent magnetization, locked in the cycloidal spiral structure. The optical band gap and refractive index (nr) of films are tuned from 3.386 eV to 3.479 eV and 2.30 to 2.52 respectively with increase of Mn-doping concentrations.

Aerosol microphysical parameters' vertical profiles measured by a dual Raman-Mie lidar during 2007-2013 at Hefei, China.

L625 4-wavelength dual Raman-Mie lidar was used to detect elastically Mie backscattered light at emitting wavelengths (532 and 355nm) emitted by one Nd:YAG laser, and the nitrogen Raman light (607 and 386nm) inelastically backscattered by nitrogen molecules at Hefei (117.3°E, 31.9°N), China from 2007 to 2013. From the four return signal profiles, highly accurate aerosol extinction and backscatter coefficients, lidar ratio, Ångström exponent, and aerosol Junge exponent can be determined. Furthermore, with a priori assumption of the real part of complex refractive index nr=1.50, the profiles of more aerosol microphysical parameters can be retrieved with their respective errors in the free troposphere, such as the imaginary part of the refractive index, Junge number density coefficient, and particle mass index. The profiles of aerosol microphysical parameters were obtained for 179 nights. Their variation and statistical features were discussed.

Evaluation of a flow cytometry method to determine size and real refractive index distributions in natural marine particle populations.

A flow cytometric (FC) method was developed to retrieve particle size distributions (PSDs) and real refractive index (nr) information in natural waters. Geometry and signal response of the sensors within the flow cytometer (CytoSense, CytoBuoy b.v., Netherlands) were characterized to form a scattering inversion model based on Mie theory. The procedure produced a mesh of diameter and nr isolines where each particle is assigned the diameter and nr values of the closest node, producing PSDs and particle real refractive index distributions. The method was validated using polystyrene bead standards of known diameter and polydisperse suspensions of oil with known nr, and subsequently applied to natural samples collected across a broad range of UK shelf seas. FC PSDs were compared with independent PSDs produced from data of two LISST-100X instruments (type B and type C). PSD slopes and features were found to be consistent between the FC and the two LISST-100X instruments, but LISST concentrations were found in disagreement with FC concentrations and with each other. FC nr values were found to agree with expected refractive index values of typical marine particle components across all samples considered. The determination of particle size and refractive index distributions enabled by the FC method has potential to facilitate identification of the contribution of individual subpopulations to the bulk inherent optical properties and biogeochemical properties of the particle population.

Trapping two types of particles using a focused partially coherent circular edge dislocations beam

A focused partially coherent circular edge dislocations beam used to trap Rayleigh dielectric sphere with different refractive indices is studied. The dependence of radiation forces on the number of circular edge dislocations p, the spatial correlation length σ0, relative refractive index nr, and particle radius a are analyzed and illustrated by numerical examples. It is shown that the focused partially coherent circular edge dislocations beam can be used to trap high index of refraction particles at focus F and bright ring R2, and simultaneously to capture low index of refraction particles at dark ring R1. It is much easier to capture the high index of refraction particles at focus F and the low index of refraction particles at dark ring as for the larger number of circular edge dislocations p and the spatial correlation length σ0, therefore it is necessary to optimally choose on p and σ0 for obtaining an optimal optical guiding. The ranges of the radius for two types of particles stably captured also have been determined. The obtained results are useful for analyzing the trapping efficiency of circular edge dislocations beams applied in micromanipulation technology.

Synthesis, surface tension, optical and dielectric properties of bismuth oxide thin film

AbstractBismuth oxide thin film was deposited by chemical bath deposition (CBD) technique onto a glass substrate. The grain size (D), dislocation density (δ) and number of crystallites per unit area (N), i.e. structural properties of the thin film were determined as 16 nm, 39.06× 10–4line/nm2, 31.25 × 10–31/nm2, respectively. Optical transmittance properties of the thin film were investigated by using a UV-Vis spectrophotometer. The optical band gap (Eg) for direct transitions, optical transmission (T %), reflectivity (R %), absorption, refractive index (nr), extinction coefficient (k), dielectric constant (∊) of the thin film were found to be 3.77 eV, 25.23 %, 32.25 %, 0.59, 3.62, 0.04 and 2.80, respectively. The thickness of the film was measured by AFM, and was found to be 128 nm. Contact angles of various liquids on the oxide thin film were determined by Zisman method, and surface tension was calculated to be 31.95 mN/m.

All-optical bistable switching, hard-limiter and wavelength-controlled power source

In this paper, an all-optical bistable switching operation of resonant-tunneling devices with ultra-small photonic crystal cavity was demonstrated. The whole structure was based on a square lattice photonic crystal formed by rods of refractive index nr= 3.4 in an air background. The cavity was surrounded by eight nonlinear rods of refractive index nL0= 3.1 and nonlinear Kerr coefficient n2= 9 × 10–17 W/m2. Nonlinear finite difference time domain method was used to get a bistability hysteresis loop. Next, all-optical wavelength controlled power source (WCPS), hard-limiter and switching operation based on optical nonlinearity were shown. And that small cavity structure has a small length of 12 mm. Considering the numerous applications and small length, this proposed structure has various potential function in all-optical circuits. Keywords

Photonic crystal all-optical switch based on a nonlinear cavity

We demonstrate high-speed all-optical switch structure using an ultra-small nonlinear cavity coupled to input and output waveguide. The whole structure is based on a square lattice photonic crystal formed by rods of refractive index nr=3.4 in an air background. Finite-difference time-domain method is used to analyze the device characteristics. By analyzing of behavior of structure, we show that switching from OFF to ON occurred because resonant wavelength shift is caused by Kerr effect. The simulation result shows that switch has a high-speed response of ∼26ps. Since the structure has an ultra-small length of 12μm, it has a potential to use in integrated optical-circuits.

Optical and thermal investigations on vanadyl doped zinc lithium borate glasses

Using standard melt-quench technique, transition metal oxide (2 mol% of V2O5) doped glasses having composition xZnO·(30 − x)Li2O·70B2O3 (x = 0, 2, 5, 7 and 10) are prepared. The density (D) is measured using buoyancy and found to be lying between 2.21 and 2.45 g/cm3 with an increasing trend on substituting ZnO contents in place of Li2O. The theoretical optical basicity (Λth) is calculated and found to increase with increasing inclusion of ZnO indicating an increase in the ionic character. The molar refraction (Rm), refractive index (nr) and molar polarizability (αm) are calculated and explained on the basis of structural changes. The optical absorption spectra have been used to evaluate the values of optical band gap (Eopt) and band tailing parameter (B). It is observed that Eopt decreases with the increasing contents of ZnO in base glass matrix. The decrease in Eopt is an evidence of enhancement in the number of non-bridging oxygen atoms (NBOs) thereby increasing the four-coordinated boron atoms. The as-quenched samples in bulk form are subjected to differential thermal analysis (DTA) to assess the glass transition temperature (Tg), which is 476 °C for pure lithium borate glass. The variations suggest that the structure is being modified by the substitution of ZnO.

Preliminary study of Venus cloud layers with polarimetric data from SPICAV/VEx

We present unique polarization data from the SPICAV-IR spectrometer onboard ESA׳s Venus Express (VEx) spacecraft and a first retrieval of cloud parameters. The polarization data have been collected from 2006 to 2010, and cover mostly the northern hemisphere, in the 0.65 to 1.7μm spectral range. They contain information about latitudinal and longitudinal variations in the properties of Venus clouds and hazes, and about temporal variations in these properties. The degree of polarization measured on a few test orbits is in agreement with previous observations from the ground and from Pioneer Venus. Using numerical modeling to interpret the nadir observations, we retrieve mean values of reff~1μm and νeff~0.07 for, respectively, the effective radius and variance of the cloud particle size distribution and a refractive index nr=1.42±0.02 at λ=1.101μm. We also derive an upper limit τh=0.17 at λ=1.101μm for the haze optical thickness at high latitudes. All these values are in good agreement with previous determinations.

Omnidirectional mirror based on Bragg stacks with a periodic gain-loss modulation

In this work we demonstrate that a Bragg Stack with a periodic gain-loss modulation can function as an Omnidirectional Mirror (OM) with complete reflection at any angle of incidence irrespective of the light polarization. The Bragg Stack is composed by the periodic variation of two layers with the same value of the real part of the refractive index (nr) and a periodic modulation in the imaginary part (ni). The origin of the band gaps is due to the interference of complex waves with propagating and evanescent fields in each layer. It is found that the band gaps are wider as the contrast ni/nr increases. We have found the ambient conditions to obtain an OM considering an auxiliary medium n′ external to the Bragg Stack.

Retrieval of jovian cloud structure from the Cassini ISS limb-darkening data: I. Continuum scattering phase functions for cloud and haze in the South Tropical Zone

We have deduced the scattering properties of aerosols in the jovian upper troposphere by analyzing imaging data obtained at a wide variety of solar phase angles (4–140°) by the Cassini Imaging Science Subsystem (ISS) Narrow Angle Camera (NAC) during its flyby of Jupiter. The limb-darkening curves along the South Tropical Zone (STrZ) are extracted from CB2 images (effective wavelength: 750nm) to constrain the single scattering phase functions of aerosols. The best-fit Mie scattering phase function for cloud is obtained with the real part of the refractive index nr,cloud=1.85 and the effective radius reff,cloud=0.3μm. The best-fit combination of nr,cloud and reff,cloud would strongly suggest the idea that the abundant small particle population in the upper troposphere is not composed of pure NH3 ice. Although the optical properties of the stratospheric haze are not well constrained compared with those of cloud, the haze is found to be optically thin (<0.06) and to be strongly forward scattering (effective radius reff,haze=0.5μm).We compare our results with the scattering phase function at red wavelength (640nm) for the STrZ derived by Tomasko et al. (Tomasko, M.G., West, R.A., Castillo, N.D. [1978]. Icarus 33, 558–592), which was deduced from analysis of the Pioneer 10 Imaging Photopolarimeter (IPP) data (12–150° for solar phase angles). Our new Mie scattering phase function can reproduce the Pioneer 10 observations well. In contrast, their scattering phase function described by the double Henyey–Greenstein function does not reproduce the Cassini ISS observations. This is attributed to the fact that their scattering phase function is underconstrained, primarily due to a considerable gap in observations for an intermediate solar phase angle range (34–109°).Our new Mie scattering phase function has advantages over that of Tomasko et al. (Tomasko, M.G., West, R.A., Castillo, N.D. [1978]. Icarus 33, 558–592).(1)Since the Cassini ISS data do not have a large gap in solar phase angle, the new Mie scattering phase function is better constrained.(2)The Mie scattering phase function can be applied easily to different wavelengths.With such characteristics, we now have a reliable baseline scattering phase function that can be used to interpret the ever-changing appearance of jovian clouds as changes of the vertical cloud structure and/or distribution of chromophores in the atmosphere.

Annealing temperature effect on the structural, optical and electrical properties of ZnS thin films

Zinc sulfide thin films were prepared on glass substrates at room temperature using a chemical bath deposition method. The obtained films were annealed at temperatures ranging from 100 to 500°C in steps of 100°C for 1h. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray analysis (EDX), optical absorption spectra, and electrical measurements. X-ray diffraction analysis indicates that the deposited films have an amorphous structure, but after being annealed at 500°C, they change to slightly polycrystalline. The optical constants such as the refractive index (nr), the extinction coefficient (k), and the real (ε1) and imaginary (ε2) parts of the dielectric constant are calculated depending on the annealing temperature. Aside from the ohmic characteristics of the I–V curve, a nonlinear I–V curve owing to the Schottky contact is also found, and the barrier heights (ϕbn) for Au/n-ZnS and In/n-ZnS heterojunctions are calculated. The conductivity type was identified by the hot-probe technique.

Features of the field of a cylindrical wave scattered and focused by an isolated perfect Veselago lens with finite dimensions or by a system of three lenses

The results of solving a scattering problem for the field of a cylindrical wave incident onto an isolated Veselago lens with finite dimensions or onto a system of three lenses are presented for the lens refractive index nr = −1 and loss parameter ν. The influence of geometric dimensions, the loss in the lens medium, and the position of the source of cylindrical wave on the field structure near the focusing region are studied. It is shown that the resolution of this system cannot be increased via an increase in the geometric dimensions of the lens or the number of lenses.

Wave scattering by a prism made of a lossy metamaterial

The results of rigorous calculation of the scattering pattern of a Gaussian beam incident onto a finite prism made of a metamaterial are presented for different values of the refractive index nr < 0 and loss factor ν of the medium. It is shown that geometric optics can correctly predict the tilt of the scattering-pattern maximum, while consideration for the medium’s loss factor 0.001 ≤ |ν| ≤ 0.1 affects the amplitudes of the transmitted and reflected fields.

Guiding optical modes in chains of dielectric particles

We have investigated low frequency guiding polariton modes in finite linear chains of closely packed dielectric spherical particles of different optical materials. These guiding (chain bound) modes cannot decay radiatively, because photon emission cannot take place with simultaneous conservation of energy and momentum. For extending previous work on infinite chains of spherical particles [1] and infinite rods [2, 3], we were able to apply the multisphere Mie scattering formalism to finite chains of dielectric particles to calculate quality factors of most bound modes originating from the first two Mie resonances depending on the number of particles N and the material's refractive index nr. We found that, in agreement with the earlier work [4], guiding modes exist for n(r) > 2 and the quality factor of the most bound mode scales by N(3). We interpreted this behavior as the property of "frozen" modes near the edges of guiding bands with group velocity vanishing as N increases. In contrast with circular arrays, longitudinal guiding modes in particle chains possess a higher quality factor compared to the transverse ones.

Beat frequencies in a ring laser gyro with its refractive index over unity

A frequency shift Δf during rotation in a ring laser gyro with its refractive index of unity was already well known. However, when the refractive index nr is over unity, several expressions for a beat frequency such as 2Δf∝nr, nr0, nr−1, and nr−2 were proposed. In this article, a beat frequency in a uniformly rotating ring laser gyro with nr&amp;gt;1 is calculated using nonrelativistic, special relativistic, and general relativistic theories. To the first order, all the results obtained from these theories show a common beat frequency, which is proportional to the refractive index nr, as far as the dispersion is neglected. When the dispersion is considered, the beat frequency is in proportion to nr0[1−(rΩ/λ0)2(dnr/df)2]−1, where f is a frequency of a laser beam, λ0 is a wavelength of a laser beam when the ring laser stands still, and nr0 is a refractive index at λ0. If nr0=1−(rΩ/λ0)2(dnr/df)2 is satisfied, the beat frequency seems to be independent of the refractive index.

GeO2-ZnO-K2O glass as the cladding material of 940-cm−1 CO2 laser-light transmitting hollow-core waveguide

A hollow-core optical waveguide for 940-cm−1 CO2 laser light was fabricated with 80 mol % GeO2-10 mol % ZnO-10 mol % K2O glass functioning as the cladding, of which the refractive index nr is about 0.6 at 940 cm−1. The waveguide transmission loss is minimized at 940 cm−1 using the glass and is on the order of 0.1 dB/m for a 1-mm-i.d. hollow-core waveguide. Preliminary experiments of CO2 laser-light transmission for 0.6-mm-diam waveguides are also given. Measured loss, normalized to 1-mm-i.d. standard waveguide, is obtained to be 2 dB/m. The transmission mode observed is of the HE11-type only.

Loss calculations of the hollow-core, oxide-glass-cladding, middle-infrared optical waveguides

The loss characteristics of hollow-core, oxide-glass-cladding, middle infrared (near 1000 cm−1) optical waveguide is calculated numerically for TE01, TM01, and HE11 modes. The oxide-glass cladding used has its refractive index nr less than unity; their transmission losses of the waveguide are relatively small due to total reflection effect. The necessity condition of complex refractive index nr -ik of the cladding is clarified to be used with such hollow-core optical waveguides.