Determination Of Refractive Index Research Articles

Pulse propagation in hollow-core fiber at high-pressure regime: application to compression of tens of μJ pulses and determination of nonlinear refractive index of xenon at 1.03 μm: publisher's note.

This publisher's note corrects an author surname in the abstract and a reference in Appl. Opt.57, 4659 (2018)APOPAI0003-693510.1364/AO.57.004659.

Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb.

We present broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS), a technique for calibration-free determination of the complex refractive index of entire molecular bands via direct measurement of transmission modes of a Fabry-Perot cavity filled with the sample. The measurement of the cavity transmission spectrum is done using an optical frequency comb and a mechanical Fourier transform spectrometer with sub-nominal resolution. Molecular absorption and dispersion spectra (corresponding to the imaginary and real parts of the refractive index) are obtained from the cavity mode broadening and shift retrieved from fits of Lorentzian profiles to the individual cavity modes. This method is calibration-free because the mode broadening and shift are independent of the cavity parameters such as the length and mirror reflectivity. In this first demonstration of broadband CE-CRIS we measure simultaneously the absorption and dispersion spectra of three combination bands of CO2 in the range between 1525 nm and 1620 nm and achieve good agreement with theoretical models. This opens up for precision spectroscopy of the complex refractive index of several molecular bands simultaneously.

Exotic Metamaterials from Noncommutative Theory

AbstractExotic optical properties in materials are investigated as a consequence of noncommutative geometry (NCG) originated from deformed Heisenberg algebra. The NCG leads to modified eletromagnetism and then changes the constitutive relations that allow the determination of refractive index and impedance of the medium for different materials. Considering different situations where permittivity and permeability are obtained depending on NCG parameters, in dielectric, nonmagnetic, and magnetic cases, exotic conditions associated with metamaterial properties are obtained as the presence of negative index refraction under a generalized susceptibility depending on NCG. These results show that a class of optical metamaterials can be modeled based on NCG depending on noncommutative parameters.

Pulse propagation in hollow-core fiber at high-pressure regime: application to compression of tens of μJ pulses and determination of nonlinear refractive index of xenon at 1.03 μm.

Classical expression for the propagation constant and absorption coefficient derived by Narcatilli and Schmeltzer for hollow-core fiber (HCF) has been slightly modified to account for noble gas material dispersion at high gas pressure. As a proof of concept, the nonlinear refractive index of xenon (Xe) gas has been investigated by numerically fitting to experimentally obtained spectral broadening in HCF under intense high repetition rate pulses. By varying the Xe pressure inside the HCF, a pressure-dependent nonlinear refractive index value of κ2=(50.1±0.3)×10-20 cm2/W atm at 1.03μm is obtained, which compares favorably with literature reported values. Finally, temporal compression of 50μJ, 320fs pulses at 0.6MHz repetition rate to 61fs with 0.29GW peak power in a HCF filled with 5 bars of Xe gas has been demonstrated using a single HCF compression stage.

Determination of Refractive Indices of a Layered Medium under Pulsed Irradiation

Problems related to determination of refractive indices of layered strongly scattering biological media by means of an optical tomography are investigated. Methods of reconstruction of refractive indices of layers, which are based on the smoothness properties of the solution to the initial-boundary problem, are proposed within the framework of the nonstationary radiative-transfer model. The influence of the probe-pulse duration on the accuracy of recovery of the sought-for characteristics of the medium is investigated numerically.

Ab-initio determination of porous silicon refractive index confirmed by infrared transmittance measurements of an omnidirectional multilayer reflector

We report a multiscale design of omnidirectional Bragg mirrors based on dielectric multilayers by combining quantum mechanical and electromagnetic theories. This design begins with the calculation of electric permittivity for each layer using the density functional theory, followed by a transfer matrix study of light propagation along the multilayer reflector. The theoretical results were further validated by fabricating free-standing porous silicon multilayer films obtained through electrochemical etching of p+-type [100]-oriented crystalline Si wafers, alternating two anodic current densities. The measured infrared transmittance spectra confirm the position and width of the photonic bandgap predicted by the multiscale design.

Determination of refractive index and thickness of YbF3 thin films deposited at different bias voltages of APS ion source from spectrophotometric methods

Abstract Ytterbium fluoride (YbF3) single thin films were prepared on sapphire and monocrystalline silicon substrates through conventional thermal evaporation and ion beam-assisted deposition (IAD), at bias voltages ranging from 50 to 160 V of the Leybold advanced plasma source (APS). By using the Cauchy dispersion model, the refractive index and thickness of the YbF3 thin films were obtained by fitting the 400–2500 nm transmittance of the monolayer YbF3 thin films on the sapphire substrate. At the same time, the refractive index and thickness of the YbF3 thin films on the monocrystalline silicon substrates were also measured using the VASE ellipsometer at wavelength from 400 to 2200 nm. The results showed that the refractive index deviation of the YbF3 thin films between the fitted values by the transmittance spectra and the measured values by the VASE ellipsometer was <0.02 and the relative deviation of the thickness was <1%. Furthermore, the refractive index of the YbF3 thin films increased with increasing APS bias voltage. The conventional YbF3 thin films and the IAD thin films deposited at low bias voltage revealed a negative inhomogeneity, and a higher bias voltage is beneficial for improving the homogeneity of YbF3 thin films.

SURVEY OF SELECTED PROCEDURES FOR THE INDIRECT DETERMINATION OF THE GROUP REFRACTIVE INDEX OF AIR

The main aim of the research was to evaluate numeric procedures of the indirect determination of the group refractive index of air and to choose the suitable ones for requirements of ordinary and high accuracy distance measurement in geodesy and length metrology. For this purpose, 10 existing computation methods were derived from various authors’ original publications and all were analysed for wide intervals of wavelengths and atmospheric parameters. The determination of the phase and the group refractive indices are essential parts in the evaluation of the first velocity corrections of laser interferometers and electronic distance meters. The validity of modern procedures was tested with respect to updated CIPM-2007 equations of the density of air. The refraction model of Leica AT401 laser tracker was analysed.

Time-domain Brillouin scattering assisted by diffraction gratings

Absorption of ultrashort laser pulses in a metallic grating deposited on a transparent sample launches coherent compression/dilatation acoustic pulses in directions of different orders of acoustic diffraction. Their propagation is detected by the delayed laser pulses, which are also diffracted by the metallic grating, through the measurement of the transient intensity change of the first order diffracted light. The obtained data contain multiple frequency components which are interpreted by considering all possible angles for the Brillouin scattering of light achieved through the multiplexing of the propagation directions of light and coherent sound by the metallic grating. The emitted acoustic field can be equivalently presented as a superposition of the plane inhomogeneous acoustic waves, which constitute an acoustic diffraction grating for the probe light. Thus, the obtained results can also be interpreted as a consequence of probe light diffraction by both metallic and acoustic gratings. The realized scheme of time-domain Brillouin scattering with metallic grating operating in reflection mode provides access to acoustic frequencies from the minimal to the maximal possible in a single experimental configuration for the directions of probe light incidence and scattered light detection. This is achieved by monitoring of the backward and forward Brillouin scattering processes in parallel. Applications include measurements of the acoustic dispersion, simultaneous determination of sound velocity and optical refractive index, and evaluation of the samples with a single direction of possible optical access.

Influence of absorption on the refractive index determination accuracy by the minimum deviation method.

By means of computer simulation, the influence of absorption index, κ, on the accuracy of determining the refractive index, n, of optical materials by the minimum deviation method (prism method) is studied at different measuring angular accuracies from 5'' to 0.1''. The n values within 1.0-4.0 and κ values within 0-0.1 are considered. It is shown that (1) except for the far-infrared region, the error in determining n by formula (1)commonly used in the minimum deviation method, i.e., neglecting absorption, is less than the error due to the accuracy of measuring the prism and minimum deviation angles; (2)the difference between n values calculated with and without absorption taken into consideration is, in most cases, negligible throughout the optical range; (3)however, the total error in determination of n is higher when absorption is taken into account than that in the case when absorption is neglected. The further the increase in accuracy of measuring the angles and sensitivity of radiation detectors, the more the proposed calculation technique will allow one to optimize the prism angle value and to calculate more correctly the values of n and error in its determination.

Extinction spectra of suspensions of microspheres: determination of the spectral refractive index and particle size distribution with nanometer accuracy.

A method is presented to infer simultaneously the wavelength-dependent real refractive index (RI) of the material of microspheres and their size distribution from extinction measurements of particle suspensions. To derive the averaged spectral optical extinction cross section of the microspheres from such ensemble measurements, we determined the particle concentration by flow cytometry to an accuracy of typically 2% and adjusted the particle concentration to ensure that perturbations due to multiple scattering are negligible. For analysis of the extinction spectra, we employ Mie theory, a series-expansion representation of the refractive index and nonlinear numerical optimization. In contrast to other approaches, our method offers the advantage to simultaneously determine size, size distribution, and spectral refractive index of ensembles of microparticles including uncertainty estimation.

Determination of refractive index by a U-shaped multimode fiber sensor

ABSTRACTThe U-shaped multimode fiber structure is proposed to measure the refractive index of liquid. In the previous work, the U-shaped structure by single-mode fiber has been widely investigated. However, the large bending loss restricted its practical applications, especially for the reflection-type fiber probe. To reduce the bending losses, the multimode fiber is used as the bending section of the fiber sensor in this study. The structures with different bending radiuses are fabricated to verify this design. Moreover, to simplify the interrogation method, the differential intensity interrogation method is used by cascading two fiber Bragg gratings after the U-shaped fiber structure. The low bending loss of the proposed structure is helpful to measure the reflected light power by fiber Bragg gratings. The influence of incident light power fluctuation was largely suppressed by this differential method. In addition, the sensitivity is also increased by a factor of 2 compared with the intensity interrogation method using one-cascaded fiber Bragg grating. The experimental results show that the refractive index sensitivities are −115.09 dB/RIU in the refractive index range of 1.3405–1.3874 and −260.24 dB/RIU in the refractive index range of 1.3874–1.4223, respectively.

Physico-Chemical Characterizations and Fuel Potential Assessment of <i>Chrysophyllum albidum</i> Fruits from Benin

This study aims to enhance agricultural resources and reduce post-harvest losses by assessing the physical and chemical characteristics of fruits and non-conventional vegetable oil extracted from <i>Chrysophyllum albidum</i> seeds in Benin. In this context, the fruits of <i>Chrysophyllum albidum</i> were collected in Tori (South Benin) and the morphological characteristics (mass, height and diameter at the equator) of the fruits, as well as the physico-chemical parameters (dry matter content, moisture content, ash content) were evaluated. The pH, soluble dry matter (Brix) and glucose levels of the juice were also evaluated. The extraction of vegetable oil from the seeds was carried out in Soxhlet followed by the determination of biochemical parameters such as quality indices such as acid, peroxide, saponification and iodine indices. The physicochemical characterisation of this oil was also carried out through the determination of density, refractive index and net calorific value (PCI). Analysis of these results reveals that the fruits of <i>Chrysophyllumalbidum</i> have a mean equator mass, size and diameter of 43.79±3.15g, 48.73±2.97mm and 41.11±1.13mm respectively. The levels of dry matter, moisture, and ash are respectively 51.60±0.47%, 48.40±0.47%, and 24.7±0.96% with a pH of 3.67±0.12 a Brix of 27.47±0.99 and a glucose level of 27.57mg/mL. The oil extraction efficiency is 21.52 ± 0.86% with a water and volatile matter content of 2.21 ± 0.64%. This vegetable oil has a dark red colour with an iodine value of 33.21 ± 0.08 g I2 /100 g-Oil, a saponification value of 188.40 ± 4.18 mg KOH / g-Oil, an acid value of 3.60 ± 0.23 mg KOH / g-Oil, a peroxide value of 10.46 ± 0.12 meq O2/g-Oil and an ester value of 155.19 ± 0.17 mg KOH / g-Oil. The density of vegetable oil at 30°C is 0.89. The refractive index of vegetable oil at 30°C is 1.48 with a lower calorific value of 40287.92 kJ/kg. The results thus obtained indicate possible ways of using <i>Chrysophyllum albidum</i> fruits as biofuel.

Determination of refractive index and direct bandgap of lattice matched BGaP and (BGa)(AsP) materials on exact oriented silicon

High quality lattice matched III-V semiconductor material, boron gallium phosphide (B2.8%Ga)P and boron gallium arsenide phosphide (BGa)(AsP), layers were deposited on exact oriented (001) 300 mm silicon (Si) substrates by metal organic chemical vapor deposition. An industrial Aixtron Crius R (CCS close coupled showerhead) 300 mm system was used. The material compositions were varied systematically to keep the lattice match to the silicon substrate on one hand, but to change the optical properties and thereby investigate the relationship between the refractive index and different material compositions on the other hand. By in situ measurements, the reflectance was measured during growth, and the refractive index for the wavelength of λ = 950 nm was determined. The results are compared and confirmed with the measurement results of Rogowsky et al. [J. Appl. Phys. 109, 053504 (2011)] which had been achieved by ellipsometry and show a linear dependence in relation to the arsenide and boron content. The refractive index of B2.8%GaP is found to be 3.14, and therefore is larger than the refractive index of GaP of 3.13. This confirms former investigations which lead to the conclusion that the direct band gap of B2.8%GaP is smaller than the direct band gap of GaP. The refractive index of B6.2%GaAs15%P is found to be 3.20, which is a change of 2.3% in comparison to GaP. Based on the measurement results of the direct band gap of BGaP samples with a boron content of up to 6% by surface photo voltage, the direct band gaps of the (BGa)(AsP) samples were calculated and related to the refractive index values. As a result, a change of 2% in the refractive index relates to a reduction of 400 meV in the direct band gap of (BGa)(AsP).

Refractive index distributions in dehydrated cells of human oral cavity epithelium

We present the results of refractive index determination in dehydrated cells of human oral cavity epithelium by means of digital holographic microscopy. Statistical analysis of the obtained results provided the mean value of the refractive index of 1.478 (0.025). The measurement accuracy for refractive index and thickness in both living and dehydrated cells was estimated. As shown, the absolute error of holographic measurements of refractive index in living cells is more than an order of magnitude higher than that in dry cells. The results obtained demonstrate that monitoring of refractive index distributions in nonstained label-free biopsic or histological samples can be considered as a promising tool for the development of rapid diagnostics of pathological changes in cells and tissues.

Determination of refractive index and layer thickness of nm-thin films via ellipsometry.

Ellipsometric measurements give information on two film properties with high precision, thickness and refractive index. In the simplest case, the substrate is covered with a single homogenous, transparent film. Yet, with ellipsometry, it is only possible to determine the two film properties thickness and refractive simultaneously if the layer thickness exceeds 15 nm - a restriction well known for a century. Here we present a technique to cross this limitation: A series expansion of the ellipsometric ratio ρ to the second order of the layer thickness relative to the wavelength reveals the first and second ellipsometric moment. These moments are properties of the thin film and independent of incident angle. Using both moments and one additional reference measurement enables to determine simultaneously both thickness and refractive index of ultra-thin films down to 5 nm thickness.

Determination of size and refractive index of single gold nanoparticles using an optofluidic chip

We report a real-time method to determine the size, i.e. diameter, and refractive index of single gold nanoparticles using an optofluidic chip, which consists of a quasi-Bessel beam optical chromatography. The tightly focused (∼ 0.5 μm) quasi-Bessel beam with low divergence (NA ∼ 0.04) was used to trap sub-100 nm gold nanoparticles within a long trapping distance of 140 μm. In the experiment, 60 to 100 nm gold nanoparticles were separated efficiently with at least 18 μm. The diameter and refractive index (real and imaginary) of single gold nanoparticles were measured at high resolutions with respect to the trapping distance, i.e. 0.36 nm/μm, 0.003/μm and 0.0016/μm, respectively.

A complete parameterisation of the relative humidity and wavelength dependence of the refractive index of hygroscopic inorganic aerosol particles

Abstract. Calculations of aerosol radiative forcing require knowledge of wavelength-dependent aerosol optical properties, such as single-scattering albedo. These aerosol optical properties can be calculated using Mie theory from knowledge of the key microphysical properties of particle size and refractive index, assuming that atmospheric particles are well-approximated to be spherical and homogeneous. We provide refractive index determinations for aqueous aerosol particles containing the key atmospherically relevant inorganic solutes of NaCl, NaNO3, (NH4)2SO4, NH4HSO4 and Na2SO4, reporting the refractive index variation with both wavelength (400–650 nm) and relative humidity (from 100 % to the efflorescence value of the salt). The accurate and precise retrieval of refractive index is performed using single-particle cavity ring-down spectroscopy. This approach involves probing a single aerosol particle confined in a Bessel laser beam optical trap through a combination of extinction measurements using cavity ring-down spectroscopy and elastic light-scattering measurements. Further, we assess the accuracy of these refractive index measurements, comparing our data with previously reported data sets from different measurement techniques but at a single wavelength. Finally, we provide a Cauchy dispersion model that parameterises refractive index measurements in terms of both wavelength and relative humidity. Our parameterisations should provide useful information to researchers requiring an accurate and comprehensive treatment of the wavelength and relative humidity dependence of refractive index for the inorganic component of atmospheric aerosol.

Determination of the complex refractive index of powder phosphors

We demonstrate a novel 2-step method to precisely determine both n and k of phosphors, luminescent inorganic particles, in the visible spectrum. To measure n we modified the Becke Line immersion method and verified its applicability in the absorption/ emission regions of phosphor particles (step 1). Particles were then embedded into a transparent binder and coated in thick layers (100-500 µm) on glass. Absorptance of the layers was measured with a novel approach: spectral angular resolved measurements. This method delivers accurate results by avoiding any errors from intense scattering inside the layers. A computational model was employed to extract k of particles from the measured absorptance data taking into account luminescence, scattering and re-absorption (step 2). The entire method was verified on reference materials. Finally, based on the proposed method, we determined in a broad wavelength range the n and k parameters for a variety of commonly used phosphors with few or no earlier reports on their n and k values (the complete set of numerical data is fully disclosed in the supplementary materials).

Determination of the complex refractive index and optical bandgap of CH3NH3PbI3 thin films

We report the complex refractive index of methylammonium lead iodide (CH3NH3PbI3) perovskite thin films obtained by means of variable angle spectroscopic ellipsometry and transmittance/reflectance spectrophotometry in the wavelength range of 190 nm to 2500 nm. The film thickness and roughness layer thickness are determined by minimizing a global unbiased estimator in the region where the spectrophotometry and ellipsometry spectra overlap. We then determine the optical bandgap and Urbach energy from the absorption coefficient, by means of a fundamental absorption model based on band fluctuations in direct semiconductors. This model merges both the Urbach tail and the absorption edge regions in a single equation. In this way, we increase the fitting region and extend the conventional (αℏω)2-plot method to obtain accurate bandgap values.