Experimental determination of optical constants of MgF2 and AlF3 thin films in the vacuum ultra-violet wavelength region (60-124 nm), and its application to optical designs

The investigation of some solar radiations of interest for astrophysicists requires optics in the 80-130 nm vacuum ultra-violet spectral range (VUV). In this domain, where both transmittance and reflectance of most materials are very low, the measurement of optical constants is specifically difficult, and optical data are consequently often either inexistent or uncertain. Reliable modelling of optical components for VUV, like polarizing multi-layered mirrors, necessitates prior measurement of complex indices of the thin films involved in the coating. Fluorides like MgF₂ or AlF₃ are among the rare materials capable to contribute to multi-layer mirrors in the VUV.We have determined optical constants of thin films of these two materials by using a two media reflectance method at normal incidence and a graphical determination particularly suited to this VUV region, which we presented in a previous paper. Optical constants are determined in the range 60-124 nm with 2 nm step, and are compared to existing data. On the basis of these measured indices, polarizing mirrors for λ₁ = 121.6 nm or λ₂ = 103.2 nm have been modelled and fabricated. Their reflectance measured versus incidence angle by using monochromatized synchrotron radiation at the above wavelengths is found in agreement with the calculated predictions.     

Determination of the depth of formation of magnetooptical effects in CoNi films

The optical constants of CoNi films with magnetic properties that are nonuniform across their thickness are determined in reflected light by two methods, viz., optical and magnetooptical measurements. The values of the parameters L=λ/4πk and Z ₀=λ/8n, one of which (specifically, the one which has the smaller value at a given value of λ) determines the depth of formation of reflective magnetooptical effects (l _mo) according to the current theories, are calculated on the basis of the values obtained for the optical constants n and k of the films (λ is the wavelength of the light used, and n and k are the refractive index and the absorption coefficient of the magnet). It is established for the CoNi films investigated that l _mo is determined by L and varies from about 200 to 300 ? in the range 0.33 μm⩽λ⩽0.83 μm. In CoNi films, which are inhomogeneous across their thickness and are characterized by significant variation of the magnetic properties over distances ∼l _mo, variation of the form of the magnetization curves determined by measuring the equatorial Kerr effect is observed as λ increases. Zh. Tekh. Fiz. 68, 69–72 (February 1998)     

Measurement of magnetostriction and anisotropy of Mg-ferrite

The magnetostriction constants λ₁₀₀ and λ₁₁₁ and the anisotropy constant K₁ of Mg-ferrites [Mg_η;Fe_1?η][Mg_1?ηFe_1+η]O₄, (η = 0·101, 0·154, 0·184, 0·219) at room temperature, liquid N₂ temperature and liquid He temperature were observed by ferrimagnetic resonance techniques at 9·5 GHz.The signs of the magnetostriction constants λ₁₀₀ and λ₁₁₁ are always negative and positive, respectively and the magnitudes of these constants increase with decreasing temperature. These constants λ₁₀₀ and λ₁₁₁ at liquid He temperature are found to be ? 14·4 × 10^?6 and 2·4 × 10^?6 respectively, when η is 0·101, and then the magnitudes of those constants decrease linearly with increasing η.     

An optical study of the stretching absorption band near 3 microns from OH- defects in LiNbO3

A near infrared absorption band (λ = 2.87 μ), identified as the 0–1 stretching vibrational band of OH^- defects in LiNbO₃, has been observed at 6, 77, and 300 K. This band was completely polarized perpendicular to the crystallographic c-axis within experimental error and two peaks, separated by approximately 13 cm^?1, were resolved. Both the structure and optical anisotropy of this band were independent of stoichiometry and sample treatments and may be understood in terms of a simple model where protons are captured by O^2- anions forming OH^- defects whose orientations are determined by neighboring O^2- ions.     

Phase resolved near-field imaging of propagating waves in infrared tapered slot antennas

Tapered slot antennas (TSAs) consist of a planar non-resonant structure which couples incident radiation to a propagating waveguide mode. They are commonly used at microwave and radio frequencies because they are fundamentally broadband and have small profiles. Because of their planar layout and broadband response they have recently been scaled to infrared frequencies where they have advantages for sensing and energy harvesting. We use scattering-type scanning near-field optical microscopy (s-SNOM) to study the mode transformation of two types of TSA operating in the thermal infrared (λ₀ = 10.6 μm) with respect to electric field amplitude and phase. The results agree well with simulation showing both the phase reversal across the tapered slot and the traveling of wave fronts along the tapered slot, yet they also reveal high sensitivity of device performance to inhomogeneities in the geometry or illumination. This study will aid future design and analysis of practical non-resonant antennas operating at optical and infrared frequencies.     

Structural and optical properties of thermally evaporated 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile thin films

The structural and optical properties of as-deposited and γ-rays irradiated 2-(2,3-dihydro-1,5dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile (DOPNA) thin films have been reported. The structural properties of as-deposited and γ-rays irradiated DOPNA thin films are characterized by Fourier transformation infrared, X-ray diffraction and transmission electron microscope techniques. The transmittance, T(λ), and reflectance, R(λ), are measured at the normal incidence of light by a double beam spectrophotometer in the wavelength range 200-2200 nm. The refractive and absorption indices have been calculated. The dispersion parameters such as dispersion energy, oscillator energy and dielectric constant at high frequency are evaluated. The data of the absorption coefficient are analyzed in order to determine the type of inter-band electronic transitions and the optical band gap of the films. Other optical absorption parameters, namely, the extinction molar coefficient, oscillator strength and the electric dipole strength, are also calculated.     

Radiation properties of soot from diffusion flames

The spectral extinction coefficients k_λ of soot from flame transmission data are obtained for small pool diffusion flames of various fuels including solid polystyrene and plexiglas; foam polystyrene and polyurethane; and liquid isooctane and toluene. Good agreement between experimental and predicted k_λ from Mie theory and soot optical properties throughout the visible and infrared ranges substantiates the general applicibility of these optical properties. On the other hand, the determination of soot sizes and volume fractions from visible range data and optical properties requires the form of the size distribution be known. The effect of using different size distributions on these soot results is evaluated by using the three-parameter distribution for the particle number density N(r) = ar^b exp (?br/r_m), with b varied to create different functional dependence on radius r. The most probable radius r_m is found to increase by about 80% as b is changed from 2 to 6, while the volume fraction changes by less than 10%. Hence, the most probable radius is rather sensitive to this functional dependence, while the volume fraction is only slightly affected.     

The corrected Enskog theory and the transport properties of molecular liquids

Analytical expressions for the transport coefficients of liquids based on the corrected Enskog theory have been used in order to determine the self-diffusion coefficient (D) for molecular liquids as a function of density and temperature. The liquids considered are those composed of linear molecules and NH₃. The calculated D values agree with the experimental ones for those molecular liquids for which experimental self-diffusion data are available. The translational part of the thermal conductivity (λ_trans) has also been calculated and compared with the experimental thermal conductivity (λ). It turns out that λ_trans for diatomic molecular liquids practically represents the whole of λ in a substantial fraction of the liquid range, indicating that the internal degrees of freedom hardly contribute to the thermal conductivity in these dense liquids. A comparison is made with recently published results based on the modified Enskog theory.     

Infrared structure of non-abelian gauge theories: An instructive calculation

As a step towards an understanding of the infrared structure of non-Abelian gauge theories, we have calculated the anomalous magnetic moment of a colored quark up to fourth-order in the quark-gluon coupling constant g. The fourth-order result is infrared divergent. The infrared divergence is governed by the one loop contribution to the function β_λ(g) = λ dg/dλ, where λ is a small gluon-mass regulator. A differential equation which describes the infrared structure of the electromagnetic quark-form factors is proposed.     

Recursive wavefront aberration correction method for LCoS spatial light modulators

We present two accurate and relatively simple interferometric methods for the correction of wavefront aberrations of about 3 wavelengths (3λ) in spatial light modulators (SLMs) of the liquid crystal on silicon (LCoS) type. The first is based on a recursive use of a wavefront fitting algorithm in a Wyko™ interferometer, in which Zernike polynomials are employed as the basis functions. We show here that the successive use of only three measurements is required to obtain a peak-to-valley (PV) error as low as λ/10, with an uncertainty of λ/30, in the compensated wavefront. The second method makes use of the actual optical path difference (OPD) computed by the interferometer at each pixel of the image of the interferogram of the LCoS modulator (LCoS-M). From numerical interpolation of these OPD values we were able to assign the required OPD compensation at each pixel of the LCoS-M. With this method, PV errors of the compensated wavefront as low as λ/16, with an uncertainty of λ/30, were obtained for the entire LCoS-M, or of λ/33 for the disk that we used as the domain of the Zernike polynomials in the first method.     

Analysis of correlation between electrical and infrared optical properties of anatase Nb doped TiO2 films

Optical and electrical analysis are required to clarify infrared reflection behavior of anatase Nb doped TiO₂ (NTO) films, a novel transparent conductive oxide (TCO). In this paper, UV–vis-near infrared transmission spectrum, Fourier transformed infrared (FTIR) reflection and ellipsometry analysis are conducted on anatase NTO films (Nb doping concentration: 6, 4 and 2 at%) deposited by pulse laser deposition (PLD). NTO samples show good transparency from 400 nm to 1000 nm, but no obvious plasmon induced high IR reflection even when wavelength >3000 nm. Assuming inhomogeneous resistivity (ρ) and mean scattering time (τ) along film thickness, dielectric constants (ε_r, ε_i) and optical constants (n, k) are extracted by fitting spectroscopic ellipsometry using Code-Lorentz (CL) & Drude exponential model. It is shown that unique optical constants and small τ (1.1–2.6 fs) intrinsically prevent NTO to be high infrared reflective TCO.     

The vapor phase Raman spectra,Raman band contour analyses,Coriolis constants,force constants,and values for thermodynamic functions of the trihalides of group V

The vapor phase Raman spectra have been recorded of the molecules PX₃ (X = F, Cl, or Br), AsX₃ (X = F, Cl, Br, or I), and SbX₃ (X = Cl, Br, or I) in sealed tubes at 22–365°C as appropriate. Attempts to record the vapor phase Raman spectra of the molecules PI₃, SbF₃, and BiX₃ (X = F, Cl, Br, or I) were unsuccessful. The infrared and Raman rotational branch separations of the a₁ species fundamentals for these molecules are in agreement with the theoretically calculated values. The Raman band contours of the e-species fundamentals have been analyzed to yield, in favorable cases, values for the corresponding Coriolis constants which have been compared with those obtained from infrared band contour analyses, and which have been employed to constrain the e-species force constants. It is concluded that the Raman contour method for defining Coriolis and thus force constants should be regarded as further, but not necessarily the best, experimental method with which to help to constrain the field. Values for various thermodynamic functions of the molecules have been calculated from the new values for the fundamental frequencies and from the most recent structural data.     

Optical and electrical properties of thin NiO films deposited by reactive magnetron sputtering and spray pyrolysis

Thin NiO films are deposited by reactive magnetron sputtering and spray pyrolysis. The main optical constants, i.e., refractive index n(λ), absorption coefficient α(λ), extinction coefficient k(λ), and thickness d, are determined. The temperature dependence of the resistance of thin films is found, and the activation energy of films deposited by different methods is determined.     

Infrared optical properties of Mn1.56Co0.96Ni0.48O4 thin films prepared by chemical solution deposition

～2 μm thick Mn_1.56Co_0.96Ni_0.48O₄ (MCN) films have been prepared on a Al₂O₃ substrate by the chemical solution deposition method. X-ray diffraction and microstructure analyses show good crystallization and the thickness of the films is 2.12 μm. Mid-infrared optical properties of MCN films have been investigated using transmission spectra and infrared spectroscopic ellipsometry. The optical band gap of the MCN film has been derived to be 0.64 eV by assuming a direct transition between valence and conduction bands. The optical constants and thickness of the thin films have been obtained by fitting the measured ellipsometric parameter data with the classical infrared model. The refractive index n of the MCN films decreases as the wavelength increases, but the extinction coefficient k monotonously increases in the wavelength range of 2–7 μm. The maximal n value is 2.63, and the maximal k value is only 0.024. The above results are instructive for the applications of MCN films in infrared detecting.     

Identification of optical nonlinearities of dye-doped nematic and polymer-dispersed liquid crystals using Z-scan technique

This study investigates the nonlinear optical properties of azo-dye-doped nematic and polymer-dispersed liquid crystal (ADDPDLC) films with nano-sized LC droplets using the Z-scan technique, which is a simple but powerful technique for measuring the optical Kerr constants of materials. The results indicate that the optical Kerr constant (n₂) of the azo-dye-doped nematic LC (ADDLC) film is large because of the photoisomerization effect and the thermal effect. Therefore, the optical Kerr constant of this material can be modulated by varying the temperature of the sample and the direction of polarization of incident laser. The range of n₂ modulated is from −5.26 × 10⁻³ to 1.62 × 10⁻³ cm²/W. The optical Kerr constants of ADDPDLC films at various temperatures are also measured. The experimental results reveal that liquid crystals in the ADDPDLC film strengthen the nonlinearity. The n₂ of the ADDPDLC film is maximal at ∼35 °C, because of the decrease in the clearing temperature of the ADDPDLC films. The clearing temperatures of the liquid crystals (E7), and the ADDPDLC film used in this work were found to be 61 °C and 43 °C, respectively.     

First principles study of the vibrational,dielectric and thermal properties of SrClF

SrClF is an important optical crystal and has many technological applications. In this work, vibrational, dielectric and thermal properties of SrClF were investigated by density functional perturbation calculation. The calculated Born effective charges are close to their nominal ionic charges, revealing the ionic characteristic of SrClF. Group theory analysis indicates that there are two E _u and A _2u infrared modes at the Brillouin zone center of SrClF. The LO-TO splitting of these infrared modes were calculated and discussed and their vibrational modes were sketched. Static dielectric constants were studied, which show that SrClF has a larger ionic dielectric contribution than its electrons. Its birefringence was calculated and the infrared reflectance spectra were simulated, which can be used to explain the experimental findings. Based on the computed phonon dispersion curves, the lattice heat capacity, the Grüneisen parameter and the thermal expansion coefficient as functions of temperature were predicted.     

Large R-parity violating couplings and grand unification

We consider the possibility that R-parity violating interactions of particles which do not involve the first generation have large (up to 1) coupling constants, λ. Such couplings, if they exist, could have a number of phenomenological consequences: renormalization of the b − τ mass ratio, generation of ν_τ mass in the MeV region, etc. In grand unified models, where B- and L-violating couplings appear simultaneously, proton decay can be forbidden in virtue of the hierarchical flavor structure of λ. However, due to Cabibbo-Kobayashi-Maskawa mixing this decay is induced already at one loop. Present experimental data give the upper bound λ ⪅ 10⁻⁸ (or |λ′λ″| ⪅ 7 × 10⁻¹⁶, on products of certain L- and B-violating coupling constants, in a more general context). The bound can be avoided if there is an asymmetry between the L- and B-violating couplings of the usual matter fields. In the SU(5) model the asymmetry can be related to the doublet-triplet splitting.     

Long-wave optical vibrations of V2O5

The infrared reflection spectra of V₂O₅ single crystals have been measured in polarized light for E ∥ a, E ∥ b and E ∥ c. By Kramers-Kronig analysis the optical constants and the values of some LO- and TO-mode frequencies were evaluated. Two unknown lattice vibrations have been ascertained.     

Elastic and inelastic scattering of vector polarized deuterons from even samarium isotopes at 56 MeV

Differential cross sections and vector analyzing powers of deuteron elastic and inelastic scattering have been measured at 56 MeV over the whole range of the even samarium isotopes. Comprehensive analyses were performed with the optical model and the coupled-channels formalism. In the optical model analysis, calculations with a global parameter set could reproduce the experimental data only for the vibrational nuclei. The strong coupling approximation was applied assuming the ^{144, 148, 150}Sm to be harmonic vibrators and the ^152,154Sm symmetric rotators. The 2^λ (λ = 2, 3, 4, 6) pole deformation parameters were deduced from a systematic coupled-channels analysis. The transition strengths were extracted from the deformed optical potentials and compared with the corresponding electromagnetic ones. The transition rates for the rotational nuclei agreed with the electro-magnetic ones, but those for the vibrational nuclei gave the systematically smaller values. The latter fact was attributed to the difference between the proton and neutron transition matrix elements near the neutron-closed-shell nuclei. The ratios of the two matrix elements were obtained.     

Optical studies of chemisorption on metals

Optical techniques, particularly ellipsometry, have been highly successful in the study of chemisorption on semiconductors. Such studies on metal surfaces are more difficult because the short screening lengths limit the chemisorption-induced perturbation to a surface-layer only a few ångströms thick. Some success has been achieved using differential reflectance spectroscopy. However this necessitates (1) two independent reflectance measurements or the use of KK analysis to obtain complex optical constants, and (2) assumed or independently-measured values for the thickness of the surface layer in order to completely specify the adsorption-induced changes. The advent of extremely precise in situ modulated ellipsometers has made the optical study of gas-metal interactions less difficult, in particular eliminating the necessity of KK analysis. We briefly describe such a system here, the automated polarization-modulated ellipsometer. When this instrument is coupled with a recently developed approximation technique for obtaining surface-layer thickness and optical constants from only two ellipsometric measurements, the complete optical characterization of many metal-absorbate systems is straightforward. Recent experimental results indicating a chemisorption-induced surface state within 2.4 eV of the Fermi level for oxygen on silver are discussed.