Refractive Spectra Research Articles

Real-time characterization of film growth on transparent substrates by rotating-compensator multichannel ellipsometry

A multichannel spectroscopic ellipsometer in the fixed-polarizer-sample-rotating-compensator-fixed-analyzer (PSC(R)A) configuration has been developed and applied for real-time characterization of the nucleation and growth of thin films on transparent substrates. This rotating-compensator design overcomes the major disadvantages of the multichannel ellipsometer in the rotating-polarizer-sample-fixed-analyzer (P(R)SA) configuration while retaining its high speed and precision for the characterization of thin-film processes in real time. The advantages of the PSC(R)A configuration include (i) its high accuracy and precision for the detection of low-ellipticity polarization states that are generated upon reflection of linearly polarized light from transparent film-substrate systems, and (ii) the ability to characterize depolarization of the reflected light, an effect that leads to errors in ellipticity when measured with the P(R)SA configuration. A comparison of the index of refraction spectra for a glass substrate obtained in the real-time PSC(R)A mode in 2.5 s and in the ex situ fixed-polarizer-fixed-compensator-sample-rotating-analyzer (PCSA(R)) mode in ~10 min show excellent agreement, with a standard deviation between the two data sets of 8 x 10(-4), computed over the photon energy range from 1.5 to 3.5 eV. First, we describe the PSC(R)A ellipsometer calibration procedures developed specifically for transparent substrates. In addition, we describe the application of the multichannel PSC(R)A instrument for a study of thin-film diamond nucleation and growth on glass in a low-temperature microwave plasma-enhanced chemical vapor deposition process.

Spectroscopic Real-Time Ellipsometry of Putidaredoxin Adsorption on Gold Electrodes

Adsorption of putidaredoxin (Pdx) on gold electrodes was studied using dynamic spectroscopic ellipsometry and differential capacitance. A method to account for the metal surface optical perturbation during protein adsorption at constant potential is described. The method is based on the concept of the charged transition layer which develops between metal substrate and adsorbate. Transition-layer charge was determined from the differential capacitance and the ellipsometry measurements in buffer solutions. A three-phase (metal substrate/protein film/solution) reflecting surface model was amended with a charged metal transition layer as a fourth phase, which allowed the elucidation of the adsorbed Pdx complex index of refraction spectrum. On the basis of this spectrum, a time dependent protein surface concentration was calculated. For short times, this surface concentration was in good agreement with estimates based on mass transport limited adsorption.

Dispersive Fourier Transform Spectroscopy Of Free-Standing Porous Silicon Films

AbstractWe have investigated optical constants of free-standing porous silicon films by dispersive Fourier transform spectroscopy (DFTS) in the NIR-VIS range. This allows the spectral variation of both the absorption coefficient and the refractive index of a material to be determined from the measurements of the attenuation and phase shift imposed on an electromagnetic wave by its interaction with a specimen. Using these optical constants, we have studied the complex dielectric function and the complex conductivity. To avoid the additive error in the absorption spectra arising from the pseudocoherence, we measured the transmission spectra by conventional Fourier transform spectroscopy (FTS). Using the refraction spectrum derived from the DFTS measurements, we have corrected for reflection losses in calculation of the absorption spectrum from the FTS transmission spectrum. The changes in the absorption coefficient and the refractive index due to oxidation, which is the most common aging phenomenon in porous silicon, have been studied using samples with different types of oxidization.

Obtaining the ocean index of refraction spectrum from the acoustic amplitude fluctuations

Ewart and Reynolds [Wave Propagation in Random Media (Scintillation), edited by Tatarski, Ishimaru, and Zavorotny (SPIE, Bellingham, WA, 1993), pp. 100–123] provide a convincing comparison between the ocean spectral model determined from a stochastic inverse using the acoustic phase spectrum (measured in the Mid-ocean Acoustic Transmission Experiment) and the same model derived from oceanographic data. The success of using the acoustic phase for such inverses is based on the high accuracy of Rytov theory to predict the phase spectrum. Accurate measurement of the acoustic phases (travel times) requires fixed sources and receivers, an experimental complication. If it were possible to use Rytov theory for the amplitude fluctuations, the experiment complexity is much reduced and simpler moorings could be used. In this talk results are presented from a study of the viability of this approach using numerical simulations of propagation through internal waves to a vertical array of receivers. With the only requirement being applicability of the Rytov approximation, two-dimensional (depth/time) correlations of the oceanographic model are obtained by stochastic inversion and compared to the input internal wave model. The importance of this result to augmenting oceanographic measurements, and a discussion of the future possibilities, are presented. [Work supported by ONR.]

Structure and Properties of CeO2–Al2O3–SiO2 Glasses

The density, molar volume, refractive index, molar refractivity, and infrared and XANES spectra of CeO2–Al2O3 –SiO2 glasses prepared at 1600° C for 3 h in N2 have been investigated. The IR reflection data are treated by Kramers-Kronig transformation. Results of IR spectra show that ceria is the network modifier and favors the formation of the [ SiO4] tetrahedron with nonbridging oxygen. The XANES data of the cerium LIII edge show that the majority of cerium ions in cerium aluminosilicate glasses are the Ce3+ ions. The density and refractive index of the glass increase with increasing alumina or ceria content.

Refraction spectrum due to polariton condensation in a high magnetic field

The refraction spectrum is calculated in the case of interaction of light with the Bose-Einstein condensate of excitons in a high magnetic field, when the distance between the Landau levels exceeds the excitonic Rydberg. The appearance of the condensate in a broad range of the densities significantly changes the excitation spectrum of coupled excitons and photons (polaritons) and results in a number of interesting phenomena such as, e.g., the increase of the absorption and the amplification of light at certain frequencies depending on the exciton density and the magnetic field.

Effect of solvent vapor on optical properties of Pr4VOPc in polymethylmethacrylate

Dye-in-polymer (DIP) films consisting of soluble Pr4VOPc (vanadyl phthalocyanine having four propyl substituents) dye and polymethylmethacrylate (PMMA) were prepared by spin-coating process. Pr4VOPc precipitates as a glassy phase in pure PMMA matrix during the film formation. Upon exposure of these DIP films to organic solvent vapor, stable crystalline Pr4VOPc, which has stronger absorption in the near-IR region and larger nonlinear refractive index n2 than the glassy phase, forms. The organic solvent vapor promotes the solubilization and crystallization of the dye, plastication of the polymer chains, and migration of the dye. The nonlinear refractive index n2 and optical spectra of the DIP films were measured, and the change rule has been discussed in terms of electron transition and molecular packing of Pr4VOPc.

A theoretical analysis of absorption and refractive index changes in optically excited In1-xGaxSb

A calculation of the change in absorption and refraction spectra in the vicinity of the bandgap edge due to the optically generated carriers in In1-xGaxSb is presented. In the theoretical model used all free-carrier and many-body effects responsible for alteration of the optical properties are involved. An analysis of the relative contribution of different effects depending on the electron-hole density and the composition is performed. The large values of refractive index change obtained in a wide spectral region suggest that In1-xGaxSb alloy is a promising material for optical switching and modulation applications in the middle-infrared.

Optical absorption and refraction spectra in highly excited GaSb

A theoretical estimate of carrier-induced changes in absorption and refraction spectra in GaSb is presented. The partly phenomenological electron-hole plasma model including band filling, band-gap renormalization, screening of the Coulomb interaction and the free-carrier plasma effect is used. A dominant contribution of the band filling and screening of the continuum-state Coulomb enhancement is observed. For the first time the influence of high lying conduction band valleys is taken into account. In addition, the model is applied to calculate the absorption and refraction spectra in doped material. The obtained results may prove to be useful in the design of GaSb optoelectronic devices. >

Effective optical properties of pulverized coal particles determined from FT-IR spectrometer experiments

For accurate modeling of radiative transfer in combustion systems, radiative properties of combustion gases and particles are required. The particle properties are usually determined from the Lorenz-Mie theory assuming they are spherical in shape and their optical properties, i.e., the complex index of refraction data, are available. In the present study, an FT-IR spectrometer has been used to determine the «effective» optical properties of Blind Canyon and Kentucky no. 9 coals suspended in KBr pellets, within the wavelength interval of 2-20 μm. A detailed inversion analysis based on the Lorenz-Mie theory is employed to reduce the measured transmission data to a complex index of refraction spectra. In the analysis, the effects of both absorption and scattering by coal particles are accounted for

Bi6Te2Mo2O21 - a new synthetic crystal and its physical properties

A single crystal of Bi6Te2Mo2O21 attaining 2×2×5 mm3 was synthesized by the fusion method, and its physical properties were investigated. This is a new phase found in nature, and given a new mineral name, chilumite. The crystal belongs to the orthorhombic system and D26>−C222 space group with lattice parameters a = 5.602 Å, b = 5.553 Å, and c = 22.816 Å, according to CAD4SDP results. The other physical properties, such as DTA analysis refractive indexes, reflectivity and IR spectrum of the crystal, are also given, and the crystal has a potential applicability for acousto-optical and light-reflective material.

An Analytical Model for the Refractive Index Power Spectrum and Its Application to Optical Scintillations in the Atmosphere

Abstract A spectral model for refractive index fluctuations, showing the characteristic ‘bump’ at high wavenumbers, is proposed for theoretical studies involving optical propagation. Using this spectrum, analytical expressions are developed for the variance of log-amplitude that show good agreement with numerical results based on the Hill spectrum.

Photon-gated holography: triphenylene in a boric acid glass

The observatiqn of photon-gated hologram formation in a boric acid glass doped with triphenylene is reported. The first photon excites triphenylene to its first singlet excited state and, through intersystem-crossing, populates the first triplet stateTI. The second photon excites TI to T,, where autoionization occurs, leading to the formation of a radical cation. The gatinglight populating TI via SI is spatially uniform, while the light exciting TI to T, is spatially modulated. The long lifetime of the first triplet state allows Recording with low light intensities (mW/cm2). The spatially modulated excitation light forms three gratings (educt, intermediate state, and product). The extent of the interaction between these gratings depends on the overlap between educt, intermediate, and product absorption and refraction spectra as well as on the reading wavelength. The holograms were read at 363.8 and 632.8 nm. When the gating light is blocked, the holographic efficiency stays constant when read at 632.8 nm but increases substantially when read at 363.8 nm.

Field-induced refractive index variation spectrum in a GaInAs/InP quantum wire structure

We report the electric field induced refractive index variation spectrum in a GaInAs/InP multilayered (three layers) quantum wire structure (λg∼1.48 μm) in the range 1.484–1.65 μm with the maximum positive index variation of 4% at around 1.52 μm at an applied reverse bias voltage of 3 V. We have also observed the anisotropic property of the index variation with respect to the quantum wire direction to the input light. These multilayered quantum wire structures were fabricated by low-pressure electron cyclotron resonance reactive ion beam etching and low-pressure organometallic vapor phase epitaxy methods.

Optical and tribological properties of heat-treated diamond-like carbon

Diamond-like carbon, or DLC, films, prepared by the rf plasma decomposition of acetylene, have been deposited at substrate temperatures of 100 to 250 °C, with the substrate at a negative bias of 80 V dc. The DLC films have been annealed in vaccum at temperatures up to 600 °C for 3–4 h. The optical properties of the as-deposited and annealed films have been characterized by ellipsometry and Fourier transform infrared spectroscopy. The wear resistance of the thin DLC films and their friction coefficients have been characterized by a specially designed tribotester. The stresses in the films have also been determined. No significant differences were found between the index of refraction and IR absorption spectra of the as-deposited films, or films annealed at up to 390 °C. The DLC films begin losing hydrogen after annealing above 390 °C and only sp2 bond carbon is observed after annealing at 590 °C. The wear behavior of the as-deposited films was identical for all deposition temperatures. DLC films deposited at 250 °C were more stable and could withstand higher annealing temperature than films deposited at lower temperatures, and remained wear resistant after anneling at 390 °C.

Effect of refractive dispersion on the trichromatic correlation of irradiances for atmospheric scintillation

Formulations of the trichromatic correlation of scintillating irradiance are corrected by introducing the cospectrum of the two different refractive indices in place of the refractive index power spectrum. Receiver aperture averaging is included in the formulation. The effect of dispersion on the bichromatic correlation coefficient is studied and quantified for four specific experimental cases. Dispersion of the water vapor refractive index between wavelengths in the visible and 10 microm window is of particular significance in this study. In most cases, the effect of dispersion on the bichromatic correlation coefficient is much less than on the ratio of monochromatic irradiance correlations, and is negligible for practical considerations. The exception is the case of such strong humidity fluctuations that they (as opposed to temperature fluctuations) cause most of the scintillation of the midinfrared radiation.

Electroabsorption and refraction by electron transfer in asymmetric modulation-doped multiple quantum well structures

We present a novel heterostructure that exhibits large electroabsorption and refraction. The structure is periodic with a stackable building block, thus it allows large contrast and waveguide operation. The mechanism used is the quenching of absorption produced by transfer of electrons from a reservoir into a quantum well. We demonstrate the principle by presenting differential absorption and refraction spectra on a ten-period device.

Calculation of the time-resolved absorption and refraction spectra of direct-gap semiconductors

Dispersive optical bistability has been observed in various direct-gap semiconductors. This effect is due to the dependence of the refractive index on the intensity I. A unified microscopic theory of the observed optical bistability in direct-gap semiconductors, such as GaAs is developed by calculating the complex, non-linear dielectric function for arbitrary free-carrier concentrations. The calculation, which includes many-body effects, consists in a very accurate numerical solution of the Bethe-Salpeter equation for the polarisation function. The resulting time-resolved spectra are discussed and are compared with experimental results.

The temperature variation of the near-mm wavelength optical constants of fluorosint

The near-mm wavelength optical constants of Fluorosint have been determined at temperatures of 6, 77 and 295 K, and shown to be such as to make the material suitable for use in low pass filter applications in the spectral region below 30cm −1. The overall level of the refraction spectrum increases with decreasing temperature, while that of the absorption spectrum decreases.

Pseudocoherence in dispersive fourier transform spectroscopy—II. Reflection DFTS

Pseudocoheren ce provides a major source of possible systematic error in measurements of the optical constants of heavily absorbing solids by reflection Dispersive Fourier Transform Spectroscopy. It arises when the reflecting surface of a specimen is not perfectly flat. An analytic model of its effects on the measured absorption and refraction spectra in such a measurement is presented. This allows the tolerances required for the flatness of the reflecting surface of the specimen to be derived. These are proportional to wavelength. This demonstrates that while the replacement method of reflection DFTS is only well-suited to FIR studies, the switched field-of-view method can be used in all spectral regions for which FTS is practicable.