Complex refractive index determination

Finally, n was determined by spectroscopic ellipsometry. The main drawback with this technique when applied to anisotropic samples is that the measured ellipsometric functions tanlF and cos A are related both to the incidence angle and the anisotropic reflectance coefficient for polarizations parallel and perpendicular to the incidence plane. The parameters thus have to be deconvolved from a set of measurements performed with different orientations of the sample [see (2.15) and (2.16)]. The complex refractive index determined by ellipsometry is reliable only in the spectral region where the sample can be considered as a bulk material. In fact, below the absorption... 

In our further considerations we start from the assumption that the geometrical and physical parameters of the photodetector are already defined. Geometrical parameters include the area and the thickness of the active region, i.e., its total volume. Physical parameters are the detector material properties. These include optical properties (complex refractive index, determined by the material type and composition), and electrical ones (donor and acceptor concentration, i.e., the concentrations of majority and minority carriers at a given temperature). 

Yamamoto, K. and Masui, A. (1995) Complex refractive index determination of bulk materials from infrared reflection spectra. A/ / /. Spectrosc., 49, 639-644. 

Allen et a/. (1991) performed these computations for 1-octadecene droplets, and they measured the evaporation rate of the droplets as a function of laser power. To determine the absolute irradiance /, of the laser beam, they also measured the force on the particle exerted by the laser beam using the techniques discussed above. The photon pressure force is given by Eq. (87), which involves the complex refractive index. The real component of the refractive index n was determined from optical resonance measurements, and the imaginary component was obtained iteratively. That is, they assumed a... 

Table III shows that the experimental and predicted evaporation rates are in good agreement at all beam intensities. There is some inconsistency at the highest power levels. It was difficult to maintain the droplet in the center of the laser beam at the highest power level, and the measured evaporation rate is somewhat low as a result of that problem. Additional computations demonstrate that the predicted evaporation rate is quite sensitive to the choice of the imaginary component of N, so the results suggest that this evaporation method is suitable for the determination of the complex refractive index of weakly absorbing liquids. For strong absorbers, the linearizations of the Clausius-Clapeyron equation and of the radiation energy loss term in the interfacial boundary condition may not be valid. In this event, a numerical solution of the governing equations is required. The structure of the source function, however, makes this a rather tedious task.

The rate at which electromagnetic energy is removed from the wave as it propagates through the medium is determined by the imaginary part of the complex refractive index. If the irradiances I0 and lt (or rather their ratio) are measured at two different positions z = 0 and z = h, then a, and hence k, can be obtained in principle from the relation... 

Reagan, J. A., D. M. Byrne, M. D. King, J. D. Spinhime, and B. M. Herman, 1980. Determination of the complex refractive index of atmospheric particulates from bistatic-monostatic lidar and solar radiometer measurements, J. Geophys. Res., 85, 1591-1599. 

In the above equation, v (cm" ) is the wavenumber, vo (cm" ) the wavenumber of the absorption band center, y (cm" ) the damping constant (which gives the band width), B (cm"3 determines the intensity of the band, and e the refractive index far away from resonance. The properties of the adsorbate film are those of CO on platinum. For the middle spectrum, the complex refractive index (n— 5 + 20/) is close to that of platinum at 2000 cm" and k were varied between 2.5 and 10 and between 10 and 40, respectively, in view of the fact that and k vary drastically over the mid-IR region and from metal to metal (55). 

Ebert M, Weinbruch S, Hoffmann P, Ortner HM (2004) The chemical characterization and complex refractive index of rural and urban influenced aerosols determined by individual particle analysis. Atmos Environ 38 6531-6545... 

Fourier transform infrared microscopes are equipped with a reflection capability that can be used under these circumstances. External reflection spectroscopy (ERS) requires a flat, reflective surface, and the results are sensitive to the polarization of the incident beam as well as the angle of incidence. Additionally, the orientations of the electric dipoles in the films are important to the selection rules and the intensities of the reflected beam. In reflectance measurements, the spectra are a function of the dispersion in the refractive index and the spectra obtained are completely different from that obtained through a transmission measurement that is strongly influenced by the absorption index, k. However, a complex refractive index, n + ik can be determined through a well-known mathematical route, namely, the Kramers-Kronig analysis. 

For size quantification of these particle systems, the underlying LII model has to be extended taking into consideration the optical metal particle properties (Vander Wal et al., 1999 Kreibig and Vollmer, 1995) on the one hand side and the contact surface area, on the other hand. The optical metal properties, which are in particular determined by the high imaginary part of the complex refraction index, show low absorption coefficients. 

Less is known at this time about the complex refractive index of the sulfur aerosol, and its variation with height, in view of the role that dilution and impurities may have, particularly in determining the imaginary part n". Knowledge of the refractive index is essential in determining heating effects, and would help in assessing the aerosol composition. 

This procedure has been used to determine droplet size in sprays. Oseillations in the curve relating x and D can be smoothed out by the use of an incident laser beam having a broad speetral bandwidth [83]. An accumulation of independent scattering intensities from multiple scatterers ean be used to measure the mean droplet size of a group [84]. This procedure has been applied to water sprays and the experimental data confirmed by phase Doppler anemometry [85]. The applicability of the polarization ratio technique is strongly influenced by the complex refractive index of the dispersed media and is limited to media having a relative refractive index below about 1.44 [86]. 

The method is based on the magnetorefractive effect (MRE). The MRE is the variation of the complex refractive index (dielectric function) of a material due to change in its conductivity at IR frequencies when a magnetic field is applied. A direct measure of the changes of dielectric properties of a material can be performed by determining its reflection and transmission coefficients. Hence, IR transmission or reflection spectroscopy can provide a direct tool for probing the spin-dependent conductivity in GMR and TMR [5,6]. 

These parameters can be checked independently by their consistency with macro-scopically determined ones on mechanically polished samples. Mechanical polishing yields an amorphous and therefore isotropic Beilby layer resulting in an averaged isotropic complex refractive index niso. The correlation between niso and the anisotropic parameters is given by the equation ... 

The most complete information about aerosols would be vertical profiles of their size distribution and their chemical composition, which would allow the complex refractive index to be determined. However, such detail is usually not available. 

For soot or any other strongly absorbing material with a complex refractive index a complete morphological characterization to determine average Rg, N, a, and D can be made with in situ light scattering." The technique involves combining optical structure factor measurements and absolute... 

The thicknesses of the films were determined using an ellipsometer SE 400 (Sentech Instruments GmbH) under an incidence angle of 70° at a wavelength of 633 nm. Optical film thicknesses were determined assuming a complex refractive index N=n-ik with a real part n= 1.45 and an imaginary coefficient k = 0. The parameters n and k of the gold substrates were obtained by ellip-sometric measurements of the plasma-cleaned films before monolayer formation. 

Absorption. The possible color of the last mentioned emulsion needs further explanation. Up till now, we have implicitly assumed that light is only scattered, not absorbed. If absorption occurs, we should use the complex refractive index h = n — in, where ri determines the adsorption (i = yj — 1). The relations now become more complicated, n is related to the specific extinction y according to y Ann /X. The absorbency as determined... 

Analysis of the infrared spectra requires accounting for thin film interference effects, which, upon shock compression, change the composite reflectivity. To analyze the thin film interference effects, the infrared complex refractive index spectra for ambient samples of PVN, and the inert polymethylmethacrylate (PMMA), were determined as described in the section above. The only modification to the description above is the inclusion here of the dispersive rarefaction wave that releases the pressure [102]. 

The material structure of the particulate matter determines its complex index of refraction, which is considered to be the most fundamental property. The real part of the complex refractive index is the ratio of the speed of light in vacuum to that within the particle for light at normal incidence. In this case, the imaginary part, which is also termed the attenuation, extinction, or absorption index, is directly related to the rate of attenuation of radiation with depth within the material. For other than normal incidence, the relations between the complex index of refraction, speed of light, and attenuation within the particle are complicated and require rigorous solution of the electromagnetic (EM) wave equations (i.e., Maxwell s equations) within the medium of interest with appropriate boundary conditions. 

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