Characterization optical scattering

Several practical issues of the scatterometer must be considered in the case of characterizing nominally smooth surfaces. The incident laser beam may be collimated, but more commonly it is brought to a focus at a distance defined by the arc in which the detector rotates. In addition, a deflection mirror or an optical fiber might be used to direct light to the detector element. These features permit measurements close to the specular and transmitted beams, and this is critical to folly characterize the scattered light. This is especially significant since the scattered light intensity... 

As was mentioned in the introduction, optical properties of a pol5oner are determined by the complex combination of its basic scattering, transmission and reflection characteristics, but they depend also on the technique and conditions of illumination and detection. The number of determining factors and the complexity of the relations are in strong contradiction with the natural demand in practice to characterize optical properties with a simple number, such as transparency, haze etc. In spite of this controversy and difficulties in the interpretation of the dominating factors, optical properties of a polymer can be determined, reproduced and compared by the strict application of relevant standards. 

This chapter explains how to characterize the angular distribution of optical scatter from an opaque surface. In particular it focuses on measurement of the bidirectional reflectance distribution function (BRDF). BRDF is a convenient and well-accepted means of expressing optical scatter levels for many purposes (1, 2). 

Structural Characterization of the Banded State Rheo-Optics, Scattering, and Spectroscopy... 

Inoue, T. and Kyu, T. (2000) Optical characterization Light scattering, birefringence, and ellipsometry, in Polymer Blends (eds D.R. Paul and C.B. Budoitdl), Wiley Sons, Ltd, Chichester, pp. 319-347. 

Alekseeva, A.V., Bogatyrev, V.A., Dykman, L.A., Khlebtsov, B.N., Trachuk, L.A., Melnikov, A.G. and Khlebtsov, N.G. (2005) Preparation and optical scattering characterization of gold nanorods and their application to a dot-immunogold assay. Applied Optics, 44, 5285-95. 

Our presentation is focused on the analysis of the scattered field in the far-held region. We begin with a basic representation theorem for electromagnetic scattering and then introduce the primary quantities which dehne the single-scattering law the far-held patterns and the amplitude matrix. Because the measurement of the ampUtude matrix is a comphcated experimental problem, we characterize the scattering process by other measurable quantities as for instance the optical cross-sections and the phase and extinction matrices. 

Perhaps the best known and most used optical spectroscopy which relies on the use of lasers is Raman spectroscopy. Because Raman spectroscopy is based on the inelastic scattering of photons, the signals are usually weak, and are often masked by fluorescence and/or Rayleigh scattering processes. The interest in usmg Raman for the vibrational characterization of surfaces arises from the fact that the teclmique can be used in situ under non-vacuum enviromnents, and also because it follows selection rules that complement those of IR spectroscopy. 

R, D. Jacobson, S. R. Wilson, G. A. Al-Jumaily, J. R, McNeil, and J. M. Bennett. Microstructure Characterization by Angle-Resolved Scatter and Comparison to Measurements Made by Other Techniques. To be published in AppL Opt. This work discusses the band width and modulation transfer function of the scatterometer, stylus profilometer, optical pro-filometer, and total integrated scattering systems, and gives results of mea suring several surhices using all techniques. 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

Important parameters, characterizing fibre properties, are the attenuation a and numerical aperture NA. The attenuation (Equation 1) represents optical losses caused by absorption or scattering of the light guided through the unit fibre length. It is given by ... 

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