Spectroscopic methods, spectral ranges

In this section we focus on spectroscopic methods used to determine the real and imaginary parts of h(w). It is not our aim to discuss all the methods used in semiconductor physics, but only those commonly applied to CP, based on reflectance/transmittance and ellipsometric measurements. At the end, we report briefly on other methods that are seldom used or work only in reduced spectral ranges. 

Neural network methods require a fixed length representation of the data to be processed. Vibrational spectra recorded usually fulfill this requirement. With most applications in vibrational spectroscopy, the spectral range and resolution are fixed, and a comparison of spectra from different sources is directly possible. Appropriate scaling of the spectra allows handling different resolutions to obtain the same number of components in a descriptor. Digitized vibrational spectra typically contain absorbance or transmission values in wave-number format. Most of the spectrometers provide the standardized spectral data format JCAMP-DX developed by the Working Party on Spectroscopic Data Standards from the International Union of Pure and Applied Chemistry (lUPAC) [48]. 

Spectroscopic methods are often used as in-line or off-line analytical tools to identify chemical species or determine chemical concentrations. Optical spectroscopy may cover the entire spectral range of wavelengths from the ultraviolet (UV, 1>10 run) to the infrared (IR, A<1 mm). Spectra can be recorded in either absorption (UV, Vis, NIR, IR) or emission (IR, Raman, fluorescence). These methods are used in supercritical media and especially, but not exclusively, in supercritical carbon dioxide (SCCO2). 

This phase-shift method is a general technique and is e.g. also applied to the measurement of lifetimes of excited atoms or molecules (see Sect. 6.3). The combination of CRDS with Fourier-spectroscopy gives for a fixed detection time a better signal-to noise ratio, because now all absorption lines within the covered spectral range are detected simultaneously. In Fig. 1.22 a possible experimental arrangement for this combined spectroscopic technique is schematically depicted. The transmitted laser... 

In sim infrared (IR) spectroscopy is a spectroscopic method for the infrared spectral range which can be used in defined environments during preparation, modification, function, and reaction or analysis in natural environment. In this contribution especially liquid environments are considered with the focus on the mid-infrared (MIR) spectral range from 2.5 to 16 pm. 

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