Optical data manipulations

Raman parent spectrum is obtained simply by adding all the spectra together. However, the ROA spectrum is obtained by either adding or subtracting from the current coadded spectrum depending on the position of quarter-wave plate. After several cycles, the Raman and ROA spectra are saved on the hard disk as one data set. After several data sets, all the data are added and saved into either the Raman parent spectrum or the ROA raw data spectrum and stored for the data manipulation. Occasionally, the raw data contains parental bias or first derivative contributions due to the fluctuation of the laser intensity or the quality of the optics, and these are reduced or removed digitally. 

Optically non-linear materials show a change in their refractive index when exposed to electrical and electromagnetic fields, which opens the possibility to influence the propagation of light by means of external fields. Practical applications of these effects are in the sphere of optical data transmission and data manipulation. 

Second-order non-linear optics continne to be an area of research becanse of its tremendous potential in the design of photon-based new materials for optical switching, data manipulation, and information processing [12]. 

Dumont, M., Hosotte, S., Froc, G., and Sekkat, Z. (1994). Orientational manipulation of chromophores through photoisomerization. In Photopolymers and Applications in Holography, Optical Data Storage, Optical Sensors, and Interconnects. (R. A. Lessard, cd.), Proc. SPIE 2042,2-13. 

As for Raman and mid-IR spectroscopy, advances in data manipulation and the availability of chemometric analytical software have greatly assisted extraction of useful information from near-IR spectra. This is particularly important for NIR spectra because they are difficult to interpret in terms of chemical structure. An additional technical advance, fiber optics, has allowed the acquisition of NIR spectra by remote sensing. 

When commercial FTIR instruments were first introduced the widely touted optical advantages of the instrument sometimes gave the impression that one could place a brick in the sample chamber and still obtain a spectrum. The preparation of samples was not emphasized, but if anything the data manipulations that have since became routine have made careful and consistent sample preparation even more important, particularly for quantitative work. 

Milano et al. [153, 154] and Cook [34] introduced an approach to derivative spectra by substituting electronic wavelength modulation for the mechanical systems used in derivative spectrometers. This effect is achieved by superimposing a low-amplitude, periodic wave form on the horizontal sweep signal. In this way spectra were generated. Warner et al. [155] applied a vidicon detector for fast detection of fluorescence spectra and obtained derivatives of the stored data by digital computation. Cook et al. [156] also made use of a silicon vidicon detector for multichannel operations in rapid UV-VIS spectrophotometers with the possibility of first-order differentiation. For the same purpose Milano et al. [93, 157] used a multichannel linear photodiode array for detection of spectra in polychromator optics and stored data manipulations (d ). Technical explanations of the principles of diode array and vidicon devices cem be found in [158-161]. 

This being the case, it should be clear that no manipulations of the independent variables, in other words, the optical data, no matter how sophisticated, can improve the calibration beyond that limit. Therefore, while the use of principal components does bring advantages with it to the calibration process, those advantages will in general not include obtaining a better calibration. 

Both instrument design and capabilities of fluorescence spectroscopy have greatly advanced over the last several decades. Advancements include solid-state excitation sources, integration of fiber optic technology, highly sensitive multichannel detectors, rapid-scan monochromators, sensitive spectral correction techniques, and improved data manipulation software (Christian et al., 1981 Lochmuller and Saavedra, 1986 Cabaniss and Shuman, 1987 Lakowicz, 2006 Hudson et al., 2(X)7). The cumulative effect of these improvements have pushed the limits and expanded the application of fluorescence techniques to numerous scientific research fields. One of the more powerful advancements is the ability to obtain in situ fluorescence measurements of natural waters (Moore, 1994). 

Fluorometers designed for research purposes(31) are typically equipped with a xenon arc lamp, monochromators, one or more photomultiplier tubes, cuvet holders, and a computer interface. Some research level fluorometers, such as the Perkin-Elmer LS50, have optional microtiter plate reading accessories with fiber optic bundles. This is convenient since 96-well microtiter plates are commonly used for immunoassay development, and many commercial immunoassays are based on the use of microtiter plates. Fluorometers designed for commercial immunoassay purposes are generally dedicated instruments with few, if any, data acquisition and reduction parameters that can be manipulated by the user. 

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