Strong apodization

Infrared spectra were collected on a Perkin Elmer Spectrum 2000 infrared spectrometer equipped with an /-series IR microscope and controlled with Spectrum for Windows software (Perkin Elmer, Norwalk, CT). Spectra were coadded from 250 scans at a resolution of 8 cm with strong apodization. Reference spectra of CytC and individual amino acids were... 

Fig. 3 Reflectance and transmittance spectra at the central wavelength of a strong apodized regular FBG. The much weaker spectra of the HOCMs situated at lower wavelengths are not...

The FWHH of the ILS function given by the Happ-Genzel function is close to that of the Norton-Beer strong apodization function. Another common function that strongly suppresses the sidelobe amplimde is the Blackman-Harris function,... 

Figure 2.10. (a) Weak, medium, and strong apodization functions proposed by Norton and Beer (b) corresponding lineshape functions with the sine function shown for reference. 

For FTS data, artifact removal is a consideration that is as important as resolution improvement for most researchers in this field. Interferogram continuation methods are not as yet widely known in this area. Methods currently in widespread use that are effective in artifact removal involve the multiplication of the interferogram by various window functions, an operation called apodization. A carefully chosen window function can be very effective in suppressing the artifacts. However, the peaks are almost always broadened in the process. This can be understood from the uncertainty principle. A window that reduces the function most strongly closest to the end points will yield a transform for the modified function that must be broader than it was originally. Alternatively we may employ the convolution... 

An additional consequence of finite retardation is the appearance of secondary extrema or "wings" on either side of the primary features. The presence of these features is disadvantageous, especially when it is desired to observe a weak absorbance in proximity to a strong one. To diminish this problem the interferogram is usually multiplied by a triangular apodization function which forces the product to approach zero continuously for s = + Fourier transformation of the... 

Uniform An = const Strong side lobes o Apodized An varies Side lobes suppressed... 

Figure 5.3. Various apodization functions (left) and the instrumental lineshape produced by them (right) (a) boxcar truncation (b) triangular (c) trapezoidal (d) Norton-Beer weak, medium, and strong (e) Happ-Gen-zel (f) Blackman-Harris 3-term and 4-term. The maximum retardation is set to / = 1. In the Fourier transform the FWHH of the main lobe is indicated.

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