Wavelength-dependent normalization factor

There are also two normalization procedures that are based on the forcing of the absorbance at a specific wavelength to a specific value V. The wavelength used can be either the same for both spectra, N = SJV or the wavelength of maximum absorbance can be found over a specific wavelength range for each spectrum, N = S JV. In both cases, normalization is much more dependent on noise because a single absorbance value controls the normalization factor N. 

The measured intensity of a single Laue spot or of an energy deconvoluted spot needs correction or normalization for a variety of wavelength dependent factors if... 

The fluorescence spectrum (emission spectrum) of a sample is obtained by scanning M2 while keeping the excitation wavelength constant. Since the efficiency of M2 is wavelength dependent, and the detector (see below) also has a sensitivity that varies with wavelength, such a fluorescence spectrum is normally uncorrected , i.e., it will depend upon the instrument as well as the sample. The correction of emission spectra is less easy to achieve than for excitation spectra, and is less often performed, so published emission spectra often vary from instrument to instrument. At least three methods are available for emission correction. A sound but tedious method is to calibrate the emission system (i.e., M2 plus the detector) with a standard light source of known emission profile. Such devices are available from NIST and other standards bodies. Comparison of the output of the fluorescence spectrometer with the certified output of the lamp then provides a correction factor at each wavelength, which can be applied to subsequent sample spectra. A related technique is to... 

There are a variety of FPA detectors available that are sensitive in the NIR spectral region. The optimal choice of detectors depends on several factors desired wavelength range, whether the application will be laboratory based or part of a process environment, the sensitivity needed to adequately differentiate sample spectra and price. The figure of merit most often used to describe detector performance is specific detectivity or D, which is the inverse of noise equivalent power (NEP), normalized for detector area and unit bandwidth. NEP is defined as the radiant power that produces a signal-to-dark-current noise ratio of unity. 

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