Relative intensity noise

Recall that in laser operation stimulated emission dominates. But the spontaneous emission does not cease when stimulated dominates, thereby contributing one source of the small fluctuations in the laser intensity. In intensity modulated systems, these small fluctuations limit the minimum amplitude of the desired signal that can be used for modulation. The most commonly used measure of the laser amplitude fluctuations is the relative intensity noise (RIN) (Yammoto, 1983) it is defined as... 

For analog fiber-optic fink appHcations, the noise floor at the receiver end is an important parameter in determining the overall link performance. For APD-based receiver, the noise floor can consist of the laser relative intensity noise, the receiver thermal noise, and the APD noise associated with the photocurrent. The APD noise power can be expressed as... 

Fluctuations in the output intensity of a laser result in optical intensity noise, which is usually called the relative intensity noise [22]. The relative intensity noise is usually expressed in decibels per hertz (dB/Hz), and all types of lasers generate this noise. The power penalty due to the relative intensity noise (in linear units) is... 

Kallimani, K.l. and O Mahony, M. (1998) Relative intensity noise for laser diodes with arbitrary amounts of optical feedback. IEEE / Quantum Electron., 34 (8), 1438-1446. 

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

Two-dimensional NMR spectra are normally presented as contour plots (Fig. 3.11a), in which the peaks appear as contours. Although the peaks can be readily visualized by such an overhead view, the relative intensities of the signals and the structures of the multiplets are less readily perceived. Such information can be easily obtained by plotting slices (cross-sections) across rows or columns at different points along the Fi or axes. Stacked plots (Fig. 3.11b) are pleasing esthetically, since they provide a pseudo-3D representation of the spectrum. But except for providing information about noise and artifacts, they offer no advantage over contour plots. Finally, the projection spectra mentioned in the previous section may also be recorded. 

The fitted and calculated vibrational frequencies and normal mode composition factors corresponding to the 17 most important NIS bands are presented in Table 5.9. It is evident that the vibrational peaks in the calculated NIS spectrum are typically 0-30 cm lower than to the experimental values. In the calculated NIS spectra, there are two small peaks at 635 and 716 cm (Fig. 5.14b) that are not visible in the experimental spectrum. According to the normal mode calculations these are Fe-N-N and Fe-O-C deformation vibrations. Small admixtures of Fe-N and Fe-O stretching modes account for the calculated nonzero normal mode composition factors. Although the calculated relative intensities are slightly above detection limit dictated by the signal-to-noise ratio, they are determined by values of pea which are very small (0.028 and 0.026 for the peaks at 635 and 716 cm ). They must be considered to be within the uncertainties of the theoretical... 

Definition The signal-to-noise ratio (S/N) quantifies the ratio of the intensity of a signal relative to noise. 

Fig. 12.2. Extraction of spectra from chromatographic peak No. 50 in the TIC. Left column single scan spectra from scans 935, 936, and 937 show changing relative intensities averaging scans 935 937 levels intensity but leaves noise background subtraction reduces noise in addition. (For TIC and RICs see Fig. 12.1.)...

The relative intensities of the lines within each multiplet will be in the ratio of the binomial coefficients (Table 5.9). Note that, in the case of higher multiplets, the outside components of multiplets are relatively weak and may be lost in the instrumental noise, e.g. a septet may appear as a quintet if the outer lines are not elearly visible. The intensity relationship is the first to be significantly distorted in non-ideal cases, but this does not lead to serious errors in speetral analysis. 

Figures 24 and 25 demonstrate the success of deconvolution beyond the Doppler limit. Trace (a) in both figures is the undeconvolved data and represents the result of signal averaging over a large number of scans to produce a signal-to-noise ratio of approximately 300 1. The spectra were base-line corrected using a 0% absorption corresponding to the apparent base line between lines and a 100% absorption level was assumed, which gave reasonable relative intensities for the range of J values observed. The...

Compared to the PAS spectra of cotton cloth, in the Specular Reflectance spectra, the signal-to-noiae is higher and any noise is low enough to show clearly the spectral features described here. Even though there are differences due to the change in sampling conditions, the spectra can be compared for a one-to-one comparison and identification of absorption bands. Mote however that in the PAS spectrum relative intensities are displayed and that the Specular Reflectance spectra show an absolute response and measurement which leads to a better possibility for quantification and a more rigorous treatment of the data. 

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