Pulse light-scattering measurements

The spinodal and the cloud point can be determined as a function of pressure and temperature (up to 150C, 1000 bar) via light-scattering measurements [41]. The intensity of the scattered light of the polymer solution is measured in a high-pressure optical cell during a pressure pulse in the polymer solution. 

In the most general case of the nonresonant fifth-order light scattering measurement, five off-resonant optical pulses are injected, as shown in Fig. 1. Two pairs of pulses are used to create two consecutive vibrational coherence states, and the fifth pulse is scattered by the temporal and spatial grating thus created. The controlled delay times between the first two pairs of pulses and between the second pair of pulses and the final pulse are... 

We have performed optically heterodyne-detected optical Kerr effect measurement for transparent liquids with ultrashort light pulses. In addition, the depolarized low-frequency light scattering measurement has been performed by means of a double monochromator and a high-resolution Sandercock-type tandem Fabry-Perot interferometer. The frequency response functions obtained from the both data have been directly compared. They agree perfectly for a wide frequency range. This result is the first experimental evidence for the equivalence between the time- and frequency-domain measurements. 

Fig. 8. Time-resolved light scattering measuring system combined with a short laser pulse...

Lasers. Laser sources (discussed earlier in the Spectrophotometry section) are widely used in fluorescence applications in which highly intense, well-focused, and essentially monochromatic light is required. Examples of these applications include time-resolved fluorometry, flow cytometry, pulsed laser confocal microscopy, laser-induced fluorometry, and light-scattering measurements for particle size and shape. Several different types of lasers are available as an excitation source for fluorescence measurements (see Table 3-3). 

Figure 3.1. Dynamic light scattering measurement system. The pulse-amphfier discriminator converts the analog signal of the photodetector, I t), into a digital signal, which is further converted by the autocorrelator into the autocorrelation function of the signal.

Another interesting case is that of the fullerene molecule Ceo, which is nearly spherical [ 19,a,b] the relaxation times in various non-polar and low-polar solvents (measured by a picosecond-pulse light-scattering method) are in the range 3-13 ps, i.e., distinctly larger than the value ( 1 ps) calculated for slip conditions, but much less than the value (f 100 ps) for no-slip. The data could be accommodated by a theory of partial slip [19,c,d]. The result suggests that we need to know more about friction at various molecular surfaces. 

Fiber-optic sensors are attractive options (but more expensive) for acquiring measurements in harsh environments such as high temperature or pressure. The transducing technique used by these sensors is optical and does not involve electrical signals, so they are immune to electromagnetic interference. Raman spectroscopy uses fiber-optics and involves pulsed light scattering by molecules. It has a wide variety of applications in process control (Dakin and Culshaw, 1997). 

To eliminate the need for recalibration during a measurement and to obtain additional information, the Royco instrument was supplemented with a Nuclear Data ND-60 Multichannel Analyser (MCA). The amplified signal of the Royco 225 (which is proportional to the cimount of light scattered from each particle) was connected to the input of the MCA which cem count and classify pulsed input signals into as many as 2048 channels and display the results on a cathode ray tube (CRT). This number of cells is of course much more than required to determine the PSD. The data were therefore grouped into eleven cells whose limits were consistent with those used earlier (5), emd the counts in these cells were then printed on a Texas Instruments 743 KSR Data Terminal interfaced with the MCA. 

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