Optical mixing

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

The pump and probe pulses employed may be subjected to a variety of nonlinear optical mixing processes they may be prepared and characterized by intensity, duration, spectral band width, and polarization. They may arrive in the reaction chamber at a desired time difference, or none. The probe pulse may lead to ionizations followed by detections of ions by mass spectrometry, but many alternatives for probing and detection have been used, such as laser-induced fluorescence, photoelectron spectroscopic detection, absorption spectroscopy, and the like. 

Figure 3. Block diagram of the experimental apparatus for an optical mixing measurement...

Since it is possible to measure the rotational diffusion coefficient by optical mixing techniques, and since expressions equivalent to Equations 36 and 37 have also been calculated by Perrin (67) for rotational motion, we may solve the simultaneous equations... 

P 12] The mixing performance was analyzed by a dilution-type experiment. Here, water and the fluorescent dye uranine, sodium fluorescein [22], The latter is water-soluble. External pressure was applied to the liquids using a fluid dispenser. The flow rates of both water and the aqueous uranine solution were 5 pi min-1. A fluorescent microscope with a digital CCD camera with a 1.25x objective was used for optical mixing analysis. Fluorescent filters at 460-490 and 515-550 nm... 

Fig. 5. Typical power spectrum of the optically mixed light intensity. O/W, ripplon (capillary wave) frequency at nitrobenzene-water interface W/A, ripplon frequency at water-air interface. (Reprinted from [76] with permission. Copyright The Japan Society of Analytical Chemistry).

Hoffmelster series = lyotropic series holes (in semiconductors) 3.171 homodlsperse colloids 1.1.14. 1.1.28,1.7.53 homod me beating see optical mixing homointeraction 1.4.72... 

With the advent of the laser, another type of experiment became possible. In 1964, Pecora showed that the frequency distribution of light scattered from macs molecular solutions would yield values of the macromolecular diffusion coefficient and under certain conditions might be used to study rotational motion and flexing of macromolecules. These frequency changes are so small that conventional monochromators (or filters ) could not be used to resolve the frequency distribution of the scattered light. In 1964, Cummins, Knable, and Yeh used an optical-mixing technique to... 

In optical mixing experiments, a correlator computes time-correlation functions of the scattered field in this discrete manner (see Chapter 4). Of course in any experimental determination the averaging is done over a finite number of steps (finite time). 

For processes faster than about 10-10 sec, diffraction gratings are used as the filter. For the slower processes with relaxation times in the range of about 10-6-10-10 sec Fabry-Perot interfermeters are used (See Appendix 4.A). Filter experiments do not have sufficient resolution to study processes slower than about 10 6 sec. For fluctuations in the time range 1—10—6 sec optical mixing techniques must be used. 

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