Detection capillary waves

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 construction of experimental set-ups differ in the way of wave generation, wave propagation and damping detection. One of the possible designs is shown in Fig. 6.2. The capillary waves are produced by a vibrator attached to a drive unit of a loudspeaker. The wave damping is determined via a microscope and stroboscope. The set-up works in a frequency range from 25 Hz to 4 kHz. 

As discussed in Chapter 3, Breckenridge et al. [1981] developed a capacitance-type sensor of very flat response, by which they detected AE waves due to a break of glass capillary shown in Fig. 7.4. Later, the capillary break was replaced by the pencil-lead break by Hsu [1978]. As compared Fig. 7.3 with Fig. 7.4, first time, they showed that AE wave detected by the flat-type sensor due to the step-function force is actually identical to Lamb s solution due to the surface pulse. It was also demonstrated that Lamb s solution due to a buried pulse could be obtained by applying the force at the bottom of the block in Fig. 3.10. Thus, it is clarified by them that the displacement observed by the flat-type sensor due to capillary break or pencil-lead break is identical to G 33(x,yo,t). This implies that Green s function of the specimen can be empirically obtained by just applying the pencil-lead break and recording the displacements. 

Surface light scattering methods from thermally induced capillary waves at the interface [139-141] or from electric-field-induced surface waves [142, 143] have appeared. The technique is limited by the viscosities of the two phases if the viscosities are too large, then the spatial damping of the surface capillary waves is too rapid to be detected by the technique. The applicability of this method for highly viscous polymeric interfaces has not been verified yet. 

Under the conditions of the simulation, a small enrichment of solvent is even detectable at a planar polymer liquid— vapor interface. This is illustrated qualitatively by the snapshot in Fig. 37, which resembles the interface profiles in Fig. 10 (b). Of course, a more quantitative comparison has to consider capillary waves that broaden the interface profiles in the simulations [100] and the density correlations (packing) which are neglected in the SCF calculations. 

For many applications, diode array detection has become routine. A photodiode array was used for simultaneous detection of 100 capillaries in zone electrophoresis and micellar electrokinetic chromatography (MEKC).1516 Deflection of a laser beam by acoustic waves was reported as a means to scan six capillary channels on a microchip.17 The design of a low-noise amperometric detector for capillary electrophoresis has been reported.18... 

With respect to detection for CE, laser-induced fluorescence (LIF) detection is an attractive approach as a result of the sensitivity attainable despite the short path length. For this reason, it is well suited to microchip electrophoretic analysis of a variety of analytes including DNA fragment sizing and sequencing.The excitation source is usually a continuous-wave argon ion laser, which is focused in a capillary or on a microchannel in a microchip. 

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