Light scatter shifts

The scattering techniques, dynamic light scattering or photon correlation spectroscopy involve measurement of the fluctuations in light intensity due to density fluctuations in the sample, in this case from the capillary wave motion. The light scattered from thermal capillary waves contains two observables. The Doppler-shifted peak propagates at a rate such that its frequency follows Eq. IV-28 and... 

The phase shift is measured by comparing the phase of the fluorescence with the phase of light scattered by a cloudy but non-fluorescent solution. 

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

The emission spectra of BODIPY derivatives normally display narrow bandwidths, providing intensely fluorescent labels for biomolecules. Unfortunately, they also have very small Stoke s shifts, typically on the order of only 10-20 nm. Excitation at the optimal wavelength may cause some interference in measurements at the emission wavelength due to light scattering or cross-over from the wide bandwidth of the excitation source. The dyes usually require excitation at sub-optimal wavelengths to prevent this problem. 

The excitation maximum for BODIPY 493/503 C3 hydrazide occurs at 498 nm and its emission at 506 nm. Since this is an extremely small Stoke s shift, it may be difficult to avoid completely problems of excitation-light scattering interference in critical emission measurements unless sub-optimal excitation wavelengths are used. The molecule has an extinction coefficient in methanol of about 92,000M-1cm 1 at 493 nm. 

The excitation maximum for Br-BODIPY 493/503 is 515nm and its emission occurs at 525 nm when dissolved in methanol. Upon coupling to a sulfhydryl compound, however, the excitation wavelength of the adduct decreases to 493 nm and its emission drops to 503 nm. The very small lOnm Stoke s shift may be a problem, particularly in avoiding interference due to of excitation-light scattering in critical emission measurements. Sub-optimal excitation wavelengths... 

Light impinging on the surface of the Mediterranean Sea is scattered. Of this light, a small proportion is scattered in such a way that the frequency changes, causing it to look more blue than was the incident light. This shift in frequency causes the blue colour of the Mediterranean Sea. 

In the large off-axis light scatter detection method, the droplet size can be related, for example, to the phase shift of the light scattered by refraction in the off-axis forward direction as ... 

Fig. 4 PIC dye nanoparticles prepared by the ion-association method. (1) Particle size distributions (determined by the dynamic light scattering technique) and the corresponding electron micrographs of the dye nanoparticles. The average diameter can be controlled by tuning the molar ratio of TPB- to PIC+ (=[TPB-]/[PIC+]. With an increase in the molar ratio, the average diameter decreased. (2) Absorption spectra of PIC nanoparticles in aqueous solution with different sizes (125 and 64 nm in diameter), exhibiting size-dependent peak shift of the 0-0 band. The spectrum of the aqueous PIC-Br monomer solution is also shown...

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