Optical scatter

Turbidimetry and Nephelometry. In contrast to classical absorbance methods, immunoassay reactions frequently involve agglutination in which the optical scatter signal of the agglutinated particles is measured by turbidimetric or nephelometric means. The principles of light scattering as it relates to analytical methods is discussed in reference 6. 

J. C. Stover. Optical Scattering Measurement and Analysis. McGraw-Hill,... 

Figure 10-8. Emission spectra of a free standing film of a blend system consisting of 0.9% MEH-PPV in polystyrene with ca. I011 cm 3 TiOj-particlcs. The nanoparlicles act as optical scattering centers. The emission spectrum is depicted for two different excitation pulse energies. Optical excitation was accomplished with laser pulses of duration I Ons and wavelength 532 nm (according to Ref. 171).

The random laser is a simple optical system in which the strong optical scattering in the random medium forms an optical recurrent path. Recent reports on random lasers have described the emission of laser light by metal-oxide polycrystalline and micrometer-sized particles [46]. Because of its structural simplicity and small size, the single random laser is a promising miniature light source for optical devices, such as waveguides and optical switches. 

For correlation with most physical properties (mechanical strength, optical scattering), mass average molecular mass of a polymer Mw" appears more satisfactory. Higher-power averages like z-average molecular mass "Mz" seem to better correlate with rheological properties. Expressions of M , Mw and Mz are... 

But here is what Philip Brown did He took a different tack on the question. He set up and performed an experiment wherein he took different sugars (fructose, glucose, and sucrose) and made up solutions by dissolving them in water, each at five different concentration levels, and made solutions using all combinations of concentrations. That gave an experimental design with 125 samples. He then measured the spectra of all of those samples. Since the samples were all clear solutions there were no extraneous effects due to optical scatter. 

But to extend the work to understanding the role of nonlinearity in calibration, how to deal with it when an experimental design is not an option, and what to do when the optical scatter is the dominant phenomenon in the measurement of samples spectra are still very open questions. 

Raman spectroscopy comprises a family of spectral measurements based on inelastic optical scattering of photons at molecules or crystals. It involves vibrational measurements as well as rotational or electronic studies and nonlinear effects. Following, Raman will be used in the established but slightly inaccurate way as a synonym for the most important and most common technique of the family, linear vibrational Raman scattering. 

In optical tweezer experiments, the optical scattering force is used to trap particles, but the force can also be used to control the shape of liquid droplets26. An infrared laser with 43-mW power focused onto a microdroplet on a superhydrophobic surface enabled up to 40% reversible tuning of the equatorial diameter of the droplet26. Such effects must naturally also be taken into account when exciting laser modes in droplets in experiments with levitated drops. 

FIGURE 9.23 (a) Aerosol particle size distribution measured at Pomona during the 1972 State of California Air Resources Board ACHEX program, (b) Calculated optical scattering by particles, bsp, for measured size distribution (adapted from Waggoner and Charl-son, 1976). 

Figure 1. The optical scattering leading to a single microscopic nonlinear optical event.

A distinction between homodyne and heterodyne detection must be made in optical scattering and diffraction experiments. Without careful treatment of the background, there is always the risk of mixed or unknown coherence conditions, and the diffusion coefficient determined from such data may be off by a factor of two. At least for the signal and background levels present in TDFRS, heterodyne detection is always superior to homodyne, especially since the heterodyne signal, contrary to the homodyne one, turns out to be very stable against perturbations and systematic errors. Even under nearly perfect homodyne conditions the tail of the decay curve is almost unavoidably heterodyne [34]. 

We have outlined how TDFRS not only provides a useful tool for the study of the Ludwig-Soret effect in multicomponent liquids, but can also contribute valuable pieces of information towards solving the puzzles encountered in polymer analysis. Though TDFRS is conceptually simple, real experiments can be rather elaborate because of the relatively low diffraction efficiencies, which require repetitive exposures and a reliable homodyne/heterodyne signal separation. As an optical scattering technique it has much in common with PCS, and the diffusion coefficients obtained in the hydrodynamic limit (q —> 0) for monodisperse solutions are indeed identical. 

Bruulsema JT, Hayward JE, Farrell TJ, Patterson MS, Heinemann L, Berger M, Koschinsky T, Sandahl-Christiansen J, Orskov H. Correlation between blood glucose concentration in diabetics and noninvasively measured tissue optical scattering coefficient. Optics Letters 1997, 22, 190-192. 

UV fluorescence, UV photometry, electromagnetic absorption, optical scattering and reflection, capacitive, vapor purging, and VOC gas sensor Bacterial biosensor, biomass oxygen consumption... 

In Eq. (4), one can see that there are two terms that depend on the space-phase factor. Eq. (5) clearly shows this situation coherence is generated between the two molecules. This coherent excitation can be called as inter-molecular coherence. This type of coherent excitation can be seen in femtosecond pump-probe non-linear coherent optical scattering spectroscopy. This chapter shall only focus on ultrafast radiationless transition as well as the dynamics of the intramolecular coherence and its relaxation. 

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