Scattering medium

N.M. Lawandy, A.M. Balachandran, A.S.L. Gomes, E. Sauvain, Laser action in strongly scattering media. Nature 1994, 368, 436. 

For non-scattering media, following the classical Beer-Lambert law, L is equal to the distance between source and detector, denoted as d. For scattering media Equation (1) can be rewritten as... 

M. Oda, Y. Yamashita, G. Nishimura, and M. Tamura. Quantitation of absolute concentration change in scattering media by the time-resolved microscopic beer-lambert law. Advances in Experimental and Medical Biology, 345 861-870, 1992. 

A. Sassaroli and S. Fantini. Comment on the modified beer-lambert law for scattering media. Physics in Medicine and Biology, 49 N255-N257, 2004. 

The advantage of two-color excitation over two-photon excitation is not an improvement in imaging resolution, but the easier observation of microscopic objects through highly scattering media. In fact, in two-color excitation, scattering decreases the in-focus fluorescence but only minimally increases the unwanted fluorescence background, in contrast to two-photon excitation. 

Reabsorption and reemission. In scattering media the effect of reabsorption plays a very important role (see Section 6.3). The consecutive reemission will slow down the decay process (see Section 6.4). The effect is not very big, but it can be... 

The propagation of light in multiple scattering media is quantified usually on the level of radiative transfer or particle diffusion. Scattering, absorption, and emission are considered as independent statistical processes, and the consequences of wave character are either ignored, like polarization, or added as an additional parameter, like the phase function P(ji n) that describes the angular distribution of scattered... 

In multicomponent systems A"0 can be written as a sum of the individual absorption coefficients A ot = 2TA , where each AT,(A ) depends in a different way on the wavelength. If one or more of the components are fluorescent, their excitation spectra are mutually attenuated by absorption filters of the other compounds. This effect is included in Eqs. (8.27) and (8.28) so that examples like that of Figure 8.4 can be quantified. The two fluorescent components are monomeric an aggregated pyrene, Mi and Mn. The fluorescence spectra of these species are clearly different from each other but the absorption spectra overlap strongly. Thus the excitation spectrum of the minority component M is totally distorted by the Mi filter (absorption maxima of Mi appear as a minima in the excitation spectrum ofM see Figure 8.4, top). In transparent samples this effect can be reduced by dilution. However, this method is not very efficient in scattering media as can be seen by solving Eqs. (8.27 and 8.28) for bSd — 0. Only the limit d 0 will produce the desired relation where fluorescence intensity and absorption coefficient of the fluorophore are linearly proportional to each other in a multicomponent system. 

S. C. Park, M. Kim, J. Noh, H. Chung, Y. Woo, J. Lee and M.S. Kemper, Reliable and fast quantitative analysis of active ingredient in pharmaceutical suspension using Raman spechoscopy, Aruil. Chim. Acta, 593,46-53 (2007). P. Matousek, I.P. Clark, E.R.C. Draper, et al.. Subsurface probing in diffusely scattering media using spatially offset Raman spechoscopy, Appl. Spectrosc., 59, 393 00 (2005). 

Scattering media to which this matrix applies include randomly oriented anisotropic spheres of substances such as calcite or crystalline quartz (uniaxial) or olivine (biaxial). Also included are isotropic cylinders and ellipsoids of substances such as glass and cubic crystals. An example of an exactly soluble system to which (13.21) applies is scattering by randomly oriented isotropic spheroids (Asano and Sato, 1980). Elements of (13.21) off the block diagonal vanish. Some degree of alignment is implied, therefore, if these matrix elements... 

According to the ground rules laid down at the beginning of this book, multiple scattering is excluded from consideration. But it is not always prudent to pretend that multiple scattering does not exist. Fortunately, it is almost trivial—the mathematical apparatus of radiative transfer theory is unnecessary—to extend our treatment of scattering and circular polarization to multiple scattering media, and in this instance it is worth the small amount of effort required to do so. 

Abstract This chapter reviews emerging techniques for deep, non-invasive Raman spectroscopy of diffusely scattering media. As generic analytical tools, these methods pave the way for a host of new applications including non-invasive disease diagnosis, chemical identification and characterisation of pharmaceutical products. 

Figure 20 Dynamic holography apparatus for imaging through scattering media such as biological tissue.

Zhadin NN, Alfano RR. Correction of the internal absorption effect in fluorescence emission and excitation spectra from ahsorhing and highly scattering media theory and experiment. Journal of Biomedical Optics 1998, 3, 171-186. 

Ramella- Roman JC, Prahl SA, Jacques SL. Three Monte Carlo programs of polarized light transport into scattering media part I. Optics Express 2005, 13, 4420-4438. 

Love, T. J. and Grosh, R. J. (1965). Radiative Heat Transfer in Absorbing, Emitting, and Scattering Media. Trans. ASME, J. Heat Transfer, 87c, 161. 

If a laser beam is focused in the material, the intensity required for TPA to occur will usually only be reached close to the focus. The selectivity of the absorption process in propagation direction is excellent (Fig. 11), which enables the three dimensional resolution of TPA process as mentioned above. Furthermore, the penetration into absorbing or scattering media can be greatly improved if the fundamental wave is not depleted by one-photon absorption and if the TPA only takes place at the point of strong focussing. 

Trivic, D.N., O Brien, T.J., and Amon, C.H. Modeling the radiation of anisotropically scattering media by coupling Mie theory with Finite volume method. International Journal of Heat and Mass Transfer, 2004. 47, 5765-5780. 

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