Optical path, average concentration

Optical measurements are frequently made through the thin layer of a microfluidic device. The average concentration is then determined by the integral along the path, such as by Eq. (22) ... 

Detection typically occurs in-line, through an optical window placed in the proximity of the capillary outlet, either by spectral analysis, with average concentration sensitivities lower than in HPLC because of the shorter light path, or by laser-induced fluorescence... 

This free path value is not an estimate of the average particle size, as in addition to size there are other unmanageable factors contamination, crystalline structure defects etc. But it is quantity 1 that determines the effective optical constants of a medium, which are used in further calculations to estimate the pwameters of AgPG holograms. Comparison of effective optical parameters of "ideal" (with pjarticles 1 = 8 nm) and real (with particles 1 = 2 nm) media with identical structure piarameters, whose calculated values are given on Fig. 5a, shows the attenuation sp>ectrum of real medium to be essentially wider than that of the "ideal" one, whereas the change of refractive index due to the presence of silver particles (AnAg) is practically the same and is determined by their concentration, CAg, (the quoted calculations used the volume silver concentration in the medium equal to ICH). 

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