Diffusing-wave spectroscopy: Difference between revisions

Revision as of 08:22, 22 October 2009

Revision as of 03:27, 7 February 2010

Line 1:

'''Diffusing-wave spectroscopy''' is an optical technique derived from [[dynamic light scattering]] (DLS) that studies the dynamics of light scatterers in the case of strong multiple scattering.

<ref>G. Maret and P. E. Wolf, Z. Phys. B: Condens. Matter 65, 409 1987</ref>

<ref>D. J. Pine, D. A. Weitz, P. M. Chaikin, and E. Herbolzheimer, Phys. Rev. Lett. 60, 1134 1988</ref>

Line 13:

The signal is analysed by calculating the intensity autocorrelation function called g₂.

<math>g_2(\tau)=\frac{<I(t)I(t+\tau)>_t}{<I(t)>_t^2}</math>

<br /><br />

In general the relation between g₂-1 and the mean square displacement of the particles <Δr²> depends on the photons trajectories. Let's note P(s) the probability density function (PDF) of the photon path length s. The relation can be written as following:<ref>F. Scheffold, S. Romer, F. Cardinaux, H. Bissig, A. Stradner, L. F. Rojas-Ochoa1, V. Trappe, C. Urban, S. E. Skipetrov, L. Cipelletti and P. Schurtenberger, New trends in optical microrheology of complex fluids and gels, Progress in Colloid and Polymer Science, vol 123/2004, pp 141-146 </ref> <br />

<math>g_2(\tau)-1=[\int {ds P(s) exp(-(s/l*)k_0^2 <\Delta r^2(\tau)>) }]^2</math><br />

with <math>k_0=\frac{2\pi n}{\lambda}</math> and <math>l*</math>: the transport length.

Line 22 ⟶ 21:

<math>g_2(\tau)-1=exp[-2 \gamma \sqrt{<\Delta r^2(\tau)>k_0^2}]</math>, γ value is around 2.

For less thick cells and transmission, the relationship depends on l* (the transport length)<ref> D. A. Weitz and D. J. Pine, “Diffusing-wave spectroscopy,” in Dynamic Light scattering, W. Brown, ed., Clarendon Press, Oxford (1993) 652–720</ref>.

The multiple scattering implies a high dependence on the cell geometry and . An advantage is that the control of the geometry allows to control the studied length scale.

Line 44 ⟶ 43:

* [http://www.formulaction.com/tech_dws_gb.html Illustrated description of DWS with movies]

[[Category:Physics]]

[[Category:Optics]]

[[Category:Soft matter]]