A schlieren method for ultra-low–angle light scattering measurements

• Published in: Europhysics letters Vol. 63; no. 2; pp. 220 - 225
• Main Authors: Brogioli, D, Vailati, A, Giglio, M
• Format: Journal Article
• Language: English
• Published: Les Ulis IOP Publishing 01.07.2003; EDP Sciences; EDP sciences
• Subjects: 42.25.Fx; 42.79.Mt; Diffraction and scattering; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Optical elements, devices, and systems; Optics; Physics; Schlieren devices; Wave optics; Electromagnetic wave scattering; Light scattering; Theoretical study; Measuring methods; Small angle scattering; Schlieren method; Experimental study
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/epl/i2003-00519-4

We describe a self-calibrating optical technique that allows to perform absolute measurements of scattering cross-sections for the light scattered at extremely small angles. Very good performances are obtained by using a very simple optical layout similar to that used for the schlieren method, a technique traditionally used for mapping local refraction index changes. The scattered intensity distribution is recovered by a statistical analysis of the random interference of the light scattered in a half-plane of the scattering wave vectors and the main transmitted beam. High-quality data can be obtained by proper statistical accumulation of scattered intensity frames, and the static stray light contributions can be eliminated rigorously. The potentialities of the method are tested in a scattering experiment from non-equilibrium fluctuations during a free-diffusion experiment. Contributions of light scattered from length scales as long as $\Lambda=1$$\un{mm}$ can be accurately determined.