Speaker
Description
Louis-George Gouy (1853–1926) discovered in the late 19th century that static light scattering exhibits intense scattering at 90 degrees. This phenomenon was related to back-scattering, and he was able to quantify it by comparing its intensity to the intensity of diffraction produced by the edge of a screen—the latter being the subject of most interest at the time.
Moreover, Gouy related the angle of maximum scattering to the concentration of the medium. This key finding later allowed researchers like Rayleigh, Smoluchowski, and Perrin to quantitatively determine the concentration of colloids per unit volume.
Modern Application and Technology
Modern technology, such as the Vasco-Kin device developed by Cordouan Technology, has significantly advanced this field. By upgrading the instrument and incorporating a careful determination of the absolute value of the Rayleigh ratio—in combination with advanced time-resolved filtering—it is now possible to determine not only the apparent size but also the concentration and Rayleigh ratio of colloidal solutions and complex fluids. This is achievable even in the presence of "dusts" that typically produce intense, dominant, and parasitic scattering signals.
In the q-range limited by the scattering geometry, we utilize a massive photon flux of 5×10$^{15}$ photons/s. This flux is approximately 100 times greater than the intensity available at the world's best beamline (ID02) operating at 12 keV.
Louis-George Gouy (1853–1926) is shown in front of his original light scattering instrument (source: Wikipedia). This historical apparatus can be compared to its modern implementation, the portable Vasco-Kin device by Cordouan Technology. The Vasco-Kin counts up to 10$^{6}$ photons per second, offering an effective dynamic range of four decades for the scattered light induced by a laser beam with a flux exceeding 10$^{15}$ photons/s. This allows for studies on the probability of diffusion by colloids, even after filtering from dust, with sensitivity as low as 10$^{−10}$.
