A precise method to determine the angular distribution of backscattered light to high angles

Abstract

We present an approach to measure the angular dependence of the diffusely scattered intensity of a multiple scattering sample in backscattering geometry. Increasing scattering strength give rise to an increased width of the coherent backscattering and sets higher demands on the angular detection range. This is of particular interest in the search for the transition to Anderson localization of light. To cover a range of −60°to +85°from direct back-reflection, we introduced a new parallel intensity recording technique. This allows one-shot measurements, with fast alignment and short measuring time, which prevents the influence of illumination variations. Configurational average is achieved by rotating the sample and singly scattered light is suppressed with the use of circularly polarized light up to 97%. This implies that backscattering enhancements of almost two can be achieved. In combination with a standard setup for measuring small angles up to ±3°, a full characterization of the coherent backscattering cone can be achieved. With this setup we are able to accurately determine transport mean free paths as low as 235 nm.

Coherent Backscattering and Anderson Localization of Light

“…In order to be able to tackle this problem experimentally, a calibrated energy scale would be needed. A simple extension of the setup of Gross, Störzer, Fiebig, Clausen, Maret, and Aegerter [2007] is capable of this, as will be described below.…”

“…The different diodes are calibrated using a teflon sample, which in this angular range gives a purely incoherent signal. Reprinted figure with permission from Gross, Störzer, Fiebig, Clausen, Maret, and Aegerter [2007]. Copyright 2007 by the American Physical Society.…”

“…A radically different approach was chosen by Gross, Störzer, Fiebig, Clausen, Maret, and Aegerter [2007]. Here, moveable parts are completely absent and the backscattered intensity is measured at all angles simultaneously.…”

“…In turbid powders, the averaging over the speckle pattern is usually done by rotating the sample, which leads to a configurational average (see e.g. Gross, Störzer, Fiebig, Clausen, Maret, and Aegerter [2007]). …”

Broadband enhanced backscattering spectroscopy of strongly scattering media

“…The high spatial coherence of the source is defined by the collimated output of a single-mode photonic crystal fiber. The setup presented here has several advantages with respect to other implementations of enhanced backscattering [10,11]. The off-centered rotation technique [10] is limited to an angular range of several tens of degrees, while the presence of a beamsplitter limits the use of circular polarization channels.…”