Experimental creation and characterization of random potential-energy landscapes exploiting speckle patterns

The concept of potential-energy landscapes is applied in many areas of science. We experimentally realize a random potential-energy landscape (RPEL) to which colloids are exposed. This is achieved by exploiting the interaction of matter with light. The optical setup is based on a special diffuser, which creates a top-hat beam containing a speckle pattern. This is imposed on colloids. The effect of the speckle pattern on the colloids can be described by a RPEL. The speckle pattern and the RPEL are quantitatively characterized. The distributions of both intensity and potential-energy values can be approximated by Gamma distributions. They can be tuned from exponential to approximately Gaussian with variable standard deviation, which determines the contrast of the speckles and the roughness of the RPEL. Moreover, the characteristic length scales, e.g., the speckle size, can be controlled. By rotating the diffuser, furthermore, a flat potential can be created and hence only radiation pressure can be exerted on the particles.