Coherent optical fluctuations in a white cavity: new spectroscopies for soft matter and beyond.
Light scattering and interferences are essential for understanding a wide range of phenomena in nature. In the context of soft matter, the dynamical properties of speckles induced by coherent multiple scattering reveal important information on the properties of disordered materials. I will first show how the activity of a motor protein, namely myosin, can generate multiple scattering, and speckle fluctuations that reveal the conformational dynamics of that mechano-enzyme. Second, I will introduce a new kind of optical field obtained by injecting a single frequency light into a Lambertian cavity with highly diffuse reflecting walls. We obtain the coherent superposition of a very large number of waves that follow a probability distribution, with spherical symmetry and translation invariance. While the cavity acts as a random interferometer, it produces a 3D speckle field with strongly amplified fluctuations. With a pico-meter sensitivity, a 10-decades frequency range and a 4-decades signal dynamics, we can detect fluctuations of the geometry of the cavity, or the sample it contains. Our concept of Lambertian coherent optical cavity forms the basis for the development of new fluctuation spectroscopies to explore soft matter physics and beyond.
IBS Center for Soft and Living Matter, Ulsan National Institute for Science and Technology Ulsan South Korea