We show that mesoscopic coherent fluctuations of light propagating in random media induce fluctuating radiation forces. A hydrodynamic Langevin approach is used to describe the coherent light fluctuations, whose noise term accounts for mesoscopic coherent effects. This description—generalizable to other quantum or classical wave problems—allows us to understand coherent fluctuations as a nonequilibrium light flow, characterized by the diffusion coefficient $D$ and the mobility $\sigma$, otherwise related by a Einstein relation. The strength of these fluctuating forces is determined by a single dimensionless and tunable parameter, the conductance $g_{\mathcal{L}}$. Orders of magnitude of these fluctuation forces are offered that show experimental feasibility.

• Received 5 September 2019
• Accepted 24 February 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.136803