Café com Física
Philippe Wilhelm Courteille
Instituto de Física de São Carlos - USP
Collective scattering of light
The irradiation of light into ultracold gases can induce long-range interactions and phase transitions to non-equilibrium states. Matter wave superradiance and collective atomic recoil lasing, which are famous examples for collective instabilities, are caused by correlations between scattering events. However, collective scattering even occurs with single photons. Recent experiments demonstrated collective effects via radiation pressure measurements and pinned down the respective roles of cooperativity, disorder and finite volume effects in the scattering process. In cases, where the atomic cloud is ordered within an optical lattice, cooperative scattering may give rise to photonic band structures, reminiscent to what is observed in photonic crystals. Being directly linked to the classical phenomenon of Mie scattering, the viewpoint of collective scattering may also shed new light on long standing questions, like the correct value of photonic momentum in dielectric media. The goal of a new experiment at the Instituto de Física de São Carlos is to study these effects with ultracold strontium clouds.