Pauli blocking of light scattering in degenerate fermions

Pauli blocking occurs when free atoms scatter light elastically and the final external momentum states are already occupied. Suppression of the total rate of light scattering requires a quantum-degenerate Fermi gas with a Fermi energy larger than the photon recoil energy. Pauli blocking was predicted 30 years ago, but the experimental realization was elusive due to the difficulty of prepare cold fermi gas at high density. Here we report the creation of a dense Fermi gas of ultracold lithium atoms and show that at low temperature light scattering is suppressed. We also demonstrated the suppression of inelastic light scattering when two colliding atoms emit light shifted in frequency. Our platform enables future studies of light-matter interaction at high density.