Optical properties of low-dimensional systems: the Bechgaard salts case

We review our optical investigations on the organic Bechgaard salts. These prototype quasi-one dimensional systems reveal non-Fermi liquid features in their electrodynamic response. We show that various aspects of the exotic normal state properties along the chains are consistent with the predictions of the Tomonaga-Luttinger liquid theory or Luther-Emery model for one-dimensional systems. The role played by the interchain coupling will be also addressed. (orig.)