Faraday Instability in a Multimode Laser

We show theoretically and experimentally that a basic pattern formation mechanism in hydrodynamics, the Faraday instability, can be observed in optics (for modulated class $B$ lasers with inhomogeneous broadening). As for the Faraday problem, stationary waves are excited parametrically and wave numbers are selected by the dispersion curve of the medium. The mechanism is evidenced by a multiple-scale analysis of the physical laser model, and is confirmed experimentally using a Nd-doped fiber laser.