High-power multi-wavelength external cavity laser

A high-power external cavity laser source is described. The laser source includes a free space external cavity. At least two multimode optical gain elements are positioned in the cavity. Each gain element generates multimode optical radiation having one of at least a first and a second wavelength and one of at least a first and a second free space optical path, respectively. In another embodiment, at least two optical fiber gain media are positioned in at least two respective free space optical paths and each gain media generates optical radiation having one of at least a first and a second wavelength, respectively. An optical element is positioned in the cavity such that its focal plane is substantially located at the at least two optical gain elements and such that it intercepts the at least two respective free space optical paths. A dispersive element is positioned in the at least two optical paths. A partially reflecting element is also positioned in the at least two optical paths. The partially reflecting element and the gain media together form a free space laser cavity that defines the at least first and second wavelength. In operation, the partially reflecting element transmits an overlapping or coaxial beam comprising radiation having the at least first and second wavelength.