Abstract: A Raman laser conversion device for generating a single longitudinal mode, SLM, laser output is disclosed. The device comprises a Raman medium that exhibits a Stokes emission when subject to pumping by a laser pump input, the laser pump input having a pump linewidth and the Raman medium having a Raman linewidth; wherein the Raman medium is configured to define feedback interfaces of a resonator such that the Stokes emission resonates within the Raman medium; and further wherein the free spectral range, FSR, of the resonator with respect to the pump linewidth and/or the Raman linewidth or a function thereof is such that only one longitudinal mode of the Stokes emission is able to resonate within the Raman medium; whereby the laser conversion device generates a SLM laser output that is frequency shifted with respect to the laser pump input.

Abstract: An inventive composite optical gain medium capable includes a thin-disk gain layer bonded to an index-matched cap. The gain medium's surface is shaped like a paraboloid frustum or other truncated surface of revolution. The gain medium may be cryogenically cooled and optically pumped to provide optical gain for a pulsed laser beam. Photons emitted spontaneously in the gain layer reflect off or refract through the curved surface and out of the gain medium, reducing amplified spontaneous emission (ASE). This reduces limits on stored energy and gain imposed by ASE, enabling higher average powers (e.g., 100-10,000 Watts). Operating at cryogenic temperatures reduces thermal distortion caused by thermo-mechanical surface deformations and thermo-optic index variations in the gain medium. This facilitates the use of the gain medium in an image-relayed, multi-pass architecture for smoothed extraction and further increases in peak pulse energy (e.g., to 1-100 Joules).