Laser crystals with high-damage-threshold coatings, supplied in quantity to OEM and R&D customers, and nonlinear crystals for frequency doubling. Second-harmonic generation is a special case of sum-frequency generation with two identical input wavelengths; the simplest scheme is extracavity doubling, where the laser passes through the crystal once, while focused beams, intracavity doubling or an external resonant cavity are used to raise the power density on the crystal when the laser power density is low.
