The YLR-600, a high-power single-mode ytterbium fiber laser from IPG Photonics Corp. of Oxford, Mass., has demonstrated enhanced cutting, welding and scribing performance in industrial applications. The ytterbium active fiber is side-pumped with single-emitter telecom-grade diodes that are coupled to the active medium with multimode fiber. More than 90 percent of the pump light is delivered to the fiber. Diodes are individually packaged and have a projected lifetime of more than 100,000 hours in either continuous-wave or pulsed operation. The front and rear reflectors are fusion-spliced to the active medium with a single-mode fiber spliced to the output reflector, resulting in a 600-W fiber laser that operates at 1070 nm with M2 <1.1. It can operate modulated to 40 kHz and is completely monolithic, requiring no adjustment or alignment. Wall-plug efficiency is greater than 20 percent. The compact units, measuring 24 × 24 × 24 in., are available with delivery fiber up to 20 m in length. Each laser is supplied with a collimator, a collinear red aiming diode, a power monitor, current control, and an analog and an RS-232 interface. The standard collimator focal length is 33 mm, producing a 1/e2 of 5 mm and a full angle divergence of less than 0.3 mrad. With a 100-mm lens, the spot size is 21 µm, and with a 66-mm lens, 14 µm.