The first cw high-power UV laser at 266 nm is accomplished by an intracavity frequency doubled and externally quadrupled diode-pumped Nd:YAG laser. The quadrupling stage is an actively stabilized unidirectional ring cavity based on the patent-pending DeltaConcept, where a minimum number of optical components -- two mirrors and one prism are used. The symmetrical Brewster-angled beam path through the piezo-driven prism guarantees an extremely stable cavity length stabilization and provides a geometry-invariant alignment. Minimum losses result in a power enhancement up to 150. By using Brewster-cut BBO crystals the high-power cw UV laser can deliver 266 nm radiation with an output power of 1.5 Watt at a green pumping power of 5 W.

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