Appl. Phys. Lett. 103, 051114 (2013)

There is a pressing need to find convenient and effective ways to generate deep ultraviolet light for techniques such as photoemission spectroscopy and semiconductor lithography. Frequency conversion of the output of continuous-wave diode and solid-state lasers is one approach, but reaching wavelengths shorter than 200 nm has proved problematic because of the limitations of nonlinear crystals. Now, Matthias Scholz and co-workers from Germany and China have produced a continuous-wave laser source that can achieve a high output power of over 15 mW at 193 nm. Their scheme quadruples the frequency of the 772-nm output of a diode laser in two stages; both stages consist of an enhancement cavity containing a crystal — a lithium triborate crystal in the first stage and a potassium fluoro-beryllo-borate crystal in the second stage. The researchers demonstrate that this laser can produce a stable output of 8 mW over a period of 80 h and that its short-term noise characteristics are superior to those of excimer lasers by one order of magnitude. It is thus a promising replacement for ArF excimer lasers for both scientific and commercial applications, potentially offering superior coherence properties, spectral density, reliability and ease of use.