Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm

Blue diode lasers emitting 5 mW continuous-wave power around 400 nm have re cently become available. We report on the use of a blue diode laser togethe r with a 30 mW red diode laser for sum-frequency generation around 254 nm. The ultraviolet power is estimated to be 0.9 nW, and 35 GHz mode-hop-free t uning range is achieved. This is enough to perform high-resolution ultravio let spectroscopy of mercury isotopes. The possibility to use frequency modu lation in the ultraviolet is demonstrated; however, at present the ultravio let power is too low to give advantages over direct absorption monitoring. Mercury detection at atmospheric pressure is also considered which is of gr eat interest for environmental monitoring. (C) 2000 American Institute of P hysics. [S0003-6951(00)02810-2].