Sum frequency generation at 309 nm using a violet and a near-IR DFB diode laser for detection of OH

We have used a violet diode laser at 404 nm and a distributed feedback diode laser at 1320 nm to produce 0.8 nW of radiation at 309 nm by sum frequency generation in beta-barium borate. The UV radiation was tuned mode-hop-free over 30 GHz and used to detect OH radicals produced in a microwave discharge. By chopping the UV light at 500 Hz, we observed a concentration of 2 x 10(12) cm(-3) with a signal to noise ratio of 30:1.