Abstract
We report a doubly resonant continuous-wave CO2 laser frequency-quadrupling device that generates 200 nW of 2.55-µm 4ω and as much as 2 mW of 5.1-µm 2ω radiation out of 1.7-W fundamental radiation at 10.2 µm ω. The quadrupling process results from two resonant cascading second-harmonic generations by use of a walk-off-compensated twin AgGaSe2 device ω2ω and a ZnGeP2 nonlinear crystal 2ω4ω.