Several original schemes for intracavity frequency doubling of CO2 laser radiation (TEA and cw systems) in AgGaSe2 nonlinear crystals have been proposed and studied experimentally. Computer modeling was used for optimization of the optical schemes and cavity parameters. The enhancement by several fold in conversion efficiency was achieved for intracavity SHG in comparison with traditional schemes. A 60% peak power efficiency and 15% energy conversion efficiency has been obtained with a TEA CO2 laser. More than 100 mW at 5 micrometers was generated in the crystal with L equals 17 mm, which is a record output for SHG of a cw CO2 laser. This output is more than 10 times higher than 5 micrometers power measured with standard focusing the CO2 laser beam.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.