Results are presented on observations of active 

 switching of the CO
2laser by intracavity Stark modulation with a sine-wave or square-wave electric field using methyl chloride and 1-1 difluoroethane. Passive 

 switching of the 

 branch of the 10.4-μm band by methyl fluoroform, at a repetition rate variable by a dc Stark field, is also reported.