Spark gap optical isolator for high power infrared lasers

A zero insertion loss optical isolator has been developed and tested in a short pulse CO2 laser oscillator–amplifier system. The device, which uses a narrow plasma column produced by a streamer discharge in air and situated at the common focus of two cylindrical mirrors, provides effective isolation of the oscillator and pulse forming system against retroreflected laser light. Using this arrangement a reflected 1 nsec CO2 laser pulse of ∼2 cm diam and energy density up to 1 J/cm2 has been completely blocked after an optical delay as short as 4 nsec. The device should also find application in other infrared laser systems for which no isolators at present exist.