The Nova plasma shutter

A method is presented to protect the Nova laser system against damaging back-reflected light. A plasma shutter shoots a reflective plasma across the beam path in the 400 ns-interval between the passage of the main beam pulse and the return of the reflected light. Testing shows that this light is more than adequate to stop light of the intensity expected from Nova. Calculations with LASNEX (a code for simulating the interactions of laser light with plasma) indicate that a beam with an intensity of 1 TW/sq mm will burn through only 2% of the plasma thickness. Prices of the plasma shutter are compared with those of the alternative system, the Faraday rotator-polarizer isolator, and it is found that each plasma shutter will cost only $80,000 as opposed to $500,000 for each isolator.