Optical feedback from the target can destroy laser components unless it is prevented from reentering the laser. Conventional Faraday rotator-polarizer isolators are lossy, and their cost increases nonlinearly with the beam diameter to the 2.5 power, precluding their use at large aperture. A 46-cm isolator, for example, costs $500,000 for each of the 20 Nova beams. Each plasma shutter will cost $80,000/beam line.

© 1982 Optical Society of America

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