High-power laser systems require optical isolation to prevent back-reflected radiation causing component damage. The isolation is usually supplied by Faraday rotators located after the final amplifiers in each arm of the laser. Additionally, large lasers also require spatial filters to maintain the quality of the propagating beam. The author reports on the performance of a novel spatial filter pinhole shutter that obviates the need for Faraday rotator isolators in the laser output beams. The shutter uses an orthogonal laser pulse to generate an absorbing plasma. Pinhole transmission of <1% for times of approximately 30 ns have been obtained with shutter pulses of only approximately 40 mJ energy. A simple model is proposed to explain the plasma development and absorption.