We demonstrated a novel technique for low power optical limiting using self-diffraction in bacteriorhodopsin (bR) films. A cw Ar-Kr laser is used as the pump (input beam, 568 nm) and the output is the first order self-diffracted beam with an observed efficiency of about 0.01%. Input beam intensity is varied over three orders of magnitude in the range of milliwatt to watts per cm2 with output clamped at eye safe level of about 0.13 mW/cm2. Threshold intensity for limiting is governed by the saturation intensity of M-state of bR and hence can be varied by choosing films with different lifetimes.
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