OPTICAL sensors used in connection with bright sources such as lasers and arc welders must commonly be protected from damaging light levels by the use of optical limiters1. One approach to optical limiting makes use of materials whose optical transmittance decreases at high light levels2-5. For most protective applications, the response must be rapid and the saturation threshold low; a lower threshold provides a greater safety margin. Studies of the optical properties of Cave shown that the absorption cross-section of the photoexcited triplet state is greater than that of the ground state6, suggesting that it may have a nonlinear optical response of the sort useful for optical limiting. Here we report measurements of the optical response of solutions of Cand Cin methylene chloride and toluene, using 8-ns pulses of 532-nm-wavelength laser light. We observed optical limiting behaviour in all cases, with saturation thresholds equal to or lower than those reported for other optical-limiting materials currently in use.
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