18 August 1992 Optical nonlinearities and optical limiting in GaP at 532 nm
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We demonstrate a proof-of-principle, GaP optical energy limiter for 532 nm, 25 ps, pulsed radiation that exhibits an output limiting level of less than 1 (mu) j/cm2. Optical limiting at this level is significant for use in systems designed to protect the human eye from laser radiation damage. The device employs a standard configuration that is realized by placing the GaP at the intermediate focal plane of a 1-to-1 inverting telescope, which is followed by an aperture set to clip the linearly transmitted beam at the 1/e point of the irradiance profile. The linear (indirect) absorption in GaP at this wavelength results in the optical generation of very large densities of free carriers. We therefore anticipate the performance of this device to be highly dependent on free carrier nonlinearities. This is confirmed by performing both two beam and single beam measurements on the material itself in order to determine both the absorptive and refractive parameters at this wavelength. We find that the free carrier absorption cross section is is congruent to 2 X 10-18 cm2, and the change in index per photogenerated electron hole pair is is congruent to -2.4 X 10-22 cm3.
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Steven J. Rychnovsky, Graham R. Allan, Clark H. Venzke, Arthur L. Smirl, and Thomas F. Boggess "Optical nonlinearities and optical limiting in GaP at 532 nm", Proc. SPIE 1692, Nonlinear and Electro-Optic Materials for Optical Switching, (18 August 1992); doi: 10.1117/12.138062; https://doi.org/10.1117/12.138062

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