30 August 1989 Utilisation Of Nonlinear Absorption And Refraction For Optical Limiting
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External self-focusing and nonlinear interference phenomena can arise when a laser beam interacts with a nonlinear medium, and may be utilised to limit the transmitted beam power. The limiting mechanism may be complicated by the interplay of nonlinear absorption and refraction, and also by the shape of the incident beam profile. These effects have been investigated for Kerr-type media through analytic and numerical solutions of the nonlinear wave equation. Strong modulations in the transmitted irradiance can appear with optically thin nonlinear media in principle, even where very pronounced nonlinear absorption is present. This type of interference modulation does not necessarily decay as the incident power increases, depending upon the shape of the incident laser beam. Furthermore, the amplitude and periodicity of the modulations depend markedly upon nonlinear absorption. Structural features attributable to the nonlinearity appear at the vicinity of a focus in both the radial and axial directions, and increase in proportion to the magnitude of the nonlinear optical phase shift. Analytic techniques have established that relatively small changes in beam shape can markedly affect the transmitted irradiance. It is also shown that external self-focusing can be viewed, at least in terms of the incident power dependence of the nonlinear "focal shift", as a compromise between the opposing tendencies of nonlinear absorption and refraction.
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John A. Hermann, John A. Hermann, } "Utilisation Of Nonlinear Absorption And Refraction For Optical Limiting", Proc. SPIE 1105, Materials for Optical Switches, Isolators, and Limiters, (30 August 1989); doi: 10.1117/12.960619; https://doi.org/10.1117/12.960619

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