Numerical Modeling of Nonlinear Beam Propagation Phenomena
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ECE Dept., University of Wisconsin, Milwaukee, WI 53201
ABSTRACT A user-friendly beam propagation program has been developed for use over the worldwide-web to aid the optical limiting community in modeling the transmission of light through nonlinear refractive and absorptive media having local intensity-dependent or nonlocal fluencedependent mechanisms. INTRODUCTION We have developed software, complete with a user-friendly interface, which gives members in the optical limiting community device-independent access to a powerful computer program that models the propagation of light through an optical system containing a nonlinear optical material. Unlike most commonly available software packages, this program can be run from virtually any computer because the memory-intensive computing is performed on a remote computer. This is accomplished by making extensive use of the world wide web and electronic mail. A suite of simple optical systems has been developed to help facilitate the verification of the numerical codes with experimental measurements. Various nonlinear refractive and absorptive mechanisms are modeled, including Kerr, two-photon, bleaching, reverse-saturable absorption, and thermal heating processes. Presently, the optical system may be configured with a single thin lens having an f-number greater than 3.5 and either pill-box or partially apodized Gaussian beam profiles at the input aperture. The design of any nonlinear optical device, e.g., limiters and rectifiers, cross-bar switches, logic gates, or soliton encoders, require that demanding engineering constraints be satisfied. As is generally characteristic of nonlinear systems, the performance of these devices may be sensitive to the characteristics of the input beam, the optical system, and the properties of the nonlinear medium. The marginal performance of current nonlinear optical materials requires one to optimize the device and material systems to achieve adequate limiting without sacrificing optical quality. Though partial differential equations governing the propagation of light in nonlinear media are known, analytic solutions are rare; hence, numerical methods are required to determine parameter values which provide acceptable levels of exposure at the 269 Mat. Res. Soc. Symp. Proc. Vol. 479 01997 Materials Research Society
sensor. Whereas such information may be experimentally measured for a given set of optical and material parameters, only numerical solutions are capable of providing data for arbitrary parameters. Thus, numerical modeling may be used as a powerful guide in the development of nonlinear materials and systems for sensor protection. While many system and material parameters can be included in the numerical model, it is not practical to scan over all permutations of the parameter values to determine the optimal combination. Instead, a few special cases can provide significant insight into the underlying optical processes which occur as the beam propagates through the system. Several optical schemes have been incorporated into t
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