Depleted-Wave Electric-Field Solver for Pulsed Bessel-Gaussian Type-II Frequency Doubling in KTP Crystals

This toolkit addresses the computational modeling of three-dimensional time-dependent electric-field distributions in type-II pulsed Bessel-Gaussian second-harmonic generation within potassium titanyl phosphate (KTP) crystals, where depleted-wave dynamics dominate nonlinear optical conversion. The toolkit solves three coupled nonlinear wave equations for ordinary and extraordinary fundamental waves and extraordinary second-harmonic waves using finite difference methods in cylindrical coordinates. It accepts user-defined parameters including pulse energy, beam spot size, crystal dimensions, and optical properties as inputs, and produces spatiotemporal electric-field amplitude distributions and conversion efficiency profiles as outputs. A unified Fortran codebase provides reproducible simulation pipelines, parametric sweep capabilities for examining interaction length dependencies, and computational optimizations that enable execution on standard desktop systems despite the fine radial meshes required for Bessel-Gaussian beam fluctuations. The implementation reproduces previously published quantitative predictions, specifically confirming that for ωf ≈ 80 μm spot sizes and 0.8 J pulse energies, complete energy exchange occurs over approximately 5 mm, which validates the necessity of depleted-wave formalism for crystals exceeding this interaction length. The toolkit is available as an open-source GitHub repository and is released as version v1.0.1 under the MIT License, with a permanently archived distribution identified by DOI 10.5281/zenodo.17362587.