Semi-Analytic Fresnel Propagation Simulation

Wave-optics simulations are critical tools for analysis of laser directed energy systems. The primary method for conducting these simulations is to evaluate the Fresnel diffraction integral using the angular spectrum method based on the fast Fourier transform (FFT). While FFTs are considered computationally efficient, their use in the Fresnel integral results in difficult grid constraints including zero-padding. In simulating airborne laser systems, Monte Carlo methods are needed to represent random processes like platform jitter and optical turbulence. This combines with the need for time-series to represent beam control systems to create many evaluations. The Fresnel diffraction integral must be evaluated at least once for each time step or random draw. Therefore, we seek the fastest possible numerical calculation of Fresnel diffraction integral. MZA proposes to circumvent the FFT use with a semi-analytic evaluation. This leaves fewer numerical computations and provides numerous benefits over the angular-spectrum method. With this method, zero-padding is unnecessary, and the output grid points are arbitrary.