Laser beam shaping by binary and multi-level phase-only diffractive optical elements

摘要

This contribution focuses on the study and comparison of different design methods for designing phase-only diffractive optical elements (PDOEs) for different possible applications in laser beam shaping. Both binary and multilevel phase-only diffractive optical elements are considered, theoretically studied, and compared, using diffusive types of input objects. Especially, new results and approaches, concerning the iterative Fourier transform algorithm, are analyzed, implemented, and compared (the scale factor and the algorithm convergence characterization through the spectrum representation). The two important output design parameters, i.e. the signal-to-noise ratio and the diffraction efficiency characteristics are presented by means of evaluating their dependencies on, e.g. the number of iterations, the number of phase levels, and the signal-window position). Next, we concentrate on the design of Fresnel domain PDOEs, generalizing the classical IFTA scheme (both with a single and double focus) types of PDOEs. The application of the appropriate scale factors for each particular case is presented, and typical design results for both cases are shown. For practical realization, e-beam lithography technology is used, showing a good qualitative agreement with theoretical designs.