Diffraktive Phasenelemente für partiell-kohärente UV-Laserstrahlung

Abstract

Diffractive phase elements (DPE) are suited for beam shaping of coherent laser radiation. The height profile of the DPE changes the phase of the incomming laser beam to shape the angular intensity distribution of the outgoing beam into a desired pattern. Iterative Fourier Transform Algorithms (IFTA) are a proven method for calculating the phase function of DPE because of their high flexibility. In this thesis the IFTA-concept is transferred to calculate the phase function of DPE for partial-coherent UV laser radiation emitted by excimer lasers. The aperture of the DPE is divided into many facets. Illumination of a single facet reconstructs the entire predetermined signal. The different bundles illuminating different facets are modeled to be mutually incoherent. By superposition of the signal waves from all facets the original inhomogeneous intensity distribution of the excimer laser is transformed into a homogeneous signal distribution. The quality of the beam shaping is limited by the divergence of the bundles relative to each other and by the coherence properties within a single bundle passing through a single facet. The divergence of the bundles is measured with a Hartmann-Shack-sensor. Corrections are derived from these measurements and included into the DPE. Spatially resolved far-field intensity measurements are used to determine the coherence function of each bundle. A deconvolution algorithm is developed to integrate the measured coherence function into the design of the DPE. For all these design concepts DPE have been fabricated in fused silica. The experimental and the simulated beam shaping results are presented and analysed.