Comparison of infrared laser beam shaping by diffractive and refractive methods

Abstract

Infra-red laser beam shaping has the inherent difficulty that simple ray tracing methods often yield anomalous results, due primarily to the propagation effects at longer wavelengths. Techniques based on diffraction theory have been developed to overcome this, with associated parameters to determine when one approach is needed versus another. In this paper, infra-red (IR) beam shaping by diffractive methods is investigated and compared to refractive methods. Theoretical results on the beam shapers are calculated through a combination of analytical and numerical techniques, and using both ideal and non-ideal inputs. The authors show that the diffractive optical element (DOE) is remarkably resilient to input errors of wavelength and beam quality, while the refractive shaper is found to be difficult to model. Optical elements based on the two approaches were designed, and then fabricated from ZnSe. A comparison between the fabricated elements and the designed elements is presented, and some of the findings on practical problems in having such elements fabricated are highlighted.