Partially coherent beam smoothing using a microlens array

Abstract

The main issue in applying a microlens array as a beam homogenizer is the high intensity contrast resulting from the periodic structure. We present a practical solution to eliminate speckle patterns by using a diffuser that can convert a coherent source into a Gaussian Schell source with an adjustable coherence length. Based on numerical simulation and experimental results, the microlens should have the Fresnel number above 15, a large pitch when the target plane is fixed, and an appropriate D / σ f ratio to obtain a spot with high uniformity. Moreover, a slight defocus of the observation surface within the range of ±1mm has a negligible effect on the uniformity of shaped spots the homogenized spot. Finally, the applications of the findings are presented.