Comparison of fly's eye condensers based on regular, chirped, and stochastic tandem microlens arrays

Abstract

Fly's eye condensers are commonly used for the beam shaping of an arbitrary input intensity distribution into a top hat. The setup usually consists of a Fourier lens and two identical regular microlens arrays - often referred to as tandem lens array - where the second one is placed in the focal plane of the first microlenses. The output intensity distribution is modulated by equidistantly located sharp intensity peaks due to the periodic structure of the regular arrays. In a chirped array, the inflexibility of a regular structure has been overcome. Hence, an array can be formed which is non-periodic and consequently the equidistantly located intensity peaks can be suppressed. A far field speckle pattern results with more densely and irregularly located intensity peaks leading to an improved homogeneity of the intensity distribution. Additionally, a stochastic array which features a nonperiodic layout can be used in order to avoid the equidistantly located intensity peaks. Again, a far field speckle pattern results with more densely and irregularly located intensity peaks leading to an improved homogeneity of the intensity distribution. We compare fly's eye condensers based on regular, chirped and stochastic tandem microlens arrays in terms of achievable intensity homogenization, design and fabrication methods and their advantages and disadvantages in their applications.