Characterization of collimation quality of Gaussian beams produced with engineered diffusers

Abstract

In this paper, we explore the collimation quality of collimated Gaussian beams generated via the deployment of engineered diffusers. Various aspects of beam propagation through engineered diffusers are explored using results from carefully designed experiments. Raw Gaussian beam is incident on a sample engineered diffuser. The beam is then collimated and propagated over several meters to clearly estimate beam divergence for different test cases. These test cases include raw and focused beams incident on engineered diffusers, the effect on collimation with the use of speckle reducers, and the evolution of the collimated beam wavefront during propagation. To measure and document the spatial coherence properties of beam propagation and its spatial coherence properties after propagating through the engineered diffuser, we measure the beam profile with knife-edge measurement, CCD imaging, and Shack-Hartmann sensor-based wavefront measurements along the beam propagation path. We do so for all different type of beam conditioning before incidence at the engineered diffuser – this includes analyzing the effects of a speckle reducer in the system. We present detailed experimental results and parameters of the propagating collimated beam in the paper. We hope that this paper will lay foundations for our understanding of using engineered diffusers for short distance free-space optical links using a beam collimation approach which is several times optically efficient than a pinhole based spatial filtering-based beam collimation approach.