Wavefront shaping to improve beam quality: converting a speckle pattern into a Gaussian spot

TL;DR

This paper investigates how wavefront shaping can convert a speckle pattern into a high-quality Gaussian beam, breaking traditional optical constraints and exploring the efficiency and variability of this process.

Contribution

It demonstrates the potential of wavefront shaping to transform speckle patterns into focused beams, highlighting its advantages and limitations in controlling scattered light.

Findings

Significant energy can be converted into a low M2 beam

Wavefront shaping can break etendue conservation in scattering media

Output quality varies due to multiple scattering effects

Abstract

A perfectly collimated beam can be spread out by multiple scattering, creating a speckle pattern and increasing the etendue of the system. Standard optical systems conserve etendue, and thus are unable to reverse the process by transforming a speckle pattern into a collimated beam or, equivalently, into a sharp focus. Wavefront shaping is a technique that is able to manipulate the amplitude and/or phase of a light beam, thus controlling its propagation through such media. Wavefront shaping can thus break the conservation of etendue and, in principle, reduce it. In this work we study how much of the energy contained in a fully developed speckle pattern can be converted into a high quality (low M2) beam, and discuss the advantages and limitations of this approach, with special attention given to the inherent variability in the quality of the output due to the multiple scattering.