Efficient method for controlling the spatial coherence of a laser

TL;DR

This paper introduces a simple, efficient method to control the spatial coherence of a degenerate laser by adjusting an internal spatial filter, enabling high-brightness speckle-free microscopy.

Contribution

It presents a novel technique to tune the number of lasing modes in a degenerate laser with minimal power variation, enhancing its application in speckle-free imaging.

Findings

Supported up to 320,000 lasing modes

Maintained less than 50% power variation

Enabled bright speckle-free microscopy

Abstract

An efficient method to tune the spatial coherence of a degenerate laser over a broad range with minimum variation in the total output power is presented. It is based on varying the diameter of a spatial filter inside the laser cavity. The number of lasing modes supported by the degenerate laser can be controlled from 1 to 320,000, with less than a 50% change in the total output power. We show that a degenerate laser designed for low spatial coherence can be used as an illumination source for speckle-free microscopy that is 9 orders of magnitude brighter than conventional thermal light.