Sensitive control of broad-area semiconductor lasers by cavity shape

TL;DR

This paper demonstrates that slight modifications to the cavity shape of broad-area semiconductor lasers near bifurcation points can significantly enhance their performance, stability, and suitability for speckle-free imaging applications.

Contribution

It introduces a method to control laser dynamics by adjusting cavity shape near bifurcation points, improving stability and output quality.

Findings

Increased number of transverse modes in near-planar cavities.

Enhanced stability of spatio-temporal lasing dynamics.

Higher brightness and better directionality for speckle-free imaging.

Abstract

The ray dynamics of optical cavities exhibits bifurcation points: special geometries at which ray trajectories switch abruptly between stable and unstable. A prominent example is the Fabry-Perot cavity with two planar mirrors, which is widely employed for broad-area semiconductor lasers. Such cavities support lasing in a relatively small number of transverse modes, and the laser is highly susceptible to filamentation and irregular pulsations. Here we demonstrate experimentally that a slight deviation from this bifurcation point (planar cavity) dramatically changes the laser performance. In a near-planar cavity with two concave mirrors, the number of transverse lasing modes increases drastically. While the spatial coherence of the laser emission is reduced, the divergence angle of the output beam remains relatively narrow. Moreover, the spatio-temporal lasing dynamics becomes significantly more stable compared to that in a Fabry-Perot cavity. Our near-planar broad-area semiconductor laser has higher brightness, better directionality and hence allows shorter integration times than an incandescent lamp while featuring sufficiently low speckle contrast at the same time, making it a vastly superior light source for speckle-free imaging. Furthermore, our method of controlling spatio-temporal dynamics with extreme sensitivity near a bifurcation point may be applied to other types of high-power lasers and nonlinear dynamic systems.