Fast-to-slow axis mode imaging for brightness enhancement of a broad-area laser diode array

Andrew M Jones,Juliet T Gopinath

doi:10.1364/oe.21.017912

Abstract

Broad-area laser (BAL) diodes have found use in numerous applications requiring multi-watt powers, but remain limited by poor spatial beam quality. A novel laser cavity that enhances the brightness of a BAL array has been demonstrated. Wavelength beam combining (WBC) is used to spatially overlap output from the emitters. Improved beam quality is achieved by imaging the fast-axis mode onto the slow axis of the BAL array. The brightness is enhanced twofold over a typical Littman-Metcalf WBC cavity, reaching 47 MW·cm(-2)·sr(-1) at an output power of 1.16 W.

Highlights

High power laser sources with good spatial beam quality are desirable for many applications including printing and marking, pumping of solid state lasers, imaging and tracking, and for use in nonlinear optical processes including optical parametric amplification and difference frequency generation
The behavior suggests the formation of a thermal lens within the broad-area laser (BAL) emitters [21] and increased overlap of higher order modes with the gain profile within the emitters relative to overlap of the fundamental mode
A novel technique to dramatically improve beam quality produced from BALs in which the emitted fast-axis mode is reimaged back onto the slow-axis dimension of the laser facet has

Summary

Introduction

High power laser sources with good spatial beam quality are desirable for many applications including printing and marking, pumping of solid state lasers, imaging and tracking, and for use in nonlinear optical processes including optical parametric amplification and difference frequency generation. Improvements in the beam quality of BALs have been demonstrated using external cavities which employ unstable resonator structures [9], off-axis optical feedback [10,11,12], intracavity spatial filtering [13,14], and phase locking via the Talbot effect [15,16]. Using these external cavity techniques, the output from individual emitters within a BAL array can be spatially combined to produce a single output beam with increased total spatial radiance or brightness (power per square area per solid angle) [17]. The method is versatile and broadly applicable to BAL single emitters and arrays employing either coherent or wavelength beam combining

Laser concept

Results and discussion

Conclusion