Abstract
Broad-area vertical-cavity surface-emitting lasers (BA-VCSELs) can exhibit a state of spatially incoherent emission, as we recently reported in [M. Peeters et al., Opt. Express, 13, 9337 (2005)]. Here, we experimentally study the evolution of a BA-VCSEL under pulsed operation from well-defined modal emission with a multitude of transverse cavity modes to such spatially incoherent emission. The transition is studied using a high-speed intensified CCD camera and differential image analysis with which single-shot measurements of the imaged nearfield, farfield, spatial coherence, and spectral emission properties are acquired. This combination of experimental characterization tools allows for a detailed description of the BA-VCSEL's emission behavior, which is necessary for an in-depth understanding of the processes involved. We find the interplay between the thermal chirp and the build-up of a spatially distributed thermal lens to be decisive for the break-up of the global cavity modes.
Highlights
Over the last 20 years, some attractive emission properties of vertical-cavity surface-emitting lasers (VCSELs) compared to edge-emitting semiconductor lasers have led to VCSELs’ establishment as a prominent device within the semiconductor laser family
Broad-area vertical-cavity surface-emitting lasers (BAVCSELs) can exhibit a state of spatially incoherent emission, as we recently reported in [M
We experimentally study the evolution of a BA-VCSEL under pulsed operation from well-defined modal emission with a multitude of transverse cavity modes to such spatially incoherent emission
Summary
Over the last 20 years, some attractive emission properties of vertical-cavity surface-emitting lasers (VCSELs) compared to edge-emitting semiconductor lasers have led to VCSELs’ establishment as a prominent device within the semiconductor laser family. The large Fresnel number of these broad-area VCSELs (BA-VCSELs) typically leads to the onset of a multitude of higher order transverse modes [2, 3] This results in a structured and more divergent farfield (FF) beam profile, deteriorating the beam quality of the emitted light. We recently demonstrated that next to the well-known modal emission, BA-VCSELs in pulsed operation can exhibit a state of nonmodal, or spatially incoherent emission [10]. The BA-VCSEL studied in [10] exhibits such an incoherent, Gaussian FF profile under a wide range of operating conditions Such high power, spatially incoherent sources can be useful in projection systems as the low degree of spatial coherence might help to reduce the speckle contrast. We will demonstrate how the modal emission reappears after a few tens of microseconds
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