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Low spatial coherence electrically pumped semiconductor laser for speckle-free full-field imaging

Redding, Brandon, Cerjan, Alexander, Huang, Xue, Lee, Minjoo Larry, Stone, A. Douglas, Choma, Michael A., Cao, Hui
Proceedings of the National Academy of Sciences of the United States of America 2015 v.112 no.5 pp. 1304-1309
image analysis, lasers, microscopes, semiconductors
The spatial coherence of laser sources has limited their application to parallel imaging and projection due to coherent artifacts, such as speckle. In contrast, traditional incoherent light sources, such as thermal sources or light emitting diodes (LEDs), provide relatively low power per independent spatial mode. Here, we present a chip-scale, electrically pumped semiconductor laser based on a novel design, demonstrating high power per mode with much lower spatial coherence than conventional laser sources. The laser resonator was fabricated with a chaotic, D-shaped cavity optimized to achieve highly multimode lasing. Lasing occurs simultaneously and independently in ∼1,000 modes, and hence the total emission exhibits very low spatial coherence. Speckle-free full-field imaging is demonstrated using the chaotic cavity laser as the illumination source. The power per mode of the sample illumination is several orders of magnitude higher than that of a LED or thermal light source. Such a compact, low-cost source, which combines the low spatial coherence of a LED with the high spectral radiance of a laser, could enable a wide range of high-speed, full-field imaging and projection applications.