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

Significance There has been an intense search for the ideal light sources for high-speed, full-field imaging applications ranging from next-generation microscopes and laser projectors to digital holography and photolithography. Traditional lasers, although providing the required brightness (i.e., power per mode), exhibit high spatial coherence, which introduces coherent artifacts such as speckle, corrupting image formation. At the other extreme, low spatial coherence sources such as thermal sources and light emitting diodes (LEDs) avoid speckle but lack sufficient power per mode for high-speed imaging. In this work, we demonstrate a new type of semiconductor laser based on a chaotic cavity, which combines low spatial coherence with high power per mode. Such a laser could enable a wide range of full-field imaging applications. 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.

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