Pulsed lasers with pulse durations of nanosecond to millisecond are very important tools for free-space optical communication, LADAR, laser material processing, and optical sensing. Although Q-switched solid-state lasers or gas lasers are currently the most popular light sources for these purposes, pulsed semiconductor lasers have the potential for the above applications because of their compactness, accessibility of direct modulation, and inherently large electrical to optical conversion efficiency. The drawbacks with high-power semiconductor lasers are their poor beam quality and low coherence factors. This work addresses the above issues through experimental demonstration of frequency locking, wavelength tuning, and synchronization of nanosecond pulsed broad-area semiconductor lasers. Nanosecond optical pulses with the peak power of 25 W and the repetition rates of 4 KHz to 240 KHz are generated from a broad-area laser. An external cavity with a diffractive grating is used to reduce the linewidth of the laser from over 5 nm to less than 0.1 nm. The wavelength of the pulsed laser is tunable over more than 10 nm. We have conducted injection locking of a nanosecond pulsed broad-area laser with optical injection from a frequency-locked master laser. Successful injection locking strongly support the feasibility of synchronization and beam combination of pulsed broad-area lasers.
We present experimental results on the locking of a 19-broad-area semiconductor laser array using a novel design of external cavity containing a lens array, projection optics, and a diffractive grating. All lasers are locked to single longitudinal mode. Significant improvement of the spatial profile of the entire laser array output beam has been observed. The center lobe of the far-field pattern of the laser array shows a single wavelength which can be tuned over a range more than 10 nm. The proposed technology can be applied to larger arrays including the stacked arrays.