17 February 2010 Coherent polarization locking of a diode emitter array
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Abstract
Coherent beam combining has been actively explored as a technique to increase the brightness of laser sources. Passive phase-locking of a diode array in a common resonator, in particular, is an attractive approach owing to its inherent simplicity and good beam quality. In this work, we present the coherent combining of an array of diode emitters in a conventional diode bar configuration using the coherent polarization locking technique. An external laser cavity is designed so that the diode emissions from several 976 nm diode emitters are spatially overlapped via a series of birefringent walk-off crystals and passively phase-locked by a polarizing beam splitter. The key optical element in this beam combining scheme is the novel YVO4 birefringent spatial beam combiner that not only provides spatial overlap, but also identical optical path lengths for the diode beams. This facilitates design of the cavity for achieving a close match between the mode size of the Gaussian beam and the asymmetric emitting area at the front facet of the diode emitters. The phase-locking technique, coupled with the required standard bulk optical crystals and standard diode bar configuration, yields a robust laser architecture which retains the advantages of diode lasers in terms of cost, size and wavelength tunability. With the coherent combining of four diode emitters, we achieved a nearly diffraction limited beam at 1030 mW, which represents a 50 times increase in brightness over the standard incoherent diode bar. The coherent locking approach is highly scalable. Further experiments to coherently combine eight to sixteen diode emitters are in progress.
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S. P. Ng, P. B. Phua, "Coherent polarization locking of a diode emitter array", Proc. SPIE 7583, High-Power Diode Laser Technology and Applications VIII, 758311 (17 February 2010); doi: 10.1117/12.839557; https://doi.org/10.1117/12.839557
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