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Compared to the maturity of today’s blue laser diodes, which exhibit high efficiencies, low threshold currents, and long lifetimes, deep-ultraviolet (<280 nm) lasers have essentially just been born. We have only recently witnessed the first deep-UV, continuous-wave edge-emitting lasers operating at room temperature under electrical injection. And more complex laser structures in the deep-UV, such as vertical-cavity surface-emitting lasers and photonic crystal surface emitting lasers, are even further behind, having only been demonstrated under pulsed optical pumping. Among the many difficulties in transitioning from blue to deep-UV are the problems of efficient electrical injection, creation of optical waveguides and cavities in materials with low refractive index contrast, and high material defect densities. The question is, are these problems fundamental limitations to the technology, or just temporary growing pains to be overcome with hard work and persistence as we push lasers deeper into unseen wavelengths and frontiers?
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