Sunday, May 22, 2016

Abstract-Multimode, Aperiodic Terahertz Surface-Emitting Laser Resonators

1 NEST, CNR—Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy2 School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
* Author to whom correspondence should be addressed.
Received: 5 April 2016 / Revised: 13 May 2016 / Accepted: 16 May 2016 / Published: 20 May 2016
Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric (vertically radiative but low quality factor Q) and anti-symmetric (non-radiative, high Q) modes is indeed here fully overcome, offering a concrete perspective of highly efficient vertical emitting resonators. We here exploit electrically pumped terahertz quantum cascade heterostructures to devise two-dimensional seven-fold quasi-crystal resonators, exploiting rotational order or irregularly distributed defects. By lithographically tuning the lattice quasi-periodicity and/or the hole radius of the imprinted patterns, efficient multimode surface emission with a rich sequence of spectral lines distributed over a 2.9–3.4 THz bandwidth was reached. We demonstrated multicolor emission with 67 mW of peak optical power, slope efficiencies up to ≈70 mW/A, 0.14% wall plug efficiencies and beam profile results of the rich quasi-crystal Fourier spectrum that, in the case of larger rotational order, can reach very low divergence.

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