title: Photonic quasi-crystal terahertz lasers.
abstract: Quasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of 'defects', which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser; specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1-0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum.
authors.affiliation: NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Miriam Serena
authors.initials: MS
authors.lastname: Vitiello
authors.affiliation: NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Nobile
authors.affiliation: NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Ronzani
authors.affiliation: NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Tredicucci
authors.affiliation: NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Castellano
authors.affiliation: NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Talora
authors.affiliation: School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Lianhe
authors.initials: L
authors.lastname: Li
authors.affiliation: School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Edmund H
authors.initials: EH
authors.lastname: Linfield
authors.affiliation: School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: A Giles
authors.initials: AG
authors.lastname: Davies