Abstract-Frequency-tunable continuous-wave random lasers at terahertz frequencies

Simone Biasco, Harvey E. Beere, David A. Ritchie, Lianhe Li, A. G. Davies, Edmund Linfield,  Miriam S. Vitiello

Fig. 1: Device schematics and electromagnetic simulations

https://www.nature.com/articles/s41377-019-0152-z

Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure, providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence. However, for many applications ranging from sensing and spectroscopy to speckle-free imaging, it is essential to have high-radiance sources operating in continuous-wave (CW). In this paper, we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional (2D) random distribution of air holes is patterned into the top metal waveguide. We obtain a highly collimated vertical emission at ~3 THz, with a 430 GHz bandwidth, device operation up to 110 K, peak (pulsed) power of 21 mW, and CW emission of 1.7 mW. Furthermore, we show that an external cavity formed with a movable mirror can be used to tune a random laser, obtaining continuous frequency tuning over 11 GHz.

Abstract-Multimode, Aperiodic Terahertz Surface-Emitting Laser Resonators

Simone Biasco 1

, Lianhe Li 2

, Edmund H. Linfield 2

, A. Giles Davies 2

 and Miriam S. Vitiello 1,* 

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

http://www.mdpi.com/2304-6732/3/2/32
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.