Yongquan Zeng†, Guozhen Liang†, Hou Kun Liang‡, Shampy Mansha§, Bo Meng†, Tao Liu†, Xiaonan Hu†, Jin Tao†, Lianhe Li∥, Alexander Giles Davies∥, Edmund Harold Linfield∥, Ying Zhang‡, Yidong Chong§, and Qi Jie Wang*†§ 
† Centre for OptoElectronics and Biophotonics, School of Electrical and Electronic Engineering & The Photonic Institute, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
‡ Singapore Institute of Manufacturing Technology, 2 Fusionopolis Way, Singapore 138634, Singapore
§ School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
∥ School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
ACS Photonics, Article ASAP
DOI: 10.1021/acsphotonics.6b00711
Publication Date (Web): November 29, 2016
Copyright © 2016 American Chemical Society
Random lasers are a special class of laser in which light is confined through multiple scattering and interference process in a disordered medium, without a traditional optical cavity. They have been widely studied to investigate fundamental phenomena such as Anderson localization, and for applications such as speckle-free imaging, benefiting from multiple lasing modes. However, achieving controlled localized multimode random lasing at long wavelengths, such as in the terahertz (THz) frequency regime, remains a challenge. Here, we study devices consisting of randomly distributed pillars fabricated from a quantum cascade gain medium, and show that such structures can achieve transverse-magnetic polarized (TM) multimode random lasing, with strongly localized modes at THz frequencies. The weak short-range order induced by the pillar distribution is sufficient to ensure high quality-factor modes that have a large overlap with the active material. Furthermore, the emission spectrum can be easily tuned by tailoring the scatterer size and filling fraction. These “designer” random lasers, realized using standard photolithography techniques, provide a promising platform for investigating disordered photonics with predesigned randomness in the THz frequency range and may have potential applications such as speckle-free imaging.
