title: Low divergence single-mode surface-emitting concentric-circular-grating terahertz quantum cascade lasers.
abstract: We report the design, fabrication and experimental characterization of surface-emitting terahertz (THz) frequency quantum cascade lasers (QCLs) with distributed feedback concentric-circular-gratings. Single-mode operation is achieved at 3.73 THz with a side-mode suppression ratio as high as ~30 dB. The device emits ~5 times the power of a ridge laser of similar dimensions, with little degradation in the maximum operation temperature. Two lobes are observed in the far-field emission pattern, each of which has a divergence angle as narrow as ~13.5° × 7°. We demonstrate that deformation of the device boundary, caused by anisotropic wet chemical etching is the cause of this double-lobed profile, rather than the expected ring-shaped pattern.
authors: Guozhen
authors: G
authors: Liang
authors: Houkun
authors: H
authors: Liang
authors: Ying
authors: Y
authors: Zhang
authors: Lianhe
authors: L
authors: Li
authors: A Giles
authors: AG
authors: Davies
authors: Edmund
authors: E
authors: Linfield
authors: Siu Fung
authors: SF
authors: Yu
authors: Hui Chun
authors: HC
authors: Liu
authors: Qi Jie
authors: QJ
authors: Wang