Fig. 2: Collective oscillations and emission in gain-guided metacavity.
From: Chiral orbital lasing in a twisted bilayer metasurface
a Schematic of the gain-guided cavity with its refractive index spatially following the carrier density distribution. The red circle denotes the rotational-invariant pumped region. b Instantaneous and time-averaged field distributions of the collective guided resonance modes of ∣l∣ = 0, 1, 2 with p = 0. All modes except for ∣l∣ = 0 are twofold degenerate due to reciprocity. These modes carry nontrivial orbital angular momentum (OAM) and exhibit doughnut patterns in the time-averaged field. c Schematic of one collective mode l = 1, p = 0 rotating along CCW direction in real space (lower panel), which diffracts to out-of-plane radiation, creating two lobes with equal intensity along any polarized direction (upper-left panel) and a fork-like self-interference pattern (upper-right panel).
