Lasing from Brillouin Zone Folding Guided Resonances

High-quality factor (<i>Q</i>-factor) nanophotonic cavities are critical components in applications such as lasing and nonlinear optics. However, to obtain out-of-plane lasing emission and a low lasing threshold, the lasing mode must fulfill the contradictory requirement of coupling to the light cone while maintaining a high <i>Q</i>-factor. One relatively unexplored method to design such modes consists of using a Brillouin Zone folding guided resonance (BZF-GR) as the high <i>Q</i>-factor mode for lasing. In such a design, guided modes are "folded" into the light cone via periodic perturbations, allowing fine control of the <i>Q</i>-factor throughout momentum space. In this paper, we experimentally demonstrate the use of such a BZF-GR to achieve vertical emission lasing from a nanophotonic cavity with colloidal quantum dots as a gain medium. The lowest lasing threshold fluence under nanosecond pump is (20.4 ± 0.3) μJ cm^-2. When considering the absorption, this value falls to (4.08 ± 0.08) μJ cm^-2. This work presents a method of designing lasing modes that may be further developed for use in low-threshold nanoscale lasers.