Bound state in the continuum in slab waveguide enables low-threshold quantum-dot lasing

TL;DR

This paper demonstrates low-threshold room-temperature lasing in a quantum-dot film coupled with nanoantenna arrays exploiting bound states in the continuum, advancing solution-processed laser technology.

Contribution

It introduces a novel approach combining CQD films with TiO2 nanoantennas to achieve BIC-based lasing with high quality factors and low thresholds.

Findings

Achieved room-temperature lasing with an 11 kW/cm2 threshold.

Engineered BICs with good spatial and spectral overlap with CQDs.

Highlighted BICs as effective modes for surface-emitting lasers.

Abstract

Colloidal quantum dots (CQDs) are a promising gain material for solution-processed, wavelength-tunable lasers, with potential application in displays, communications, and biomedical devices. In this work, we combine a CQD film with an array of titanium dioxide (TiO2) nanoantennas to achieve lasing via bound states in the continuum (BICs), which are symmetry-protected cavity modes with giant quality factors. Here, the BICs arise from slab waveguide modes in the planar film, coupled to the periodic nanoantenna array. We engineer the thickness of the CQD film and size of the nanoantennas to achieve a BIC with good spatial and spectral overlap with the CQDs, based on a 2nd-order TE-polarized waveguide mode. We obtain room-temperature lasing with a low threshold of approximately 11 kW/cm2 (peak intensity) under 5 ns-pulsed optical excitation. This work sheds light on the optical modes in solution-processed, distributed-feedback lasers, and highlights BICs as effective, versatile, surface-emitting lasing modes.