Optofluidic Lasers with Aqueous Quantum Dots

Abstract

We achieved two types of laser emissions from aqueous quantum dots (QDs) using the same high-Q-factor optofluidic ring resonator (OFRR) platform. In the first type, 2 μM QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 μJ/mm2, over 3 orders of magnitude lower than the state-of-the-art. In the second type of laser, the QDs were immobilized as a single layer on the interface between the OFRR inner wall and buffer solution with a surface density as low as 3 × 109–1010 cm–2. The lasing threshold of 60 μJ/mm2 was achieved. In both bulk solution and single-layer lasing cases, the laser emission persisted even under 5–10 min of uninterrupted pulsed optical excitation that was well above the corresponding lasing threshold, indicative of high photostability of the QD laser. This was in sharp contrast to organic-dye-based lasers, which underwent quick photobleaching during the laser operation under similar pumping conditions. Theoretical analysis is also carri...