Optofluidic lasers with aqueous quantum dots

Abstract

We achieved two types of laser emissions from aqueous quantum dots (Qps) using the same high-Q:factor optofluidic ring resonator (OFRR) platform. In the first type, 2 mu M QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 mu J/mm(2), 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 X 10(9)-10(10) cm(-2). The lasing threshold of 60 mu J/mm(2) 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 carried out to elucidate the advantages of QD-based optofluidic lasers over those based on dyes. Our work opens the door to a plethora of applications where optofluidic QD lasers can replace dye-based optofluidic lasers in biosensing and on-chip miniaturized laser development.