Near-infrared self-assembled laser based on Ag<sub>2</sub>Se quantum dots

Abstract

The development of colloidal near-infrared quantum dot (QD) lasers has been hindered by the high state degeneracy of lead salt QDs and the difficulty in coupling colloidal QDs to the resonant cavity. In this study, we show that the above challenges can be addressed by the self-assembly laser based on Ag<sub>2</sub>Se QDs. The Ag<sub>2</sub>Se QDs with the lowest quantized states 2-fold degeneracy are used to replace lead salt quantum dots to achieve low threshold near-infrared optical gain. We employ the finite element method to in depth analyze the mode field distribution and oscillation mechanism of the coffee-ring microcavity. Our results reveal that the light field oscillates in a zig-zag path along the cross-sectional area, indicating strong coupling between the QDs and the cavity mode. Furthermore, we investigate the relationship of cavity length with free spectrum range and laser emission wavelength. Using this relationship and the gain spectrum characteristics of Ag<sub>2</sub>Se QDs, we design a single-mode near-infrared laser and conduct a comprehensive analysis. The simulation results are used to fabricate a single-mode near-infrared Ag<sub>2</sub>Se QD coffee-ring microlaser, which exhibits a linewidth of 0.3 nm and a threshold of 158 μJ/cm<sup>2</sup>. Currently, it holds the record for the lowest laser threshold among near-infrared colloidal QD lasers. The increasing of the laser cavity length leads the emission wavelength to increase from 1300 nm to 1323 nm. In addition, the toxicity of Ag<sub>2</sub>Se QD is remarkably negligible. Our work promotes the development of environment-friendly near-infrared lasers toward practical lasers.