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

Abstract

The development of colloidal near-infrared quantum dots (QD) lasers has been hindered by the high state degeneracy of lead salt QDs and the difficulty in coupling colloidal quantum dots to the resonant cavity. In this study, we show that above challenges can be addressed by the self-assembly laser based on Ag<sub>2</sub>Se QDs. 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 deeply 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 between cavity length and free spectrum range and laser emission wavelength. Leveraging 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. Using simulation results 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. Increasing the laser cavity length, resulting in an increase in the emission wavelength from 1300 nm to 1323 nm. In addition, the toxicity of Ag<sub>2</sub>Se QDs is remarkably negligible. Our work promotes the development of environment-friendly near-infrared lasers to practical lasers.