▎ 摘　　要

Owing to their unique characteristics, two-dimensional (2-D) materials and their complexes have become very attractive in photoelectric applications. Two-dimensional heterojunctions, as novel 2-D complex materials, have drawn much attention in recent years. Herein, we propose a 2-D heterojunction composed of MXene (Ti2CTx) materials and graphene oxide (GO), and apply it to an Nd:YAG solid-state laser as a saturable absorber (SA) for passive Q-switching. Our results suggest that a nano-heterojunction between MXene and GO was achieved based on morphological characterization, and the advantages of a broadband response, higher stability in GO, and strong interaction with light waves in MXene could be combined. In the passively Q-switched laser study, the single-pulse energy was measured to be approximately 0.79 mu J when the pump power was 3.72 W, and the corresponding peak power was approximately 7.25 W. In addition, the generation of a stable ultrashort pulse down to 109 ns was demonstrated, which is the narrowest pulse among Q-switched solid-state lasers using a 2-D heterojunction SA. Our work indicates that the MXene-GO nano-heterojunction could operate as a promising SA for ultrafast systems with ultrahigh pulse energy and ultranarrow pulse duration. We believe that this work opens up a new approach to designing 2-D heterojunctions and provides insight into the formation of new 2-D materials with desirable photonic properties.