A robust and tuneable mid-infrared optical switch enabled by bulk Dirac fermions

Chunhui Zhu,Xiang Yuan,Yongbing Xu,Yi Shi,Shining Zhu,Rong Zhang,Junfeng Liu,Jianfeng Li,Fengqiu Wang,Yafei Meng,Xinjie Lv,Hongyu Luo,Chao Zhang,Liang He,Yazhou Wang,Faxian Xiu

doi:10.1038/ncomms14111

Abstract

Pulsed lasers operating in the mid-infrared (3–20 μm) are important for a wide range of applications in sensing, spectroscopy, imaging and communications. Despite recent advances with mid-infrared gain platforms, the lack of a capable pulse generation mechanism remains a significant technological challenge. Here we show that bulk Dirac fermions in molecular beam epitaxy grown crystalline Cd3As2, a three-dimensional topological Dirac semimetal, constitutes an exceptional ultrafast optical switching mechanism for the mid-infrared. Significantly, we show robust and effective tuning of the scattering channels of Dirac fermions via an element doping approach, where photocarrier relaxation times are found flexibly controlled over an order of magnitude (from 8 ps to 800 fs at 4.5 μm). Our findings reveal the strong impact of Cr doping on ultrafast optical properties in Cd3As2 and open up the long sought parameter space crucial for the development of compact and high-performance mid-infrared ultrafast sources.

Highlights

Pulsed lasers operating in the mid-infrared (3–20 mm) are important for a wide range of applications in sensing, spectroscopy, imaging and communications
An optical switch may take different physical forms, semiconductor saturable absorber mirrors (SESAMs), a breakthrough in ultrafast photonics in the early 1990s, are at present the most prevalent approach used for ultrashort pulse generation in the near-infrared
A most compelling advantage of SESAMs is the ease with which device parameters can be precisely customized with great reproducibility[5], thanks to the use of mature semiconductor growth techniques, for instance, molecular beam epitaxy (MBE)

Summary

Introduction

Pulsed lasers operating in the mid-infrared (3–20 mm) are important for a wide range of applications in sensing, spectroscopy, imaging and communications. We show that bulk Dirac fermions in molecular beam epitaxy grown crystalline Cd3As2, a three-dimensional topological Dirac semimetal, constitutes an exceptional ultrafast optical switching mechanism for the mid-infrared. The development of compact short-pulsed lasers in the midinfrared has historically been hindered by the poor availability of gain materials, expedient techniques based on near-infrared sources and nonlinear frequency conversion have become today’s norm for mid-infrared pulse generation[6,7,8]. Improving the performance levels of current mid-infrared short-pulsed lasers critically depends on the availability of a capable mid-infrared optical switch, preferably with figures of merit on par with those of SESAMs. Cd3As2, a representative three-dimensional topological Dirac semimetal (TDS), exhibits stable bulk Dirac states where conduction and valence bands touch at the Dirac nodes and the Dirac fermions disperse linearly along all three momentum directions[27,28]. Various exotic physical phenomena, such as ultrahigh mobility and giant negative magnetoresistance, have been uncovered in three-dimensional TDS systems[29,30,31,32], our findings show that this emerging class of quantum materials can be harnessed to fill a long known gap in the field of mid-infrared lasers and photonics

Methods

Results

Conclusion