Wavelength-Tunable Mid-Infrared Lasing from Black Phosphorus Nanosheets.

Van der Waals layered semiconductor materials own unique physical properties and have attracted intense interest in developing high-performance electronic and photonic devices. Among them, black phosphorus (BP) is distinct for its layer number-tuned direct band gap which spans from near- to mid-infrared (MIR) waveband. In addition, the puckered honey comb crystal lattice endows the material with highly linear-polarized emission and marked anisotropy in carrier transportation. These unique material properties render BP as an intriguing and promising building block for constructing mid-infrared-ranged coherent light sources. Here, a room temperature surface-emitting MIR laser based on single crystalline BP nanosheets coupled with a distributed Bragg reflector cavity is reported. MIR stimulated emission at 3611 nm is achieved with a near-unity linear polarization, which exhibits robust thermal stability up to 360 K. Most importantly, the lasing wavelength can be tuned from 3425 to 4068 nm by varying the cavity length via thickness control of BP layer. The demonstrated highly polarized lasing output and wavelength-tunable capacity of the proposed device scheme in MIR spectral range opens up promising opportunities for a broad array of applications in polarization-resolved IR imaging, range-finding, and free space quantum communications.