Highly Efficient Spintronic Terahertz Emitter Enabled by Metal-Dielectric Photonic Crystal

Spintronic terahertz (THz) emitter provides the advantages such as apparently broader spectrum, significantly lower cost, and more flexibility compared with the commercial THz emitters, and thus attracts great interest recently. In past few years, efforts have been made in optimizing the material composition and structure geometry, and the conversion efficiency has been improved close to that of ZnTe crystal. One of the drawbacks of the current designs is the rather limited laser absorption-more than 50% energy is wasted and the conversion efficiency is thus limited. Here, a novel device that fully utilizes the laser intensity and significantly improves the conversion efficiency is theoretically proposed and experimentally demonstrated. The device, which consists of a metal-dielectric photonic crystal structure, utilizes the interference between the multiple scattering waves to simultaneously suppress the reflection and transmission of the laser, and to reshape the laser field distributions. The experimentally detected laser absorption and THz generation show one-to-one correspondence with the theoretical calculations. The strongest THz pulse emission that presents a 1.7 times improvement compared to the currently designed spintronic emitter is achieved. This work opens a new pathway to improve the performance of spintronic THz emitter from the perspective of optics.