THz time-domain characterization of amplifying quantum-cascade metasurface

An amplifying quantum-cascade (QC) metasurface, the key component of the QC vertical-external-cavity surface-emitting-laser (VECSEL), is studied as a function of injected current density using reflection-mode terahertz time domain spectroscopy. Nearly perfect absorption is measured at zero bias, which is associated with the transition from the weak to strong coupling condition between the metasurface resonance and an intersubband transition within the QC material. An increase in reflectance is observed as the device is biased, both due to reduction in intersubband loss and the presence of intersubband gain. Significant phase modulation associated with the metasurface resonance is observed via electrical control, which may be useful for electrical tuning of QC-VECSEL. These results provide insight into the interaction between the intersubband QC-gain material and the metasurface and modify the design rules for QC-VECSELs for both biased and unbiased regions.

Automated summary

An amplifying quantum-cascade (QC) metasurface, a key component of the QC vertical-external-cavity surface-emitting-laser (VECSEL), was studied using reflection-mode terahertz time domain spectroscopy. Perfect absorption at zero bias, increase in reflectance with bias, and significant phase modulation associated with metasurface resonance were observed. The results provide insight into the interaction between intersubband QC-gain material and metasurface, and modify the design rules for biased and unbiased QC-VECSELs.