Perfect Impedance Matching with Meta-Surfaces Made of Ultra-Thin Metal Films: A Phenomenological Approach to the Ideal THz Sensors

Terahertz Biosensor Based on Mode Coupling between Defect Mode and Optical Tamm State with Dirac Semimetal

Bulk Dirac semimetal (BDS) has emerged as a "3D graphene" material for the development of optical devices in the past few years. In this study, a BDS-based tunable highly sensitive terahertz (THz) biosensor is proposed by using a Dirac semimetal/Bragg reflector multilayer structure. The high sensitivity of the biosensor originates from the sharp Fano resonance peak caused by coupling the Optical Tamm State (OTS) mode and defect mode. Besides, the sensitivity of the proposed structure is sensitive to the Fermi energy of Dirac semimetal and the refractive index of the sensing medium. The maximum sensitivity of 1022°/RIU is obtained by selecting structural and material parameter appropriately, which has certain competitiveness compared to conventional surface plasmon resonance (SPR) sensors. From the standpoint of the fabrication facility and integration, we judged that the BDS-based layered structure has the potential application in biosensor field.

Harmonic Generation in Biased Semiconductor Superlattices

Semiconductor superlattices are proven nanomaterials for THz nonlinear optics by means of high order harmonic generation. Seminal approaches leading to a perfectly antisymmetric current-voltage (I-V.) curve predict the generation of odd harmonics only in the absence of a bias. However, even harmonics at high orders have been detected in several experiments. Their generation has been explained by considering deviations from the current flow symmetry that break the exact antisymmetry of the I-V. curve. In this paper, we focus on another issue found experimentally that has also not been explained, namely the harmonic power output asymmetry from negative to positive applied bias. Once more, breaking the I-V. flow symmetry explains the experiments and leads to a further tool to design the power output of these materials. Furthermore, a new approach for the Boltzmann Equation under relaxation-rate approximation eliminates numerical difficulties generated by a previous theory. This leads to very efficient analytical expressions that can be used for both fundamental physics/optics/material sciences and realistic device development and simulations.