THz photoconductive antennas

In this chapter, the theoretical modeling, numerical simulation and experimental study of PCA are thoroughly discussed. The principles of three representative models, namely, Drude-Lorentz model, equivalent circuit model and full-wave model, were introduced. After summarizing the pros and cons of each model, the full-wave model was chosen for numerical simulation of PCA, as it has least physical assumptions and thus should be the most accurate. The numerical simulation was carried out using in-house codes on the MATLAB® platform, which was also verified using commercial software. The radiation properties of a PCA were then thoroughly studied by varying several important parameters, such as laser power, bias voltage, photoconductor material properties and laser pulse width. To demonstrate the application of this model, two new PCAs were designed and simulated, and enhanced THz radiations were predicted for both. The influences of the photoconductive material, antenna structures, etc. on the THz radiation power and bandwidth are systematically investigated to gain a more comprehensive understanding of a PCA. The general radiation mechanism of the PCAs is further studied by implementing the polarization effect and cancellation effect measurements. Recent progresses of the PCA structure development using nanostructure and plasmonic antenna electrodes to improve the THz radiation power/efficiency are briefly reviewed. In addition, the THz near-field spectroscopic technique based on PCAs is proposed to overcome the resolution limit and achieve sub-wavelength resolution. Specifically, incorporating the Hadamard multiplexing method with an emitter array for the THz near-field configuration, the system SNR is enhanced, agreeing well with theoretical prediction. With more array elements, the system SNR can be further improved. Various THz applications are explored utilizing the far-field and near-field THz-TDS setup, including material characterization, imaging and sensing. With the advancement of THz far-field and near-field systems incorporating PCAs in recent years, more innovative and practical THz applications will be enabled.