Generation and Detection of Free-Space Terahertz Waveforms

The work within this chapter presents the theoretical and experimental frameworks necessary to generate and detect free-space terahertz (THz) waveforms. To begin with, we introduced a 100 μm wide GaAs PC THz emitter. The theoretical and experimental attributes of the device were analyzed, and it was determined that the operation of the GaAs emitter is limited by both space-charge and near-field THz screening under high optical pump fluences. To scale the THz power to higher levels, therefore, the ZnSe PC THz emitter was designed and tested. The large bandgap of ZnSe allowed this emitter to be operated under high bias field strengths (rather than high pump power fluences). The fact that the operation of the emitter output remained linear with the pump power and the bias voltage for optical fluences up to 28.3 mJ/cm2 and peak bias fields up to 128 kV/cm, means that the device can be successfully scaled to large-area, high-power THz applications where bias field screening effects dominate the saturation characteristics. Finally, crystalline ZnSe sample was tested toward the potential application of THz radiation detection. It was found that the crystalline sample could be used for THz sensing applications. Theoretical and experimental work showed that the operation of the crystalline ZnSe sensors was highly dependent upon the azimuthal symmetries within the crystal lattice.