A Modified 8f Geometry with Reduced Optical Aberrations for Improved Time Domain Terahertz Spectroscopy

We present a modified 8f geometry for time domain terahertz (THz) spectroscopy (TDTS) experiments. We show, through simulations and data, that a simple rearranging of the off-axis parabolic mirrors, which are typically used to focus and direct THz radiation in TDTS experiments, results in a nearly 40 % reduction in the THz focal spot diameter. This effect stems from significant reduction of the principle optical aberrations which are enhanced in the conventional 8f geometry but partially compensated in the modified 8f experimental setup. We compare data from our home-built TDTS spectrometer in the modified 8f geometry to that of previous iterations that were designed in the conventional 8f geometry to demonstrate the effect.