Beam profiling of a commercial lens-assisted terahertz time domain spectrometer

Abstract

To undertake THz spectroscopy and imaging, and accurately design and predict the performance of quasi-optical components, knowledge of the parameters of the beam (ideally Gaussian) emitted from a THz source is paramount. Despite its proliferation, relatively little work has been done on this in the frame of broadband THz photoconductive antennas. Using primarily pinhole scanning methods, along with stepwise angular spectrum simulations, we investigate the profile and polarization characteristics of the beam emitted by a commercial silicon-lensintegrated THz photoconductive antenna and collimated by a TPX (polymethylpentene) lens. Our study flags the limitations of the different beam profiling methods and their impact on the beam Gaussianity estimation. A non-Gaussian asymmetric beam is observed, with main lobe beam waists along x and y varying from 8.4 ± 0.7 mm and 7.7±0.7 mm at 0.25THz,to1.4±0.7 mm and 1.4 ± 0.7 mm at 1 THz, respectively. Additionally, we report a maximum cross-polar component relative to the ON-axis co-polar component of -11.6 dB and -21.2 dB, at 0.25 THz and 1 THz, respectively.