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.
Highlights
R ECENT years have witnessed a significant technological development of commercial THz instruments [1], [2], increasing the accessibility of time-domain spectroscopy (TDS)
Our full-wave simulations reveal the increasing significance of the side lobes when a longer temporal window is considered. This undesirable effect is due to the reflections inside the silicon lens and diffraction on the boundaries of the emitter chip. It should be of concern for spectroscopy and imaging applications requiring long time delays and CW system using these type of lens-assisted PCAs [29]
The beam profile characterization of a commercial all fiber-coupled TDS system in collimated beam configuration is undertaken though a number of profiling techniques
Summary
R ECENT years have witnessed a significant technological development of commercial THz instruments [1], [2], increasing the accessibility of time-domain spectroscopy (TDS). We will show that fiber-coupled systems enable us to de-embed the influence of the (quasi-)optics on the detector side, given the ability to scan the pinhole and detector coaligned. Such a serious consideration to the impact of the detection transfer function on the beam profiling is limited in the open literature. We compile a rigorous beam characterization of the commercial TERA K15 Mark II all fiber-coupled THz TDS system from Menlo Systems, scrutinizing the impact of the detection side (quasi-)optics on the beam profile estimate. The spectral response is obtained by Fourier transformation with Hanning windowing
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