## 7 Conclusions  
To conclude, we have presented our THz-TDS system designed for pumping with high average power sources such as Yb-doped laser. Through the use of a redesigned THz beamline and water-cooling of the GaP generation crystal, the pump is effectively rejected and the signal-to-noise ratio improved by a factor of almost 2. Pulse compression based on a commercial OPA allowed us to use a 55 fs, resulting in \(\simeq\)0.5 THz broader detected spectrum (at \(-\)3 dB). The proposed improvements are carried out using instruments commonly found in laboratories using high average power laser sources and off-the-shelf components, introducing minimal additional complexity to existing THz-TDS designs. As such, these improvements represent solutions that are feasibly applicable to many THz-TDS systems utilizing high average pump power. Figure 8: FROG scan of the compressed probe pulse. (**a**) shows the amplitude of the pulse in the time domain. The dashed red line indicates the phase of the pulse. (**b**) shows the frequency spectrum of the pulse. Again, the dashed blue line indicates the phase of the pulse. The dashed black lines indicate the position of the zero phase (shown on the right ordinate). The lines indicating the phase of the pulse are almost ideally flat across the pulse profile, indicating the pulse is free of chirp. Figure 9: Comparison of THz traces taken with a 55 fs probe and a 245 fs probe. (**a**) Time-domain traces were taken with compressed (red) vs. uncompressed (blue) probe pulses. The improved resolution of the trace taken with a compressed probe is visible. The initial rise in the region between \(-\)0.1 ps and \(-\)0.4 ps shows a sharper definition in the compressed case. (**b**) Experimental (solid) and simulated (dashed) frequency spectra of the THz field probed with compressed (red) and uncompressed (blue) probe pulses. The THz trace recorded with a compressed probe exhibits \(\simeq\)0.54 THz greater FWHM bandwidth compared to the uncompressed case. We note that the figure has been zoomed in to highlight the difference in detection bandwidth between the compressed and uncompressed probe pulse; the noise floor is not visible in the figure and lies at \(\sim\)\(-\)60 dB. **Author Contributions:** [PERSON] and [PERSON] designed the experiment. [PERSON] performed the measurements with contributions from [PERSON] and [PERSON]. [PERSON] and [PERSON] analyzed the data and interpreted the results. [PERSON], [PERSON], [PERSON] and M.C. provided technical support to the experiment, data analysis, and interpretation of the results. [PERSON] and [PERSON] drafted the manuscript. All authors contributed to writing the final version of the manuscript. [PERSON] supervised the research activity. All authors have read and agreed to the published version of the manuscript. **Funding:** [PERSON] and [PERSON] acknowledge the support from the Defence Science and Technology Laboratory (DSTL) (scholarship number DSTLX-1000144632). [PERSON] acknowledges the support from UK Research and Innovation (UKRI), as the UK Engineering and Physical Sciences Research Council (EPSRC) (Fellowship \"In-Tempo\" EP/S001573/1) and Innovate UK, Application Number PN 10001572 (HiQuED). [PERSON] acknowledges the support from Innovate UK, Application Number PN 10001572 (HiQuED) and from the University of Glasgow Impact Acceleration Account (EP/X525716/1). [PERSON] acknowledges support from the Royal Academy of Engineering; [PERSON] acknowledges support from the Leverhulme Trust, Research Project Grant number RPG-2022-090 and from the DEVCOM ARL Army Research Office, Grant number W911 NF2310313. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original data presented in the study are openly available at [[https://doi.org/10.5525/gla.researchdata.1675](https://doi.org/10.5525/gla.researchdata.1675)]([https://doi.org/10.5525/gla.researchdata.1675](https://doi.org/10.5525/gla.researchdata.1675)).