## 11 Conclusions  
A new femtosecond EUV beamline was developed for ultrafast materials research and development. The beamline is an integral part of the \"Ultrafast Spintronic Materials Facility\" at Nanjing University. The facility also comprises materials engineering stations by molecular beam epitaxy (MBE), sputtering and pulsed laser deposition (PLD), all in the same experimental area. This leads to a fast turn-around time from the production of a new sample material to its being analyzed in the TR-Spin-ARPES station. Therefore, the facility will provide not only fast \"analysis\" but also \"development\" of new ultrafast materials for the electronics industry. The EUV beamline is composed of the: 50-fs laser driver; excitation laser pulse beamline; HHG EUV source, pulse-preserving EUV monochromator; focusing and recombination of the EUV and excitation laser pulse; and Spin-ARPES spectrometer end-station. The EUV beamline was fully characterized and optimized for TR-Spin-ARPES spectroscopy. The HHG EUV spectra from  
Figure 14: The EUV Beamline scaling to \(\sim\)MHz, \(\sim\)kW class femtosecond fiber laser-driver. 10 eV-75 eV were measured after the monochromator slit. A maximum flux of \(\sim\)5.5 \(\times\) 10\({}^{10}\) ph/s is measured at the H17 (26.4 eV) using Argon gas and 3 \(\times\) 10\({}^{8}\) ph/s is measured at the H29 (45 eV) using Neon gas. The EUV flux is increased when the SHG of the TiS laser (400 nm) is used to drive the HHG, due to the wavelength-scaling effect. The spectral bandwidth and wavefront tilt of the EUV beamline can be measured and in good agreement of calculation. The EUV monochromator can enable the narrow bandwidth of the EUV beamline and also preserve its pulse duration. The space charge effect on static ARPES spectra was measured as a function of EUV pulse photon density at the sample material. The space charge effect is minimized when the photon density is below 200 ph/\(\upmu\)m\({}^{2}\)/pulse. This is obtained by controlling the EUV flux and focal spot-size on sample material. Time resolved ARPES measurements of the of p-GaAs (100) were performed over 30 ps temporal delay range, with fine temporal steps of 67 fs for the first 1000 fs delay between the excitation laser pulse and the EUV pulse. TR-ARPES spectra measured the ultrafast surface photovoltaic effect with a 650 fs rise-time of the valence band electronic structure. The TR-Spin-ARPES data acquisition time could be reduced from tens of hours to minutes by upgrading the femtosecond TiS, kHz, 4 W laser driver to the new, femtosecond, \(\sim\)MHz repetition rate and \(\sim\)kW average power fiber-lasers. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] ([PERSON]) and [PERSON] conceived and designed the experiments; [PERSON]. ([PERSON]), [PERSON], [PERSON] and [PERSON]. ([PERSON]) performed the construction of the EUV beamline; [PERSON], [PERSON] and [PERSON] designed and constructed the EUV monochromator; [PERSON]. ([PERSON]), [PERSON], [PERSON], [PERSON] ([PERSON]), [PERSON], and [PERSON] performed the EUV beamline characterization and optimization; [PERSON], H.X., [PERSON], [PERSON], Q.L., C.L., T.K., and C.C. performed the measurement of ARPES and TR-ARPES; [PERSON] and X.W. performed the materials engineering in the growth stations; Y.Z., W.L., F.W., Y.S., and R.Z. provided helpful advice during the construction of the whole facility. All authors participated in writing the manuscript. This research was funded by the National Natural Science Foundation of China (No. 61427812) and the National Key Research and Development Program of China (No. 2016 YFA0300803, No. 2017 YFA0206304). Z.N. (Zhonghui Nie), I.C.E.T., Y.L., X.Z., L.H., J.T., Z.N. (Zhiqiang Ni), H.X., Y.C., X.R., X.W., F.W., Y.S., R.Z., and Y.X. acknowledge the support from the National Natural Science Foundation of China (No. 11774160, 11574137, 61470461, 61674079, 61805116, 61822403, 11874203 and 11504159), the National Basic Research Program of China (No.