## 2 Laser System
Before the incidence to the BBO crystal for the TH generation, polarization and optical path lengths of the SH and the fundamental beams are tuned by a half wave-plate and a delay line. The maximum energy and pulse duration of the fundamental, SH, and TH pulses are summarized in Table 1. At EH2, an \"optical parametric amplifier (OPA)\" (TOPASHE-PRIME, Light Conversion, Vilnius, Lithuania) enables users to use tunable ultrafast pulses in the wavelength range from 0.24 to 2.6 \(\upmu\)m. Figure 5 indicates the output energy of OPA as a function of wavelength. The shapes of the fundamental pulses are optimized by tuning the compressor and the AOPDF parameters, monitored with \"Spectral Phase Interferometry for Direct Electric-field Reconstruction (SPIDER)\" [29] (Venteon SPIDER, Laser Quantum) in periodic maintenance. Figures 6 and 7 show interfeometrical traces measured by SPIDER (Figures 6a and 7a) and reconstructed pulses with a \(\sim\)40-fs pulse duration (Figures 6b and 7b) at EH2 and EH4c, respectively, after the pulse shape optimization in each hutch. The optimized pulses are available in either of the experimental hutches because the difference in optical path lengths to the hutches makes it difficult to find a common condition for the optimization. We constructed a \"frequency-resolved optical gating (FROG)\" [30], which captures spectra of nonlinear signals with scanning an optical delay, to characterize the SH and TH pulses in the ultraviolet region. As an inspection of the home-build FROG, we measured the shape of the fundamental pulse with SH generation FROG at EH2, as shown in Figure 8. Although dispersion caused by internal optics in the FROG remains, the reconstructed pulse shape is consistent with the SPIDER measurement. Figures 9 and 10 show the FROG traces measured by the self-diffraction  
Figure 2: Optical layout at EH2 and EH4c. A compressor, delay line, and THG unit are set up on an optical bench at EH2 and EH4c. An optical parametric amplifier (OPA) is available at EH2. The optical laser beam is focused on a sample with an almost parallel direction to the XFEL beam. Setup for time-resolved X-ray diffraction is indicated as a typical pump-probe experiment. Figure 8: (**a**) FROG image; (**b**) Reconstructed intensity (red) and phase (blue) of the fundamental pulse at EH2. Figure 6: (**a**) SPIDER trace; (**b**) reconstructed intensity (red) and phase (blue) at EH2. Figure 7: (**a**) SPIDER trace; (**b**) reconstructed intensity (red) and phase (blue) at EH4c. As a typical pump-probe experiment, a time-resolved X-ray diffraction setup is illustrated in Figure 2.0 The optical laser beam is propagated to a sample almost parallel to the XFEL beam through a prism shape mirror. A typical spot profile focused by a 1-m focal-length lens at the focal position of XFEL in EH2 is indicated in Figure 10(a). We evaluated the pointing stability by measuring the centroid position of the beam spot in a shot by shot manner at EH2. Figure 10(b) shows the trends of the vertical and horizontal positions in 24 h. Although the beam spot drifted by about 10% of the beam size in the warming-up period (the first 4 h), the pointing fluctuations were kept at \(\sim\)3% (rms). We performed the same measurement at EH4c and obtained almost the same results of the pointing stability. Figure 2.1 (a) FROG image; (b) reconstructed intensity (red) and phase (blue) of the TH pulse at EH2. Figure 2.2 (a) FROG image; (b) reconstructed intensity (red) and phase (blue) of the SH pulse at EH2.