## 3 Recent Scientific Highlights and New Instruments  
To enable a deeper understanding of the photosynthetic process so that we can design artificial photosynthesis, it is important to determine the structures and functions of photosystem II (PSII), a key catalytic protein complex for photosynthesis. [PERSON] and team achieved a milestone by determining the \"radiation-damage-free\" structure of PSII in the S\({}_{1}\) state at a resolution of 1.95 A with SACLA. Their results show differences at the sub-angstrom level, compared to those obtained with a quasi-CW X-ray source of synchrotron radiation [10]. Furthermore, they determined the structure of an intermediate S\({}_{3}\) state with two-flash illumination at room temperature at a resolution of 2.35 A with a time-resolved (TR) serial femtosecond crystallography (SFX) method. This finding suggests the insertion of a new oxygen atom close to an existing oxygen atom in the molecule [11]. These results provide a critical basis for understanding the mechanisms underlying oxygen evolution in photosynthesis. The TR-SFX method was also used to determine conformational changes in bacteriorhodopsin (bR), a light-driven proton pump, and a model membrane transport protein, at 13 time points in a scale ranging from nanoseconds to milliseconds following photo activation [12]. The resulting molecular movie elucidated a fundamental mechanism for directional proton transport in bR. These achievements were supported by an experimental platform named DAPHNIS developed by the SACLA team [34]. This instrument is composed of a small He chamber for sample injection and a short-work-distance MPCCD detector with octal sensors that is separated from the chamber [31]. This design offers great flexibility to efficiently meet various demands from users, including introduction of new types of sample injectors, such as grease-matrix and droplet injectors [9; 42], and extensions to pump-probe experiments. The pump-probe scheme was applied for X-ray analysis based on wide-angle scattering (WAXS) of solution. [PERSON] and [PERSON] et al. observed a formation process for a gold complex [Au(CN)\({}_{2}\)]\({}_{3}\) in solution after excitation of an ultrafast laser pulse with a wavelength of 267 nm [14]. The time  
Figure 2: Major optical and diagnostic systems of SACLA BL3. SCM: screen monitor; S(FE): frontend slit; BW: beryllium window; BM: beam intensity and position monitor; WM: wavelength monitor; M1, M2a, M2b: plane mirrors; DCM: double crystal monochromator; S(TC): transport-channel slit; SA: solid attenuator; TG: transmission grating; XPR: X-ray phase retarder; GM: gas intensity monitor; TSM: timing and spectrum monitor; CRL: compound refractive lens; 2 SFM-U(-D): two-stage focusing mirrors on the upstream (downstream) side (50 nm spot size); FM: focusing mirrors (1 μm spot size); SR: synchrotron radiation from SPring-8. resolution in this experiment was sub-picosecond, limited mainly by arrival timing jitter between the XFEL and optical laser pulses. To improve the time resolution, we developed an arrival timing monitor by probing the ultrafast change in optical transmittance induced by intense XFEL light with a spatial decoding technique [36; 37]. A unique feature of our optical design is the utilization of an X-ray elliptical mirror for increasing X-ray intensity to form a line-focused profile, which suppresses the X-ray pulse energy that is required to be as small as several microjoules at ~10 keV. Furthermore, we developed a beam branching system for enabling timing diagnostics to be determined simultaneously with experiments. The system is based on a transmission grating that creates two branches dedicated for timing and spectral diagnostics in addition to the 0 th order branch used for the main experiments [43]. We evaluated the accuracy of the monitor by constructing a similar setup in the main branch and found that the error was as small as 7 fs in rms.