Fig. 1. Schematic overview of the optical synchronization system for SHINE. L, LINAC; LH, laser heater; BC, bunch compressor; INJL, injector laser; LHL, heater laser; BAM, bunch arrival time monitor; CBPM, cavity beam position monitor; Dia.L., diagnostic laser; PPL, pump-probe laser; SEL, station of extreme light.

Fig. 2. (a) Basic optical architecture of Sagnac loop interferometer by a 3×3 coupler. (b) Sagnac phase relationship of the three output ports.

Fig. 3. Experimental setup for in-loop phase locking and out-of-loop relative jitter measurement. ODL, optical delay line; PM, phase modulator; PZT, piezoelectric transducer; PD, photodiode; BPD, balanced photodetector.

Fig. 4. (a) 3×3 based optical to microwave phase detector; (b) OMO electronic synchrolock module for SHINE.

Fig. 5. (a) Jitter spectral density (black) and the corresponding integrated timing jitter (red) between RF-signal and phase-locked OMO measured by the out-of-loop phase detector for the frequency offset ranging from 10 Hz to 10 MHz; (b) long-term stability measurement over 10 h.

Fig. 6. Typical fiber link stabilization setup. SM, silver mirror; PRM, partially reflecting fiber mirror; MDL, motorized delay line; PM-FS, polarization-maintaining fiber stretcher; PM-EDFA, polarization-maintaining erbium-doped optical fiber amplifier; PMF, polarization-maintaining fiber; DCF, dispersion-compensating fiber.

Fig. 7. Fiber length stabilizer at SHINE.

Fig. 8. Schematic of balanced optical cross-correlator based on PPKTP crystal. DBS, dichroic beam splitter; DM, dichroic mirror; PPKTP, periodically poled KTiOPO₄.

Fig. 9. (a) Measured spectral timing jitter density; the integrated RMS jitter from 10 Hz to 10 MHz is 1.3 fs. (b) Long-term stability measurement; the RMS jitter over 24 h is 4.8 fs.

Fig. 10. Schematic of a two-color optical cross-correlator. DBC, dichroic beam combiner; DBS, dichroic beam splitter; BBO, beta barium borate crystal; DM, dichroic mirror; SM, sliver mirror.

Fig. 11. Measurement result of laser-to-laser synchronization between mode-locked laser and seed laser using TC-BOC: (a) jitter spectral density and integrated timing jitter; (b) long-term drift measurement.

Fig. 12. Laser-to-laser synchronization module in SHINE.