Fig. 1. Schematic layout of the SG II-Up laser facility and the key unit that causes FM-to-AM conversion. DFB fiber laser, distributed feedback fiber laser; AOM, acoustic-optical modulator; YDFA, ytterbium-doped fiber amplifier; BS, beam splitter; APC, automatic polarization controller; 2-stage-PM, two-stage phase modulator; AFG, arbitrary function generator; AWG, arbitrary waveform generator; EOM, electro-optical modulator; SYNC, synchronization controller; EAMP, electric amplifier; ATD, adjustable time delay; CSF, cavity spatial filter; TSF, transmission spatial filter; AMP, amplifier; FCC, frequency conversion crystal; WFL, wedge focusing lens; BSG, beam sampling grating.

Fig. 2. Beam smoothing technology for a single laser beam.

Fig. 3. (a) The 3 GHz sinusoidal phase modulation spectrum; (b) the 3 + 20 GHz sinusoidal phase modulation spectrum.

Fig. 4. AM spectrum of several transfer functions: (a) pure phase transfer function; (b) symmetric exponential amplitude transfer function; (c) asymmetric exponential amplitude transfer function; (d) linear amplitude transfer function.

Fig. 5. Analysis diagram of FM-to-AM influencing factors of the high-power laser facility.

Fig. 6. Schematic diagram of dispersion compensation for the parallel grating pair.

Fig. 7. Temporal modulation (a) before and (b) after GVD compensation for 0.3 nm @ 3 GHz + 20 GHz phase modulation.

Fig. 8. Principle of pinhole aperture selection.

Fig. 9. Configuration of the final optics components of the SG II-Up facility.

Fig. 10. When the FM-to-AM is 5% @ 3 GHz, 0.15 nm after the main amplifier, the FM-to-AM on the subsequent optical components and the target surface: (a) last transmission reflector surface; (b) incident surface of the WFL; (c) BSG; (d) target.

Fig. 11. Time-domain modulation (measured by an Agilent DSO93004L with 30 GHz and an EOT ET-3600 with 22 GHz) at different wavelengths for the High Energy Integrated Laser Beam of the SG II-Up facility: (a) wavelength at 1052.5 nm (4.3%); (b) wavelength at 1053 nm (4.9%).

Fig. 12. Phase modulation with 3 GHz + 20 GHz: (a) after the main amplifier (); (b) incident surface of the WFL; (c) BSG; (d) target.

Fig. 13. (a) Temporal modulation before (blue) and after (red) the WFL; (b) AM spectral transfer function.