Fig. 1. Schematic illustration of conjugate rotation smoothing scheme for laser quad based on dual-frequency laser and spiral phase plate

Fig. 2. Focused intensity distribution of the laser quad at different time (without continous phase plate), red areas denote the intensity distribution of beam 1 and beam 3, green areas denote the intensity of beam 2 and beam 4

Fig. 3. Variations of the coherence length and the rotation period with the wavelength difference when the helical charge l＝±1

Fig. 4. Surface shape of an original CPP (a) and its conjugate CPP (b). (c) is the far-field intensity distributions of a same laser beam after propagating through these two CPPs. Red regions shows the speckles generated by the original CPP, and green regions within the focal spot show the speckles generated by the conjugate CPP

Fig. 5. Variation of the linear velocity of the speckles at different locations inside the focal spot

Fig. 6. Comparison of the conjugate spin-light smoothing scheme at different combination of helical charges with smoothing by spectral dispersion.

Fig. 7. Focused intensity distribution of the laser quad at different time (without CPP), red areas denote the intensity distribution of beam 1 and beam 3, and green areas denote the intensity distribution of beam 2 and beam 4

Fig. 8. (a) Variation of the contrast of the focal spot with the integral time when the beamlets have different beam quality. PV denotes the peak-to-mean value of the wavefront distortion, and a denotes the max-to-mean value of the amplitude modulation. (b) FOPAI curves of the focal spot when the integral time is 5 ps

Fig. 9. Focal spots at different time without the use of continuous phase plates, when both spin-light smoothing scheme and radial smoothing are adopted

Fig. 10. Variation of the contrasts of the focal spot with the integral time and FOPAI curves with the integral time 20 ps