Conjugate rotation smoothing scheme for laser quad based on dual-frequency laser and spiral phase plate

Conjugate rotation smoothing scheme for laser quad based on dual-frequency laser and spiral phase plate was proposed. The dual-frequency laser provides frequency shift among the beamlets, the spiral phase plates with same helical charge but opposite sign transform the beamlets into Laguerre-Gaussian beams, and the polarization control is applied to make these beamlets coherently superposed on the target plane. On this basis, the conjugate continuous phase plates are adopted to enable the beamlets with different central wavelength and orthogonal polarization form focal spots with rapid rotation. Moreover, the spatiotemporal focal spot of the laser quad looks like conjugate spin light because of the frequency beats. It is indicated that, the scheme enables the fine-scale speckles within the focal spot rotate in a period of a few picoseconds, and even exhibit different intensities and wavelengths at different time and different positions. Hence, the novel scheme can effectively smooth the irradiation uniformity of the laser quad and even has the potential to mitigate laser plasma interactions.