Extended Data Fig. 5: SH generations in 2D and 3D periodic domain structures.

a, The typical QPM configuration⁴⁵. b, c, The QPM SH patterns in 2D and 3D LiNbO₃ domain structures, respectively. The intensities of the SH spots depend on whether the QPM condition is fully satisfied. At input fundamental wavelengths of 755 nm, 742 nm, and 726 nm, the non-collinear QPM SH generations from 2D domain array are realized by involving \({{\boldsymbol{G}}}_{0,1,-1}{/{\boldsymbol{G}}}_{0,1,1}\), \({{\boldsymbol{G}}}_{0,1,-2}{/\overrightarrow{G}}_{0,1,2}\), and \({{\boldsymbol{G}}}_{0,1,-3}{/{\boldsymbol{G}}}_{0,1,3}\), respectively. The corresponding SH pattern presents two symmetric bright spots (b). In comparison to 2D case, the number of the SH spots from 3D domain structure clearly increases because the QPM condition is simultaneously satisfied by more reciprocal vectors (c). Notably, the central SH spot is bright because it is produced through a collinear SH generation process that has a much longer interaction length than those under non-collinear SH generation configurations. d, e, The measured and calculated emitting angles of the output SH beams.