Fig. 1. Schematic of the experimental setup. HWP, half-wave plate; G-T prism, Glan–Taylor prism; L1–L4, lens with the focal length of 50, 100, 200, and 50 mm, respectively; medium, 5% (mole fraction) magnesium-oxide-doped periodically poled lithium niobate (MgO:PPLN); F, filter; S, screen.

Fig. 2. Generation of the SH vortex patterns carrying different l₂, where l₂ = 2l₁, and l₁ is the TC of the structured FW. The first row is the phase masks of the FW beams with different TCs for (a1) l₁ = 1, (a2) l₁ = 2, (a3) l₁ = 3, (a4) l₁ = 2.5, (a5) l₁ = 2.7, and (a6) l₁ = 2.9, respectively. The second and third rows show the corresponding simulation and experimental intensity profiles of the SH vortex with different TCs for (c1) l₂ = 2, (c2) l₂ = 4, (c3) l₂ = 6, (c4) l₂ = 5, (c5) l₂ = 5.4, and (c6) l₂ = 5.8, respectively. In this case, the obliquity factor is constant (a = 1).

Fig. 3. Intensity patterns of the SH vortices with different obliquity factors. The first row denotes the phase profiles of the FW beams with different obliquity factors for (a1) a = 1, (a2) a = 2, (a3) a = 4, (a4) a = 0.5, (a5) a = 1.5, and (a6) a = 4.5, respectively. The TC l₁ = 2 is fixed in this case. The simulation and experimental intensity patterns of the SH wave are arranged and displayed in the second and the third rows, respectively.

Fig. 4. Experimental comparison on the intensity patterns of generated SH waves by switching the sign of the TC of the structured FW beam and the obliquity factor, respectively. (a)–(d) Corresponding to cases of input OAM and obliquity factors that are l₁ = +2, a = 3, l₁ = −2, a = 3, l₁ = 1, a = +2, and l₁ = 1, a = −2, respectively. The insets are the corresponding simulation of SH vortex beams. The experiments are in good agreement with the simulations.

Fig. 5. Conversion efficiency of SH waves pumped by different OAM states with the fixed obliquity factor a = 1.