Multi-channel third-harmonic generation via period 3D nonlinear photonic crystals

• Systematic calculations were performed to optimize the efficiency of non-collinear third-harmonic generation. • A 3D nonlinear photonic crystal with dimensions of 250 × 3000 × 250 µm 3 (X × Y × Z) was fabricated using femtosecond laser polarization • Effective collinear and non-collinear third-harmonic generation was successfully observed. • Achieved maximum second-harmonic and third-harmonic efficiencies of 3.1 % and 8.4 × 10 -3 %, respectively. We report the cascaded third-harmonic generation (THG) via 3D quasi-phase matching (QPM) both theoretically and experimentally. A systematic demonstration of periodic 3D nonlinear photonic crystal (NPC) design for efficient THG is presented. A nonlinear photonic structure contains two subsections was fabricated by all-optical poling technique in an Sr 0.61 Ba 0.39 NbO 3 crystal. The first segment is a 1D χ (2) grating for efficient collinear second-harmonic generation (SHG), while the second is a designed 3D NPC for THG. Effective collinear and non-collinear TH waves were realized, achieving maximum conversion efficiencies of 3.1 % for SHG and 8.4 × 10 -3 % for THG. Our findings deepen the understanding of cascaded THG in 3D NPCs and advance the development of multi-channel high-harmonic generation via high-dimensional QPM processes.