1：Experimental Design and Method Selection:

The study employed the electric-field poling method with liquid electrodes to fabricate periodically poled Mg:LN (PPMgLN). A SiO2 dielectric layer was deposited on the -z surface to suppress leakage current, and the multipulse application method was used to control resistance reduction.

2：Sample Selection and Data Sources:

5 mol.% Mg:LN wafers with a diameter of 76.2 mm and thickness of 0.5 mm, grown by the Czochralski method and polarization processed, were used as the matrix.

3：2 mm and thickness of 5 mm, grown by the Czochralski method and polarization processed, were used as the matrix. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes a plasma enhanced chemical vapor deposition (PECVD) system for SiO2 deposition, photolithography setup with S1828 photoresist, arbitrary waveform generator, high voltage amplifier, atomic force microscope (AFM), prism coupling meter, thin-film analyzer, field-emission scanning electron microscope (FESEM), electron probe microanalyzer (EPMA), optical microscope, piezoelectric force microscope (PFM), and a TSL-510 laser with erbium-doped fiber amplifier for SHG characterization. Materials include Mg:LN wafers, SiO2 layer, photoresist, hydrofluoric acid for etching, and saturated aqueous solution of lithium chloride for liquid electrodes.

4：Experimental Procedures and Operational Workflow:

The -z surface was coated with SiO2 of varying thicknesses (0, 400, 700, 900 nm) via PECVD. The +z surface was patterned with photoresist gratings (20 μm period) using photolithography and hard-baking. Poling was done with liquid electrodes, applying high voltage pulses (2 ms width, 10 ms repetition rate) using an amplifier. After poling, samples were etched in HF to reveal domains and characterized with microscopy and SHG tests.

5：Data Analysis Methods:

AFM and SEM for morphology, prism coupling for refractive index, thin-film analyzer for thickness uniformity, EPMA for elemental analysis, optical microscopy and PFM for domain observation, and SHG efficiency calculation for performance evaluation.