1：Experimental Design and Method Selection:

The study uses THz emission spectroscopy in a transmission configuration with femtosecond laser excitation to analyze nonlinear optical processes in monolayer WS2. Theoretical models include optical rectification mechanisms and symmetry considerations based on the D3h point group.

2：Theoretical models include optical rectification mechanisms and symmetry considerations based on the D3h point group. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Monolayer WS2 samples grown on sapphire substrates via chemical vapor deposition were used, characterized by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and UV-Vis absorption to confirm monolayer structure and properties.

3：List of Experimental Equipment and Materials:

Equipment includes a mode-locked Ti:sapphire regenerative amplifier laser, half-wave plate, quarter-wave plate, wire-grid polarizers, off-axis parabolic mirrors, zinc telluride crystal, balanced diodes, Wollaston prism, and various characterization instruments (e.g., XRD, Raman spectrometer, AFM). Materials include monolayer WS2 on sapphire substrates.

4：Experimental Procedures and Operational Workflow:

The pump beam excites the sample at a 45° incident angle; polarization is adjusted using wave plates. THz radiation is collected and detected using electro-optic sampling with a ZnTe crystal. Measurements include dependence on azimuthal angle, pump polarization angle, and circular polarization excitation.

5：Data Analysis Methods:

Data analysis involves fitting experimental results with theoretical equations derived from nonlinear optics, using parameters related to second-order susceptibility. Fourier transform spectra and linear fittings are applied to analyze THz emission amplitudes and spectra.