1：Experimental Design and Method Selection:

The experiment leverages intermodal Brillouin scattering within a 2.3-cm silicon waveguide to achieve optomechanical cooling. The design rationale is based on the phase-matching-induced symmetry breaking that decouples Stokes (heating) and anti-Stokes (cooling) processes.

2：3-cm silicon waveguide to achieve optomechanical cooling. The design rationale is based on the phase-matching-induced symmetry breaking that decouples Stokes (heating) and anti-Stokes (cooling) processes. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The sample is a 2.3-cm-long photonic-phononic waveguide fabricated from a single-crystal silicon-on-insulator (SOI) wafer, supporting low-loss guidance of TE-like symmetric and antisymmetric spatial modes.

3：3-cm-long photonic-phononic waveguide fabricated from a single-crystal silicon-on-insulator (SOI) wafer, supporting low-loss guidance of TE-like symmetric and antisymmetric spatial modes. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: The setup includes a continuous-wave (cw) tunable external cavity laser, an acousto-optic frequency shifter, an erbium-doped fiber amplifier (EDFA), a variable optical attenuator (VOA), and a fast photoreceiver for heterodyne detection.

4：Experimental Procedures and Operational Workflow:

Probe light is coupled into the symmetric spatial mode of the waveguide, interacting with thermal phonon fields to produce Stokes and anti-Stokes sidebands. The scattered light is demultiplexed and analyzed using heterodyne spectroscopy.

5：Data Analysis Methods:

The spectral width of the sidebands is analyzed to determine the dissipation rates and lifetimes of the phonons, with the anti-Stokes spectrum broadening indicating cooling.