Coherent Anti-Stokes Raman Scattering (CARS) is a nonlinear optical process used to probe molecular vibrational information. By using pump and Stokes beams simultaneously, the condition $$ \omega_{\text{pump}} - \omega_{\text{Stokes}} = \omega_{\text{vib}} $$ is satisfied, where \( \omega_{\text{vib}} \) is the molecular vibrational frequency, enabling excitation of specific vibrational modes. The anti-Stokes signal frequency is $$ \omega_{\text{anti-Stokes}} = 2\omega_{\text{pump}} - \omega_{\text{Stokes}} $$ By detecting this signal, the vibrational spectrum of the sample can be obtained. CARS is widely used in chemical analysis, biological imaging, and materials science.