Measurement of the Surface-Enhanced Coherent Anti-Stokes Raman Scattering (SECARS) Due to the 1574 cm −1 Surface-Enhanced Raman Scattering (SERS) Mode of Benzenethiol Using Low-Power (<20 mW) CW Diode Lasers

Abstract

The surface-enhanced coherent anti-Stokes Raman scattering (SECARS) from a self-assembled monolayer (SAM) of benzenethiol on a silver-coated surface-enhanced Raman scattering (SERS) substrate has been measured for the 1574 cm⁻¹ SERS mode. A value of 9.6 ± 1.7 × 10⁻¹⁴ W was determined for the resonant component of the SECARS signal using 17.8 mW of 784.9 nm pump laser power and 7.1 mW of 895.5 nm Stokes laser power; the pump and Stokes lasers were polarized parallel to each other but perpendicular to the grooves of the diffraction grating in the spectrometer. The measured value of resonant component of the SECARS signal is in agreement with the calculated value of 9.3 × 10⁻¹⁴ W using the measured value of 8.7 ± 0.5 cm⁻¹ for the SERS linewidth Γ (full width at half-maximum) and the value of 5.7 ± 1.4 × 10⁻⁷ for the product of the Raman cross section σ_SERS and the surface concentration N_s of the benzenethiol SAM. The xxxx component of the resonant part of the third-order nonlinear optical susceptibility |3χ^(3)R _xxxx | for the 1574 cm⁻¹ SERS mode has been determined to be 4.3 ± 1.1 × 10⁻⁵ cmg⁻¹·s². The SERS enhancement factor for the 1574 cm⁻¹ mode was determined to be 3.6 ± 0. 9 × 10⁷ using the value of 1.8 × 10¹⁵ molecules/cm² for N_s.