Enhancement of four-wave mixing in stimulated Raman scattering processes by hydrogen bonding in tetrahydrofuran

Typically, the occurrence of four-wave mixing (FWM) relies on the corresponding nonlinear polarizability and phase-matching conditions. However, it has been proposed that hydrogen bonding (HB) can enhance the SRS signal of FWM in tetrahydrofuran (THF). In pure THF, only strong CH SRS peaks at 2870 cm⁻¹ and 2946 cm⁻¹ are observed. In contrast, when THF is mixed with carbon tetrachloride (CTC), additional FWM peaks appear at 2713 cm⁻¹ and 3083 cm⁻¹. When the volume ratio of the THF and CTC is 4:6 (molar ratio of 2:1), the enhancement of FWM in THF is the strongest, while the all-orders Stokes SRS of CTC is also enhanced. Combined with density-functional theory calculation, the HBs formed in the two organic molecules have a strong influence on the vibrational coupling between neighboring molecules. The formation of hydrogen bonds promotes the emergence of seed photons, while the addition of CTC and the generation of laser-induced plasma improve the phase-matching environment and adjust the nonlinear susceptibility, thereby enhancing the FWM signals.