Cascaded stimulated Raman scattering
(SRS) of benzene, bromobenzene,
chlorobenzene, ethylbenzene, and toluene was investigated by a pulsed
Nd:YAG laser with 532 nm wavelength. The results showed that the third-order
Stokes SRS of the ring skeleton vibration (CC at 3006 cm–1) accompanied by another higher-frequency Stokes SRS of the CH stretching
vibration (at 3066 cm–1), which arose only when
the third-order Stokes SRS of the ring skeleton was produced, can
be attributed to the vibration energy transfer between vibration energy
levels of CC and CH. The Stokes and anti-Stokes SRS rings, which originated
from the intramolecular energy-transfer-enhanced four-wave mixing
(FWM) processes, can be observed only in the forward direction along
different angles apart from the pump beam direction. The phenomenon
also existed in other derivatives of benzene. We propose the intramolecular
energy-transfer-enhanced SRS for the first time, which can be used
for a broadband Raman laser.
Supercontinuum radiation has found numerous applications in diverse fields encompassing spectroscopy, pulse compression, and tunable laser sources. Anomalous enhanced stimulated Raman scattering (SRS) of cyclohexane-benzene mixtures was obtained in this study. SRS of the pure solvent, the multi-order Stokes of the strongest fundamental vibration modes, and energy transfer in intra-molecular modes were observed. SRS of the mixture revealed that the cross-pumping effect was generated between the C-H stretching ( ) mode of cyclohexane and the C=C ring skeleton ( ) mode of benzene, thereby producing the intermolecular secondary stimulated Raman emission and the appearance of two super-broadband radiations at 664.36~673.9 nm and 704.62~729.22 nm. The results suggest that the energy transfer of intermolecular vibrational modes, where the strongest vibrational mode excited other vibrational modes, is a simple approach for generating supercontinuum coherent radiation.
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