Controlling cross pumping between C-N and C-H vibration in nitromethane by selective fluorescence-enhanced stimulated Raman scattering.

To investigate the vibrational features of nitromethane (NM), which is a kind of energy material and a well known low-sensitivity and high explosive, experiments are performed to obtain the stimulated Raman scattering (SRS) of NM by employing a 532 nm pulsed pump laser. The Raman signal involves two stimulated emissions at 918 and 2,963 cm-1, attributed to the C-N and C-H stretching vibrations, respectively. To overcome the complexity of cross pump in the pure NM, one stimulated Raman radiation is chosen as a pump source to excite the other Raman mode. Two fluorescence dyes were added to selectively enhance each Raman cross section. By internally seeding the Raman gain medium with fluorescent photons, a significant modification in the stimulated Raman scattering spectrum has been observed. The enhanced Stokes emission at 918 cm-1 was able to induce the 2,963 cm-1 vibration mode when the all-trans-β-carotene was internal seeding in the NM, while the Raman radiation at 2,963 cm-1 was enhanced to excite the C-N mode with the addition of m-Cresol purple. The output energy of both 918 and 2,963 cm-1 under different input energy was also measured to illustrate this result.