Cascaded four-wave mixing process: A key to realize super-continuous coherent radiation with dual stimulated Raman scattering in mixed solutions

We proposed a coherent radiation scheme based on double-stimulated Raman scattering (SRS) induced cascaded four-wave mixing (FWM) in a mixed methanol–ethanol solution. The SRS of methanol has two characteristic vibrational peaks, which are attributed to the symmetric stretching vibration of –CH3 and the antisymmetric stretching vibration of –CH3. The addition of ethanol enhances the antisymmetric stretching vibration mode, and intensities of two peaks were similar when the volume ratio of methanol to ethanol was 7.5:2.5. Resonant amplification of the two SRS signals is achieved by refocusing the scattered light, and the stronger self-focusing effect not only converges the two beams but also generates a plasma-enhanced SRS process, realizing cascaded FWM. The frequency difference Δω between two FWM beams matches the frequency difference ΔΩ between the vibrational energy levels of the symmetric and antisymmetric stretching vibrations, and the stimulated excitation enhances FWM signals. The output coherent radiation light is a large broadband ranging from 592 to 668 nm and 721 to 797 nm, with a wavelength interval of about 3 nm. The intensity of light radiated at different wavelengths is not the same, with the strongest light at the center of the wavelength (630 and 759 nm). This technique has the potential to contribute to the development of a multi-wavelength cascaded Raman laser.