Third Harmonic Generation of Chirped Laser Pulse in Anharmonic Clustered Plasma Enhanced by Stimulated Raman Scattering

In the present research, we investigate resonant third harmonic generation (THG) arising from electron density oscillations in clustered plasma driven by a frequency-chirped laser pulse through stimulated Raman scattering (SRS). SRS involves the interaction of incident laser light with clustered plasma, which excites a backscattered side-band electromagnetic wave and a plasma wave. Further interaction between the incident laser and the generated plasma wave leads to nonlinear coupling of waves, resulting in harmonic generation. The energy of the resultant third harmonic wave is significantly enhanced due to surface plasmon resonance, while the growth of Raman instability affects its amplitude. An anharmonic clustered plasma implies that the electron-restoring force inside each cluster deviates from Hooke's law, strengthening coupling among the pump, Langmuir, and harmonic waves. This analytical study, supported by numerical evaluation of the derived expressions, demonstrates that chirped pulses and SRS in anharmonic clustered plasma enable stable and efficient generation of high-intensity third harmonic pulses.