Fig. 4: Numerical stimulation for the nonlinear interaction induced spectral evolution throughout the HCF-LN-CPPLN system.

a Simulated output spectra (normalized against the peak intensity) from HCF (purple), bare LN (yellow), and the original pump mid-IR femtosecond laser spectrum from OPCPA (red), respectively. The spectrum broadens due to 3rd-NL SPM effects. b Simulated output spectra from the CPPLN sample pumped by the laser pulse emitted from the bare LN crystal (purple) with different nonlinear mechanisms. The green curve represents the output spectrum of the generated SHG signal and the remaining pump only via a single 2nd-NL effect, with a residual 455 nm spectral gap between them. The orange curve represents the interconnected output spectrum of the generated SHG signal and the remaining pump via the synergic action of 2nd-NL SHG and 3rd-NL SPM effects