Femtosecond laser technology is widely used in many fields, but its wavelength coverage is limited and its output wavelength cannot be flexibly adjusted. As a third order nonlinear effect, stimulated Raman scattering (SRS) requires no strict phase matching, can effectively suppress wavefront distortion, enhance beam quality, and has a simple experimental setup. It has great potential in expanding wavelength coverage and special wavelength applications. However, the SRS process of femtosecond pulses in crystals is highly transient, with relatively few research. In the generation of femtosecond laser based supercontinuum, most materials have low Raman gain, and main researches focus on the impact of self-phase modulation (SPM) on spectral broadening, neglecting the SRS process. During supercontinuum generation, multiple nonlinear effects interact. The SRS process causes frequency jumps, creating Stokes and anti?Stokes waves in the long and short wavelength directions, respectively, which expands the supercontinuum width. Moreover, SRS can suppress wavefront distortion, potentially improving the beam quality of a supercontinuum light source. It is meaningful to seek high Raman gain materials for supercontinuum generation and to study the impact of the Raman effect on spectral broadening. Ba(NO₃)₂ crystals, with the high Raman gain coefficient, offer a good platform for this research. This paper constructs a supercontinuum generation model in Ba(NO₃)₂ crystals through numerical simulation, exploring the influence of SRS and other nonlinear effects on spectral evolution during pulse propagation. By combining theoretical analysis with experimental results, it explains the spectral broadening mechanism and provides theoretical and experimental evidence for femtosecond pulse spectral broadening during propagation in Ba(NO₃)₂ crystals.

The scholarly inquiry integrates both theoretical and experimental methodologies. Theoretically, based on the nonlinear Schr?dinger equation, a supercontinuum model of the Ba(NO?)? crystal is built. The split step Fourier method is used for solution, and the Raman response function of the Ba(NO₃)₂ crystal is established by combining its spontaneous Raman scattering characteristics with nonlinear response curves to simulate spectral evolution. The impact of SRS on spectral broadening is determined by comparing spectral broadening situations with and without the Raman effect. Experimentally, a 200 fs pulse width, 1026 nm center wavelength femtosecond laser pumps the Ba(NO₃)₂ crystal to achieve a supercontinuum output. The output spectrum is collected by controlling pump power, adjusting polarization, and using long pass filters and spectrometers. Experimental spectra are compared with theoretical ones to better clarify the SRS influence mechanism.

The research combines simulation and experiment to study the Raman effect in supercontinuum generation in Ba(NO₃)₂ crystals. Simulation shows that when the pump light power exceeds the Raman threshold, the SRS effect is significant. Pump light energy transfers to the Stokes light, producing the first and second order Raman shift peaks at 1150 nm and 1306 nm. Further analysis reveals the third and weak fourth order Raman shifts, expanding the long wavelength spectral coverage by about 150 nm compared to no Raman effect cases. Meanwhile, the competition between SRS and other nonlinear effects inhibits short wavelength spectral distortion, making the spectrum flatter. Experiments show that the maximumly broadened output spectrum covers about 400 nm (1.2?1.6 μm), with simulation and experimental spectra highly consistent in peak position and broadening trend, proving the model validity. Further analysis of experimental results indicates that the higher order Raman shift gains decrease, causing spectral region intensity lower than the theoretical value. Specifically, when the pump light power exceeds the Raman threshold of the Ba(NO₃)₂ crystal, the clear Raman shift peaks appear in the spectrum. As propagation distance increases, the spectrum broadens further toward longer wavelengths, and the spectrum between the center wavelength and first order Raman peak becomes flatter, effectively suppressing long wavelength spectral distortion.

This paper systematically reveals the role and the dynamic characteristics of SRS in supercontinuum generation during femtosecond pulse pumping of Ba(NO₃)₂ crystals through theoretical modeling and experiments. Simulations show that when the pump light power exceeds the Raman threshold, SRS transfers pump energy to Stokes light (1150 nm and 1306 nm) via pump photon coupling with lattice vibration energy levels. This extends the long wavelength spectral coverage to about 400 nm, a 150 nm increase compared to that in the absence of Raman effects. The dynamic competition between SRS and other nonlinear effects also flattens the spectrum between the center wavelength and the first order Raman peak by inhibiting short wavelength spectral distortion. The combination of theory and experiment confirms the femtosecond-scale nonlinear dynamics of Ba(NO₃)₂ crystals, providing a new approach for supercontinuum generation in crystals. Due to the damage threshold of the Ba(NO₃)₂ crystal, the current spectral broadening is still limited. However, selecting other Raman materials (e.g., diamonds) with stronger Raman characteristics, higher damage thresholds, and better thermal conductivity can further expand the spectral broadening range and intensity.