与常规的自发拉曼散射相比，受激拉曼散射 (SRS) 经常使用两束光场 (泵浦光和Stokes光)，这为偏振操控SRS过程提供了一个额外的自由度。为此，开展了泵浦光分别为圆偏振和线偏振的SRS对比研究。首先，基于非线性耦合波方程，从理论上分别推导了泵浦光为圆偏振和线偏振时 (Stokes光始终保持线偏振) SRS信号强度表达式。随后，以具有球对称的甲烷分子为例，实验测量了上述两种偏振光泵浦下甲烷分子υ₁和υ₃振动模在2800~3100 cm^-1的SRS光谱。实验结果与理论分析一致表明：SRS的信号强度不仅与泵浦光的偏振态有关，还与待测分子振动模式的对称性紧密相关。本研究结果为SRS的偏振应用提供了有益启示。

Three-dimensional (3D) imaging is essential for understanding intricate biological and biomedical systems, yet live cell and tissue imaging applications still face challenges due to constrained imaging speed and strong scattering in turbid media. Here, we present a unique phase-modulated stimulated Raman scattering tomography (PM-SRST) technique to achieve rapid label-free 3D chemical imaging in cells and tissue. To accomplish PM-SRST, we utilize a spatial light modulator to electronically manipulate the focused Stokes beam along the needle Bessel pump beam for SRS tomography without the need for mechanical z scanning. We demonstrate the rapid 3D imaging capability of PM-SRST by real-time monitoring of 3D Brownian motion of polystyrene beads in water with 8.5 Hz volume rate, as well as the instant biochemical responses to acetic acid stimulants in MCF-7 cells. Further, combining the Bessel pump beam with a longer wavelength Stokes beam (NIR-II window) provides a superior scattering resilient ability in PM-SRST, enabling rapid tomography in deeper tissue areas. The PM-SRST technique provides ∼twofold enhancement in imaging depth in highly scattering media (e.g., polymer beads phantom and biotissue like porcine skin and brain tissue) compared with conventional point-scan SRS. We also demonstrate the rapid 3D imaging ability of PM-SRST by observing the dynamic diffusion and uptake processes of deuterium oxide molecules into plant roots. The rapid PM-SRST developed can be used to facilitate label-free 3D chemical imaging of metabolic activities and functional dynamic processes of drug delivery and therapeutics in live cells and tissue.

近年来，在计算物理领域提出了一种具有变革意义的利用神经网络直接求解微分方程的方案——物理信息神经网络(physics-informed neural network, PINN), 引起了广泛关注, 并且已经在多个领域的微分方程相关的问题中都得到了成功的验证。着眼于光纤非线性的建模，针对光纤中：光信号传输时受损耗、色散以及非线性等多种物理效应影响而发生演化；受激拉曼散射引起的功率转移；光模场在多种几何结构光纤中的分布与传输这三个场景展开研究。在数学上，这三个场景的控制方程分别为：非线性薛定谔方程、受激拉曼散射常微分方程以及傍轴亥姆霍兹方程，文中先后呈现了利用PINN求解这三个方程的具体实施方案及结果，并与数值方法进行对比分析，二者结果显示出较高的一致性, 且PINN具备更低的计算复杂度。PINN作为一种精准、高效的微分方程求解框架，在未来有潜力推进光纤非线性建模的发展。

With the increasing power of fiber lasers, single chirped and tilted fiber Bragg gratings (CTFBGs) cannot completely mitigate continuously enhanced system-excited stimulated Raman scattering (SRS). Although improving the loss rate of a single CTFBG or cascading multiple CTFBGs can provide better suppression of the stronger SRS, excessive insertion loss may cause significant attenuation of the output power. Confronting the challenge, we firstly present an SRS mitigation method based on a dual-structure fiber grating in this paper. The dual-structure fiber grating comprises a CTFBG and a fiber Bragg grating structure, which were designed and fabricated on a passive 25/400 double-clad fiber. To evaluate the performance of the grating, a 3 kW fiber master oscillator power amplifier laser is established. The experimental results demonstrate that the SRS mitigation rate of the grating is greater than 30 dB (99.9%), whereas the insertion loss is only approximately 3%, thus allowing for minimal deterioration of the output power. This solves the contradiction between high suppression rate and high insertion loss faced by CTFBGs, which in turn makes dual-structure fiber gratings particularly suitable for mitigating SRS in 3–5 kW high-power fiber lasers.

In this work, we experimentally investigate the dependence of the stimulated Raman scattering (SRS) effect on the seed linewidth of a high-power nanosecond superfluorescent fiber source (ns-SFS). The results reveal that the SRS in the ns-SFS amplifier is significantly influenced by the full width at half maximum (FWHM) of the ns-SFS seed, and there is an optimal FWHM linewidth of 2 nm to achieve the lowest SRS in our case. The first-order SRS power ratio increases rapidly when the seed’s linewidth deviates from the optimal FWHM linewidth. By power scaling the ns-SFS seed with the optimal FWHM linewidth, a narrowband all-fiberized ns-SFS amplifier is achieved with a maximum average power of 602 W, pulse energy of 24.1 mJ and corresponding peak power of 422.5 kW. This is the highest average power and pulse energy achieved for all-fiberized ns-SFS amplifiers to the best of our knowledge.