Emerging CsPbX₃ (X = Cl, Br, and I) perovskite nanocrystals (NCs) have been demonstrated to be efficient emitters with a high fluorescence quantum yield, making these materials interesting for optical applications as well as for fundamental physics. Interestingly, doping with transition metal ions has been extensively explored as a way of introducing new optical, electronic, and magnetic properties, making perovskite NCs much more functional than their undoped counterparts. However, there have been no reports regarding the nonlinear optical properties of transition metal ion doped perovskite NCs. Herein, by using femtosecond-transient absorption spectroscopy, we have determined the one-photon linear absorption cross-section (∼1.42 × 10⁻¹⁴ cm²) of Mn-doped CsPbCl₃ NCs (∼11.7 ± 1.8 nm size, ∼0.2% doping concentration, and ∼600 nm emission wavelength). More importantly, their nonlinear optical properties—in particular, the two-photon absorption (TPA) and resultant emission—were investigated. Notably, the NCs exhibit wavelength-dependent TPA with a maximum value up to ∼3.18 × 10⁵ GM at a wavelength of 720 nm. Our results indicate that Mn-doped CsPbCl₃ NCs show promise in nonlinear optical devices and multiphoton fluorescence lifetime imaging.

We have studied the two- and three-photon absorption (2PA and 3PA) properties of Mn-doped ${\text{CsPbCl}}_3$ two-dimensional nanoplatelets (2D NPs) and cubic nanocrystals. Compared with their cubic counterparts, the Mn-doped 2D NPs exhibit stronger quantum confinement effects that can more efficiently enhance their dopant-carrier exchange interactions and multiphoton absorption. More specifically, the maximum volume-normalized 2PA and 3PA cross sections of the 2D NPs were 6.8 and 7.2 times greater than those of their cubic counterparts, respectively, reaching up to $1237\mathrm{GM}/{\mathrm{nm}}^3$ in the visible light band and $2.24\times {10}^{-78}{\mathrm{cm}}^6·{\mathrm{s}}^2·{\mathrm{photon}}^{-2}/{\mathrm{nm}}^3$ in the second biological window, respectively.

The 316L thick plate electron beam welding (EBW) has been widely used in fusion test reactor manufacturing. Therefore, the numerical simulation of the 50 mm 316L austenitic stainless steel by two heat sources and experimental on microstructure and residual stress have been studied in this article. In the simulation study, the traditional heat source model (3D Gaussian heat source) and composite heat source (double ellipsoid heat source superimposed on the 3D Gaussian heat source) were proposed to simulate the welding of local joint. Weld cross-section, temperature curve, and residual stress after welding obtained by simulations were investigated. The experimental study involved residual stress tests and microstructure analysis. It turned out that the result of the composite heat source was closer to the actual joint. The residual stress distribution of simulation was validated and in accordance with experimental measurement. Moreover, the microstructures were studied by electro backscattered diffraction (EBSD) and compared with the temperature curve. The formation mechanism of microstructural heterogeneity was caused mainly by different thermal cycles at different positions of the thick plate. The top of the joint was more prone to stress concentration.

Multiphoton absorption (MPA) effects have become useful for real applications as well as conceptual predictions. However, most of organic molecules exhibit small Stokes shift and reduced MPA in the highly polar solvents, which may seriously hinder their related applications. In this work, one styrylpyridinium salt has been synthesized, which exhibits outstanding properties such as bright red fluorescence at the wavelength of 626 nm in a highly polar solvent (DMSO). Importantly, it is noted that the material also exhibits strong two- and three-photon absorption action cross-section (δ_2PA = 597 GM and δ_3PA = 18 × 10⁻⁸⁰ cm⁶∙s²∙photon⁻², respectively), which can be excited in near-infrared (NIR) window I (650–900 nm) and NIR window II (1000–1450 nm). Meanwhile, two-photon in vitro bioimaging and MPA induced optical limiting behavior have been successfully demonstrated based on the chromophore.

The China Fusion Engineering Test Reactor vacuum vessel has strict tolerances requirements and a large number of fully penetrated joints in the manufacturing and assembly processes. As the most complicated component of vacuum vessel, port stubs have stricter tolerance requirements, to guarantee the high assembly accuracy with the vacuum vessel. Due to the small deformation of electron beam welding, this method is adopted for the welding of port stub. However, welding deformation cannot be avoided, thus it is necessary to carry out finite element analysis to analyze and control the welding deformation of the port stub. In this paper, based on thermo-elastic–plastic theory, the double ellipsoid and cone-shaped hybrid heat source can accurately outline the electron beam weld pool contour of the 316L stainless steel with 50 mm thickness, which is further verified by the welding process experiment. The above hybrid heat source is applied to analyze the welding deformation of the lower port stub, and according to the deformation simulation results, the welding fixture is designed to reduce the welding deformation. The welding deformation analysis can effectively provide theoretical data support and practical guidance for the actual electron beam welding process of port stub.