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Optical second harmonic generation (SHG) is a nonlinear optical effect widely used for nonlinear optical microscopy and laser frequency conversion. Closed-form analytical solution of the nonlinear optical responses is essential for evaluating materials whose optical properties are unknown a priori. A recent open-source code, ♯SHAARP.si, can provide such closed form solutions for crystals with arbitrary symmetries, orientations, and anisotropic properties at asingleinterface. However, optical components are often in the form of slabs, thin films on substrates, and multilayer heterostructures with multiple reflections of both the fundamental and up to ten different SHG waves at each interface, adding significant complexity. Many approximations have therefore been employed in the existing analytical approaches, such as slowly varying approximation, weak reflection of the nonlinear polarization, transparent medium, high crystallographic symmetry, Kleinman symmetry, easy crystal orientation along a high-symmetry direction, phase matching conditions and negligible interference among nonlinear waves, which may lead to large errors in the reported material properties. To avoid these approximations, we have developed an open-source package named Second Harmonic Analysis of Anisotropic Rotational Polarimetry in Multilayers (♯SHAARP.ml). The reliability and accuracy are established by experimentally benchmarking with both the SHG polarimetry and Maker fringes using standard and commonly used nonlinear optical materials as well as twisted 2-dimensional heterostructures.

 

Optical Second Harmonic Generation (SHG) is a nonlinear optical effect widely used for nonlinear optical microscopy and laser frequency conversion. The closed-form analytical solution of the nonlinear optical responses is essential for evaluating the optical responses of new materials whose optical properties are unknown a priori. Many approximations have therefore been employed in the existing analytical approaches, such as slowly varying approximation, weak reflection of the nonlinear polarization, transparent medium, high crystallographic symmetry, Kleinman symmetry, easy crystal orientation along a high-symmetry direction, phase matching conditions and negligible interference among nonlinear waves, which may lead to large errors in the reported material properties. To avoid these approximations, we have developed an open-source package named Second Harmonic Analysis of Anisotropic Rotational Polarimetry (♯SHAARP) for single interface (si) and in multilayers (ml) for homogeneous crystals. The reliability and accuracy are established by experimentally benchmarking with both the SHG polarimetry and Maker fringes predicted from the package using standard materials. SHAARP.si and SHAARP.ml are available through GitHub https://github.com/Rui-Zu/SHAARP and https://github.com/bzw133/SHAARP.ml, respectively. 

Van der Waals (vdW) ferroelectrics have attracted significant attention for their potential in next-generation nano-electronics. Two-dimensional (2D) group-IV monochalcogenides have emerged as a promising candidate due to their strong room temperature in-plane polarization down to a monolayer limit. However, their polarization is strongly coupled with the lattice strain and stacking orders, which impact their electronic properties. Here, we utilize four-dimensional scanning transmission electron microscopy (4D-STEM) to simultaneously probe the in-plane strain and out-of-plane stacking in vdW SnSe. Specifically, we observe large lattice strain up to 4% with a gradient across ~50 nm to compensate lattice mismatch at domain walls, mitigating defects initiation. Additionally, we discover the unusual ferroelectric-to-antiferroelectric domain walls stabilized by vdW force and may lead to anisotropic nonlinear optical responses. Our findings provide a comprehensive understanding of in-plane and out-of-plane structures affecting domain properties in vdW SnSe, laying the foundation for domain wall engineering in vdW ferroelectrics.

 

The exposure of ecologically critical invertebrates to pharmaceutically active compounds in aquatic environments has been one of the major concerns over the past decade, which also adds serious risk to the aquatic ecosystem. However, the metabolic level perturbations in invertebrates in response to sub-lethal doses of pharmaceuticals are still rarely studied, especially in the marine coastal environment. In this study, the diclofenac regulation of southern hard clam Mercenaria campechiensis metabolites at different time points and concentrations was investigated using NMR-based metabolomics. As a result, clam metabolic profile perturbations were observed under both low and high concentrations of diclofenac exposure in one week according to principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA); however, the potential influenced metabolic pathways were distinctly different. The low-concentration group showed significant taurine upregulation, which indicated self-protection from osmotic stress. However, the metabolites succinate, alanine, and glutamate were significantly upregulated at the relatively high concentration of diclofenac, which was a sign of anaerobic activities. The metabolic profile perturbations in week 2 showed high similarity in both low- and high-concentration groups, and the osmotic protectants betaine and taurine were significantly downregulated. The study indicated the early markers of diclofenac exposure in M. campechiensis , which provided pioneering results for monitoring the toxicity of pharmaceuticals to marine coastal water. 

Thermally activated delayed fluorescence (TADF) is the internal conversion of triplet excitons into singlet excitons via reverse intersystem crossing (RISC). It improves the efficiency of OLEDs by enabling the harvesting of nonradiative triplet excitons. Multiple resonance (MR) induced TADF chromophores exhibit an additional advantage of high color purity due to their rigid conformation. However, owing to the strict design rules there is a limited number of known MR-TADF chromophores. For applications in full-color high-resolution OLED displays, it is desirable to extend the variety of available chromophores and their color range. We computationally explore the effect of chemical modification on the properties of the MR-TADF chromophore quinolino[3,2,1-de]acridine-5,9-dione (QAD). QAD derivatives are evaluated based on several metrics: The formation energy is associated with the ease of synthesis; The spatial distribution of the frontier orbitals indicates whether a compound remains an MR-TADF chromophore or turns into a donor-acceptor TADF chromophore; The change of the singlet excitation energy compared to the parent compound corresponds to the change in color; The energy difference between the lowest singlet and triplet states corresponds to the barrier to RISC; The reorganization energy is associated with the color purity. Based on these metrics, QAD-6CN is predicted to be a promising MR-TADF chromophore with a cyan hue. This demonstrates that computer simulations may aid the design of new MR-TADF chromophores by chemical modification. 

In Proc. of the IEEE Int’l. Workshop on Benchmarking, Performance Tuning, and Optimization for Big Data Applications (BPOD 2022)