Zhou Wang

Second-harmonic generation (SHG) is a sensitive optical probe of symmetry breaking because the allowed nonlinear susceptibility components are directly constrained by crystal and magnetic symmetry. In magnetic materials, the onset of spin order commonly activates additional SHG channels or redistributes intensity among polarization geometries, often producing an enhanced nonlinear response. Here we demonstrate the opposite phenomenology in the van der Waals antiferromagnet CrOCl: SHG is strongly quenched across the incommensurate and commensurate magnetic transitions. The suppression occurs broadly across polarization angles, in both co- and cross-polarized detection channels, and in all fitted magnetic-dipole tensor elements. By ruling out structural distortion, classical optical effects, and optical-resonance shifts as dominant origins, we assign the anomalous quench to a bulk magnetic-dipole SHG process whose radiative matrix element is reduced by reconstruction of the Cr d-orbital wave function assisted by spin–orbit coupling. This mechanism can be understood as magnetic-order-induced rotation of orbital pseudospin within the even-parity d manifold, revealing a novel route to nonlinear optical control that is distinct from conventional symmetry activation.

The 2D magnet Fe3GaTe2 has received considerable attention for its high Curie temperature (TC), robust intrinsic ferromagnetism, and significant perpendicular magnetic anisotropy (PMA). In this study, the dynamic magnetic properties of Fe3GaTe2 are systematically investigated using an all-optical pump–probe technique. We find that the spin precession frequency (f) is as high as 351.2 GHz at T = 10 K under a field of H = 70 kOe. However, it decreases to 242.8 GHz at 300 K, mainly due to the reduced effective PMA field (Hkeff). The Gilbert damping factor (α) is modest, which increases from 0.039 (10 K) to 0.075 (300 K) owing to the enhanced scattering rate. Interestingly, when Fe3GaTe2 is coupled with 2 nm of Co, the Hkeff, f, and α just decrease slightly, highlighting the dominant influence of Fe3GaTe2. These findings substantially deepen our understanding of Fe3GaTe2, promoting the development of spintronic devices based on advanced 2D magnetic materials.

Birefringence, which modulates the polarization of electromagnetic wave, has been commercially developed and widely used in modern photonics. Fostered by high‐frequency signal processing and communications, feasible birefringence technologies operating in gigahertz (GHz) range are highly desired. Here, a coherent phonon‐induced GHz optical birefringence and its manipulation in SrTiO₃ (STO) crystals are demonsrated. With ultrafast laser pumping, the coherent acoustic phonons with low damping are created in the transducer/STO structures. A series of transducer layers are examined and the optimized one with relatively high photon–phonon conversion efficiency, i.e., semiconducting LaRhO₃ film, is obtained. The most intriguing finding here is that, by virtue of high sensitivity to strain perturbation of STO, GHz optical birefringence can be induced by the coherent acoustic phonons and the birefringent amplitudes possess crystal orientation dependence. Optical manipulation of both coherent phonons and its induced GHz birefringence by double pump technique are also realized. These findings reveal an alternative mechanism of ultrafast optical birefringence control, and offer prospects for applications in high‐frequency acoustic‐optics devices.

The influence of deposition property to the cake filtration process was considered and the deposition factor was introduced to correct cake resistance for dead-end mode at constant transmembrane pressure. The values of model parameters in the traditional and corrected cake resistance expressions were determined for activated sludge, yeast, kaolin suspensions, and humic acid solution, respectively. The higher adsorption and sedimentation ability will make the deposition factor bigger. In addition, the predictions of the corrected cake resistance expression are in good agreement with experimental data at different TMPs and concentrations. The applicability of the corrected cake resistance expression was also validated.