This work demonstrates weak-birefringence sensing using periodic nonlinearity (PNL) in a quadrature interferometer, where PNL is utilized as a sensing mechanism rather than treated solely as an error source. A weak birefringence-induced phase perturbation is converted into a measurable change in the PNL amplitude at a dedicated spatial frequency, enabling static retardance sensing without polarization modulation. Experimentally, the measured PNL response exhibited a highly linear region over the 5--60nm retardance range, with R2=0.9999. The observed amplitude fluctuations corresponded to an equivalent retardance standard deviation of approximately 36pm, or about 0.36mrad of phase retardation at 632.8nm. The measured response also revealed distinct effects of quadrature phase offset and gain imbalance, consistent with the predicted deformation of the PNL minimum. These results show that PNL-based phase-to-amplitude transduction provides a simple and sensitive approach for static weak-retardance measurements in quadrature interferometric systems.
Ensuring the safety of high-pressure hydrogen infrastructure requires the precise characterization of hydrogen transport in polymer materials. Conventional differential pressure methods, such as ISO 15105-1, are often limited by complex high-vacuum requirements and prolonged stabilization periods needed to reach a steady-state flux. In this study, we present a three-channel, time-effective and real-time in situ integrated platform that couples high-resolution manometric sensors with a Nelder–Mead simplex nonlinear optimization framework for measurements at atmospheric pressure. Unlike traditional ex situ approaches that characterize transport properties only after decompression, the developed integrated platform enables the continuous monitoring of permeation dynamics under sustained high-pressure exposure, accurately reproducing actual operating conditions. The core innovation lies in the direct extraction of intrinsic transport parameters—permeability (P), diffusivity (D), and solubility (S)—from unsteady-state (transient) pressure responses. By leveraging the initial permeation phase, the system effectively bypasses the need for high-vacuum evacuation and prolonged steady-state stabilization, reducing the total measurement time by more than three-fold compared to conventional protocols. Validation using LDPE and HDPE specimens confirmed that the extracted parameters are intrinsic material properties independent of specimen geometry, with hydrogen uptake strictly adhering to Henry's Law. The system ensures metrological traceability by generating automated evaluation reports with a 0.4 % Figure of Merit (FOM) and an expanded uncertainty for permeability of 9.1 % at a 95 % confidence level. This physics-based transient methodology provides a transformative, high-throughput tool for the accelerated assessment of polymer compatibility in demanding high-pressure hydrogen environments.
The properties of La3Ni2O7, a superconductor near 80 K under pressure, depend sensitively on the oxygen stoichiometry. We report the crystal and electronic structures of polycrystalline La3Ni2O7±δ from the oxygen-deficient La3Ni2O6.5-type phase to an oxygen-excess phase, examined by X-ray diffraction, soft X-ray absorption spectroscopy, and transport. Reduction removes the apical oxygen bridging the bilayer and turns the orthorhombic phase tetragonal; annealing under 5 MPa of oxygen produces a second, distinct tetragonal phase. Upon reduction the Ni valence falls toward Ni2+, the O K-edge pre-peak of the ligand-hole state is strongly suppressed, and the resistivity rises by nearly four orders of magnitude; upon oxidation the valence rises toward Ni3+ and the pre-peak grows as the resistivity decreases. The electronic ground state is thus governed by the ligand-hole density rather than by lattice symmetry or nominal oxygen content, and the pre-peak may serve as a common reference for comparing samples.
Metal halide perovskites are promising solution-processable gain media for amplified spontaneous emission (ASE) and laser applications, yet their performance is often limited by high excitation thresholds and instability under intense optical pumping. Here, we demonstrate that ASE in perovskite thin films can be effectively enhanced through integrated compositional and waveguide control. By systematically tuning the A-site cation composition, we identify how cation composition modulates the gain, loss, and stability landscape of perovskite light amplification. An optimized composition exhibits an approximately 40% reduction in ASE threshold, accompanied by enhanced modal gain, reduced optical loss, and substantially improved photostability under intense operation. Beyond compositional control, we further show that the optical waveguide structure provides an additional route to improve ASE performance even in perovskite films with the same chemical composition. Waveguide-mode analysis reveals that the ASE threshold is governed by the balance between optical confinement and pump-mode overlap, while polymer cladding further improves the guided-mode environment and lowers the threshold. These results establish an integrated design strategy for perovskite gain media, highlighting that compositional optimization and waveguide control should be considered together to realize low threshold and stable thin film light amplification.
