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High-sensitivity and high-resolution collaborative determination of birefringence coefficient using weak measurement

arXiv:2504.15571v2 Announce Type: replace-cross Abstract: Precise nanofilm birefringence characterization is essential for high-sensitivity polarization response and strong anti-interference detection in photodetectors. We present a high-sensitivity and high-resolution birefringence coefficient determination system for nm-level membranes based on weak measurement, addressing the sensitivity-resolution trade-off. A tunable bandwidth light source is exploited to achieve simultaneous and complementary measurements of momentum (P-pointer) and intensity (I-pointer), enabling calibration-free operation across various bandwidths, and to realize high-precision phase difference monitoring of the measured membranes. This method maps the birefringence effect to a weak-value amplified signal of spectral shift and light intensity. The optimal resolution, achieved at a spectral width of 6 nm, is $1.12 \times 10^{-8}$ RIU, while the optimal sensitivity is achieved when the light source is a narrow-linewidth coherent laser, reaching 4710 mV/RIU. The linear range of the system covers a broad birefringence coefficient range for crystals, from $10^{-6}$ to 0.1. Furthermore, the auxiliary optical path eliminates substrate interference, achieving a detection limit of birefringence coefficient as low as $10^{-8}$ RIU. This approach, characterized by high precision, high sensitivity, and strong robustness, provides an effective solution for the detection of optical nano-thin membrane parameters.

NOVA: NOise-aware Verbal Confidence CAlibration for Robust Large Language Models in RAG Systems

Accurately assessing model confidence is essential for deploying large language models (LLMs) in mission-critical factual domains. While retrieval-augmented generation (RAG) is widely adopted to improve grounding, confidence calibration in RAG settings remains poorly understood. We conduct a systematic study across four benchmarks, revealing that LLMs exhibit poor calibration performance especially when noisy contexts are retrieved. Specifically, contradictory or irrelevant evidence tends to exacerbate the model's overconfidence issue. To address this, we propose NOVA Rules (NOise-Aware Verbal Confidence CAlibration Rules) to provide a principled foundation for resolving overconfidence under noise. We further design NOVA, a noise-aware calibration framework that synthesizes supervision from ~2K HotpotQA examples guided by these rules. By performing supervised fine-tuning (SFT) with this data, NOVA equips models with intrinsic noise awareness without relying on stronger teacher models. Empirical results show that NOVA yields substantial gains, improving ECE scores by 10.9% in-domain and 8.0% out-of-domain. By bridging the gap between retrieval noise and verbal calibration, NOVA paves the way for both accurate and epistemically reliable LLMs.