Integrated lithium niobate photonics for sub-ångström snapshot spectroscopy

Spectroscopy is a pivotal tool for determining the physical structures and chemical compositions of materials and environments, and it is commonly used across diverse scientific fields^1-16. Conventionally, spectroscopic techniques rely on narrow slits or gratings, which impose a trade-off between spectral resolution and optical transmittance^17-22, thus precluding measurements with simultaneous high sensitivity and high efficiency. Here we introduce RAFAEL, a sub-ångström ultra-high-transmittance snapshot spectroscopic technique, which targets this trade-off with integrated and reconfigurable photonics based on lithium niobate. Its design comprises bulk lithium niobate as an interference mask with a pixel-wise electrically tunable spectral response and delivers picometre-scale modulation with a high optical transmittance. Our approach achieves 88-Hz snapshot spectroscopy with a spectral resolution of approximately 0.5 Å at 400-1,000 nm (R = 12,000), spatial resolution of 2,048 × 2,048 and 73.2% total optical transmittance. Compared with state-of-the-art spectroscopic imagers^23-34, RAFAEL offers double the total transmittance and a nearly two orders of magnitude improvement in spectral resolving power, as verified by extensive experiments. In particular, RAFAEL captured sub-ångström spectra, including all atomic absorption peaks, of up to 5,600 stars in a single snapshot, indicating ×100-10,000 improvement in observational efficiency compared with world-class astronomical spectrometers^17-21. This high-performing yet easily integrated snapshot spectroscopic method could drive advances in fields ranging from material science to astrophysics.