Multi-physics coupled perturbation mode recognition and accuracy preservation technology in the confined space of ultra-precision grating

To satisfy nanometer-level positioning demands in high-end equipment such as advanced lithography machines and ultra-precision machine tools, coupled optical-thermal-fluid disturbances in the interferometric gap of ultra-precision grating displacement sensors have become a key barrier to further reducing measurement uncertainty. In the narrow gap between the grating readhead and the scale, local heat sources, high-speed motion, and the air-bath flow act simultaneously. They induce strong fluctuations in temperature, pressure, and density. As a result, the gas refractive-index field varies in space and time, and the interference fringes are distorted, which ultimately degrades nanometer-level measurement performance. This paper clarifies the formation mechanisms of these multiphysics disturbances and their error-transmission pathways. We review aero-optical effects, multiscale flow models, and coupled optical-thermal-fluid theories and numerical solution methods. We also summarize recent progress in identifying cross-scale disturbance modes. For accuracy preservation, we compare three representative routes. The first is disturbance suppression via global air-bath conditioning and local micro-jet control. The second is immersion-type gratings and refractive-index homogenization within the gap. The third is digital-physical, model-and-data-driven error compensation based on interferometric signal features and multisource information fusion. Based on recent studies from the Xi’an Jiaotong University grating group, we further propose an integrated framework for gap disturbances, namely source suppression-path regulation-output compensation. Finally, we discuss future directions, including high-fidelity multiphysics modeling, digital-twin-enabled online disturbance prediction, multi-technique synergy, and new optical-field modes. These insights provide references for developing engineering-grade ultra-precision grating metrology systems for high-end equipment.