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Femtosecond laser direct writing is widely exploited in surface periodic structures processing. However, this technique still faces challenges in obtaining high surface homogeneity and flexible morphology controllability. In this study, a flexible and efficient approach has been proposed to fabricate highly homogeneous and controllable nanogratings on silicon via chemical etching-assisted femtosecond laser modification. By precisely manipulating the laser-material interaction process, alternating amorphous-crystalline nanofringes are generated when employing femtosecond laser scanning over a Si sample, with almost no material removal. Following auxiliary chemical etching, highly homogeneous nanograting structures are obtained, and the morphology of the nanogratings can be flexibly managed through precisely controlling the duration of the etching process. Complex cross-scale patterns with remarkable structural colors that are visible under indoor light illumination are readily achieved on the sample surfaces exploiting our method. In addition, compared with traditional methods for laser-induced periodic surface structures, the fabrication efficiency is considerably improved. Our processing procedure offers potential applications in the fields of optics, nanoelectronics, and mechatronics.

Periodic surface structures are core components for controlling the dispersion and steering characteristics of light. Here, a mask‐free approach using nonablative femtosecond laser processing is proposed and demonstrated to fabricate extremely long‐range uniform periodic surface structures on silicon with tunable diffraction efficiency. First, a cylindrically focused femtosecond laser scans over silicon substrates to efficiently produce large‐area periodic modified stripes in a nonablation regime. Second, the modified stripes act as fine etch stops to generate the desired structures on sample surfaces during the subsequent chemical etching process. The structures produced by the method achieve optimal long‐range uniformity compared to the reported laser‐induced periodic surface structures, which possess a minimum divergence of structure orientation angles of <5°. In addition, the optical characteristics of the prepared structures are measured experimentally. Distinguishable polychromatic diffraction patterns can be clearly observed by broadband light irradiation. Significantly, the chemical etching process endues the structures with ingenious morphology controllability, so that the diffraction efficiency of the incident light can be flexibly tuned, which exhibits a near‐linear function of the etching duration. Such morphology‐controllable periodic surface structures may facilitate applications in broad fields, such as optical communications and optical sensors.

Previous studies have shown that thermal infrared radiation (TIR) changes with stress for loaded rocks. TIR changes were mainly attributed to temperature change without considering the change in surface emissivity. And it remains unclear whether there was a change in emissivity during the rock loading process. Therefore, based on the spectral radiance observations in this paper, an experimental study involving the emissivity variation in the 8.0-13.0 µm range for elastic loaded quartz sandstone under outdoor conditions was conducted. The experiments yield the following results. First, a variation in the stress condition led to the emissivity change in addition to the temperature change. The spectral radiance change was the combined result of the temperature changes and emissivity changes. Second, the emissivity changes linearly with the stress change, and the amplitude is relatively large in the 8.0-10.0 µm range. The waveband features of emissivity variation are the main factor leading to the waveband features of stress-induced radiance change. Third, the explanations for the changes in temperature and emissivity during loading process are analyzed. And the significance and difficulty for further satellite remote sensing purpose is discussed. The experimental results provide an experimental foundation for crustal stress field monitoring.

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