Auto-focusing femtosecond laser manufacturing system via acoustic emission technology.

Auto-focusing technology in ultrafast laser processing, especially for non-planar structures, holds paramount importance. The existing methodologies predominantly rely on optical mechanisms, thereby being limited by the original system and material reflectivity. This work proposes an approach that utilizes laser-induced sound as a feedback signal for system control, thereby circumventing the need for optical system adjustments and facilitating almost real-time tracking. We established an ultrafast laser processing system augmented by acoustic emission technology, allowing for focus tracking on inclined planes. This system also exhibits the capability to generate diverse microscopic morphologies, including grooves and differently oriented laser-induced periodic surface structures (LIPSS), through the manipulation of the acoustic signal threshold. This method can be easily integrated into existing laser processing systems, offering new capabilities for curved surface processing, microstructure manufacturing, and transparent material processing.

Calcium isotope constraints on the end-Permian mass extinction.

The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (delta(13)C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (delta(44/40)Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report delta(44/40)Ca across the Permian-Triassic boundary from marine limestone in south China. The delta(44/40)Ca exhibits a transient negative excursion of approximately 0.3 per thousand over a few hundred thousand years or less, which we interpret to reflect a change in the global delta(44/40)Ca composition of seawater. CO(2)-driven ocean acidification best explains the coincidence of the delta(44/40)Ca excursion with negative excursions in the delta(13)C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average delta(13)C of CO(2) released was heavier than -28 per thousand and more likely near -15 per thousand; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction.

Large perturbations of the carbon cycle during recovery from the end-permian extinction.

High-resolution carbon isotope measurements of multiple stratigraphic sections in south China demonstrate that the pronounced carbon isotopic excursion at the Permian-Triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the Early Triassic before ending abruptly early in the Middle Triassic. The unusual behavior of the carbon cycle coincides with the delayed recovery from end-Permian extinction recorded by fossils, suggesting a direct relationship between Earth system function and biological rediversification in the aftermath of Earth's most devastating mass extinction.