Yu Lu

Studying various non-repeatable transient phenomena such as the transfer of photosynthetic energy and protein folding is crucial for gaining in-depth insights into multiple disciplines, while single-shot ultrafast compressed imaging provides a potent method for revealing the ultrafast dynamic process. The principle of this technology involves projecting encoded transient phenomena along a one-dimensional spatial axis onto the focal plane array and reconstructing the transient data via compressed sensing, enabling an extremely high imaging sequence depth at THz frame rates. However, this imaging method relying on single-dimensional spatial-temporal projection (SSP) suffers from severe directional constraints on reconstruction resolution, due to the suppressing of spatial features along non-projection direction. Consequently, this bottleneck seriously restricts the observation of complex transient features, hindering this technology to balance both high sequence depth and ultra-high spatial resolution. In this paper, we propose a multi-dimensional spatial-temporal projection ultrafast compressed imaging technique (MSP), which integrates multi-angle spatial-temporal data projection module into traditional SSP system. By computationally coupling projection images from both systems, MSP effectively restores omnidirectional frequency information, significantly enhancing spatial resolution. Static experiments demonstrate that both the lateral resolution and longitudinal resolution of MSP have reached 813 lp mm ^-1 (620 nm spatial resolution). Using MSP, we have successfully observed the transient process of femtosecond laser-material interaction with sub-micron all-directional accuracy under a 60-frame acquisition in a single-shot. MSP provides a new method for observing complex and changeable transient processes, and shows important potential in promoting the basic research of transient phenomena.

Ultrafast laser-induced micro–nano hierarchical structures show broad applicability in optoelectronics, functional surfaces, and biomedicine. However, precisely controlling their formation through light field manipulation remains a relatively unexplored area. This work demonstrates a rapid drilling strategy on silicon using an emission-programmed, high-repetition-rate femtosecond Bessel beam. This spatiotemporal modulation enables a unique manufacturing synergy that integrates subtractive drilling and thermo-fluidic redistribution by the central lobes with additive nanostructuring by the peripheral lobes, directly fabricating a micro–nano hierarchical structure comprising tapered micro-holes, elevated micropillars, and dense nanocoatings. Meanwhile, areal scanning enables programmable geometry control through line interval adjustment. This approach offers new insights into laser-matter interactions and facilitates applications in infrared photodetection or drag-reduction surfaces.

Single-shot ultrafast compressed imaging (UCI) is an effective tool for studying ultrafast dynamics in physics, chemistry, or material science because of its excellent high frame rate and large frame number. However, the random code (R-code) used in traditional UCI will lead to low-frequency noise covering high-frequency information due to its uneven sampling interval, which is a great challenge in the fidelity of large-frame reconstruction. Here, a high-frequency enhanced compressed active photography (H-CAP) is proposed. By uniformizing the sampling interval of R-code, H-CAP capture the ultrafast process with a random uniform sampling mode. This sampling mode makes the high-frequency sampling energy dominant, which greatly suppresses the low-frequency noise blurring caused by R-code and achieves high-frequency information of image enhanced. The superior dynamic performance and large-frame reconstruction ability of H-CAP are verified by imaging optical self-focusing effect and static object, respectively. We applied H-CAP to the spatial-temporal characterization of double-pulse induced silicon surface ablation dynamics, which is performed within 220 frames in a single-shot of 300 ps. H-CAP provides a high-fidelity imaging method for observing ultrafast unrepeatable dynamic processes with large frames.

Over millions of years of evolution, arthropods have intricately developed and fine-tuned their highly sophisticated compound eye visual systems, serving as a valuable source of inspiration for human emulation and tracking. Femtosecond laser processing technology has attracted attention for its excellent precision, programmable design capabilities, and advanced three-dimensional processing characteristics, especially in the production of artificial bionic compound eye structures, showing unparalleled advantages. This comprehensive review initiates with a succinct introduction to the operational principles of biological compound eyes, providing essential context for the design of biomimetic counterparts. It subsequently offers a concise overview of crucial manufacturing methods for biomimetic compound eye structures. In addition, the application of femtosecond laser technology in the production of biomimetic compound eyes is also briefly introduced. The review concludes by highlighting the current challenges and presenting a forward-looking perspective on the future of this evolving field.

We have theoretically investigated the spatial-temporal dynamics of extraordinary optical transmission (EOT) through a two-slit plasmonic antenna under femtosecond laser dual-beam irradiation. The dynamic interference of the crossed femtosecond laser dual-beam with the transiently excited surface plasmon polariton waves are proposed to characterize the particular spatial-temporal evolutions of EOT. It is revealed that the dynamic EOT can be flexibly switched with tunable symmetry through the respective slit of a two-slit plasmonic antenna by manipulating the phase correlation of the crossed femtosecond laser dual-beam. This is explained as tunable interference dynamics by phase control of surface plasmon polariton waves, allowing the dynamic modulation of EOT at optimized oblique incidences of dual-beams. Furthermore, we have obtained the unobserved traits of symmetry-broken transient spectra of EOT from the respective up- and down-slit of the antenna under crossed femtosecond laser dual-beam irradiation. This study can provide fundamental insights into the ultrafast dynamics of EOT in two-slit plasmonic antennas, which can be helpful to advance a wide range of applications, such as ultrafast plasmonic switch, ultrahigh resolution imaging, the transient amplification of non-linear effects, etc.

The preparation of the wavelength-scale micropores on metallic surfaces is limited by the high opacity of metal. At present, most micropores reported in the literature are more than 20 µm in diameter, which is not only large in size, but renders them inefficient for processing so that it is difficult to meet the needs of some special fields, such as aerospace, biotechnology, and so on. In this paper, the rapid laser fabrications of the wavelength-scale micropores on various metallic surfaces are achieved through femtosecond MHz burst Bessel beam ablation. Taking advantage of the long-depth focal field of the Bessel beam, high-density micropores with a diameter of 1.3 µm and a depth of 10.5 µm are prepared on metal by MHz burst accumulation; in addition, the rapid fabrication of 2000 micropores can be achieved in 1 s. The guidelines and experimental results illustrate that the formations of the wavelength-scale porous structures are the result of the co-action of the laser-induced periodic surface structure (LIPSS) effect and Bessel beam interference. Porous metal can be used to store lubricant and form a lubricating layer on the metallic surface, thus endowing the metal resistance to various liquids’ adhesion. The microporous formation process on metal provides a new physical insight for the rapid preparation of wavelength-scale metallic micropores, and promotes the application of porous metal in the fields of catalysis, gas adsorption, structural templates, and bio-transportation fields.

In recent years, the demand for optical components such as microlenses has been increasing, and various methods have been developed. However, fabrication of submillimeter microlenses with tunable numerical aperture (NA) on hard and brittle materials remains a great challenge using the current methods. In this work, we fabricated a variable NA microlens array with submillimeter size on a silica substrate, using a femtosecond laser-based linear scanning-assisted wet etching method. At the same time, the influence of various processing parameters on the microlens morphology and NA was studied. The NA of the microlenses could be flexibly adjusted in the range of 0.2 to 0.45 by changing the scanning distance of the laser and assisted wet etching. In addition, the imaging and focusing performance tests demonstrated the good optical performance and controllability of the fabricated microlenses. Finally, the optical performance simulation of the prepared microlens array was carried out. The result was consistent with the actual situation, indicating the potential of the submillimeter-scale microlens array prepared by this method for applications in imaging and detection.