Femtosecond laser micro/nano processing: from fundamentals to emerging applications

The ultrafast laser pulses in the femtosecond (fs) time regime are endowed with super-high peak intensities, allowing the fs laser-matter interactions on timescales shorter than lattice disorder and heat diffusion processes (electron-phonon coupling). These unique qualities provide fs laser-powered processing/fabrication technologies with the precise control and manipulation of material states on a micro-nanoscale level, enabling the creation of novel nanostructures with special optical features and freeform manufacture of three-dimensional (3D) micro/nano functional devices in one-step and maskless fashion that no other methods can achieve.

Published in the International Journal of Extreme Manufacturing, Prof. Min Gu’s team from the University of Shanghai for Science and Technology comprehensively introduced femtosecond laser based processing technology, one of the most powerful and versatile fabrication methods in advanced manufacturing. With the ability to process a wide range of materials and enable hybrid functionalities across disciplines, this technology holds vast research potential.

This review, with a comprehensive focus on several topics, offers readers a platform for a general understanding of fs laser processing technology. Specifically, it zooms in on some intriguing subjects, including fs laser processing in transparent materials, pulse shaping and high throughput strategies, heterogeneous integration, and 4D printing. It also presents 3D micro functional devices and structures manufactured by this technique, along with cross-disciplinary applications, especially in artificial intelligence (AI) empowered nanophotonics. In the final section, the review summarizes the current challenges surrounding fs laser based fabrication technology and provides future perspectives for further improvements.

The uniqueness of the irradiation process of a material from an ultra-short pulse laser (i.e., fs laser) is the generation of a state of intense thermal, electronic, mechanical, and phase non-equilibrium, triggering a series of structural transformations that lead to complex multiscale surface morphologies. “Understanding how fs laser pulses interact with matter and the associated unique physical modifications and chemical reactions that can only be induced by fs laser pulses is fundamental to unlocking their broader potential,” the researchers explained. These mechanisms underpin many of the most promising directions in laser based material processing.

With this foundation, fs laser based 2D/3D printing has been successfully demonstrated in various transparent materials, including glass, polymer, diamond, sapphire, crystals, and other non-solid materials in gel or liquid form.

However, to meet the growing demand for high-speed and large-area manufacturing, pulse-shaping and high-efficiency/high-throughput strategies are essential. “The original pulses from the fs-laser powered direct laser writing (DLW) method may not be sufficient to meet fabrication demands in certain scenarios. This requires pulses shaping techniques in both temporal and spatial domains to increase fabrication efficiency,” the researchers noted, “Multiple strategies have been employed to massively augment the throughput of traditional point-by-point scanning fs-laser based DLW method, including adjustments of laser source and optical processing system, pulse shaping and incorporation of multi-foci fabrication fashion and development of ultra-sensitive materials.”

Further advances include 4D micro-nano printing of smart materials and superresolution lithography. Heterogeneous integration is another novel domain, where fs laser based processing technology can showcase significant potential thanks to its capability of generating heterogeneously integrated 2D/3D photonic structures from different materials. 3D functional micro-devices produced by subtractive, additive, under-formative, or hybrid approaches are also gaining traction in fields such as optics, electronics engineering, optoelectronics, biomedical, biochemistry, lab-on-chip, sensing, and newly emerged AI photonics, demonstrating broad potential in cross-disciplinary applications.

Despite significant progress, several challenges continue to limit further development of fs laser based processing technology. These include an incomplete understanding of fs-laser-matter interactions and some unique phenomena, undesired thermal effects in high-quality nanoscale fabrication, commercial non-readiness and industrial immaturity of the fabrication system, and challenges in further enhancing fabrication resolution. “Fabrication with sub-10 nm feature size and resolution is a highly desirable quality and is much needed for nanophotonics study,” said Dr. Le Gao, first author of the review, “but it remains a daunting task for current fs laser processing technology.”

To overcome the aforementioned challenges and improve fs laser processing technology, the researchers propose several key directions, including further improvement of the fs-based fabrication system, developing hybrid processing procedures revolving around the physical/chemical features of the to-be-processed materials, gaining deeper insight into laser-material interaction mechanism, innovating new and hybrid materials, and expanding applications into more cross-disciplinary fields.

Newly emerged AI-enabled photonics study has been a hot and intriguing research domain for the last few years. Researchers in physics around the world have just begun to realize the potential and power of AI, with “AI+” mode of study in photonics opening up novel and exciting applications and solving issues that traditional physics approaches cannot tackle. Both categories of physics and chemistry from the 2024 Nobel Prize went to AI-related studies, further highlighting the significance and wide impact of AI in the cross-disciplinary field of research.

“Entering the big data and AI-dominated era, AI technology is revolutionizing physics in a way that no one has fathomed before. Many of the most significant and high-impact upcoming accomplishments in photonics study will be involved with AI in one way or another,” said Professor Min Gu. “The future of fs processing technology as a powerful aid will also be heavily invested in AI-powered cross-disciplinary research domains and applications.”

About IJEM:

International Journal of Extreme Manufacturing (IF: 16.1, consecutive 1st in the Engineering, Manufacturing category) is a multidisciplinary and double-anonymous peer-reviewed journal uniquely publishing original articles and reviews of the highest quality and impact in the areas related to extreme manufacturing, ranging from fundamentals to process, measurement, and systems, as well as materials, structures, and devices with extreme functionalities.

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