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Laser has been demonstrated to be a mature and versatile tool that presents great flexibility and applicability for the precision engineering of a wide range of materials over other established micromachining techniques. Past decades have witnessed its rapid development and extensive applications ranging from scientific researches to industrial manufacturing. Transparent hard materials remain several major technical challenges for conventional laser processing techniques due to their high hardness, great brittleness, and low optical absorption. A variety of hybrid laser processing technologies, such as laser-induced plasma-assisted ablation, laser-induced backside wet etching, and etching assisted laser micromachining, have been developed to overcome these barriers by introducing additional medium assistance or combining different process steps. This article reviews the basic principles and characteristics of these hybrid technologies. How these technologies are used to precisely process transparent hard materials and their recent advancements are introduced. These hybrid technologies show remarkable benefits in terms of efficiency, accuracy, and quality for the fabrication of microstructures and functional devices on the surface of or inside the transparent hard substrates, thus enabling widespread applications in the fields of microelectronics, bio-medicine, photonics, and microfluidics. A summary and outlook of the hybrid laser technologies are also highlighted.Schematic of the dynamic process of the laser-induced plasma assisted ablation. The process consists of laser heating, plasma generation, absorption enhancement and material removal.

Surface‐enhanced Raman scattering (SERS) spectroscopy provides a noninvasive and highly sensitive route for fingerprint and label‐free detection of a wide range of molecules. Recently, flexible SERS has attracted increasingly tremendous research interest due to its unique advantages compared to rigid substrate‐based SERS. Here, the latest advances in flexible substrate‐based SERS diagnostic devices are investigated in‐depth. First, the intriguing prospect of point‐of‐care diagnostics is briefly described, followed by an introduction to the cutting‐edge SERS technique. Then, the focus is moved from conventional rigid substrate‐based SERS to the emerging flexible SERS technique. The main part of this report highlights the recent three categories of flexible SERS substrates, including actively tunable SERS, swab‐sampling strategy, and the in situ SERS detection approach. Furthermore, other promising means of flexible SERS are also introduced. The flexible SERS substrates with low‐cost, batch‐fabrication, and easy‐to‐operate characteristics can be integrated into portable Raman spectroscopes for point‐of‐care diagnostics, which are conceivable to penetrate global markets and households as next‐generation wearable sensors in the near future. Flexible surface‐enhanced Raman scattering (SERS) sensors have attracted great research attention owing to their distinct superiorities that the traditional rigid SERS substrates are not accessible to. Recent innovative strategies in developing flexible SERS sensors based on actively tunable plasmonic resonance, swab‐sampling route, and the in situ detection approach are highlighted, which affords unprecedented opportunities to realize point‐of‐care diagnostics in diverse applications.

Holography, with the capability of recording and reconstructing wavefronts of light, has emerged as an ideal approach for future deep-immersive naked-eye display. However, the shortcomings (e.g., small field of view, twin imaging, multiple or-ders of diffraction) of traditional dynamic holographic devices bring many challenges to their practical applications. Metasurfaces, planar artificial materials composed of subwavelength unit cells, have shown great potential in light field manipulation, which is useful for overcoming these drawbacks. Here, we review recent progress in the field of dynamic metasurface holography, from realization methods to design strategies, mainly including typical research works on dy-namic meta-holography based on tunable metasurfaces and multiplexed metasurfaces. Emerging applications of dynam-ic meta-holography have been found in 3D display, optical storage, optical encryption, and optical information pro-cessing, which may accelerate the development of light field manipulation and micro/nanofabrication with higher dimen-sions. A number of potential applications and possible development paths are also discussed at the end.

Optical microsphere nanoscope has great potential in the inspection of integrated circuit chips for semiconductor industry and morphological characterization in biology due to its superior resolving power and label-free characteristics. However, its resolution in ambient air is restricted by the magnification and numerical aperture (NA) of microsphere. High magnification objective lens is required to be coupled with microsphere for nano-imaging beyond the diffraction limit. To overcome these challenges, in this work, high refractive index hyper-hemi-microspheres with tunable magnification up to 10× are proposed and realized by accurately tailoring their thickness with focused ion beam (FIB) milling. The effective refractive index is put forward to guide the design of hyper-hemi-microspheres. Experiments demonstrate that the imaging resolution and contrast of a hyper-hemi-microsphere with a higher magnification and larger NA excel those of a microsphere in air. Besides, the hyper-hemi-microsphere could resolve ~50 nm feature with higher image fidelity and contrast compared with liquid immersed high refractive index microspheres. With a hyper-hemi-microsphere composed microscale compound lens configuration, sub-50 nm optical imaging in ambient air is realized by only coupling with a 10× objective lens (NA = 0.3), which enhances a conventional microscope imaging power about an order of magnitude. The hyper-hemi-microsphere fabricated by FIB milling can resolve ~50 nm feature by only coupling with a 10× objective lens (NA = 0.3) in virtual imaging mode.

Metasurfaces, two-dimensional equivalents of metamaterials, are engineered surfaces consisting of deep subwavelength features that have full control of the electromagnetic waves. Metasurfaces are not only being applied to the current devices throughout the electromagnetic spectrum from microwave to optics but also inspiring many new thrilling applications such as programmable on-demand optics and photonics in future. In order to overcome the limits imposed by passive metasurfaces, extensive researches have been put on utilizing different materials and mechanisms to design active metasurfaces. In this paper, we review the recent progress in tunable and reconfigurable metasurfaces and metadevices through the different active materials deployed together with the different control mechanisms including electrical, thermal, optical, mechanical, and magnetic, and provide the perspective for their future development for applications.

Bioinspired superhydrophobic surfaces have attracted many industrial and academic interests in recent years. Inspired by unique superhydrophobicity and anisotropic friction properties of snake scale surfaces, this study explores the feasibil-ity to produce a bionic superhydrophobic stainless steel surface via laser precision engineering, which allows the realiza-tion of directional superhydrophobicity and dynamic control of its water transportation. Dynamic mechanism of water slid-ing on hierarchical snake scale structures is studied, which is the key to reproduce artificially bioinspired multifunctional materials with great potentials to be used for water harvesting, droplet manipulation, pipeline transportation, and vehicle acceleration.

Mechanical properties of hydrogels are crucial to emerging devices and machines for wearables, robotics and energy harvesters. Various polymer network architectures and interactions have been explored for achieving specific mechanical characteristics, however, extreme mechanical property tuning of single-composition hydrogel material and deployment in integrated devices remain challenging. Here, we introduce a macromolecule conformational shaping strategy that enables mechanical programming of polymorphic hydrogel fiber based devices. Conformation of the single-composition polyelectrolyte macromolecule is controlled to evolve from coiling to extending states via a pH-dependent antisolvent phase separation process. The resulting structured hydrogel microfibers reveal extreme mechanical integrity, including modulus spanning four orders of magnitude, brittleness to ultrastretchability, and plasticity to anelasticity and elasticity. Our approach yields hydrogel microfibers of varied macromolecule conformations that can be built-in layered formats, enabling the translation of extraordinary, realistic hydrogel electronic applications, i.e., large strain (1000%) and ultrafast responsive (~30 ms) fiber sensors in a robotic bird, large deformations (6000%) and antifreezing helical electronic conductors, and large strain (700%) capable Janus springs energy harvesters in wearables. Tuning of mechanical properties of single composition hydrogel materials and application in integrated devices remains challenging. Here, the authors introduce a macromolecule conformational shaping strategy that enables mechanical programming of polymorphic hydrogel fibre-based devices.

Metamaterials open up various exotic means to control electromagnetic waves and among them polarization manipulations with metamaterials have attracted intense attention. As of today, static responses of resonators in metamaterials lead to a narrow-band and single-function operation. Extension of the working frequency relies on multilayer metamaterials or different unit cells, which hinder the development of ultra-compact optical systems. In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO 2 ), with a metasurface. Before the phase transition, VO 2 behaves as a semiconductor and the metasurface operates as a quarter-wave plate at 0.468 THz. After the transition to metal phase, the quarter-wave plate operates at 0.502 THz. At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light. This work reveals the feasibility to realize tunable/active and extremely low-profile polarization manipulation devices in the terahertz regime through the incorporation of such phase-change metasurfaces, enabling novel applications of ultrathin terahertz meta-devices.

Ultrafast lasers have garnered significant interest in the realm of surface nanofabrication. However, their dynamic electric field distribution is influenced by the polarization direction when pursuing high machining precision, which leads to high polarization dependence of laser nanostructuring. Here, polarization-independent surface nanostructuring is realized on Sb 2 S 3 thin films by femtosecond laser irradiation via a microsphere in the far field and ambient air. The formation of nanogrooves is ascribed to surface thermal stress during melting, re-solidification, and super-cooling under high-repetition-rate femtosecond laser irradiation. The influence of materials melting and ablation on the electric field distribution during the laser processing is analyzed. In the molten state, the distribution of the electric field remains unaffected by polarization, enabling the realization of polarization-independent nanoprocessing based on the thermal stress induced by a temperature gradient. The feature sizes of surface nanostructures can be precisely adjusted by varying laser fluence, and the minimum size down to approximately 38 nm (λ/27) is achieved. This innovative laser nanostructuring technique, operating in the far field and ambient air, holds considerable promise for advancing next-generation nanofabrication. Polarization-independent Surface Nanostructuring

A shining example of doping Many technological materials are intentionally 'doped' by the introduction of trace amounts of foreign elements to impart new and useful properties — a classic example is the doping of semiconductors. Feng Wang et al . describe a system in which lanthanide doping can be used to control the growth of NaYF 4 nanocrystals, making it possible to simultaneously tune the size, crystallographic phase and optical properties of the resulting materials. These findings increase our understanding of doping-induced structural transformations, and provide a straightforward route for the controlled synthesis of luminescent nanocrystals for many applications. Many technological materials are intentionally 'doped' with foreign elements to impart new and desirable properties, a classic example being the doping of semiconductors to tune their electronic behaviour. Here lanthanide doping is used to control the growth of nanocrystals, allowing for simultaneous tuning of the size, crystallographic phase and optical properties of the hybrid material. Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase 1 , modifying electronic properties 2 , 3 , 4 , modulating magnetism 5 as well as tuning emission properties 6 , 7 , 8 , 9 . Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF 4 nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion 10 , 11 , 12 emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF 4 upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels 12 to volumetric three-dimensional displays 13 .