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Live imaging of living cells in 3D micro/nano‐environment is important for advanced biological studies. An issue for super‐resolution imaging is refractive index mismatch between the materials used for imaging platform and medium containing cells (water). Fluoropolymer CYTOP is the ideal platform material due to its refractive index close to that of water. Herein, femtosecond laser (220 fs) is exploited to ablate CYTOP at three laser wavelengths of 257, 515, and 1030 nm. Linear power dependences of the ablation rate obtained for all wavelengths indicate that ablation mechanisms of CYTOP are attributed to the production of fragmented CYTOPs (frag‐CYTOPs) inside the film to induce efficient light absorption for subsequent laser pulses. The frag‐CYTOPs can effectively absorb UV–Vis light, whereas those left behind generate green fluorescence. Importantly, the shortest wavelength of 257 nm offers the best ablation quality in terms of surface smoothness and low fluorescence with the highest ablation rate. We elucidate that the refractive‐index matching of CYTOP/water is effective for clear imaging of shapes/fluorescence of cells on 3D structures, e.g., HeLa cells on V‐shaped trenches. The fabrication of a microscopic 3D fluorescence code tag embedded in the CYTOP films is further demonstrated. [ABSTRACT FROM AUTHOR]

We investigate the mechanism of laser-induced plasma-assisted ablation (LIPAA), by which high-quality and high-efficiency ablation of transparent materials, such as glass, can be performed with a single conventional pulsed laser. The laser-induced plasma induces transient absorption of the laser beam (532 nm) by the glass substrate. The origin of the transient absorption is electron excitation by ions with kinetic energy more than approximately 10 eV in the plasma, which is observed by measuring transient polarization change in the glass substrate applied with a high external pulsed electric field during the plasma-assisted electron excitation (plasma-conductivity measurement). A possible mechanism of LIPAA is proposed based on the results obtained. [ABSTRACT FROM AUTHOR]

Ultrafast laser synthesis and processing of materials is a burgeoning field that is still in its infancy. This article and the theme articles in this issue review recent developments in the fundamental physics of ultrafast laser–solid interactions as well as the state of our understanding of ultrafast laser-driven surface morphology, modification of transparent media, 3D photo-polymerization and additive fabrication, spallation of graphene, and biological interactions. Also reviewed is the current state of emerging commercial high average power lasers, central to the widespread adoption of ultrafast laser synthesis and processing of materials. It is remarkable that ultrafast lasers with 20 to 600 femtosecond pulse duration can have such a dramatic impact on materials. As we learn more about the fundamental mechanisms that drive the ultrafast laser-material response, even more applications are anticipated to emerge. This revolutionary approach to materials synthesis and processing has already spawned several commercial technologies and promises to create many more in the near future. [ABSTRACT FROM AUTHOR]

Space-selective metallization of the inside of glass microfluidic structures using femtosecond laser direct-write ablation followed by electroless plating is demonstrated. Femtosecond laser direct writing followed by thermal treatment and successive chemical etching allows us to fabricate three-dimensional microfluidic structures inside photosensitive glass. Then, femtosecond laser ablation followed by electroless metal plating enables flexible deposition of patterned metal films on desired locations of not only the top and bottom walls but also the sidewalls of fabricated microfluidic structures. A volume writing scheme for femtosecond laser irradiation inducing homogeneous ablation on the sidewalls of microfluidic structures is proposed for sidewall metallization. The developed technique is used to fabricate electrofluidics in which microelectric components are integrated into glass microchannels. The fabricated electrofluidics are applied to control the temperature of liquid samples in the microchannels for the enhancement of chemical reactions and to manipulate the movement of biological samples in the microscale space. [ABSTRACT FROM AUTHOR]

A periodic array of nanoholes with high aspect ratios was successfully fabricated by using a multi-scan laser irradiation technique, in which each position in the array is irradiated one time per scan with a femtosecond laser pulse. This technique can easily avoid interference to the laser pulses by micro-bubbles generated in the wet-chemical-assisted ablation process. As a result, we obtained nano-sized ablation holes with an aspect ratio of 1.6, which is much higher than that possible with single pulse ablation. The depth of the ablation craters formed by multi-scan irradiation technique was found to saturate at higher pulse number, presumably due to the limited depth of focus. We also revealed that the ablated depth strongly depends on the refractive index of the medium facing the GaN substrate. In fact, compared to ablation in air followed by HCl etching, the wet-chemical-assisted ablation process enhances the aspect ratio by about 30 % because of the high refractive index of the HCl solution. In addition, by controlling the synchronization of the laser pulses and the motion of the piezo-stage, an almost perfectly periodic arrangement of nanoholes was fabricated on the GaN substrate. The technique developed in this study is likely to make a significant contribution towards realization of two-dimensional photonic crystal structures on GaN-based blue light-emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: For micro/nanofabrication of Gallium nitride (GaN), we developed wet-chemical-assisted femtosecond-laser ablation method. Obtained ablation craters exhibit higher quality and better uniformity without residual debris compared with those produced by femtosecond-laser ablation in air followed by etching. Multi-scan irradiation was performed to fabricate periodic structure composed of high aspect ratio nano-holes using the wet-chemical-assisted ablation method. The aspect ratio is much improved () compared to the case of using single pulse irradiation. This periodic structure of uniform nano-holls arranged on GaN surface can act as a two-dimensional photonic crystal which is expected to enhance a light extraction efficiency of blue LED. [ABSTRACT FROM AUTHOR]

Abstract: We investigated micro- and nano-fabrication of wide band-gap semiconductor gallium nitride (GaN) using a femtosecond (fs) laser. Nanoscale craters were successfully formed by wet-chemical-assisted fs-laser ablation, in which the laser beam is focused onto a single-crystal GaN substrate in a hydrochloric acid (HCl) solution. This allows efficient removal of ablation debris produced by chemical reactions during ablation, resulting in high-quality ablation. However, a two-step processing method involving irradiation by a fs-laser beam in air followed by wet etching, distorts the shape of the crater because of residual debris. The threshold fluence for wet-chemical-assisted fs-laser ablation is lower than that for fs-laser ablation in air, which is advantageous for improving fabrication resolution since it reduces thermal effects. We have fabricated craters as small as 510nm by using a high numerical aperture (NA) objective lens with an NA of 0.73. Furthermore, we have formed three-dimensional hollow microchannels in GaN by fs-laser direct-writing in HCl solution. [Copyright &y& Elsevier]

Vacuum ultraviolet (VUV)–ultraviolet (UV) multiwavelength excitation processing for precision microfabrication of hard materials, in which simultaneous irradiation of the VUV and the UV laser beams leads to high-quality ablation and high-efficiency modification, is reviewed. A coaxial irradiation system of F2 and KrF excimer lasers has been developed. This system achieves well-defined micropatterning of fused silica and GaN with little thermal influence and little debris deposition. Ablation mechanism is explained as absorption of KrF excimer laser by excited-states formed by F2 laser (excited-state absorption: ESA). Additionally, this technique is applied for more efficient refractive index modification of fused silica compared with single-F2 laser irradiation, which is attributed to resonance photoionization-like process based on ESA. The discussion includes characterization of optimum experimental conditions and features of the multiwavelength excitation processing. [Copyright &y& Elsevier]

In this work, we present the possibility of producing multiscale hierarchical micro/nanostructures by the femtosecond laser ablation of transition metals (i.e., Ta and W) in water and investigate their polarization-dependent reflectance. The hierarchical micro/nanostructures are composed of microscale-grooved, mountain-like and pit-rich structures decorated with hybrid laser-induced periodic surface structures (LIPSSs). The hybrid LIPSSs consist of low/high and ultrahigh spatial frequency LIPSSs (LSFLs/HSFLs and UHSFLs). LSFLs/HSFLs of 400–600 nm in a period are typically oriented perpendicular to the direction of the laser polarization, while UHSFLs (widths: 10–20 nm and periods: 30–50 nm) are oriented perpendicular to the curvatures of LSFLs/HSFLs. On the microstructures with height gradients, the orientations of LSFLs/HSFLs are misaligned by 18°. On the ablated W metasurface, two kinds of UHSFLs are observed. UHSFLs become parallel nanowires in the deep troughs of LSFLs/HSFLs but result in being very chaotic in shallow LSFLs, turning into polygonal nanonetworks. In contrast, chaotic USFLs are not found on the ablated Ta metasurfaces. With the help of Fourier transform infrared spectroscopy, it is found that microgrooves show an obvious polarization-dependent reflectance at wavelengths of 15 and 17.5 μm associated with the direction of the groove, and the integration of microstructures with LSFs/HSFLs/UHSFLs is thus beneficial for enhancing the light absorbance and light trapping in the near-to-mid-infrared (NIR-MIR) range. [ABSTRACT FROM AUTHOR]

Abstract: We show that uniform nanoripples can be produced on the sidewalls of the micro-cell vertically embedded in fused silica glass by femtosecond laser direct ablation. The nanoripples can be used for homogeneous liquid crystal (LC) alignment with different azimuthal angles. The azimuthal anchoring energy at the interface between the LC and nanoripples is obtained by measuring the twist angle of LC director in the fabricated twisted nematic LC micro-cell. This method allows for fabrication of LC micro-cells integrated in glass chip with three-dimensional (3D) configurations, opening a new venue to fabrication of 3D miniaturized LC devices. [ABSTRACT FROM AUTHOR]