Hao Bian

Maskless fabrication of concave microlens arrays on silica glasses by a femtosecond-laser-enhanced local wet etching method

A simple and efficient technique for large-area manufacturing of concave microlens arrays (MLAs) on silica glasses with femtosecond (fs)-laser-enhanced chemical wet etching is demonstrated. By means of fs laser in situ irradiations followed by the hydrofluoric acid etching process, large area close-packed rectangular and hexagonal concave MLAs with diameters less than a hundred of micrometers are fabricated within a few hours. The fabricated MLAs exhibit excellent surface quality and uniformity. In contrast to the classic thermal reflow process, the presented technique is a maskless process and allows the flexible control of the size, shape and the packing pattern of the MLAs by adjusting the parameters such as the pulse energy, the number of shots and etching time.

Rapid Fabrication of Large-Area Concave Microlens Arrays on PDMS by a Femtosecond Laser

A fast and single-step process is developed for the fabrication of low-cost, high-quality, and large-area concave microlens arrays (MLAs) by the high-speed line-scanning of femtosecond laser pulses. Each concave microlens can be generated by a single laser pulse, and over 2.78 million microlenses were fabricated on a 2 × 2 cm(2) polydimethylsiloxane (PDMS) sheet within 50 min, which greatly enhances the processing efficiency compared to the classical laser direct writing method. The mechanical pressure induced by the expansion of the laser-induced plasmas as well as a long resolidifing time is the reason for the formation of smooth concave spherical microstructures. We show that uniform microlenses with different diameters and depths can be controlled by adjusting the power of laser pulses. Their high-quality optical performance is also demonstrated in this work.

Bioinspired transparent underwater superoleophobic and anti-oil surfaces

Reported here is a bioinspired fabrication of transparent underwater superoleophobic and anti-oil surfaces using a femtosecond laser treatment. Rough nanoscale structures were readily created on silica glass surfaces by femtosecond laser-induced ablation. Underwater superoleophobicity and ultralow oil-adhesion were obtained by the rough nanostructures with a wide variation of processing parameters, and the as-prepared surfaces exhibited a high transparency in water. This phenomenon is attributed to the presence of the water environment because scattering and refraction are effectively weakened. As a maskless and cost-effective method, the femtosecond laser processing of transparent materials (glass) may provide a new method to create biomimetic transparent underwater surfaces, allowing for the development of novel underwater anti-oil optical devices.

Fabrication of large-area concave microlens array on silicon by femtosecond laser micromachining

In this Letter, a novel fabrication of large-area concave microlens array (MLA) on silicon is demonstrated by combination of high-speed laser scanning, which would result in single femtosecond laser pulse ablation on surface of silicon, and subsequent wet etching. Microscale concave microlenses with tunable dimensions and accessional aspherical profile are readily obtained on the 1  cm × 1  cm silicon film, which are useful as optical elements for infrared (IR) applications. The aperture diameter and height of the microlens were characterized and the results reveal that they are both proportional to the laser scanning speed. Moreover, the optical property of high-performance silicon MLAs as a reflective homogenizer was investigated for the visible wavelength, and it can be easily extended to IR light.

Fabrication of three-dimensional helical microchannels with arbitrary length and uniform diameter inside fused silica.

We demonstrate an improved femtosecond laser irradiation followed by chemical etching process to create complex three-dimensional (3D) microchannels with arbitrary length and uniform diameter inside fused silica. A segmented chemical etching method of introducing extra access ports and a secondary power compensation is presented, which enables the fabrication of uniform 3D helical microchannels with length of 1.140 cm and aspect-ratio of 522. Based on this method, a micromixer which consists of a long helical microchannel and a y-tape microchannel was created inside the fused silica. We measured the mixing properties of the micromixer by injecting the phenolphthalein and NaOH solution through the two inlets of the y-tape microchannel. A rapid and efficient mixing was achieved in the 3D micromixer at a low Reynolds number.

Direct fabrication of seamless roller molds with gapless and shaped-controlled concave microlens arrays

This Letter demonstrates the direct fabrication of gapless concave microlenses on glass cylinders, which can be used as seamless roller molds for the continuous imprinting of large-area microlens arrays. The method involves femtosecond laser exposures followed by a chemical wet-etching process. A honeycomb-like concave microlens array was fabricated on a glass cylinder with a diameter of 3 mm. We demonstrated the flexibility of the method in tuning the shape and depth of the concave structures by the arrangements of the laser exposure spots and laser powers, and examined the replicating ability of the roller mold by the polymer castling method.

Facile fabrication of true three-dimensional microcoils inside fused silica by a femtosecond laser

This paper presents a facile method for the fabrication of on-chip three-dimensional (3D) microcoils inside fused silica. The main fabrication process involves two steps: (1) creating 3D helical microchannels inside fused silica using an improved femtosecond laser irradiation assisted by chemical etching (FLICE) technology and (2) conductive treatment by injecting metal gallium into the helical microchannels. The high aspect ratio 3D helical microcoil was prepared inside fused silica with a diameter of 100 μm, a length of 880 μm and a pitch of coil of 44 μm. The method is flexible to fabricate microcoils inside fused silica with arbitrary geometry configurations and different coil properties. This type of microcoils can be easily integrated into ‘lab on a chip’ (LOC) platform inside fused silica substrate. (Some figures may appear in colour only in the online journal)

Bioinspired superhydrophobic surfaces with directional Adhesion

Butterfly wings have the ability to directionally control the movement of water microdroplets. However, the realization of artificial directional sliding biosurfaces has remained challenging. Inspired by butterfly wings, a new kind of directional patterned surface is developed to achieve superhydrophobicity and anisotropic adhesive properties at the one-dimensional level. The surface is composed of a hydrophobic triangle array and surrounding superhydrophobic structure. On the as-prepared surface, a droplet rolls along one direction distinctly easier than its opposite direction. The maximum anisotropy of sliding angles along two opposite directions can reach 21°. This unique ability is ascribed to the direction-dependent arrangement of the two-dimensional (2D) triangle array patterns. The directional adhesive superhydrophobic surfaces could be potentially applied in novel microfluid-controllable devices and directional easy-cleaning coatings.

Rapid fabrication of a large-area close-packed quasi-periodic microlens array on BK7 glass

Large-area close-packed microlens arrays (MLAs) are highly desirable for structured light and integrated optical applications. However, efficient realization of ultralarge area MLAs with a high fill factor is still technically challenging, especially on glass material. In this Letter we propose a high-efficiency MLA fabrication method using single-pulsed femtosecond laser wet etch and close-packed quasi-periodic concave MLAs consisting of three million units fabricated on silica glass within an hour. The fabricated MLAs are demonstrated to have extreme optical smoothness (∼8.5 nm) by an atomic force microscope. It has also been demonstrated that the profile of the quasi-periodic concave structures could be easily tuned by changing the laser scanning speed or the pulse energy. Additionally, the optical performances of the MLA diffusers were investigated by using sharp focusing, high-resolution imaging, and flat-top illumination.

Ultrafast electron dynamics manipulation of laser induced periodic ripples via a train of shaped pulses

We present the electron dynamics manipulation of laser induced periodic nanoripples on fused silica via a train of shaped femtosecond pulses. The non-linear ionization used for supporting the surface plasmon polaritons (SPPs) is taken into account in the analysis of the ripple dynamics. It is revealed that the ripple periods are closely related to both the pulse-to-pulse separation and the laser fluence. The result is attributed to the ultrafast dynamics manipulation for the SPP dispersion wavelength through the unusual ionization arising via a train of shaped pulses. This study should be helpful for the fundamental understanding of the ripple formation mechanism arising from a train of shaped pulses, used for controlling the ripple features.