Zefang Deng

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.

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.

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.

A facile method to fabricate close-packed concave microlens array on cylindrical glass

This work presents a facile method to fabricate concave microlens arrays (MLAs) with controllable shape and high fill factor on cylindrical silica glass by a femtosecond laser-enhanced chemical wet etching process. The hexagonal and rectangular MLAs are flexibly fabricated on the silica glass cylinder with a diameter of 3?mm. The morphological characteristics of MLAs are measured by a scanning electron microscope and a laser scanning confocal microscope. The measurements show that the good uniformity and high packing density MLA structures are generated. It has also been demonstrated that the shape and size of the concave structures could be easily tuned by changing laser power and the arrangement of laser exposure spots. The convex MLAs replicated by the polymer casting method experience excellent image quality.

Direct Fabrication of Microlens Arrays on PMMA With Laser-Induced Structural Modification

Reported here is the direct fabrication of the convex microlens arrays on poymethylmethacrylate using laser-induced structural modification. Based on single femtosecond pulse in situ modification, sixty thousand convex microlenses, whose diameters was <;12 μm, could be fabricated per minute, exhibiting much higher efficiency than conventional laser direct writing technique. The formation mechanism was mainly attributed to photodecomposition, which would result in the scission of polymer chains. The shape of microlenses could be tuned by the laser power. In addition, the good optical performance of the microlens was revealed by its ability of high resolution imaging. This technique may open up a new way of preparing low-cost and large-area convex structure which is widely used in many advanced microdevices, such as lab-on-chips and biomimetic compound eyes.

High-Performance Laser Beam Homogenizer Based on Double-Sided Concave Microlens

Microlens array (MLA) has attracted increasing interest as its application in micro-optical device and system. In this letter, we proposed a new approach that applies rotational displacement MLA to the laser homogenization system. These are nonregular arrays consisting of close-packed concave MLAs on two sides with specific rotation angle. And, the double-sided MLAs diffusers with new design parameter were successfully fabricated using single pulse femtosecond laser assisted chemical wet etching. Simulation and experimental results reveal the good homogenization performance of the double-sided MLAs. In addition, we fabricated diffusers with different rotation angles (θ), and when θ = 60°, the diffuser obtains the best optical performance.

Lens-on-lens microstructures.

Microlenses with multiple focal lengths play an important role in three-dimensional imaging and the real-time detection of unconfined or fluctuating targets. In this Letter, we present a novel method of fabricating lens-on-lens microstructures (LLMs) using a two-step femtosecond laser wet etching process. A 3×3 LLM array was made with a diameter of 129.0 μm. The fabricated LLM has two focal lengths, 80.4 and 188.7 μm, showing excellent two-level focusing and imaging abilities. Its size and focal length can be controlled by adjusting laser power and etching time. Its surface roughness remains about 61 nm. This simple and efficient method for large-scale production of LLMs has potential applications in diverse optical systems.

Scalable shape-controlled fabrication of curved microstructures using a femtosecond laser wet-etching process.

Materials with curvilinear surface microstructures are highly desirable for micro-optical and biomedical devices. However, realization of such devices efficiently remains technically challenging. This paper demonstrates a facile and flexible method to fabricate curvilinear microstructures with controllable shapes and dimensions. The method composes of femtosecond laser exposures and chemical etching process with the hydrofluoric acid solutions. By fixed-point and step-in laser irradiations followed by the chemical treatments, concave microstructures with different profiles such as spherical, conical, bell-like and parabola were fabricated on silica glasses. The convex structures were replicated on polymers by the casting replication process. In this work, we used this technique to fabricate high-quality microlens arrays and high-aspect-ratio microwells which can be used in 3D cell culture. This approach offers several advantages such as high-efficient, scalable shape-controllable and easy manipulations.