Abstract
Silica microlens arrays (MLAs) with multiple numerical-apertures (NAs) have high thermal and mechanical stability, and have potential application prospects in 3D display and rapid detection. However, it is still a challenge to rapidly fabricate silica MLAs with a larger range of NAs and how to obtain multiple NAs in the same aperture diameter. Here, a wet etching assisted spatially modulated femtosecond laser pulse fabricating technology is proposed. In this technology, Gaussian laser pulse is modulated in the axial direction to create a pulse with a large aspect ratio, which is used to modify the silica to obtain a longer modification distance than traditional technology. After that, a microlens with a larger NA can be obtained by etching, and the NA variable range can be up to 0.06-0.65, and even under the same aperture, the variable NA can range up to 0.45-0.65. In addition, a single focus is radially modulated into several focus with different axial lengths to achieve a single exposure fabricating of MLA with multiple NAs. In characterization of the image under a microscope, the multi-plane imaging characteristics of the MLA are revealed. The proposed technology offers great potential toward numerous applications, including microfluidic adaptive imaging and biomedical sensing.
Highlights
With the development of society and advancements in science and technology, the requirements for product integration have become more stringent
A femtosecond laser was modulated by the spatial light modulator (SLM), which was loaded with the Bessel computer-generated hologram (CGH) consisting of four Bessel phases with different base angles (BAs) to generate four Bessel laser beams (BLBs) with varying focusing lengths
Zm′ ax, which is the length of the micro-Bessel region corresponding to the BA of 2.5°, was 395 μm according to Eq (4)
Summary
With the development of society and advancements in science and technology, the requirements for product integration have become more stringent. Microlens arrays (MLAs) are widely used in the aerospace industry, optics, microelectronics, communications, and other fields because of their small size, light weight, excellent optical performance, and high level of integration in applications such as bionic compound eye structures [1,2,3], 3D display [4, 5], virtual reality imaging [6], laser field homogenization [7], fiber coupling [8], and enhancement of light output [9]. Many methods are used to fabricate microlens, such as photolithography [10], surface tensionassisted molding [11, 12], ink-jet printing [13], nanoimprinting [14], and dewetting [15].
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