Abstract
In this study, a high-efficiency single-pulsed femtosecond laser assisted with chemical wet etching method has been proposed to obtain large-area concave microlens array (MLA). The quasi-periodic MLA consisting of about two million microlenses with tunable diameter and sag height by adjusting laser scanning speed and etching time is uniformly manufactured on fused silica and sapphire within 30 minutes. Moreover, the fabricated MLA behaves excellent optical focusing and imaging performance, which could be used to sense the change of the liquid refractive index (RI). In addition, it is demonstrated that small period and high RI of MLA could acquire high sensitivity and broad dynamic measurement range, respectively. Furthermore, the theoretical diffraction efficiency is calculated by the finite domain time difference (FDTD) method, which is in good agreement with the experimental results.
Highlights
Monitoring refractive index (RI) of liquid is critical in the field of optofluidics, medical, chemical, industrial and environmental applications[1,2]
The uniform microlens array (MLA) has been employed to sense liquid RI based on optical diffraction, which is confirmed by the finite difference time domain (FDTD) method
We have developed a high-efficiency method to fabricate large area concave MLA by femtosecond laser assisted with chemical wet etching
Summary
Monitoring refractive index (RI) of liquid is critical in the field of optofluidics, medical, chemical, industrial and environmental applications[1,2]. A high speed scanning approach to fabricate large-area high quality concave MLA by chemical-etching-assisted femtosecond laser irradiation is proposed. In order to obtain bright focusing and clear imaging of MLA, the diameter, sag height, focal length, numerical aperture and period could be properly controlled by laser scanning speed and etching time. This indicates that the high speed scanning method is able to manufacture smooth and uniform microstructures. The diameter and sag height are apparently enlarged with the increase of etching time
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