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Effects of azimuthal angles on laser interference lithographyThis paper discusses the effects of azimuthal angles on two-, three-, and four-beam laser interference. In two- or three-beam laser interference, periodic surface structures of lines or dots were obtained. In fourbeam laser interference with the polarization mode of TE-TM-TE-TM, the modulation in a particular direction was formed and calculated. In the work, a He-Ne laser system was used to simulate two-, three-, and four-beam laser interference, and the interference pattern was detected by a CCD. A high-power Nd:YAG laser interference lithography system was set up to pattern silicon wafers. In the experiments, one azimuthal angle was changed every time to form interference patterns when polarization states were fixed and incident angles were equal. The experimental results have shown that the azimuthal angle affects the periods and feature sizes of the interference patterns and the fabricated surface structures, which are in accordance with the theoretical and computer simulation results.
Fabrication of hierarchical moth-eye structures with durable superhydrophobic property for ultrabroadband visual and mid-infrared applicationsMultifunctional antireflective coatings have practical applications as important optical components in many fields, particularly for optical devices and imaging systems. However, a good antireflection application in the visible region is often unsatisfactory for mid-infrared devices, and the difficulty in obtaining multiple capabilities simultaneously is one of the main factors limiting their applications. In this work, hierarchical moth-eye structures with superhydrophobicity were fabricated via inductively coupled plasma reactive ion etching (ICP-RIE) using nanodisk-array masks, which were formed by three-beam laser interference lithography (LIL), for improving the ultra-broadband optical properties. The uniform antireflection efficiency, which was close to 1% reflectivity covering over the visible and mid-infrared wavelength range, was exhibited by the moth-eye structures with high-quality pillar arrays. Additionally, irregular nanostructures were tailored onto the top of the pillars to generate hierarchical moth-eye structures for simultaneously obtaining both the superhydrophobic and anticorrosive properties. The fabricated antireflective structures, with the features of self-cleaning and durability, have the advantage of being for long-term use in harsh environments.
Linewidth study of pixelated aluminum nanowire gratings on polarization performanceNowadays, nanowire gratings are widely used in various applications such as imaging sensors and high-resolution microscopes. Structure parameters are the main factors that affect the optical performance of the gratings. This work aims to present the influence of the linewidth of pixelated aluminum nanowire gratings with a fixed period on the transmittance and extinction ratio in the visible region. By controlling the exposure doses of electron beam lithography (EBL), different linewidths of pixelated aluminum nanowire gratings with a period of 170 nm were fabricated. The significant effects of linewidth difference on the polarization performance were verified by the simulations of finite-difference time-domain (FDTD) software. The simulations were divided into two parts: the discussion of the pure aluminum without considering oxidation and the discussion of the surface aluminum being oxidized into the aluminum oxide. An optical system was built to evaluate the performance of the fabricated structures. The results show that the trends of the measurement results are consistent with that of simulation. This work will give a guide to the fabrication and evaluation of the nanowire gratings.
Nanoantenna arrays combining enhancement and beam control for fluorescence-based sensing applicationsThis paper presents measured fluorescence enhancement results for ~250 × 250 element aluminum nanoantenna arrays fabricated using electron beam lithography. The arrays have been designed to use diffractive coupling to enhance and control the direction of fluorescent emission. Highly directional emission is obtained at the designed angles with beam widths simulated to be in the range of 4–6°. Angle-resolved spectroscopy measurements of dye-coated nanoantenna arrays were in good agreement with finite difference time domain modeling. Critically, these results were obtained for near UV wavelengths (~360 nm), which is relevant to a number of biosensing applications.