Efficient fabrication method for non-periodic microstructures using one-step two-photon lithography and a metal lift-off process

This paper presents a mask-less, flexible, efficient, and high-resolution fabrication method for non-periodic microstructures. Sub-wavelength micro-polarizer arrays, (MPAs) which are the most essential part of the focal plane polarimeters, are typical non-periodic structures. The grating ridges of each polarizer were oriented in four different directions offset by 45°, corresponding to different polarization directions. The finite element method was introduced to optimize the structural parameters of the MPA in the far-infrared region. The numerical results demonstrated that the designed MPA had a TM transmittance of more than 55% and an extinction ratio no less than 7 dB. An aluminum MPA that operates in the 8-14 µm infrared region was prepared by one-step two-photon lithography (TPL) and the metal lift-off process. The femtosecond laser exposed the photoresist with only a single scan, making TPL very efficient. The fabricated single-layer sub-wavelength MPAs with a period of 3 µm, a duty cycle of 0.35-0.5, and a height of 150 nm, were analyzed by an optical microscope and an atomic force microscope. The successful fabrication of the MPA indicated that one-step TPL could be a viable and efficient method for pattern preparation in the fabrication of non-periodic microstructures.