Fabricating subwavelength array structures using a near-field photolithographic method

This work presents a photolithographic approach for producing high aspect ratio arrays in photoresist. The photomask is composed of hexagonal/square rod arrays with a thickness of 0.2μm and a period of 600nm. Illuminating the photomask with a blue laser generates periodically focused beams up to 1μm long and less than 300nm wide. A hexagonal rod array provides a better focused beam than a square array due to its higher symmetry. Finite-difference time-domain calculations elucidate the existence of long focused beams above the photomask. Optical near-field measurements verified those subwavelength beams originating from the rod regions.