Fabrication of diffractive microlens array by femtosecond laser-assisted etching process

The study presents the fabrication of diffractive microlens array on glass substrate by using the femtosecond laser (FS-laser) and chemical etching process. Here, the laser is based on an all-in-one FS-laser system with the central wavelength of 517 +/- 2.5 nm for fabricating the embedded grating structures inside glass substrate. The laser beam focused distance between the surface and sample is 25 mu m. The repetition rate and pulse duration of FS-laser are 100 kHz and 350 fs, respectively. The attenuated laser beam is directly into objective lens (20x) with the numerical apertures (NA = 0.4). Hence, the microstructures can be patterned by the routes of X-Y motion stage. The glass sample is then be etched by hydrofluoric acid (HF) in an ultrasonic bath to use for the 15 min for developing structures. Finally, the results show a successful process for forming the microlens array of the diffractive patterns, in which two types of cross and octagon are obtained from the single and double diffraction, respectively. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.