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 μm. 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 (20×) 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 etched by hydrofluoric acid (HF) in an ultrasonic bath for 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.