Abstract
Three processes of femtosecond laser machining on different transparent materials are demonstrated in this study. The characteristics of micromachining by femtosecond laser on transparent materials are discussed in three parts: surface treatment, inner modification and modification with etching process. Additionally, the numerical methods are proposed to fit the experimental results of modification with etching process. For the surface treatment, the hydrophobic effect on the surface of flexible and transparent material, poly(ethylene terephthalate) (PET), is studied. A femtosecond laser beam is focused on the surface of PET samples for patterning micro-grating structure with different pitches to increase contact angles. The study provides a novel and effective way to control the wettability of surfaces. For the inner modification, a diffraction grating inside a flexible polydimethylsiloxane (PDMS) fabricated by femtosecond laser direct writing is investigated. The laser beam is focused inside the PDMS substrate, and scribes in line structure. An embedded PDMS diffraction grating is successfully demonstrated based on a calculated optical phase shift structure. For the modification with etching process, a new kind of micro-prism structures on glass substrate is fabricated. Different pitches of embedded gratings are fabricated inside glass samples by laser-induced modification firstly. Then, the glass samples are placed in hydrofluoric acid (HF) solution for structure development. The V-cut micro-prisms are formed successfully by controlling etching ratio between intrinsic glass material and laser-modified areas. To improve the process, two and three-dimension structures of microlens array and photonic crystal are fabricated, respectively. For the numerical method on simulating the modification with etching process, a fast approach for calculating the modified volume and shape by considering the relationship between laser fluence and material absorption is proposed. The obtained structure formed by anisotropic etching between modified region and intrinsic material can be simulated for different etching selectivity. The simulated results are agreed well with the experimental results.