Fabrication Process for Direct Femtosecond Laser Writing of Phase Masks in Polydimethylsiloxane

Femtosecond direct laser writing of phase masks presents a highly versatile and simplified prototyping alternative to conventional lithography. In this work, we demonstrate a process capable of inducing controlled localized phase shifts up to 2π inside bulk polydimethylsiloxane (PDMS), a flexible and biocompatible substrate, using femtosecond pulses at 515 nm by varying line density and number of layers. We validated the process by fabricating several masks such as a cylindrical Fresnel lens, a Dammann diffraction grating, and a Fourier computer-generated hologram.