Ultrafast Laser Filament-Assisted Microstructuring of Polymers

Ultrafast laser filamentation can be used for 3D modification of transparent dielectrics. This phenomenon is based on the dynamic balance between nonlinear self-focusing of a beam in dielectric and plasma defocusing [1]. As a result a beam is propagating without diffracting in form of narrow plasma channel. Strongly localized excitation of dielectric medium along filamentation channel leads to refractive index change or formation of narrow cavity with very high aspect ratio. Those effects were observed in poly(methyl methacrylate) PMMA [2,3] and other polymeric media [4]. This method is often used for diffractive optical elements or waveguide fabrication. Filaments generated in water film above biodegradable polymer surface were applied as a method of micromachining [5]. In the most cases filamentation is obtained by tight focusing of femtosecond laser beam using fixed microscope objectives and/or by converting Gaussian to Bessel intensity profile [6].