Near-infrared femtosecond laser machining initiated by ultraviolet multiphoton ionization

We report on the experimental study of microstructures fabricated on the surface of fused silica by two femtosecond laser pulses, a tightly focused 266 nm beam followed by a loosely focused 800 nm beam. By setting the fluence of each pulse below the damage threshold, visible microstructures are fabricated using the combined beams. Our results suggest that the ultraviolet pulse generates seed electrons through multiphoton absorption, and the near-infrared pulse utilizes these electrons to cause damage by avalanche ionization. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794946]