3D laser microfabrication inside narrow gap solids like silicon will require the use of long wavelength intense pulses. This experimental study concentrates on the specificity of the nonlinear ionization physics with tightly focused femtosecond laser beams over a wavelength range of 1300-2200 nm. The measured nonlinear absorption is independent of the wavelength in dielectrics revealing the increased importance of tunnel ionization with long wavelength. This can open up an alternative to pulse shortening toward ultraprecision optical breakdown in dielectrics. Using n-doped silicon, we study the multiphoton-avalanche absorption yields and thresholds inside semiconductors. Also observations of the irradiated materials reveal that the intrinsic properties of semiconductors prevent efficient direct energy deposition in the bulk for applications. This work illustrates opportunities for 3D laser micromachining in dielectrics and challenges for its extension to semiconductors.
