Controlled energy deposition and void-like modification inside transparent solids by two-color tightly focused femtosecond laser pulses.

We report a bulk void-like micromodification of fused silica using two-color lJ-energy level tightly focused (NA = 0.5) co-propagating seeding (visible, 0.62 µm) and heating (near-IR, 1.24 µm) femtosecond laser pulses with online third harmonic diagnostics of created microplasmas as well as subsequent laser-induced void-like defects. It has been shown experimentally and theoretically that production of seeding electrons through multiphoton ionization by visible laser pulses paves the way for controllability of the energy deposition and laser-induced micromodification via carrier heating by delayed infrared laser pulses inside the material. Experimental results demonstrate wide possibilities to increase the density of energy deposited up to 6 kJ cm^-3 inside the dielectric by tight focusing of two color fs-laser pulses and elliptical polarization for infrared heating fs-laser pulses. The developed theoretical approach predicts the enhancement of deposited energy density up to 9 kJ cm^-3 using longer (mid-IR) wavelengths for heating laser pulses. [ABSTRACT FROM AUTHOR]