High-aspect ratio nanochannel formation by single femtosecond laser pulses

Single femtosecond pulsed laser damage can be confined radially to regions smaller than the focus spot size due to the highly nonlinear mechanisms for energy absorption and ablation in transparent dielectrics. Along the propagation axis, however, we show that channels can be machined much deeper than the Rayleigh range of the laser focus. Using focused ion beam cross sections and acetate imprints, we analyze these channels and show that spherical aberration is not the primary source for this elongated damage, which is likely caused by microscale filamentation.