  It is well known that when the fused silica is irradiated with focused
femtosecond laser beams, space selective chemical etching can be achieved. The
etching rate depends sensitively on the polarization of the laser.
Surprisingly, we observe that by chirping the Fourier-transform-limited
femtosecond laser pulses to picosecond pulses, the polarization dependence of
the etching rate disappears, whereas an efficient etching rate can still be
maintained. Observation with a scanning electron microscope reveals that the
chirped pulses can induce interconnected nanocracks in the irradiated areas
which facilitates efficient introduction of the etchant into the microchannel.
The reported technology is of great use for fabrication of three-dimensional
(3D) microfluidic systems and glass-based 3D printing.
