Enhanced Conditions Inside Silicon by Interactions with Tightly Focused Counterpropagating Ultrafast Laser Pulses

The achievement of laser-assisted direct microexplosion inside narrow-bandgap materials such as silicon (Si) could lead to potential applications including direct fabrication of 3D microfluidic channels or the formation of new dense crystallographic phases for the field of microelectronics. This requires extreme temperature-pressure conditions as it has been observed with the use of tightly focused ultrashort pulses in the volume of dielectrics. However, transposing similar conditions is still elusive in semiconductors due to the insufficient energy delivery near the focal volume hindered by strong propagation nonlinearities and prefocal plasma screening. To mitigate these physical limitations, our attempts using solid-immersion [1], and axicon-lens doublet focusing techniques [2], demonstrated the importance of spatial optimizations to cross the modification threshold and write ultra-high-aspect-ratio optical channels in Si, respectively. Thereby, a precise spatial control of the energy delivery within the material is expected to be essential to enhance excitation conditions up to the microexplosion regime.