Competing Nonlinear Delocalization of Light for Laser Inscription Inside Silicon with a 2-µm Picosecond Laser

Recent advances in ultrafast laser 3D writing offer direct fabrication of in-chip silicon microsystems, but this technique remains extremely challenging, because of propagation nonlinearities that limit energy localization inside narrow-band-gap materials. This study examines the complex energy flux and subsequent unusual modification of silicon due to intense picosecond pulses from a thulium-doped fiber laser. The best conditions for reliable data inscription deep inside silicon are identified, which is a critical step toward engineering solutions to this problem. Also, the wavelength used here points to facing the next challenges associated with materials of even narrower band gap.