Ultra-High Space-Time Localization of Laser Energy for 3D Fabrication Inside Semiconductors

3D fabrication of semiconductor devices is important for numerous advanced applications from integrated microelectronics/photonics to micro-electro-mechanical systems (MEMS). Direct laser writing creates a promising alternative to lithographic methods which can require tedious steps. This relies on the possibility to penetrate inside the materials with ultrashort laser pulses in the infrared region of the spectrum to precisely induce micro/nano-scale structures. However, recent research [1]–[3] shows severe difficulties specific to semiconductors. The narrow bandgaps and large nonlinear refractive indices cause strong limitations on the achievable focusing conditions, which in conjunction with important nonlinear propagation effects prevents the high space-time energy localization required for precise and controllable fabrications [3]. Accordingly, there is a strong motivation to monitor and optimize the applied laser conditions inside semiconductors to achieve high-quality 3D fabrication.