Monitoring Ultrafast Laser Micro-Excitation and Modification Deep inside GaAs

Creating 3D micro/nano-structures inside semiconductors, such as Silicon or GaAs, is a key for numerous advanced applications from microelectronics to integrated photonics, micro-electro-mechanical systems (MEMS) manufacturing. Direct ultrafast laser writing introduces a promising alternative to lithographic methods for this purpose because of its capability with focused infrared beams to precisely induce micro/nano-scale structures. This has already been successfully applied in wide bandgap materials, but recent research indicates more severe difficulties for applications in semiconductors [1] - [3] . The inherent properties of narrow bandgap and large nonlinear refractive index materials lead to strong deteriorations of the ideal laser focusing conditions that prevents to access high space-time energy localization with the shortest pulses [2] . The nonlinear propagation distortions lead to limited fluence delivery and consequently low-quality writing in most cases, or even to the absence of modifications when femtosecond pulses are used. Accordingly, there is a strong motivation to monitor and optimize the conditions inside semiconductors to achieve high-quality 3D fabrication inside semiconductors.