Fig. 2: Precision 3D writing in silicon using critical plasma seeds.
From: In-chip critical plasma seeds for laser writing of reconfigurable silicon photonics systems
a Infrared microscopy observations of modifications (lateral view) made inside silicon with varying energies by using 200-fs pulses (no modification), 10-ps pulses (non-seeded writing) and double-pulse sequences (seeded writing) composed of a 200-fs pre-pulse of 0.14-µJ energy and a 10-ps pulse (energy indicated below) at a 20-ps delay. The irradiations are performed with 0.85NA focusing conditions at 1550-nm wavelength. The number of applied pulses is 100 for each irradiation. At low energy smaller additional features are produced with the seeded writing configuration. b Volume of the written voxels as a function of the energy for each applied pulse in the double-pulse sequences and comparison of the lateral and longitudinal writing resolutions with and without the use of a femtosecond pre-pulse of 0.14-µJ energy. Plasma seeding with double-pulse irradiation leads to decreased writing thresholds and smaller features. c Demonstration of improved writing performances (digital and line scanning) by critical-plasma seeding. Dots are produced applying 100 pulses. The writing speed for the lines written at different energy levels is 100 μm/s and the repetition rate 1 kHz. d 3D Eiffel tower written below the surface of a silicon wafer with a precision level only accessible by plasma-seeded writing. Observations are made using lateral transmission and top-view dark field infrared microscopy. The structure is designed on the basis of written voxels separated by 2 µm. Each voxel is written using optimum double-pulse irradiations as identified in b. Scale bars are 20 μm.
