Ultrafast Laser Writing Deep inside Silicon with THz-Repetition-Rate Trains of Pulses
Improved performances for laser writing in bulk Si using ultrafast pulse trains. (a–c) Modification attempts with 4.7 ps (a) single-pulse, (b) double-pulse, and (c) four-pulse irradiations. From top to bottom, the attempts are repeated with identical conditions on each row for different energies: 2.1 μJ, 1.9 μJ, 1.5 μJ, 1.1 μJ, and 0.6 μJ. The dotted circles represent irradiated sites without apparent modification. (d, e) Modifications obtained with 1.8 μJ (d) single-pulse and (e) 4-pulse sequences at the pulse duration of 6.7 ps. (a)–(e) share the same scale bar shown in the corner of (e). (f) Statistics on the apparent area of the modifications (top view) shown in (d) and (e). (g–i) Modifications produced at different depths inside Si. (g) Modification attempts while varying the focusing depth using a z-scan procedure () centered at 300 μm for which spherical aberration is corrected. The experiment is repeated with 1.5 μJ single-pulse (left), double-pulse (center), and four-pulse sequences (right). (h) Illustration of laser writing experiments with 1.9 μJ 4-pulse sequences at distinct planes 100 μm, 300 μm, and 500 μm, respectively. Aberrations are corrected for each plane allowing reliable writing of “LP3” with each letter in a separated plane and next to each other (top image) or stacked (bottom images). Scale bar 50 μm.