Crossing the threshold of ultrafast laser writing in bulk silicon

Margaux Chanal (1) , Vladimir Yu. Fedorov , Maxime Chambonneau (1) , Raphaël Clady (1) , Stelios Tzortzakis , David Grojo (1)

1 LP3 - Laboratoire Lasers, Plasmas et Procédés photoniques

An important challenge in the field of three-dimensional ultrafast laser processing is to achieve permanent modifications in the bulk of silicon and narrow-gap materials. Recent attempts by increasing the energy of infrared ultrashort pulses have simply failed. Here, we establish that it is because focusing with a maximum numerical aperture of about 1.5 with conventional schemes does not allow overcoming strong nonlinear and plasma effects in the pre-focal region. We circumvent this limitation by exploiting solid-immersion focusing, in analogy to techniques applied in advanced microscopy and lithography. By creating the conditions for an interaction with an extreme numerical aperture near 3 in a perfect spherical sample, repeatable femtosecond optical breakdown and controllable refractive index modifications are achieved inside silicon. This opens the door to the direct writing of three-dimensional monolithic devices for silicon photonics. It also provides perspectives for new strong-field physics and warm-dense-matter plasma experiments.

Domaines: Optique [physics.optics]

Margaux Chanal, Vladimir Yu. Fedorov, Maxime Chambonneau, Raphaël Clady, Stelios Tzortzakis, et al.. Crossing the threshold of ultrafast laser writing in bulk silicon. Nature Communications, 2017, 8 (1), ⟨10.1038/s41467-017-00907-8⟩. ⟨hal-01629428⟩