Crossing the threshold of ultrafast laser writing in bulk silicon. Academic Article uri icon


  • 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.Ultrafast laser processing is a versatile three-dimensional photonic structuring method but it has been limited to wide band gap materials like glasses. Here, Chanal et al. demonstrate direct refractive-index modification in the bulk of silicon by extreme localization of the energy deposition.

published proceedings

  • Nat Commun

altmetric score

  • 19.5

author list (cited authors)

  • Chanal, M., Fedorov, V. Y., Chambonneau, M., Clady, R., Tzortzakis, S., & Grojo, D.

citation count

  • 57

complete list of authors

  • Chanal, Margaux||Fedorov, Vladimir Yu||Chambonneau, Maxime||Clady, RaphaĆ«l||Tzortzakis, Stelios||Grojo, David

publication date

  • October 2017