# Three-dimensional femtosecond laser nanolithography of crystals

## TL;DR

This paper introduces a laser-based method for creating precise three-dimensional nanostructures inside large crystals, overcoming previous limitations due to stress and crack formation, enabling advanced photonic applications.

## Contribution

The authors demonstrate a novel laser nanolithography technique that produces 3D nanostructures within crystals without causing fractures, significantly enhancing internal chemical reactivity.

## Key findings

- Achieved >5 orders of magnitude increase in chemical etching reactivity inside crystals.
- Fabricated cm-scale 3D nanostructures with 100 nm features inside large crystals.
- Created photonic structures like diffraction gratings and waveguides capable of sub-wavelength light propagation.

## Abstract

Nanostructuring hard optical crystals has so far been exclusively feasible at their surface, as stress induced crack formation and propagation has rendered high precision volume processes ineffective. We show that the inner chemical etching reactivity of a crystal can be enhanced at the nanoscale by more than five orders of magnitude by means of direct laser writing. The process allows to produce cm-scale arbitrary three-dimensional nanostructures with 100 nm feature sizes inside large crystals in absence of brittle fracture. To showcase the unique potential of the technique, we fabricate photonic structures such as sub-wavelength diffraction gratings and nanostructured optical waveguides capable of sustaining sub-wavelength propagating modes inside yttrium aluminum garnet crystals. This technique could enable the transfer of concepts from nanophotonics to the fields of solid state lasers and crystal optics.

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Source: https://tomesphere.com/paper/1904.08264