# Single-pulse lithography of amorphous photonic architectures inside all-inorganic dielectric crystals

## TL;DR

A new laser-based method allows precise 3D shaping of light-controlling structures inside transparent crystals, improving optical device efficiency.

## Contribution

A single ultrafast laser pulse enables direct 3D lithography of amorphous photonic units in dielectric crystals.

## Key findings

- The technique achieves high-purity amorphization with a regular sheet-like morphology (aspect ratio up to 190:1).
- Nonlinear beam shaping efficiency improves by more than an order of magnitude (~3% second harmonic and ~0.1% third harmonic).
- The method relies on ultrafast laser-driven anisotropic thermal deposition and free electron effects.

## Abstract

High-efficiency light modulation within transparent substrates is critically important for advancing in-chip integrated optical technologies. However, current micro/nanophotonic platforms primarily rely on 2D surface configurations, rendering them inadequate for 3D optical design in dielectric environments. Here, we introduce a precise phase-transition technique that enables the direct lithography of highly regular amorphous units in multiple transparent dielectric crystals (lithium niobates, quartz, yttrium vanadate, etc.). This unit can be rapidly written with a single ultrafast laser pulse, exhibiting a high-purity amorphization phase transition interior structure and a regular sheet-like anisotropic spatial morphology (aspect ratio reaching 190:1). We reveal that this amorphization stems from ultrafast laser-driven anisotropic thermal deposition, achieved through the synergy of the light-induced high-density free electrons and thermal effects. Such embedded units achieve more than an order of magnitude improvement in the efficiency of nonlinear beam shaping (~3% second harmonic and ~0.1% third harmonic) and offer multiple degrees of freedom for device design. This study establishes a versatile platform for on-demand production of all-dielectric micro/nanophotonic architectures in the free space of transparent dielectrics, unlocking new avenues for 3D integrated photonics.

A technique utilizing ultrafast laser-induced anisotropic thermal deposition enables precise amorphous phase transitions, achieving single-pulse 3D lithography of highly regular nonlinear photonic architectures within all-inorganic dielectric crystals.