# Self-driving lab discovers principles for steering spontaneous emission beyond conventional Fourier optics

## TL;DR

A self-driving lab uses machine learning to discover new ways to control light emission from metasurfaces beyond traditional methods.

## Contribution

The study introduces a self-driving lab platform that discovers new principles for steering spontaneous emission using metasurface refractive index gradients and curvatures.

## Key findings

- Combinations of positive gratings and lenses are as effective as negative ones for emission control.
- The platform achieves up to 77% peak emission directivity within ~300 experiments.
- Both spatial gradient and curvature of refractive index are key for steering spontaneous emission.

## Abstract

We develop an autonomous experimentation platform to accelerate interpretable scientific discovery in ultrafast nanophotonics, targeting a novel method to steer spontaneous emission from reconfigurable semiconductor metasurfaces. Despite the potential of reconfigurable semiconductor metasurfaces with embedded sources for spatiotemporal control, achieving arbitrary far-field control remains challenging. Here, we present a self-driving lab (SDL) platform that addresses this challenge by discovering the governing equations for predicting the far-field emission profile from light-emitting metasurfaces. We discover that both the spatial gradient (grating-like) and the curvature (lens-like) of the local refractive index are key factors in steering spontaneous emission. The SDL employs a machine-learning framework comprising: (1) a variational autoencoder for generating complex spatial refractive index profiles, (2) an active learning agent for guiding experiments with real-time closed-loop feedback, and (3) a neural network-based equation learner to uncover structure-property relationships. The SDL demonstrates up to a four-fold enhancement in peak emission directivity (up to 77%) over a 74° field of view within ~300 experiments. Our findings reveal that combinations of positive gratings and lenses are as effective as negative lenses and gratings for all emission angles, offering a novel strategy for controlling spontaneous emission beyond conventional Fourier optics.

Sandia researchers used machine learning and autonomous experiments to discover new principles for controlling incoherent light emission from metasurfaces. Combining lens and grating elements steers emission more effectively than gratings alone—beyond conventional Fourier optics.