arXiv subjects

Sarah E. Dean

Publications and source records attributed to Sarah E. Dean.

3 recordsLinked to original sources

arXiv2026

Inverse designed metasurfaces for multi-wavelength full-Stokes polarisation imaging

Multispectral full-Stokes polarisation imaging has a broad range of applications, from biological cell imaging to agricultural remote surveying. For such applications, especially involving lightweight unmanned aerial vehicles like drones, it is necessary to have compact, single-shot, efficient optical systems. We present a topology-optimised metasurface design that diffractively separates a scene into spectral and polarimetric measurements, operating for 532 nm and 700 nm in a single-shot imaging system. The polarisation imaging performance of the design is shown in simulation to be robust to critical performance metrics, matching both spectral and angular bandwidth requirements. We fabricated our metasurface design by nanopatterning a TiO$_2$ thin film, and experimentally demonstrate polarisation reconstruction for two wavelengths with a single metasurface structure.

physics.optics↗

arXiv2024

Metasurface-enabled small-satellite polarisation imaging

Polarisation imaging is used to distinguish objects and surface characteristics that are otherwise not visible with black-and-white or colour imaging. Full-Stokes polarisation imaging allows complex image processing like water glint filtering, which is particularly useful for remote Earth observations. The relatively low cost of small-satellites makes their use in remote sensing more accessible. However, their size and weight limitations cannot accommodate the bulky conventional optics needed for full-Stokes polarisation imaging. We present the modelling of an ultra-thin topology-optimised diffractive metasurface that encodes polarisation states in five different diffraction orders. Positioning the metasurface in a telescope's pupil plane allows the diffraction orders to be imaged onto a single detector, resulting in the capability to perform single-shot full-Stokes polarisation imaging of the Earth's surface. The five rectangular image swaths are designed to use the full width of the camera, and then each successive frame can be stitched together as the satellite moves over the Earth's surface, restoring the full field of view achievable with any chosen camera without comprising the on-ground resolution. Each set of four out of the five orders enables the reconstruction of the full polarisation state, and their simultaneous reconstructions allow for error monitoring. The lightweight design and compact footprint of the polarisation imaging optical system achievable with a metasurface is a novel approach to increase the functionality of small satellites while working within their weight and volume constraints.

physics.optics↗

arXiv2024

Metasurface-based Toroidal Lenslet Array Design for Addressing Laser Guide Star Elongation

The Giant Magellan Telescope will use laser tomography adaptive optics to correct for atmospheric turbulence using artificial guide stars created in the sodium layer of the atmosphere (altitude ~95km). The sodium layer has appreciable thickness (~11km) and this results in the laser guide star being an elongated cylinder shape. Wavefront sensing with a Shack-Hartmann is challenging, as subapertures located further away from the laser launch position image an increasingly elongated perspective of the laser guide star. Large detectors can be used to adequately pack and sample the images on the detector, however, this increases readout noise and limits the design space available for the wavefront sensor. To tackle this challenge, we propose an original solution based on nano-engineered meta-optics tailored to produce a spatially varying anamorphic image scale compression. We present meta-lenslet array designs that can deliver ~100% of the full anamorphic image size reduction required for focal lengths down to 8mm, and greater than 50% image size reduction for focal lengths down to 2mm. This will allow greatly improved sampling of the available information across the whole wavefront sensor, while still being a viable design within the limits of current-generation fabrication facilities.

astro-ph.IM↗