arXiv subjects

Daomu Zhao

Publications and source records attributed to Daomu Zhao.

4 recordsLinked to original sources

arXiv2024

Triad of Equivalence Theorems for the Radiant Intensity of Partially Coherent Beams on Scattering

By using Laplace's method for double integrals and the so-called beam condition obeyed by a partially coherent beamlike light field, we report the equivalence theory (ET) of partially coherent beams on scattering for the first time. We present the necessary and sufficient condition for the two scattered fields that have the same normalized radiant intensity distribution when Gaussian Schell-model beams whose effective beam widths are much greater than the effective transverse spectral coherence lengths are scattered by Gaussian Schell-model media. We find that the condition contain three implications, and each of them corresponds to a statement of an ET of radiant intensity in a scattering scenario, which exposes the concept of a previously unreported triad of ETs for the radiant intensity of partially coherent beams on scattering. We further find that the existing ET of plane waves on scattering, which only asserts that two scatterers with scattering potentials' correlations whose low-frequency antidiagonal spatial Fourier components are identical, essentially is merely the first member of our triad of ETs, while the other two hidden important members are completely ignored. Our findings are crucial for the inverse scattering problem since they contribute to avoid possible reconstruction errors in realistic situations, where the light field used to illuminate an unknown object is a partially coherent beam rather than an idealized plane wave.

physics.optics↗

arXiv2024

Observation of Moir\'e Plasmonic Skyrmion Clusters

Skyrmions are topological defects belonging to nontrivial homotopy classes in particle theory. Their remarkably stable topology has recently been observed in electromagnetic waves. For the evanescent fields near a surface, this has been realized so far only for elementary optical skyrmions, with a fixed skyrmion number. Here we report, both in theory and experiment, the concept of moir\'e plasmonic skyrmion clusters, where multi-skyrmions are nested to form a large optical skyrmion cluster. By leveraging twistronics engineering of plasmonic nanostructures, we demonstrate both crystallized and quasi-crystallized optical skyrmion lattices, revealing an unprecedented degree of topological control. In a misaligned composite nanostructure, the rapid inverting of optical skyrmion number is achieved, which is explained by a lattice model. This topological change of moir\'eplasmonic skyrmion clusters can serve as a precise beacon of the relative alignment deviation between composite nanostructures.

physics.optics↗

arXiv2023

Arbitrary Engineering of Spatial Caustics with 3D-printed Metasurfaces

Caustics occur in diverse physical systems, spanning the nano-scale in electron microscopy to astronomical-scale in gravitational lensing. As envelopes of rays, optical caustics result in sharp edges or extended networks. Caustics in structured light, characterized by complex-amplitude distributions, have innovated numerous applications including particle manipulation, high-resolution imaging techniques, and optical communication. However, these applications have encountered limitations due to a major challenge in engineering caustic fields with customizable propagation trajectories and in-plane intensity profiles. Here, we introduce the compensation phase via 3D-printed metasurfaces to shape caustic fields with curved trajectories in free space. The in-plane caustic patterns can be preserved or morphed from one structure to another during propagation. Large-scale fabrication of these metasurfaces is enabled by the fast-prototyping and cost-effective two-photon polymerization lithography. Our optical elements with the ultra-thin profile and sub-millimeter extension offer a compact solution to generating caustic structured light for beam shaping, high-resolution microscopy, and light-matter-interaction studies.

physics.optics↗

arXiv2022

Pixel super-resolution interference pattern sensing via the aliasing effect for laser frequency metrology

The superposition of several optical beams with large mutual angles results in sub-micrometer periodic patterns with a complex intensity, phase and polarization structure. For high-resolution imaging thereof, one often employs optical super-resolution methods such as scanning nano-particle imaging. Here, we report that by using a conventional arrayed image sensor in combination with 2D Fourier analysis, the periodicities of light fields much smaller than the pixel size can be resolved in a simple and compact setup, with a resolution far beyond the Nyquist limit set by the pixel size. We demonstrate the ability to resolve periodicities with spatial frequencies of ~3/$μ$m, 15 times higher than the pixel sampling frequency of 0.188/$μ$m. This is possible by analyzing high-quality Fourier aliases in the first Brillouin zone. In order to obtain the absolute spatial frequencies of the interference patterns, we show that simple rotation of the image sensor is sufficient, which modulates the effective pixel size and allows determination of the original Brillouin zone. Based on this method, we demonstrate wavelength sensing with a resolving power beyond 100,000 without any special equipment

physics.optics↗