Sculpturing light pulses spatiotemporally with sophisticated controls of various degrees of freedom is one of the powerful tools for material interrogations and manipulations, as well as information transmission and processing. Even though exotic light fields are part of Maxwell’s solutions or wave equation’s eigenmodes, their presence and richness still surprise us with new or renewed physical insights and understandings. Also, the diversity of the modes and states of such light fields has inspired us to pursue their potential new applications, from information technologies to light-based sensing and imaging. In this talk, I will briefly review the recent progress in spatiotemporal light fields and then focus on our recent experimental efforts to generate, manipulate, and characterize such light pulses from strong-field (or high-field) to single photon levels.
Understanding topological spin textures is important because of scientific interests and technological applications. However, observing nanoscale magnetization and mapping out their interactions in 3D have been challenging–due to the lack of nondestructive vector nanoimaging techniques that penetrate thick samples. Recently, we developed a new characterization technique, soft x-ray vector ptycho-tomography, to image spin textures with a 3D vector spatial resolution of 10 nm. Using 3D magnetic metamaterial as an example, we demonstrated the creation and observation of topological magnetic monopoles and their interactions. We expect this method to be applied broadly to image vector fields in magnetic samples and beyond.
Spatiotemporal orbital angular momentum (ST-OAM) of light is an emergent, spatiotemporally sculptured light. Such spatiotemporal optical vortices carry transverse OAM and exhibit novel properties. However, the lack of a simple and straightforward characterization method substantially slows its progress and potential adaptions for future applications. Here we demonstrated a simple, stationary, single-frame method to quantitatively characterize ST-OAM pulses. Our new method can measure the presence of ST-OAM, space-time topological charge numbers, OAM helicity, pulse dispersion, and beam divergence. We also investigated the nonlinear properties of ST-OAM pulses, uncovering the conservation of space-time topological charges in a second-harmonic generation process.
Coherent Fourier scatterometry (CFS) via laser beams with a Gaussian spatial profile is routinely used as an in-line inspection tool to detect defects on, for example, lithographic substrates, masks, reticles, and wafers. New metrology techniques that enable high-throughput, high-sensitivity, and in-line inspection are critically in need for next-generation high-volume manufacturing including those based on extreme ultraviolet (EUV) lithography. Here, a set of novel defect inspection techniques are proposed and investigated numerically [Wang et al., Opt. Express 29, 3342 (2021)], which are based on bright-field CFS using coherent beams that carry orbital angular momentum (OAM). One of our proposed methods, the differential OAM CFS, is particularly unique because it does not require a pre-established database for comparison in the case of regularly patterned structures with reflection symmetry such as 1D and 2D grating structures. We studied the performance of these metrology techniques on both amplitude and phase defects. We demonstrated their superior advantages, which shows up to an order of magnitude higher in signal-to-noise ratio over the conventional Gaussian beam CFS. These metrology techniques will enable higher sensitivity and robustness for in-line nanoscale defect inspection. In general, our concept could benefit EUV and x-ray scatterometry as well.
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