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Publisher: Washington, DC : ACS × Subject: plasmonics ×

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    Mapping Nanoscale Absorption of Femtosecond Laser Pulses Using Plasma Explosion Imaging
    (Washington, DC : ACS, 2014) Hickstein, Daniel D.; Dollar, Franklin; Ellis, Jennifer L.; Schnitzenbaumer, Kyle J.; Keister, K. Ellen; Petrov, George M.; Ding, Chengyuan; Palm, Brett B.; Gaffney, Jim A.; Foord, Mark E.; Libby, Stephen B.; Dukovic, Gordana; Jimenez, Jose L.; Kapteyn, Henry C.; Murnane, Margaret M.; Xiong, Wei
    We make direct observations of localized light absorption in a single nanostructure irradiated by a strong femtosecond laser field, by developing and applying a technique that we refer to as plasma explosion imaging. By imaging the photoion momentum distribution resulting from plasma formation in a laser-irradiated nanostructure, we map the spatial location of the highly localized plasma and thereby image the nanoscale light absorption. Our method probes individual, isolated nanoparticles in vacuum, which allows us to observe how small variations in the composition, shape, and orientation of the nanostructures lead to vastly different light absorption. Here, we study four different nanoparticle samples with overall dimensions of ∼100 nm and find that each sample exhibits distinct light absorption mechanisms despite their similar size. Specifically, we observe subwavelength focusing in single NaCl crystals, symmetric absorption in TiO2 aggregates, surface enhancement in dielectric particles containing a single gold nanoparticle, and interparticle hot spots in dielectric particles containing multiple smaller gold nanoparticles. These observations demonstrate how plasma explosion imaging directly reveals the diverse ways in which nanoparticles respond to strong laser fields, a process that is notoriously challenging to model because of the rapid evolution of materials properties that takes place on the femtosecond time scale as a solid nanostructure is transformed into a dense plasma. (Figure Presented).
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    Photonics and Plasmonics in 4D Ultrafast Electron Microscopy
    (Washington, DC : ACS, 2015) Barwick, Brett; Zewail, Ahmed H.
    Light-matter interactions at the nanoscale are fundamental to the rapidly developing fields of plasmonics and nanophotonics. These fields hold the promise of advancing both the speed of computers along with communications and may also provide methods to create a new generation of ultrasensitive molecular biosensors. While there are a variety of techniques that can provide static images of these devices with suboptical wavelength precision there are only a few that are capable of capturing the ultrafast dynamics of electromagnetic fields interacting with or produced by nanomaterials. In this Perspective, we aim to introduce the reader to the newly developed field of 4D ultrafast electron microscopy (4D UEM), which provides a unique window into ultrafast dynamics at the nanoscale. We will describe the basic technique and how internal structural, bulk electronic, and surface near-field dynamics can all be obtained with nanometer and femtosecond resolutions. In addition, we will discuss how a variety of different ultrafast electron microscopes have been used to map the evolution of photonics-related phenomena. Throughout, we discuss the direction of research that will help advance the understanding of light-matter interactions near the atomic scale in both space and time.