Digital plasmonic holography

Abstract

We demonstrate digital plasmonic holography for direct in-plane imaging with propagating surface-plasmon waves. Imaging with surface plasmons suffers from the lack of simple in-plane lenses and mirrors. Lens-less digital holography techniques, however, rely on digitally decoding an interference pattern between a reference wave and an object wave. With far-field diffractive optics, this decoding scheme provides a full recording, i.e., a hologram, of the amplitude and phase of the object wave, giving three-dimensional information from a two-dimensional recording. For plasmonics, only a one-dimensional recording is needed, and both the phase and amplitude of the propagating plasmons can be extracted for high-resolution in-plane imaging. Here, we demonstrate lens-less, point-source digital plasmonic holography using two methods to record the plasmonic holograms: a dual-probe near-field scanning optical microscope and lithographically defined circular fluorescent screens. The point-source geometry gives in-plane magnification, allowing for high-resolution imaging with relatively lower-resolution microscope objectives. These results pave the way for a new form of in-plane plasmonic imaging, gathering the full complex wave, without the need for plasmonic mirrors or lenses.

Plasmonic nano-aperture label-free imaging (PANORAMA)

“…Recently, improved spatial resolution has been demonstrated by interferometric SPRI with image processing [13]. The concept of digital holography has also been implemented to image single nanoparticles by SPR with near-field optics [14]. Longitudinally, the evanescent field of SPP extends into the medium with a 1/e distance ~240 nm, which can be considered as the first order approximation of its sensing range above the gold film [12,[15][16][17].…”

Dynamic Imaging of Multiple SERS Hotspots on Single Nanoparticles

“…Surface-enhanced Raman scattering (SERS) is an increase in Raman efficiency due to extremely localized electromagnetic fields at the surface of, for instance, Au and Ag nanoparticles . These fields can be excited using visible radiation and are tightly confined to only certain areas, known as “plasmonic hotspots”. − Molecules in these hotspots experience enhanced excitation and scattering when probed with the proper laser wavelength and/or polarization. , In recent years, there have been several spectroscopic studies of SERS hotspots consisting of either random structures − or nanofabricated plasmonic antennas. − Plasmonic hotspots are widely explored not only for chemical analysis via SERS, but also for particle/molecule trapping, , enhanced photochemistry, − and even nanolithography. , Images of plasmonic hotspots have been obtained with ∼10 nm resolution by near-field scanning optical microscopy − and with higher resolution by scanning (transmission) electron microscopes using electron energy-loss spectroscopy. − However, while many experiments concentrate on the average optical properties (e.g., the extinction spectrum from a nanoparticle suspension or the transmission spectrum from a nanofabricated substrate) to predict SERS performance, fewer experiments directly probe Raman scattering from single nanostructures (e.g., imaging of subnanoparticle interactions ,− ). Moreover, most reports do not completely explore the time evolution or local origin of fluctuations in the SERS signal.…”

Quantitative Amplitude and Phase Imaging with Interferometric Plasmonic Microscopy

“…Figure A shows typical snapshots from an iPM image sequence recorded during the binding process of 40 nm Ag nanoparticles onto the Au film in a buffer solution. The correspondence between the far-field iPM holograms and reported near-field NSOM holograms of a point scatterer indicates that the field reconstructed in eq represents the far-field emission of the near-field SP waves. The amplitude (Figure B) and phase (Figure C) images of SP fields scattered by one or more nanoparticles were reconstructed.…”

“…However, it relies on either sophisticated nanoscopic probes, i . e ., near-field scanning optical microscopy (NSOM), − or complex optics and nanostructures, i . e ., leakage radiation microscopy (LRM), − to map the full complex SP fields.…”