Historical research guide · 0910 · 2009

Photon-induced near-field electron microscopy

Brett Barwick · David J. Flannigan · Ahmed H. Zewail

In one minute

Light hugging a nanostructure does not fly away from it. It clings, dies off within a wavelength, and carries no photons to a distant lens — which is why for a century it could be calculated but not photographed. Brett Barwick, David Flannigan and Ahmed Zewail at Caltech photographed it. In their ultrafast electron microscope a femtosecond laser pulse and a packet holding a single electron are steered onto the same carbon nanotube or silver nanowire at the same instant, and the electron, travelling at 200 kiloelectronvolts, comes out having swallowed or shed whole photons — one, two, three quanta, never a fraction. Filter the microscope so it forms its picture only from electrons that gained energy, and the clinging field itself appears, in place, at nanometre resolution. Shift the timing and you watch it rise and fall over femtoseconds; rotate the laser’s polarization and the pattern rearranges. The authors named the method photon-induced near-field electron microscopy, PINEM.

Connection

Chapter 10 is about the parts of an electromagnetic field that carry structure without radiating, and the standing objection to taking them seriously is that you cannot see them. PINEM sees them, in space and in femtoseconds, and shows a free electron trading whole quanta of energy with a field that never leaves the surface.

From the source

The precise spatiotemporal overlap of femtosecond single-electron packets with intense optical pulses at a nanostructure — an individual carbon nanotube or silver nanowire in this work — results in the direct absorption of integer multiples of photon quanta by relativistic electrons accelerated to 200 kiloelectronvolts. The exchange is quantized: the electron leaves the interaction one, two or three whole photons up or down, never in between.Abstract, third sentence; Nature 462, pages 902 to 906
By energy-filtering only those electrons resulting from this absorption, it is possible to image directly in space the near-field electric field distribution. The image is formed from electrons that could only have gained their extra energy inside the near field, so the picture is of the field itself, at the spatial resolution of the electron microscope rather than that of light.Abstract, fourth sentence
The same method obtains the temporal behaviour of the field on the femtosecond timescale and maps its spatial polarization dependence. Scanning the delay between the light pulse and the electron packet turns the still image into a film of the field appearing and dying away; rotating the polarization of the light rearranges where the field sits on the structure.Abstract, fourth sentence; Supplementary Figure 1, lower panel
The electron energy spectrum recorded at coincidence shows the signature the mechanism predicts. Against the zero-loss peak measured when the electron packet arrives two picoseconds early, the spectrum at zero delay grows discrete gain and loss peaks at plus and minus one, two and three photon quanta, spanning about plus or minus 7.2 electronvolts either side of the zero-loss energy.Supplementary Figure 1, upper panel and caption
The effect is not confined to one material or one field strength. Silver nanowires give absorption and emission of photon quanta similar to that shown for carbon nanotubes, at a laser fluence an order of magnitude smaller — and their energy-filtered images change between the light polarized along the long axis of the wire and across it, both frames taken at zero delay.Supplementary Figure 1 caption
What to watch: the authors set out what the method is for. Observing the photon-induced near-field effect in ultrafast electron microscopy demonstrates the potential for many applications, including direct space-time imaging of localized fields at interfaces and the visualization of phenomena related to photonics, plasmonics and nanostructures. Every one of those is a measurement of field structure that was previously inferred rather than seen.Abstract, final sentence

The way in

https://doi.org/10.1038/nature08662

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

SOURCE NOT REACHED IN FULL. Published as Nature volume 462, issue 7275, pages 902 to 906, 17 December 2009; received 11 September 2009, accepted 10 November 2009. The article is closed: Unpaywall, OpenAlex and Semantic Scholar all report no open copy on 2026-09-08, and the only licence Crossref carries is Springer’s text-and-data-mining licence, which is not a Creative Commons grant, so no text of the paper is reproduced here. Two author-side sources could be read and this page is written from them. First, the authors’ own abstract, read from the National Library of Medicine record for PubMed 20016598 and confirmed word for word against the CaltechAUTHORS record at authors.library.caltech.edu/records/3jrhk-ra736. Second, the authors’ Supplementary Information, nature08662-s1.pdf, deposited open at that same CaltechAUTHORS record and downloaded and read for this sheet; it carries the electron energy spectra and the polarization frames, and claims located to ’Supplementary Figure 1’ come from it. The CaltechAUTHORS record prints the copyright line, copyright 2009 Macmillan Publishers Limited, and states the funding: the National Science Foundation and the Air Force Office of Scientific Research, through the Gordon and Betty Moore Center for Physical Biology at the California Institute of Technology. Affiliation as printed: Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena. Ahmed Zewail won the 1999 Nobel Prize in Chemistry and died in 2016; Brett Barwick is also a coauthor of the macroscopic Aharonov-Bohm test summarised elsewhere in this library.

How to cite it

Brett Barwick, David J. Flannigan, Ahmed H. Zewail (2009) Photon-induced near-field electron microscopy doi:10.1038/nature08662

Where it sits in the curriculum

Scalar waves and the field behind the fields