Schematic of the oscillating field of the IR laser beam and the XUV pulse train. It is possible to align the distance between the XUV attosecond pulses with the cycle period T of the electric field. The delay between the train and the IR field can now be varied with high precision. Charge oscillations on the surface following the IR pulse (such as surface plasmons) should now be visible by comparing images obtained at different delays (Δt).
(a) Schematic model of the experimental setup. The label BS denotes the beam splitter, FM the focusing mirror, RM the recombination mirror, and TM the toroidal mirror. (b) Energy structure of the XUV beam recorded with a magnetic-bottle TOF spectrometer. (c) Time structure of the XUV attosecond pulses in the central part of the train with a 200 nm Al filter. (d) 3 kV low magnification PEEM image of the electron emission spot from the XUV laser pulse at high intensity. (e) Profile measured across (d), as indicated by the broken (blue) line in (d).
(a) SEM image of part of the lithographic pattern. In total, nine square arrays of holes were fabricated in a square region of of the Au film. [The magnification in this image is so low that the hole arrays cannot be seen, instead see Fig. 3(c).] Each region is divided using wide lithographic lines, and at the center of each divided region there is an array of holes covering a area. The hole diameter and the separation is indicated using text numbers fabricated lithographically with 200 nm wide text lines—the arrow points to this text line. (b) Schematic of the lithographic sample. The Au film is connected to the sample holder to minimize charging effects. (c) SEM image of a small part of the hole array with 100 nm in hole diameter and 400 nm in hole separation. (d) PEEM image recorded with an extractor voltage of 14 kV using a standard Hg lamp for illumination. The image shows part of a structure similar to the one in Fig. 2(a). The inset shows the array of 100 nm holes as imaged by PEEM indicating that the PEEM can obtain a resolution of . The holes could only be clearly seen when the PEEM was run with an ion pump and no turbopumps on.
(a) PEEM image recorded with an extractor voltage of 14 kV using a standard Hg lamp for illumination. The image shows the same structure similar to the one in Fig. 2(a). (b) PEEM image recorded under the same conditions using XUV attosecond pulse trains with a max energy of 30 eV. Notice that in both cases the broad lines can be clearly observed, while also the text can be observed as indicated by the arrows. The structure obtained with the XUV beam is not as sharp as with the Hg lamp and we estimate that our resolution has dropped to .
(a) PEEM image of the lithographic structure using the XUV laser source at a different focus, where the central square containing the hole array can be seen and the marking lines appear black. (b) Profile averaged along the wide lithographic. The distance 20% from the bottom to 80% from the top of the troughs can be used as a different measure of resolution with a result of .
(a) PEEM image (extraction voltage of 14 kV) of Au aerosol nanoparticles of 50 nm in diameter recorded with the standard Hg lamp as photon source. (b) PEEM image (extraction voltage of 14 kV) of the same area with Au aerosol nanoparticles of 50 nm in diameter as in Fig. 4(b), recorded with a 35 fs IR pulse with a photon energy of 1.55 eV. Some points can be observed presumably corresponding to two or more Au particles with interparticle distances leading to plasmon resonances for this IR wavelength (Ref. 36), thus allowing considerable multiphoton electron emission.
(a) PEEM image of nanowires dispersed on a Si surface recorded using monochromatized 34 eV photons from the MAX-II synchrotron with an Elmitec SPELEEM system. An energy filter of 0.7 eV was used. One nanowire is indicated by the light gray (blue) arrow, while two larger features are indicated by the dark gray (red) arrow. (b) PEEM image of the same area as in (a). The energy filter was removed and only the background structure of the PEEM micro channel plate and a few large features can be observed [at the (red) arrow]. (c) PEEM image of the same area as in (a). A small contrast aperture was inserted and again small features can be observed.
(a) PEEM image (12 kV) of lithographic structure recorded using the XUV beam. (b) PEEM image (12 kV) of the same structure and area using the 1.55 eV IR laser beam. (c) PEEM image (12 kV) of the same structure and area using the 1.55 eV IR laser beam and the XUV beam with no time delay between the two beams. (d) PEEM image (12 kV) of the same structure and area using the 1.55 eV IR laser beam and the XUV beam with a time delay of 10 ps between the two beams.
Simplified illustration of the mechanism behind the interaction of the electrons created by the IR and the XUV pulses, respectively (Refs. 37 and 38). The first stage of the PEEM lens system consists of the sample as cathode and the first lens of the PEEM as anode. (a) If only one electron excitation source (indicated by the arrows) is used, the electron paths [indicated by solid (blue) lines] will pass into the microscope being bend by the first lens, thus effectively creating a focus point behind the sample (Refs. 37 and 38). The focus point of the PEEM behind the sample is indicated by the crossing of the broken black lines. (b) If two consecutive excitation pulses follows rapidly after each other (indicated by the arrows). The electric field from the charges excited from the first pulse will act to bend the trajectories of the electrons excited by the second pulse. This also effectively moves the focus point. For some special cases it will be possible to move the focus point back by then changing the focus of the PEEM.
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