Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 micrometer. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy (STM) on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission process above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate

Erzeugung optischer Durchbrüche bei hoher numerischer Apertur : numerische Simulationen zur Submikrometer-Manipulation transparenter Materialien und biologischer Zellen mit ultrakurzen Laserpulsen

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Pulse compression with planar hollow waveguides: a pathway towards relativistic intensity with table-top lasers

International audienceWe study in detail the compression of high-energy ultrashort laser pulses to the few-cycle regime in gas-filled planar hollow waveguides. In this scheme, the laser beam is guided in only one transverse dimension, whereas the other dimension is free to adjust, allowing scalability to high pulse energies. We report on various practical aspects of the planar hollow waveguide compression scheme and characterize the dependence of the performance of the method on several experimental parameters: (i) we evaluate different materials for the construction of planar waveguides; (ii) we investigate the dependence of the pulse duration on gas type and pressure; (iii) we measure the spatial intensity and phase; (iv) we characterize the pulse duration along the transverse beam direction; and (v) we investigate the focusability. An output pulse energy of 10.6 mJ at a duration of 10.1 fs (FWHM) in the beam center after compression is demonstrated. A careful estimation reveals that the radiation should be focusable to a relativistic intensity exceeding 10^19 W.cm−2 in the few-cycle regime. The experimental results are supported by numerical modeling of nonlinear pulse propagation inside planar hollow waveguides. We discuss energy up-scalability exceeding the 100 mJ level

Filamentation without intensity clamping

We present measurements of the supercontinuum emission (SCE) from ultrashort Ti:Saph laser pulse filamentation in air in a tightly focused geometry. The spectral broadening of SCE indicates that peak intensities exceed the clamping value of a few 1013 W/cm2 obtained for filamentation in a loose focusing geometry by at least one order of magnitude. We provide an interpretation for this regime of filamenation without intensity clamping

Characterization of broadband few-cycle laser pulses with the d-scan technique

We present an analysis and demonstration of few-cycle ultrashort laser pulse characterization using second-harmonic dispersion scans and numerical phase retrieval algorithms. The sensitivity and robustness of this technique with respect to noise, measurement bandwidth and complexity of the measured pulses is discussed through numerical examples and experimental results. Using this technique, we successfully demonstrate the characterization of few-cycle pulses with complex and structured spectra generated from a broadband ultrafast laser oscillator and a high-energy hollow fiber compressor. (C)2012 Optical Society of Americ

Measurement of Ultrashort Laser Pulses With a Time-Dependent Polarization State Using the D-Scan Technique

The dispersion scan (d-scan) technique is extended to measurement of the timedependent polarization state of ultrashort laser pulses. In the simplest implementation for linearly polarized ultrashort pulses, the d-scan technique records the second harmonic generation (SHG) spectrum as a function of a known spectral phase manipulation. By applying this method to two orthogonally polarized projections of an arbitrary polarized electric field and by measuring the spectrum at an intermediate angle, we can reconstruct the evolution over time of the polarization state. We demonstrate the method by measuring a polarization gate generated from 6 fs pulses with a combination of waveplates. The measurements are compared to simulations, showing an excellent agreement

Attosecond electron-spin dynamics in Xe 4d photoionization

The photoionization of xenon atoms in the 70-100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe$^+$ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy. A time-frequency analysis of the involved transitions allows us to identify two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as. Our results provide new insight into the complex electron-spin dynamics of photo-induced phenomena

Compression of high-energy ultrashort laser pulses through an argon-filled tapered planar waveguide

International audienceWe propose a hollow tapered planar waveguide for compression of high-energy ultrashort laser pulses. Direct measurements suggest that it seems to find a very good trade-off among the energy throughput, the beam focusability, and the pulse compressibility. With a Ti:sapphire laser pulse of 12.0 mJ and 40 fs , our experiment produces an output pulse of 9.4 fs duration with energy 9.1 mJ (transverse magnetic mode) or 10.0 mJ (transverse electric mode) in argon, each exhibiting a nice spatial mode. To evaluate such a tapered waveguide, the linear wave propagation theory and the solution to its complex propagation constant are also presented