trend is consistent with a Pt-C stretching mode assignment.This assignment is also anticipated on the basis of the surface dipole selection rule which states that only vibrations which belong to totally symmetric representations can be observed.12 In C,, symmetry, the CO and Pt-CO stretches transform as the totally symmetric Z representation while the Pt-C-0 bend transforms as a II representation. For combination modes we must consider the products of representations for the two fundamentals involved. The product 2x2 is again totally symmetric while the product Z X I I is not. Thus the Pt-C-O bending mode is dipole forbidden both as a fundamental and in combination with the C-O stretch.For comparison with our data, EELS studies of CO on a flat Pt( 11 1) and a stepped Pt[(611)X(11 l)] surface showed terminal and bridging CO stretches at 21 10 and 1870 cm-'.13 Loss features at 390 and 480 cm-' were respectively assigned to Pt-C stretches for bridging and terminal CO. The 390-cm-' loss showed coverage-dependent frequency shifts. A very weak loss at 2580 cm-' was assigned to a combination loss involving CO and Pt-CO stretching modes. The frequencies of the terminal Pt-CO and CO stretching modes we find for Pt/TiO, differ from those measured by Barb and Ibach on the flat and stepped Pt surfaces. Hydrogen chemisorption measurements on a sample of Pt/TiO, reduced a t 520 K indicate that the Pt particles are large, ca. 65 A, so bulklike Pt behavior is expected.16 The discrepancies may indicate that other crystal planes are preferentially exposed on the supported Pt particles. Blyholder and Sheets studied CO adsorbed onto Pt particles suspended in an oil film on salt wind o w~. '~ Their values for the CO stretching (2045 and 1815 cm-')and the Pt-C stretching (480 cm-I) modes were also different from those measured here. It may be that components of the hydrocarbon also chemically interact with the Pt particles. It is interesting to compare the effects of varying C O coverage on the frequencies of the T-CO and proposed Pt-CO bands. When the CO-saturated sample shown in Figure 1 is evacuated for 30 min at 523 K and then cooled to room temperature, we find the T-CO band intensity decreases by 20% and its position red shifts by 12 cm-l to 2071 cm-I. At the same time the H F band increases in frequency by 11 cm-' to 2494 cm-' and the calculated position of the Pt-CO fundamental increases in frequency by 21 cm-' to 423 cm-I. Analogous coverage-dependent frequency behavior has been found for the T-CO fundamental on supported and unsupported Pt. On a Pt foil the T-CO band appears near 2065 cm-' at low CO coverage and increases in frequency to 2100 cm-' as C O coverage approaches ~aturati0n.I~ This frequency shift is in large part ascribed to increasing intermolecular dipole cou-~1 i n g . l~ At very low coverages, donation of Pt d-electron density to empty 2?r* antibonding molecular orbitals on C O (Le. ?r backbonding) is thought to play a major role in defining the CO stretching frequency. On Pt/Ti02 the T-CO frequency drops wit...

This review presents the technological infrastructure that will be available at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) international facility. ELI-ALPS will offer to the international scientific community ultrashort pulses in the femtosecond and attosecond domain for time-resolved investigations with unprecedented levels of high quality characteristics. The laser sources and the attosecond beamlines available at the facility will make attosecond technology accessible for scientists lacking access to these novel tools. Time-resolved

Continuing efforts in ultrashort pulse engineering have recently led to the breakthroughs of the generation of attosecond (10−18 s) pulse trains 1-7 and isolated pulses [8][9][10][11] . Although trains of multiple pulses can be generated through the interaction of many-optical-cycle pulses with gases-a process that has led to intense extreme-ultraviolet emission 3-5 -the generation of isolated high-intensity pulses, which requires few-cycle driving pulses, remains a challenge. Here, we report a vital step towards the generation of such pulses, the production of broad continuum extreme-ultraviolet emission using a high-intensity, many-cycle, infrared pulsed laser, through the interferometric modulation of the ellipticity of 50-fs-long driving pulses. The increasing availability of high-power many-cycle lasers and their potential use in the construction of intense attosecond radiation-with either gas or solid-surface targets 12 -offer exciting opportunities for multiphoton extreme-ultravioletpump-extreme-ultraviolet-probe studies of laser-matter and laser-plasma interactions.The generation of attosecond pulse trains through the synthesis of a comb of harmonics of an infrared many-cycle femtosecond laser pulse is well established [1][2][3][4][5][6][7] , and is essentially understood in the framework of the three-step model 13,14 . According to this model, an electron is ejected in the continuum after tunnelling through the atomic potential barrier formed by the instantaneous laser field. Subsequently, the electron accelerates away from the core until the field changes sign. Within a fraction of half the laser period, the electron may revisit the parent ion to recombine and emit a burst of continuum extreme-ultraviolet radiation. As the process is repeated twice per laser cycle, the emitted spectrum consists of a superposition of coherent continua, which in the time domain is equivalent to a train of sub-femtosecond pulses. Using high-power many-cycle laser pulses, intense attosecond pulse trains have been generated and already used for the study of nonlinear phenomena in the extreme-ultraviolet spectral region [15][16][17][18][19][20][21][22] . They thus afford the means for the temporal characterization of attosecond pulses on the basis of second-order autocorrelation techniques in the extreme-ultraviolet spectral region [3][4][5]18,19 , and open the road towards extreme-ultraviolet pump-extremeultraviolet probe experiments.In the spirit of the three-step model, if the process is confined to a single revisit of the core by the driven electron, one single continuum is emitted in the form of an isolated pulse. In mathematical terms, the Fourier synthesis of a broad continuum corresponds in the time domain to a single temporal occurrence, whereas a discrete spectrum leads to a repetitive process. Thus, the emission of a single coherent continuum is an essential prerequisite for single attosecond pulse generation [8][9][10] . Indeed, the generation of isolated single attosecond pulses is based on the synthesis of a co...

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