Attosecond extreme-ultraviolet pulses 1 have a complex space-time structure 2 . However, at present, there is no method to observe this intricate detail; all measurements of the duration of attosecond pulses are, to some extent, spatially averaged 1,3-5 . A technique for determining the full space-time structure would enable a detailed study of the highly nonlinear processes that generate these pulses as a function of intensity without averaging 6,7 . Here, we introduce and demonstrate an all-optical method to measure the space-time characteristics of an isolated attosecond pulse. Our measurements show that intensity-dependent phase and quantum-path interference both play a key role in determining the pulse structure. In the generating medium, the attosecond pulse is strongly modulated in space and time. Propagation modifies but does not erase this modulation. Quantum-path interference of the single-atom response, previously obscured by spatial and temporal averaging, may enable measuring the laser-field-driven ion dynamics with sub-cycle resolution.Fully defining an attosecond pulse requires knowledge of its phase variation both temporally and spatially. Until now, temporal 1,3-5,8,9 and spatial 10-12 measurements are achieved only separately. As the temporal characterization methods (known as RABBIT; ref. 1 and CRAB;9,13) rely on the photoelectric effect, they average over the spatial profile of a pulse, mixing the contribution from the different emitters of the extremeultraviolet (XUV) source at a secondary target. On the other hand, spatial measurements of XUV emission have been achieved using small apertures 10,11 or two foci 12 . Although temporal information remains available in principle, neither method seems compatible with RABBIT or CRAB. Therefore, space-time measurements of attosecond pulses have never been made.To solve the space-time problem, we turn to an in situ technique. The in situ method is a unique method of measurement that is feasible only for highly nonlinear processes [14][15][16] . It relies on the fact that adding a single photon to an already highly nonlinear process only weakly perturbs the process 17,18 . Yet, it can modify the spatial and spectral pattern of a beam. The in situ method has been considered in attosecond pulse metrology to determine only the temporal profile of the average attosecond pulse within attosecond pulse trains 14 . For that measurement, a weak second-harmonic beam co-propagates with the fundamental beam to break the symmetry between adjacent attosecond pulses, thereby allowing an even-order harmonic signal. Temporal information was encoded in the even-order harmonic signal as a function of the phase delay between the fundamental and second-harmonic laser pulses 14 .For our spatially encoded in situ measurement, we produce XUV radiation using the fundamental laser pulse with a time-dependent

The development of a methodology to manipulate surface properties of a self-assembled monolayer (SAM) of alkanethiol on a gold film using direct laser patterning is the objective of this paper. The present study demonstrates proof of the concept for the feasibility of laser patterning monolayers and outlines theoretical modeling of the process to predict the resulting feature size. This approach is unique in that it eliminates the need for photolithography, is noncontact, and can be extended to other systems such as SAMs on silicon wafers or potentially polymeric substrates. A homogeneous SAM made of 1-hexadecanethiol is formed on a 300-A sputtered film of gold (supported by a soda lime glass substrate). Localized regions are then desorbed by scanning the focal spot of a 488-nm continuous-wave argon ion laser beam under a nitrogen atmosphere. The desorption occurs as a result of a high substrate temperature produced by the moving laser beam with a Gaussian spatial profile at a constant speed of 200 microm/s. After completing the scans, the sample is dipped into a dilute solution of 16-mercaptohexadecanoic acid and a hydrophilic monolayer self-assembles along the previously irradiated regions. The resultant lines are viewed, and line widths are measured using both wetting with tridecane under a light microscope and scanning electron microscopy. Using the direct laser patterning method, we have produced straight line patterns with widths of 28-170 microm. A thermal model was constructed to predict the line width of the desorbed monolayer. The effect of the laser power, beam waist, and temperature dependence of the substrate conductivity on the theoretical predictions is considered. It is shown that the theoretical predictions are in good agreement with the experimental results, and, thus, the model can effectively be used to predict experimental results.

Using a chirped pulse probe technique, we have obtained single-shot measurements of temporal evolution of ac conductivity at 1.55 eV (800 nm) during electron energy relaxation in nonequilibrium warm dense gold with energy densities up to 4.1  MJ/kg (8×10(10)  J/m3). The results uncover important changes that have been masked in an earlier experiment. Equally significant, they provide valuable tests of an ab initio model for the calculation of electron heat capacity, electron-ion coupling, and ac conductivity in a single, first principles framework. While measurements of the real part of ac conductivity corroborate our theoretical temperature-dependent electron heat capacity, they point to an electron-ion coupling factor of ∼2.2×10(16)  W/m3 K, significantly below that predicted by theory. In addition, measurements of the imaginary part of ac conductivity reveal the need to improve theoretical treatment of intraband contributions at very low photon energy.

We present a model to describe thermophysical and optical properties of two-temperature systems consisted of heated electrons and cold ions in a solid lattice that occur during ultra-fast heating experiments. Our model is based on ab initio simulations within the framework of density functional theory. The optical properties are obtained by evaluating the Kubo-Greenwood formula. By applying the material parameters of our ab initio model to a two temperature model we are able to describe the temperature relaxation process of a femtosecond-laser heated gold and its optical properties within the same theoretical framework. Recent time-resolved measurements of optical properties of ultra-fast heated gold revealed the dynamics of the interaction between femtosecond laser pulses and solid state matter. Different scenarios obtained from simulations of our study are compared with experimental data. 1