Access and use of this website and the material on it are subject to the Terms and Conditions set forth at NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21276205&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21276205&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

No abstract

We report experiments on the characterization of a train of attosecond pulses obtained by highharmonic generation, using mixed-color (XUV IR) atomic two-photon ionization and electron detection on a velocity map imaging detector. We demonstrate that the relative phase of the harmonics is encoded both in the photoelectron yield and the angular distribution as a function of XUV-IR time delay, thus making the technique suitable for the detection of single attosecond pulses. The timing of the attosecond pulse with respect to the field oscillation of the driving laser critically depends on the target gas used to generate the harmonics. DOI: 10.1103/PhysRevLett.91.223902 PACS numbers: 42.65.Ky, 32.80.Rm, 42.65.Re The development of ultrashort laser pulses has led to significant advances in physics, chemistry, and biology. With femtosecond lasers the elementary motions of atoms and molecules can be observed [1], leading, for example, to a better understanding of complex biological systems [2]. Although electron dynamics often plays a crucial role in these systems, experimental studies have thus far been mostly limited to investigating the ''slow'' particles (i.e., atoms) that move under the influence of the intramolecular potentials. In order to investigate electron dynamics in real time, pulse durations have to enter the subfemtosecond (also known as attosecond, 1 as 1 10 ÿ18 s) domain [3]. Important advances have been made in the experimental realization and detection of attosecond laser pulses [4 -6] formed through the generation of high-order harmonics of femtosecond infrared (IR) laser pulses in noble gas atoms. In that process, attosecond time structure results from phase locking of a series of discrete harmonics [5,7,8] or a sufficiently broad segment of the harmonics continuum [6]. In this work, the time structure of such attosecond pulses is characterized from the angular distribution of the photoelectrons they produce in atomic mixed-color two-photon ionization.Many problems still have to be solved before well characterized and controlled attosecond pulses can be used as a routine tool for time-resolved spectroscopy [3,9]. When many-cycle IR pulses are used for the harmonic generation, the attosecond pulses appear in a pulse train, which is incompatible with most pump-probe experiments. Therefore the ultimate goal is to produce a single attosecond pulse. Another problem is the characterization of attosecond pulses. Full characterization can be done only through a nonlinear process, since linear processes do not mix different frequency components A q cos ! q t ' q and thus are insensitive to their relative phase ' q ÿ ' q 0 . Knowledge of the latter is essential and (together with the easily measurable amplitudes A q ) sufficient for determining a complete field reconstruction P A q exp i w q t ' q except for an overall phase. Thus far, mixed-color multiphoton ionization involving one extreme ultraviolet (XUV) and one or more fundamental photons has been the only process delivering enough signal to allow ...

We present the results of optimal-control experiments and calculations on the production of highly charged ions in intense laser field irradiation of large xenon clusters. Experimentally, a spectacular enhancement in the yield of highly charged ions is observed when clusters are subjected to an optimized laser field consisting of a sequence of two pulses, with a time delay that depends on the intensity of the laser and the size of the clusters. Similar results are obtained in optimal-control calculations, which demonstrate that the optimized pulse shape maximizes the efficiency of resonant heating

Time-resolved electron microscopy is based on the excitation of a sample by pulsed laser radiation and its probing by synchronized photoelectron bunches in the electron microscope column. With femtosecond lasers, if probing pulses with a small number of electrons—in the limit, single-electron wave packets—are used, the stroboscopic regime enables ultrahigh spatiotemporal resolution to be obtained, which is not restricted by the Coulomb repulsion of electrons. This review article presents the current state of the ultrafast electron microscopy (UEM) method for detecting the structural dynamics of matter in the time range from picoseconds to attoseconds. Moreover, in the imaging mode, the spatial resolution lies, at best, in the subnanometer range, which limits the range of observation of structural changes in the sample. The ultrafast electron diffraction (UED), which created the methodological basis for the development of UEM, has opened the possibility of creating molecular movies that show the behavior of the investigated quantum system in the space-time continuum with details of sub-Å spatial resolution. Therefore, this review on the development of UEM begins with a description of the main achievements of UED, which formed the basis for the creation and further development of the UEM method. A number of recent experiments are presented to illustrate the potential of the UEM method.