Attosecond

Of course, even when the world s fastest laser pulses are available, there is always a feehng that what is really required is pulses that are faster still Laser pulses with durations in the attosecond regime would open up the possibility of observing the motions of electrons in atoms and molecules on their natural time scale and would enable phenomena such as atomic and molecular ionisation (Section 1.2) and the dynamics of electron orbits about nuclei to be captured in real time. 

In this section, we present the first experimental evidence of the destructive interference (DI) and the constructive interference (Cl) in a mixed gas of He and Ne, which prove the validity of the method. The observed interference modulation is, as discussed in Sect. 4.2, attributed to the difference between the phases of the intrinsically chirped harmonic pulses from He and Ne, which leads to the novel method for broadband measurement of the harmonic phases and for observing the underlying attosecond electron dynamics. 

One of the important consequences of these results can be revealed when one regards the observed interference as an inverse problem. In fact, from (4.3), observing the relative phase corresponds to the broadband measurement of the excursion time T and thus the estimation of the individual harmonic phase [24]. Measuring attosecond excursion times offer a crucial basis... 

In this section, by applying the heterodyne interferometry to a mixed gas of H2 and D2 molecules, we probe attosecond dynamics of nuclear wavepackets in the molecules. We find that not only the single molecule responses but also the propagation effects of harmonics differ between the two isotopes and that to discuss dynamics of molecules in the single molecule responses, the propagation effects need to be excluded from the raw harmonic signals. The measured relative phase as well as intensity ratio are found to be monotonic functions of the harmonic order and are successfully reproduced by applying... 

Fig. 4.9. A schematic diagram illustrating the attosecond dynamics of the strongly correlated nuclear and electron wavepackets that lead to HHG in H2 and/or D2. When the internuclear distance is large, HHG is suppressed...

In summary, we investigated HHG in mixed gases both experimentally and theoretically. As the new nonlinear media for HHG, using mixed gases can serve as a new route not only to control and characterize harmonics but also to observe attosecond dynamics in atoms and molecules. 

We start our discussion of laser-controlled electron dynamics in an intuitive classical picture. Reminiscent of the Lorentz model [90, 91], which describes the electron dynamics with respect to the nuclei of a molecule as simple harmonic oscillations, we consider the electron system bound to the nuclei as a classical harmonic oscillator of resonance frequency co. Because the energies ha>r of electronic resonances in molecules are typically of the order 1-10 eV, the natural timescale of the electron dynamics is a few femtoseconds to several hundred attoseconds. The oscillator is driven by a linearly polarized shaped femtosecond... 

Because electrons are much lighter than nuclei, they move much faster. The intrinsic temporal regime for valence bond electron dynamics is the few femtosecond to several hundred attosecond timescale. Therefore, efficient and accurate control of electron dynamics requires extreme precision regarding the control field. Commonly attosecond techniques are considered to be the appropriate tools for efficient manipulation of electron motions [61-63, 111, 112]. However, attosecond pulses in the XUV region are not suited for efficient valence bond excitation (see Section 6.1). Here we demonstrate that ultrafast electron dynamics are controlled efficiently on the sub-10 as timescale employing a pair of femtosecond laser pulses with a temporal separation controllable down to zeptosecond precision [8]. 

Equation (7.5) shows that the population of each eigenstate oscillates with its transition frequency as a function of r. For B transition of the iodine molecule that we will discuss later, the pump laser wavelength is 600 nm, which corresponds to the oscillation period of 2fs. If we require Ittx 1/10 stability for the relative phase between the two interfering WPs, attosecond stability is necessary for the delay t. The details of the experimental setup to prepare the phase-stabilized double pulses will be described in the following section [38, 39,47,48]. 

Figure 7.3 The structure of the attosecond stability Michelson-type interferometer equipped with a gas cell.

We illustrate the use of multichannel single-ionization scattering states for the interpretation of time-resolved experiments in the case of the attosecond-XUV-pump IR-probe attosecond interferometric spectroscopy of the doubly... 

So far we have considered the absorption of an XUV pump pulse with attosecond extension. The next step in the simulation is to apply a probe pulse. During the time between the pump and the probe, the system undergoes two different kinds of temporal evolution. One is the semiperiodic... 

K. Kliinder, J.M. Dahlstrom, M. Gisselbrecht, T. Fordell, M. Swoboda, D. Guenot, et al., Probing single-photon ionization on the attosecond time scale, Phys. Rev. Lett. 106 (14) 143002. 

Th. Mercouris, Y. Komninos, C.A. Nicolaides, Theory and computation of the attosecond dynamics of pairs of electrons excited by high-frequency short light pulses, Phys. Rev. A 69 (2004) 032502. 

L. Argenti, E. Lindroth, Ionization branching ratio control with a resonance attosecond clock, Phys. Rev. Lett. 105 (2010) 053002. 

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