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Register a new userRescattering for extended atomic systems
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Laser-driven rescattering of electrons is the basis of many strong-field phenomena in atoms and molecules. Here, we will show how this mechanism operates in extended atomic systems, giving rise to effective energy absorption. Rescattering from extended systems can also lead to energy loss, which in its extreme form results in non-linear photo-association. Intense-laser interaction with atomic clusters is discussed as an example. We explain fast electron emission, seen in experimental and numerically obtained spectra, by rescattering of electrons at the highly charged cluster.
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We experimentally investigate an optical frequency standard based on the $^2S_{1/2} (F=0)to {}^2F_{7/2} (F=3)$ electric octupole (textit{E}3) transition of a single trapped $^{171}$Yb$^+$ ion. For the spectroscopy of this strongly forbidden transition, we utilize a Ramsey-type excitation scheme that provides immunity to probe-induced frequency shifts. The cancellation of these shifts is controlled by interleaved single-pulse Rabi spectroscopy which reduces the related relative frequency uncertainty to $1.1times 10^{-18}$. To determine the frequency shift due to thermal radiation emitted by the ions environment, we measure the static scalar differential polarizability of the textit{E}3 transition as $0.888(16)times 10^{-40}$ J m$^2$/V$^2$ and a dynamic correction $eta(300~text{K})=-0.0015(7)$. This reduces the uncertainty due to thermal radiation to $1.8times 10^{-18}$. The residual motion of the ion yields the largest contribution $(2.1times 10^{-18})$ to the total systematic relative uncertainty of the clock of $3.2times 10^{-18}$.
It is demonstrated that in photoabsorption by endohedral atoms some atomic Giant resonances are almost completely destroyed while the others are totally preserved due to different action on it of the fullerenes shell. As the first example we discuss the 4d10 Giant resonance in Xe@C60 whereas as the second serves the Giant autoionization resonance in Eu@C60. The qualitative difference comes from the fact that photoelectrons from the 4d Giant resonance has small energies (tens of eV) and are strongly reflected by the C60 fullerenes shell. As to the Eu@C60, Giant autoionization leads to fast photoelectrons (about hundred eV) that go out almost untouched by the C60 shell. As a result of the outgoing electrons energy difference the atomic Giant resonances will be largely destroyed in A@C60 while the Giant autoionization resonance will be almost completely preserved. Thus, on the way from Xe@C60 Giant resonance to Eu@C60 Giant autoionization resonance the oscillation structure should disappear. Similar will be the decrease of oscillations on the way from pure Giant to pure Giant autoionization resonances for the angular anisotropy parameters. At Giant resonance frequencies the role of polarization of the fullerenes shell by the incoming photon beam is inessential. Quite different is the situation for the outer electrons in Eu@C60, the photoionization of which will be also considered.
A method is presented to monitor the internal energy distribution of cluster anions via delayed electron detachment by pulsed photoexcitation and demonstrated on Co$_4{}^-$ in an electrostatic ion beam trap. In cryogenic operation, we calibrate the detachment delay to internal energy. By laser frequency scans, at room temperature, we reconstruct the time-dependent internal energy distribution of the clusters. The mean energies of ensembles from a cold and a hot ion source both approach thermal equilibrium. Our data yield a radiative emission law and the absorptivity of the cluster for thermal radiation.
We propose and demonstrate a momentum filter for atomic gas based on a designed Talbot-Lau interferometer. It consists in two identical optical standing wave pulses separated by a delay equal to odd multiples of the half Talbot time. The one dimensional momentum width along the long direction of a cigar shape condensate is rapidly and greatly purified to a minimum, which corresponds to the ground state energy of the confining trap in our experiment. We find good agreement between theoretical analysis and experimental results. The filter is also effective for non-condensed cold atoms and could be applied widely.
We re-examine the series of resonances found earlier in atomic three-body systems by solving the Faddeev-Merkuriev integral equations. These resonances are rather broad and line-up at each threshold with gradually increasing gaps, the same way for all thresholds and irrespective of the spatial symmetry. We relate these resonances to the Gailitis mechanism, which is a consequence of the polarization potential.
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