Indications of high-intensity adiabatic stabilization in neon

Abstract

We study the stabilization behavior of the circular 5g state in neon in a two-pulse experiment. A first pulse prepares the state. Comparison of the single-photon ionization yield, due to a second laser pulse for both short (0.1 ps) intense and long (1 ps) less intense pulses, shows an intensity-dependent suppression of ionization. The smaller yield due to the short pulses, at intensities of several times 10 13 W/cm 2 , is in accordance with recent predictions of stabilization.PACS numbers: 32.80.Rm, 42.50.HzThe photoionization rate of an atom will usually increase when the atom is exposed to increasing intensities. Recently, however, different mechanisms have been proposed that could prevent photoionization of an atom, even at the highest intensities. Collectively these are called stabilization. One such mechanism is dynamic or transient stabilization, in which part of the population is temporarily inaccessible for ionization [l].Adiabatic stabilization [2-5] is a different mechanism that suppresses photoionization. More precisely, it corresponds to an ionization rate which decreases with increasing intensity. This type of stabilization is predicted to occur in the high-frequency regime, where the photon energy is much larger than the binding energy. Classically, this means that the electron motion due to the light field is much faster than its motion in the Coulomb potential. Quantum mechanically, it means that the electron wave function cannot adiabatically respond to the oscillating light field. As a result, in the high-frequency regime, the wave function of the electron will be driven in an oscillatory motion by the light field.Adiabatic stabilization may occur once the amplitude of the oscillatory motion becomes comparable to the size of the unperturbed wave function, which usually implies a high intensity [6]. In the rest frame of the oscillating electron cloud (the Kramers-Henneberger frame), the atomic core will appear to oscillate. The electron wave function is determined by the potential of the atomic core, which, in this rest frame, is time dependent. However, in the high-frequency regime, it is valid to time average the motion of the atomic core. The potential which results is no longer Coulombic, but is deepest at the outer turning points of the oscillation, where the atomic core spends most of its time. In response the probability of finding the electron is largest at these points. One result of the electron spending more of its time further away from the nucleus is that ionization is suppressed and stabilization occurs. Ionization depends on transfer of momentum from the core to the emitted electron and once the wave function is far away from the core this becomes impossible [7], Originally, stabilization was predicted for the ground state of atomic hydrogen [2], and was later confirmed by other calculations [3], However, with present-day laser technology, the stabilization regime can only be reached when the initial state is a Rydberg state. For that case, different theoretical groups [4,5] give s...

Wave Packet Dynamics with Bose-Einstein Condensates

“…To achieve stabilization it is necessary to turn on the laser adiabatically in order to ensure that the atomic ground state will evolve to the ground state of this effective atom-laser potential. This type of stabilization [3] has never been observed experimentally [4], since it requires very intense high frequency fields, which currently can only be generated in a form of a very short pulse; as an electron in an atom is highly unstable, it would thus be most likely ionized during the turn-on of such a pulse.Let us analyze the analogy between the electron and the condensate in more detail. The electron bound by an atomic potential U ( r) and interacting with a laser field of amplitude E e z (polarized along the z-direction) is, for our purposes, best described in the Kramers-Henneberger frame of reference, in which the interaction with the laser field results in an effective time dependent "atomic" potential:…”

Stabilization of circular Rydberg atoms by circularly polarized infrared laser fields

“…27.5 a.u. Our case differs from the scenario studied earlier [26][27][28][29][30][31][32] in that we apply (in-plane) circularly polarized pulses, with components in the x and y directions, instead of z polarized fields. Thus, the axial symmetry of the problem is broken, resulting in a strong m mixing.…”

“…Up to present times, experimental confirmation of atomic stabilization in tightly bound atomic systems, such as neutral atoms in their ground state, has been obstructed due to lack of the laser technology required to produce the necessary conditions. The possibility of observing the phenomenon in excited atomic states was pointed out early [4,[22][23][24][25], and the first experimental signature of atomic stabilization in low-lying Rydberg atoms was reported in 1993 [26,27] and later * sigurd.askeland@ift.uib.no † stian.sorngard@ift.uib.no ‡ morten.forre@ift.uib.no confirmed [28], irradiating 5g circular states in neon by intense (∼10 13 -10 14 W/cm 2 ) 620-nm linearly polarized laser pulses. The experimental findings are consistent with theoretical predictions [29][30][31][32].…”

Multiphoton ionization and stabilization of helium in superintense xuv fields

“…(19)] into the TDSE and applying high-frequency Floquet theory, Gavrila et al [10,[53][54][55] showed that the n = 0 component in Eq. (20) plays an increasingly important role in the dynamics at higher values of α 0 .…”

“…Grobe and Eberly [17] demonstrated that stabilization could occur in H − at moderate intensities (∼10 13 W/cm 2 ) and photon energies (∼2 eV), and Wei et al [18] suggested an experiment in which a laser, of realistic frequency and intensity, could possibly stabilize the unstable He − ion. However, at present, the only experimental confirmations of stabilization are from studies of low-lying Rydberg states [19][20][21][22]. With recent advances in free-electron laser (FEL) technology, extremely high peak intensities have been achieved, with wavelengths ranging from vacuum ultraviolet to soft x rays [23,24], and even higher intensities are expected to be delivered in the near future [25].…”