Selective strong-field enhancement and suppression of ionization with short laser pulses

Hart, N.; Strohaber, James; Kolomenskii, A.A.; Paulus, Gerhard G.; Bauer, Dieter; Schuessler, H. A.

doi:10.1103/physreva.93.063426

Cited by 29 publications

(45 citation statements)

References 22 publications

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“…Consequently, one has to rely on calculating the ionization process with TDSE methods. Our results underline the dominance of multiphoton ionization in alkali atoms consistent with previous experiments [20][21][22] and theory [30,31].…”

Section: Non-resonant Two-photon Ionization At 511 Nmsupporting

confidence: 92%

“…For rubidium this over-the-barrier (OBI) intensity is reached at I OBI = 1.22 × 10 12 W/cm 2 (vertical black dashed line). Previous experiments [20,22] and theoretical studies [30,31] have already mentioned the peculiar situation that in alkali atoms the OBI intensity is reached well within the multiphoton regime, in particular for rubidium at a Keldysh parameter of γ = 8.4 for an optical wavelength of 511 nm (compare Fig. 3a).…”

Section: Non-resonant Two-photon Ionization At 511 Nmmentioning

confidence: 89%

“…For alkali atoms used in most cold atom experiments the transition regime separating multiphoton from tunnel ionization at a Keldysh parameter around γ ≈ 1 is reached at considerably lower intensities. Experiments accessing the strong-field regime with alkali atoms [20][21][22] have revealed that commonly used strong-field ionization models in form of a pure multiphoton-or tunnel ionization process can not be applied a priori which makes employing ab-initio calculations by solving the time-dependent Schrödinger equation (TDSE) inevitable.…”

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confidence: 99%

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Absolute strong-field ionization probabilities of ultracold rubidium atoms

et al. 2018

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We report on precise measurements of absolute nonlinear ionization probabilities obtained by exposing optically trapped ultracold rubidium atoms to the field of an ultrashort laser pulse in the intensity range of 1 × 10 11 to 4 × 10 13 W/cm 2 . The experimental data are in perfect agreement with ab-initio theory, based on solving the time-dependent Schrödinger equation without any free parameters. Ultracold targets allow to retrieve absolute probabilities since ionized atoms become apparent as a local vacancy imprinted into the target density, which is recorded simultaneously. We study the strong-field response of 87 Rb atoms at two different wavelengths representing non-resonant and resonant processes in the demanding regime where the Keldysh parameter is close to unity.

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Section: Non-resonant Two-photon Ionization At 511 Nmsupporting

confidence: 92%

Section: Non-resonant Two-photon Ionization At 511 Nmmentioning

confidence: 89%

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confidence: 99%

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Absolute strong-field ionization probabilities of ultracold rubidium atoms

et al. 2018

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“…Soon after this observation, several theoretical papers were published [20][21][22]33] detailing that the strong intensity dependence is due to low-lying excited states shifting into resonance with N -photon absorption. Hart et al [34] extended this technique to sodium atoms, demonstrating enhanced ionization at a specific intensity that corresponds to a Freeman resonance for 3-photon absorption into the Stark-shifted 5p state. These studies, however, did not include the impact on total excitation rates, which is central to the aims of the present investigation.…”

Section: Introductionmentioning

confidence: 99%

Observation of dynamic Stark resonances in strong-field excitation

et al. 2020

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We investigate AC Stark-shifted resonances in argon with ultrashort near-infrared pulses. Using 30 fs pulses we observe periodic enhancements of the excitation yield in the intensity regions corresponding to the absorption of 13 and 14 photons. By reducing the pulse duration to 6 fs with only a few optical cycles, we also demonstrate that the enhancements are significantly reduced beyond what is measurable in the experiment. Comparing these to numerical predictions, which are in quantitative agreement with experimental results, we find that even though the quantum-state distribution can be broad, the enhancements are largely due to efficient population of a select few AC Stark-shifted resonant states rather than the closing of an ionization channel. Because these resonances are dependent on the frequency and intensity of the laser field, the broad bandwidth of the 6 fs pulses means that the resonance condition is fulfilled across a large range of intensities. This is further exaggerated by volume-averaging effects, resulting in excitation of the 5g state at almost all intensities and reducing the apparent magnitude of the enhancements. For 30 fs pulses, volume averaging also broadens the quantum state distribution but the enhancements are still large enough to survive. In this case, selectivity of excitation to a single state is reduced below 25% of the relative population. However, an analysis of TDSE simulations indicates that excitation of up to 60% into a single state is possible if volume averaging can be eliminated and the intensity can be precisely controlled.

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“…The simulated detector images for different kinetic energy at ± U ext = 300 V are depicted in Fig. 2 d: photoelectrons resulting from two-photon ionization (0.68 eV) or from above-threshold ionization (ATI) processes (3.1 eV) 22 , 23 can be clearly identified.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast electron cooling in an expanding ultracold plasma

et al. 2021

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Plasma dynamics critically depends on density and temperature, thus well-controlled experimental realizations are essential benchmarks for theoretical models. The formation of an ultracold plasma can be triggered by ionizing a tunable number of atoms in a micrometer-sized volume of a 87Rb Bose-Einstein condensate (BEC) by a single femtosecond laser pulse. The large density combined with the low temperature of the BEC give rise to an initially strongly coupled plasma in a so far unexplored regime bridging ultracold neutral plasma and ionized nanoclusters. Here, we report on ultrafast cooling of electrons, trapped on orbital trajectories in the long-range Coulomb potential of the dense ionic core, with a cooling rate of 400 K ps−1. Furthermore, our experimental setup grants direct access to the electron temperature that relaxes from 5250 K to below 10 K in less than 500 ns.

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Selective strong-field enhancement and suppression of ionization with short laser pulses

Cited by 29 publications

References 22 publications

Absolute strong-field ionization probabilities of ultracold rubidium atoms

Absolute strong-field ionization probabilities of ultracold rubidium atoms

Observation of dynamic Stark resonances in strong-field excitation

Ultrafast electron cooling in an expanding ultracold plasma

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