Effects of imperfect unipolarity on the ionization of Rydberg atoms by subpicosecond half-cycle pulses

Tielking, N. E.; Bensky, Thomas J.; Jones, Robert R.

doi:10.1103/physreva.51.3370

Cited by 49 publications

(23 citation statements)

References 16 publications

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“…In previous studies of Rydberg atom/HCP interactions, classical simulations have provided valuable insight into the electron dynamics as well as quantitative agreement with experimental results [1,2,5,14]. We find that the current experiment is equally well suited to classical analy sis.…”

Section: Level Depends Only On the Peak Field In The Component Pulsessupporting

confidence: 56%

“…The data and theory clearly show that there is a significant change in the ionization dynamics as one moves from the short-pulse regime, t HCP ø t K �n ¿ 15�, to the long-pulse regime, t HCP ¿ t K �n ø 15�. We attribute the slight discrepancy in the experimental and theoretical values of n at which the transition between these two regimes occurs to small uncertainties in the temporal shape of the HCP [14].…”

Section: Level Depends Only On the Peak Field In The Component Pulsesmentioning

confidence: 89%

“…The calibration of the field amplitudes is obtained by comparing the ionization yield observed with a single HCP to that calculated classically as suggested in Ref. [14]. The traces are offset from each other for clarity.…”

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confidence: 99%

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Ionization of Na Rydberg Atoms by Subpicosecond Quarter-Cycle Circularly Polarized Pulses

1997

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We report the first observation of ionization of Rydberg atoms by subpicosecond, circularly polarized THz radiation. The field amplitude in these pulses is non-negligible for only one-quarter of an optical cycle. The experiment is performed in the short-pulse regime, where the duration of the ionizing pulse is shorter than the classical Kepler period of the Rydberg electron. We find that the ionization probability for these atoms is remarkably insensitive to the time-varying polarization of the THz field.Over the years, multiphoton ionization of atoms has been recognized as a process of fundamental importance for understanding the dynamic interaction between atoms and intense radiation fields. Very recently, a number of in vestigations have led to the discovery of novel ionization dynamics during the interaction of highly excited Rydberg atoms with strong, subpicosecond pulses of THz radiation [1][2][3][4][5][6][7]. The unipolar electric field in these pulses resembles one-half of an optical cycle of an oscillating electric field so they are commonly referred to as "half-cycle" pulses (HCPs). To date, experimental and theoretical HCP stud ies have considered only linearly polarized fields. In this configuration, HCPs provide an impulsive unidirectional "kick" that can literally push a Rydberg electron off an atom [1][2][3]8]. Although the ionization dynamics are now relatively well understood for unidirectional fields, previ ous work with multi-cycle laser [9] and microwave pulses [10], as well as classical intuition, suggests that ionization by subpicosecond far-infrared pulses might proceed very differently with circularly polarized radiation.In this Letter, we describe the results of the first experi ment on the ionization of atoms by subpicosecond circu larly polarized THz pulses. The duration of these pulses is so brief that the electric field vector rotates by only 90 ± during the pulse. In the language of classical physics, an electron exposed to this "quarter-cycle" circularly po larized pulse is subjected to a rapidly rotating force in contrast to a unidirectional kick. Therefore, one should expect to observe interesting new ionization dynamics us ing these novel pulses.The interaction of atoms with these pulses is also in teresting from the point of view of collision physics. A quarter-cycle field pulse bears a strong resemblance to the time-dependent field seen by an atom undergoing a colli sion with a charged particle, as shown explicitly in Fig. 1. In each case, the field can be described as a combination of a half-cycle cosine pulse along one axis (the transverse collision field) and a "single-cycle" sine component along an orthogonal axis (the longitudinal collision field). In contrast to true collision experiments, the relative veloc ity, impact parameter, and orientation of the colliding par ticles can be precisely controlled in a "mock collision" by adjusting the duration, field amplitude, and polarization of the quarter-cycle field pulse.It is well known that circularly polarized radiation can...

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Section: Level Depends Only On the Peak Field In The Component Pulsessupporting

confidence: 56%

Section: Level Depends Only On the Peak Field In The Component Pulsesmentioning

confidence: 89%

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Ionization of Na Rydberg Atoms by Subpicosecond Quarter-Cycle Circularly Polarized Pulses

1997

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“…Therefore, HCPs develop a long ''tail'' of opposite polarity during propagation such that in the far field, the integral of the electric field is zero. The effects of this impurity on Rydberg atom excitation have been investigated earlier [4,6,8] and are not the subject of this Letter. THz half-cycle pulses are being used for rotational spectroscopy of molecules in the gas phase [9,10].…”

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confidence: 99%

Transitions Driven by a Missing Frequency

Gürtler

Zande

2004

Phys. Rev. Lett.

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We demonstrate an intricate combination of strong and weak interactions of a broadband half-cycle pulse with Rydberg atoms. A transition, which is resonant with a frequency that was taken out of the frequency spectrum, can be enhanced. In the experiment, the broadband ultrashort terahertz half-cycle pulse propagates through water vapor, which absorbs on discrete lines in the spectrum, thus removing frequencies from the spectrum. The resulting pulse interacts with a rubidium Rydberg atom, which has a resonant transition with one of the missing frequencies. Under certain conditions, the transition probability is enhanced although the associated frequency was missing in the spectrum.

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“…The HCP is linearly po larized along the bias field axis, and its field amplitude is proportional to the bias voltage [2]. Small nonunipo lar features are removed from the HCP using a second, gated GaAs wafer as a transient attenuator [2,6]. Approxi mately 20 nsec after the HCP a 150 V pulse is applied…”

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Half-Cycle Pulse Assisted Electron-Ion Recombination

1998

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Unipolar "half-cycle" electric field pulses (HCPs) have been used to recombine free electrons and calcium ions. The field assisted process is very similar to controlled three-body recombination in plasmas. We report on experiments that utilize HCP assisted recombination to probe the probability distribution of continuum electron wave packets and produce bound wave packets that are highly localized in three spatial dimensions.The combination of free electrons and ions to form neutral atoms is a complicated process that can proceed through a variety of different mechanisms including dielectronic, radiative, or three-body recombination [1]. Al though these mechanisms are quite different in detail, in general, recombination is made possible through the trans fer of energy and momentum from the free electron to a third body. The recombination process is inherently time dependent, and the capture of a free electron can result in the formation of a complicated coherent superposition state within each atom. Because of the random nature of electron-ion scattering events in the laboratory, the bound wave packet produced via recombination varies widely from one atom to another due to the different scattering conditions through which each was formed. Consequently, standard theoretical and experimental studies parametrize the process using time-independent recombination rates and branching ratios for capture into various excited states of the atom [1].The experiments described in this Letter are aimed at studying controlled electron-ion recombination in the time domain. The results of these experiments provide new in formation on coherent recombination processes as well as demonstrate the utility of field assisted recombination for probing continuum electron dynamics and producing novel bound wave packets. Specifically, subpicosecond "half cycle" field pulses (HCPs) [2,3] have been used to assist the recombination of a well-characterized continuum wave packet with its parent ion. Although the recombination can be formally classified as radiatively assisted [1], the unique nature of the unipolar field pulse makes the process more closely related to three-body recombination. To make the analogy with three-body recombination the HCP field is equated with the transverse field produced by a passing ion or electron. The impulse provided by the field [4,5] extracts momentum and energy from the free electron, fa cilitating its capture by an ion.In the experiments, a 1.5 psec laser pulse photoionizes a tightly bound electron in calcium, producing a continuum wave packet which travels away from the Ca 1 ion in the form of a thin shell. After the ionizing laser pulse, the ions and free electrons are exposed to a HCP whose duration is so short that the continuum wave packet is essentially frozen during the pulse. The electron receives a R momentum "kick" or impulse, A � � 2 F � HCP �t� dt, from the HCP [4,5], where F � HCP �t� is the HCP field amplitude. All equations are given in atomic units unless otherwise noted. The impulse can hal...

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Effects of imperfect unipolarity on the ionization of Rydberg atoms by subpicosecond half-cycle pulses

Cited by 49 publications

References 16 publications

Ionization of Na Rydberg Atoms by Subpicosecond Quarter-Cycle Circularly Polarized Pulses

Ionization of Na Rydberg Atoms by Subpicosecond Quarter-Cycle Circularly Polarized Pulses

Transitions Driven by a Missing Frequency

Half-Cycle Pulse Assisted Electron-Ion Recombination

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