Dynamics Of Rydberg Wave Packets Research Articles

Dynamic quantum state holography

We present a pulse-shaper-based holographic technique for the time-resolved and phase-sensitive observation of ultrafast quantum dynamics. The technique combines bichromatic white light polarization pulse shaping with the tomographic reconstruction of photoelectron wave packets. The physical scheme is based on the interference of a probe wave packet from $N+1$ resonance-enhanced multiphoton ionization via the target states and a reference wave packet from $M+1$ multiphoton ionization of the ground state. To create the wave packets, we employ carrier-envelope phase stable bichromatic ($M\ensuremath{\omega}$:$N\ensuremath{\omega}$) pump-probe pulse sequences. The scheme is demonstrated on femtosecond Rydberg wave-packet dynamics in potassium atoms using corotating circularly polarized ($2\ensuremath{\omega}$:$3\ensuremath{\omega}$) pulse sequences. The interference of continuum states with different angular momenta yields a crescent-shaped photoelectron wave packet rotating in the laser polarization plane due to the interplay of the optical phase and the accumulated quantum phase. Carrier-envelope phase control of the rotation provides access to the photoelectron asymmetry, enabling background-free detection of the crescent's angular motion which maps the bound-electron dynamics.

Wavepacket dynamics of a Rydberg atom monitored by a pair of time-delayed laser pulses

We have investigated the Rydberg state population of an argon atom by an intense laser pulse and its wavepacket dynamics monitored by another successive laser pulse in the tunneling regime. A wavepacket comprising a superposition of close high-lying Rydberg states is irradiated by a multicycle laser pulse, where the sub-wave components in the wavepacket have fixed relative phases. A time-delayed second laser pulse is employed to apply on the excited Rydberg atom. If the time is properly chosen, one of the sub-wave components will be guided towards the ionization area while the rest remains intact. By means of this pump–probe technique, we could control and monitor the Rydberg wavepacket dynamics and reveal some interesting phenomenon such as the survival rate of individual Rydberg states related to the classical orbital period of electron.

Localization of electronic wave packets in H2

We demonstrate localization of electronic wave packets in the coupled channels of rotating and vibrating H2 molecules using phase-shaped excitation pulses. The dynamics of Rydberg wave packets and their controlled preparation has been studied in detail in hydrogenic systems. We report here on a more general situation, where the strong channel couplings require full shaping of the optical phase, rather than a linear or quadratic chirp which is often sufficient in hydrogenic systems, or sequences of pulses which can be applied to uncoupled Rydberg series. The complex excitation functions for the shaped pulses are calculated and illustrate the longer duration and the complicated transients of the excitation process compared to excitation by an unshaped reference pulse.

Stark-assisted population control of coherent CS2 4f and 5p Rydberg wave packets studied by femtosecond time-resolved photoelectron spectroscopy

A two-color (3+1(')) pump-probe scheme is employed to investigate Rydberg wave packet dynamics in carbon disulfide (CS(2) (*)). The state superpositions are created within the 4f and 5p Rydberg manifolds by three photons of the 400 nm pump pulse, and their temporal evolution is monitored with femtosecond time-resolved photoelectron spectroscopy using an 800 nm ionizing probe pulse. The coherent behavior of the non-stationary superpositions are observed through wavepacket revivals upon ionization to either the upper (12) or lower (32) spin-orbit components of CS(2) (+). The results show clearly that the composition of the wavepacket can be efficiently controlled by the power density of the excitation pulse over a range from 500 GWcm(2) to 10 TWcm(2). The results are consistent with the anticipated ac-Stark shift for 400 nm light and demonstrate an effective method for population control in molecular systems. Moreover, it is shown that Rydberg wavepackets can be formed in CS(2) with excitation power densities up to 10 TWcm(2) without significant fragmentation. The exponential 1e population decay (T(1)) of specific excited Rydberg states are recovered by analysis of the coherent part of the signal. The dissociation lifetimes of these states are typically 1.5 ps. However, a region exhibiting a more rapid decay ( approximately 800 fs) is observed for states residing in the energy range of 74 450-74 550 cm(-1), suggestive of an enhanced surface crossing in this region.

Coherent control in the continuum: autoionization of Xe

We explore, by time-dependent MQDT calculations, the potential for coherent control of autoionization using phase-shaped optical pulses. We investigate the effect of step-like spectral phase modulation on the autoionization dynamics of Rydberg wave packets in the Xe atom. It is found that a single step in the spectral phase has a substantial effect on the branching ratio, if the position of the step corresponds to a resonance in the Rydberg system. These effects are enhanced if the optical pulse is engineered to have multiple steps that reflect the periodicity inherent in Rydberg systems. Further calculations indicate that, to a large extent, the effects of phase manipulations are additive and independent. We also compare this new approach with approaches based on sequences of identical coherent optical pulses. The two methods are complementary, and we suggest that in the future they may be combined.

One-Dimensional versus Three-Dimensional Approaches to the Rydberg Wave Packet Dynamics

One-Dimensional versus Three-Dimensional Approaches to the Rydberg Wave Packet Dynamics

Controlling the radial dynamics of Rydberg wavepackets in Xe using phase-lockedoptical pulse sequences

We employ a sequence of two phase-locked optical pulses, separated by half aclassical orbit period, to control the radial dynamics of electron wavepackets inXe. We eliminate either even or odd principal quantum number states from thewavepacket and distinguish between these systems by looking at the wavepacketspectrum at different partial revivals. The experimentally observed dynamics arecompared with calculations based on multichannel quantum defect theory and theobservations are interpreted in terms of the time and phase evolution of thepopulation amplitudes of the Rydberg states contributing to the wavepacket.

The role of phase in molecular Rydberg wave packet dynamics

The dynamics of Rydberg wave packets in NO are investigated in the regime where the electronic period is comparable with the rotational motion of the molecular ion core. The presence of a rotating molecular core manifests itself in the wave packet dynamics as a series of peaks separated by the rotational beat period TRot, but offset by ΔμTRot, where Δμ is the difference in quantum defect between the two dominant Rydberg series in the superposition. We rationalize this by treating the dynamics of a wave packet created from a coherent superposition of two interleaved Rydberg series as two separate electron wave packets, which interfere with one another when they overlap spatially. There is a periodic phase difference between the two wave packets that depends on the rotational energy of the core in each Rydberg series and also on the quantum defects. The resulting interference pattern in the Rydberg population manifests itself as peaks in the wave packet spectrum at the stroboscopic period.

Semiclassical modeling of Rydberg wave-packet dynamics in diatomic molecules: Average decoupling theory

The semiclassical dynamics of Rydberg electronic wave packets in diatomic molecules is investigated using a sum over classical trajectories method, which is based on the semiclassical form of Feynman's path integral. Our approach allows us to calculate intramolecular energy redistribution rates based on averaging of coupling parameters over classical trajectories associated with time-dependent parts of the overall system that exhibit different periodicities. The accuracy of our method is tested against perturbation theory and good agreement is obtained. A resonance structure in the computed autocorrelation function has also been observed in the case of rotating nuclei, when the periods of the classical trajectories of the electron match an integer multiple of the rotational period. This has previously been called the stroboscopic effect.

Femtosecond time-resolved Rydberg wave-packet dynamics in the two-electron system calcium

We have investigated the radial Rydberg wave-packet dynamics in the two-valence-electron atom calcium by femtosecond pump-probe spectroscopy. The classical periodic motion of the Kepler electron as well as the quantum mechanical revival structure were observed when employing the phase sensitive detection technique. Preliminary results are reported on Rydberg wave-packet autoionization under the influence of an isolated excitation of the remaining outer core electron.

Coherent Pulse Propagation and the Dynamics of Rydberg Wave Packets

The pulse reshaping of femtosecond laser pulses tuned to Rydberg transitions of strontium vapor is observed experimentally. We show theoretically that their shape closely reflects the dynamics of Rydberg wave packets induced by the pulses. The decay and compression of Rydberg wave packets excited by both Fourier limited and chirped fs pulses is presented.

Visualization of the core-scattering dynamics of Rydberg wave packets

We present classical and quantum studies of the scattering dynamics of Rydberg electron wave packets from the electronic core of alkali atoms. In quantum systems an ideal state for studying such effects is an angularly localized wavepacket in which the primary effect of the scattering is to cause precession. The scattering is enhanced by the application of an external dc electric field. We calculate and animate the field-induced dynamics of both hydrogenic and alkali wavepackets and compare them to classical atomic models. We end that in alkali systems the scattered wave function can be divided into two components: one whose nearly hydrogenic behavior is due to quantum interference near the core, and another which exhibits the orbital precession found in classical models of nonhydrogenic atoms.

Dynamics of Rydberg wave packets generated by half-cycle pulses.

Wave packets comprising a superposition of very-high-lying Rydberg states have been created using a half-cycle pulse (HCP). The properties of the wave packet are probed using a second HCP that is applied following a variable time delay. The second pulse ionizes a fraction of the atoms and the survival probability exhibits pronounced oscillations that are associated with the quasiperiodic evolution of the wave packet. Good agreement is found between the experimental data and the results of a classical trajectory Monte Carlo simulation demonstrating that, for the times investigated, classical-quantum correspondence holds and quantum corrections are negligible.

Observation of Rydberg wave packet dynamics in a Coulombic and magnetic field.

Rydberg electron wave packets are investigated, using phase-modulated detection, In the absence of any external field we observe pure radial motion of a bound electron wave packet showing both the first integer revival and all fractional revivals up to the seventh order; in the presence of a magnetic field (0.81 T) both paramagnetic and diamagnetic effects are observed. Paramagnetism is visible in the time-correlation function of the wave packet as a sinusoidal intensity modulation, with a period of 43 ps, superimposed on the radial motion; the diamagnetism is observed as a decrease in the radial recurrence times (by up to 35%).