Train Of Half-cycle Pulses Research Articles

Population Evolution of Rydberg Rubidium Atoms by Half-Cycle Pulses

Using the B-spline basis set method combined with model potential, the Stark energy level of rubidium atoms in the vicinity of n = 30 is presented. By using a using time-dependent multilevel approach, we calculate the population redistribution of high Rydberg rubidium atoms under the interaction of external time-dependent half-cycle pulses. Our numerical results show that the population of rubidium atoms can be driven to lower or higher n levels with a train of half cycle pulses, the final population distribution of all the l states for the same n is observed after these interactions.

Half-cycle-pulse-train induced state redistribution of Rydberg atoms

Population transfer between low-lying Rydberg states independent of the initial state is realized using a train of half-cycle pulses with pulse durations much shorter than the classical orbital period. We demonstrate experimentally the population transfer from initial states around $n=50$ with $10%$ of the population de-excited down to $n<40$ as well as up to the continuum. This is a demonstration of a state-independent de-excitation technique applicable to the currently produced state distribution of antihydrogen. The measured population transfer matches well to a model of the process for one-dimensional atoms.

Quantum control of electron localization in molecules driven by trains of half-cycle pulses

We present numerical simulations demonstrating efficient control of electron localization dynamics in small molecular systems by a train of half-cycle pulses using the H2+ molecule as a prototypical model system. Simulations are performed using a direct numerical integration of the Schrödinger equation on a grid for a two-degree of freedom system (one electronic, one nuclear coordinate) as well as for an expansion in terms of Born–Oppenheimer basis states. By varying the parameters of the driving field, we systematically explore the underlying control mechanism of this periodically approximately impulsively driven molecular system and demonstrate the robustness of the proposed control scheme.

Transfer of population between Rydberg states using a train of half-cycle pulses

We discuss a protocol for efficient and quick transfer of population between nearly one-dimensional Rydberg states by a chirped train of half-cycle pulses. The chirp refers both to the time interval and relative strength between subsequent pulses. The most spectacular result obtained by the use of this protocol is the transfer of over 10% of the initial population from the high-Rydberg state of $n=50,80$ to much lower ones of ${n}^{\ensuremath{'}}\ensuremath{\approx}10$ in a short time of the order of 1 ns.

Transferring Rydberg wave packets between islands across the chaotic sea

A protocol to take a Rydberg wavepacket that is trapped in a period-1 island, i.e., that is synchronized with the period of the driving field, and transfer it to a period-2 island such that the wavepacket evolves with twice the period is theoretically analyzed and experimentally demonstrated. Such period-doubling transitions are realized using two superposed trains of half-cycle pulses whose relative time delay is varied adiabatically. It is shown that this protocol provides a tool to manipulate the angle variable of a Rydberg wavepacket while its conjugate principal action is maintained constant.

Transporting Rydberg Electron Wave Packets with Chirped Trains of Pulses

A protocol for steering Rydberg electrons towards targeted final states is realized with the aid of a chirped train of half-cycle pulses (HCPs). Its novel capabilities are demonstrated experimentally by transporting potassium atoms excited to the lowest-lying quasi-one-dimensional states in the n(i)=350 Stark manifold to a narrow range of much higher-n states. We demonstrate that this coherent state transfer is, to a high degree, reversible. The protocol allows for remarkable selectivity and is highly efficient, with typically over 80% of the parent atoms surviving the HCP sequence.

Field-Free Molecular Orientation Generated from CyclicRotational States by Using Two Trains of Half-Cycle Pulses

We show that two trains of half-cycle pulses (HCPs) with differentamplitudes irradiating alternately on polar molecules can achieve aremarkable enhancement of field-free orientation compared with the caseof an equal amplitude HCPs train for the same pulse separation. Thiskind of orientation enhancements is mainly due to an optimal adjustmentof the population distribution on every field-free angular momentumeigenstate, in which the populations on the undesired states of highangular momenta are effectively suppressed, and the populations on thedesired states of low angular momenta are correspondingly promoted.

Deexcitation of high-Rydberg-state atoms with a chirped train of half-cycle pulses

Encouraged by the experiments on production of antihydrogen atoms in high Rydberg states we have calculated the effect of deexcitation towards lower states by a chirped train of identical unidirectional half-cycle pulses. The calculations exploit both the one-dimensional and impulse approximations providing convenient analytical formulas for the Rydberg-to-Rydberg transition amplitudes. The calculated deexcitation is shown in terms of the mean value of localization of the Rydberg wave packet in the coordinate space, the Rydberg-state population distribution, the Husimi phase-space distribution function, and the probability density distribution, each of these measures vs the length of the applied train of half-cycle pulses. The results for chirped trains are compared with those for periodic trains and examples of higher deexcitation efficiency of the chirped trains are given.

Generation of attosecond unidirectional half-cycle pulses: Inclusion of propagation effects

Unidirectional half-cycle pulses (HCP) are ideally suitable for shaping, driving, and probing atomic wave packets in momentum space. The shortest HCP presently available have a width of about $500\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ restricting the manipulation of electronic wave packets to those in high-lying Rydberg states. The nonlinear harmonic response of atoms to strong two-color infrared laser pulses with frequencies $\ensuremath{\omega}$ and $2\ensuremath{\omega}$ opens up the opportunity to form trains of ultrafast HCP's on an attosecond time scale. In the present contribution, we investigate the influence of macroscopic propagation effects onto the production of HCP and show that trains of unidirectional attosecond HCP's could be produced under experimentally realistic conditions.

Engineering Very-High-nPolarized Rydberg States Using Tailored Half-Cycle-Pulse Sequences

We show that strongly polarized very-high-n (n approximately 600) potassium Rydberg atoms can be produced by manipulating lower-n (n approximately 350) polarized atoms using a tailored sequence of ultrashort half-cycle pulses (HCPs). The protocol for this involves first a weak HCP that generates transient phase-space localization whereupon a second large HCP of opposite polarity excites the electron to a broad distribution of highly elongated states. This distribution is then refocused by a short periodic train of HCPs using the properties of (un)stable manifolds near fixed points in phase space.

Field-Free Orientation of Molecules with Small PermanentDipole Moments by Using a Train of Half-Cycle Pulses

We present a scheme aiming at the field-free orientation ofmolecules with smaller permanent dipole moments under the framework ofthe half-cycle pulse (HCP) method. Taking the HCCCl molecule as anexample, we show that a train of identical HCPs with special timeintervals can considerably raise the level of the orientation. Thescheme is analytically interpreted in terms of intermittent Rabioscillations by referring to a simplified two-state model.

Field-free charge polarization of mesoscopic rings

We investigate the electron dynamics in a one-dimensional mesoscopic ring under the influence of short, linearly polarized half-cycle electromagnetic pulses. It is shown that the pulses induce a nonequilibrium coherent population of electronic states such that a time-dependent charge polarization of the ring is induced. The time-dependent charge oscillations persist after the pulses have diminished and decay on a time scale determined by the relaxation time. The overall duration of the charge polarization can be controlled by applying an appropriate train of half-cycle pulses. Furthermore, we show that the emission spectrum associated with the pulse-induced charge oscillations can be modulated appropriately by tuning the parameters of the driving pulses. It is shown theoretically how the induced charge polarization can in principle be utilized to measure experimentally the relaxation time of the system in a field-free manner.

Redistributing populations of Rydberg atoms with half-cycle pulses

Expanding the wave function in terms of eigenstates, we calculated the population redistribution of high-Rydberg hydrogen atoms under the interactions of external time-dependent electromagnetic fields. Our numerical results show that populations of Rydberg atoms can be driven down to lower $n$ levels with a train of half-cycle pulses. Oscillations of the Rydberg population through both $n$ levels and $l$ levels are observed during these interactions. The approach may have applications in providing an effective mechanism for producing near ground-state atoms from the initially high-Rydberg distributions found in recombining ultracold plasmas such as encountered in the antihydrogen trapping experiments at CERN.