Autler-Townes Splitting in the Multiphoton Resonance Ionization Spectrum of Molecules Produced by Ultrashort Laser Pulses

Abstract

We report for the first time the proper conditions to observe Autler-Townes splitting (ac-Stark splitting) from vibrationally coherent states belonging to the different electronic terms of a diatomic molecule. Wave packet dynamics simulations demonstrate that such a process is feasible by multiphoton resonance ionization of the molecule Na 2 with a single ultrashort intense laser pulse. With the ultrahigh time resolution of a femtosecond laser pulse, one can directly measure the absolute value of the transition dipole moment between any kinds of molecular states by this kind of Autler-Townes splitting, which is a function of the internuclear distance R. DOI: 10.1103/PhysRevLett.91.023002 PACS numbers: 33.80.-b, 42.50.-p Atomic Autler-Townes (AT) splitting has been observed on a radio-frequency transition for a long time [1], but AT splitting in a gas-phase molecule has only recently been investigated [2 -6]. Quesada et al. [2] reported the transition dipole moment of H 2 by measuring the ratio of AT splitting to the electric field strength. Qi et al. demonstrated that the transition dipole moment of the lithium dimer could be measured by AT splitting using cw triple resonance spectroscopy [5,6]. AT splitting on the Na atom [7] and a semiconductor [8] with an ultrashort intense pulse have also been explored recently [8]. But, perhaps, because of the relatively small size of the typical molecular transition dipole moment, few papers reported any result about molecular AT splitting on vibrationally coherent states with an ultrashort laser pulse.In this Letter, with multiphoton ionization wave packet dynamics simulations, we demonstrate that one can observe AT splitting in the photoelectron spectrum with a proper single laser pulse and a prototype dimer Na 2 . Because of the direct relation of AT splitting with the local transition dipole moment and the intensity of the electric field, AT splitting can be used to precisely measure, in principle, the peak intensity of the laser pulse if the transition dipole moment is known, which is not easy to accurately determine. On the other hand, one can also measure the internuclear-distance R-dependent local transition dipole moment by AT splitting with a properly localized wave packet if the intensity of the ultrashort laser pulse is known.Along with the development of the ultrashort laser pulse, real-time molecular dynamics has been directly observed and many new phenomena have been investigated [9-13] and will be discovered. In explanation and foreseeing the experimental results, quantum wave packet dynamics simulations play the central role [14 -18]. In order to entail the excitation of a local coherent wave packet with the common available femtosecond laser system, one must choose the target molecule characterized by small vibrational energy. From this point of view, the sodium dimer is an excellent prototype molecule [12,16 -18], also for its detailed information of potential energy curves and that of its single cation [19,20]. Therefore we employed a model of the s...

FEMTOSECOND LASER PHOTOELECTRON SPECTROSCOPY ON ATOMS AND SMALL MOLECULES: Prototype Studies in Quantum Control

“…The simultaneous excitation/ionization technique therefore permits the use of photoelectron spectra as a fingerprint of the quantum mechanical phase imparted by the interaction with the shaped laser pulse. In passing, we note that similar effects are also present in molecular systems, although the vibrational dynamics tends to obscure the interference fringes (113,116,117). The potential of phase locked pulse sequences as a novel spectroscopic tool was demonstrated on single photon molecular transitions (118).…”

Three‐peak Autler‐Townes splitting in the photoelectron spectrum of Li2 molecules caused by femtosecond laser pulses

“…Qi et al pointed out that A‐T splitting induced by cw pulse can be used as a way to facilitate all‐optical control of molecular angular momentum alignment 14, 15. Sun and Lou demonstrated that one can observe the A‐T splitting in the photoelectron spectrum of a two‐level Na 2 system with a proper ultrashort laser pulse 16. We studied theoretically this kind of A‐T splitting in the photoelectron spectrum for a Li 2 molecular system using one‐dimension wave packet method 17.…”

Attosecond-magnetic-field-pulse generation by coherent circular molecular electron wave packets

“…(X = 40 nm). The partial recovery of the ground-state population before the end of the pulse we ascribe to incomplete single-cycle Rabi oscillations which can occur with short intense laser pulses [34,35].…”