Quantum beat oscillations in the two-color-photoionization continuum of neon and their dependence on the intensity of the ionizing laser pulse

Abstract

We investigate quantum beat oscillations in the photoionization continuum of Ne atoms that are photoionized by absorption of two photons via a group of excited bound states using ultrashort extreme ultraviolet and infrared laser pulses. The extreme ultraviolet pulse starts an excited-state wave packet that is photoionized by a high-intensity infrared pulse after a variable time delay. We analyze the continuum quantum beats from this two-step photoionization process and their dependence on the photoelectron kinetic energy. We find a pronounced dependence of the quantum beat amplitudes on the photoelectron kinetic energy. The dependence changes significantly with the applied infrared laser-pulse intensity. The experimental results are in good qualitative agreement with a model calculation that is adapted to the experimental situation. It accounts for the intensity dependence of the quantum beat structure through the coupling of the excited-state wave packet to other bound Ne states induced by the high-intensity infrared laser pulse.

Ionization delays in few-cycle-pulse multiphoton quantum-beat spectroscopy in helium

“…For example, for one-photon ionization we find a considerable phase contribution stemming from depletion of the initial wavepacket that occurs for helium singly excited states already for intensities of 1 • 10 12 W/cm 2 . Similarly, modifications of beating amplitudes due to the intensity of an NIR probing pulse were also seen in neon [17] in an experiment similar to the one proposed here. Simulations based on a few-state model could identify population transfer among bound states and ac Stark shifts by the probing pulse as reasons for the intensity dependence in [17].…”

“…Similarly, modifications of beating amplitudes due to the intensity of an NIR probing pulse were also seen in neon [17] in an experiment similar to the one proposed here. Simulations based on a few-state model could identify population transfer among bound states and ac Stark shifts by the probing pulse as reasons for the intensity dependence in [17]. Such modifications by the probing step have to be understood for quantum state holography and quantum beat spectroscopy to be a valuable tool.…”

Attosecond transient absorption probing of electronic superpositions of bound states in neon: detection of quantum beats

“…A prominent quantum beat between the spin-orbit-split 3d levels is characterized in detail. These quantum beats have been previously observed via photoionization [18,19]. Here, the quantum beating is directly imprinted onto the spectrum of the extreme ultraviolet pulse.…”

Real-Time Observation of Interference between Atomic One-Electron and Two-Electron Excitations

“…The two-dimensional plot indicates that the amplitude of the oscillation that is superimposed on the decaying electron yield is a function of the photoelectron kinetic energy. This is expected and known from conventional quantum beats (see, e.g., [16]). Only at those kinetic energies where the quantum paths from the initial Kr ground state via the two Fano resonances to the final state c f are indistinguishable, quantum beats are expected to occur.…”

“…The experimental setup has been described previously [16]. Briefly, Ti:sapphire (Ti:Sa) laser pulses [central wavelength: 787 nm (1.575 eV); bandwidth (full width at half maximum [FWHM]): 32 nm (64 meV); repetition rate: 1 kHz] with a pulse width of 40 AE 5 f sec were used to generate high-order harmonic pulses in Ar gas.…”