Photoemission and photoionization time delays and rates

Abstract

Ionization and, in particular, ionization through the interaction with light play an important role in fundamental processes in physics, chemistry, and biology. In recent years, we have seen tremendous advances in our ability to measure the dynamics of photo-induced ionization in various systems in the gas, liquid, or solid phase. In this review, we will define the parameters used for quantifying these dynamics. We give a brief overview of some of the most important ionization processes and how to resolve the associated time delays and rates. With regard to time delays, we ask the question: how long does it take to remove an electron from an atom, molecule, or solid? With regard to rates, we ask the question: how many electrons are emitted in a given unit of time? We present state-of-the-art results on ionization and photoemission time delays and rates. Our review starts with the simplest physical systems: the attosecond dynamics of single-photon and tunnel ionization of atoms in the gas phase. We then extend the discussion to molecular gases and ionization of liquid targets. Finally, we present the measurements of ionization delays in femto- and attosecond photoemission from the solid–vacuum interface.

Using a passively stable attosecond beamline for relative photoemission time delays at high XUV photon energies

“…Measurement techniques like reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) [6][7][8][9][10] and attosecond streaking [11,12] have made the relative Wigner time-delays τ W [13] between different orbitals of atoms and molecules accessible. Several pioneering experiments [6,11,12] have employed isolated attosecond pulses (IAP) and attosecond pulse trains (APTs) to resolve photoemission time-delays [13][14][15][16][17][18][19][20][21][22][23] in atoms, molecules and solids.…”

Strong dependence of photoionization time delay on energy and angle in the neighborhood of Fano resonances

“…This contrasts with nonresonant time delays which are at the attosecond level. Thus, the time delays in the resonance region are about five orders of magnitude larger than nonresonant delays [10][11][12][13][16][17][18][19]; they are also considerably larger than the delays in the vicinity of a similar resonance in Ar [23].…”

“…An early review can be found in [9]. Later works are represented by [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Most of these investigations have involved nonresonant photoemission.…”

Complex interaction processes we need to visualize that successfully fill the quantum cup of a detector

“…This effect is further enhanced by the wave itself, which tries to converge (push) its energy on to the stimulated dipole. The rationale behind the introduction of this push-pull postulate is supported by, first, (i) from the theoretical modeling of radiation field converging on a resonant dipole (see Fig.2, right diagram); second, (ii) from the observations in many fast and efficient resonance fluorescence experiments, which is quantified in Fig.3; third, (iii) from the observed transition time period for photoelectron release is always below a femtosecond [15]. We summarize this collective behavior of resonantly excited atoms as behaving like a large quantum cup, which absorb the necessary quantum of energy through co-operative pushpull mechanism.…”