Abstract
In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. However on tuning the laser to the lowest resonant transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative. These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. Here we show that on tuning to a higher resonant transition, a previously unknown type of interatomic Coulombic decay, intra-Rydberg ICD occurs. In it, de-excitation of an atom to a close-lying Rydberg state leads to electron emission from another neighbouring Rydberg atom. Moreover, systems multiply excited to higher Rydberg states will decay by a cascade of such processes, producing even more ions. The intra-Rydberg ICD and cascades are expected to be ubiquitous in weakly-bound systems exposed to high-intensity resonant radiation.
Highlights
In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold
The kinetic energy distribution of the emitted electrons was measured with a velocity map imaging (VMI) spectrometer
We see that the peak becomes more prominent at higher free electron laser (FEL) intensities, has an asymmetric shape, and a developing plateau on the low-energy side
Summary
In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. On tuning the laser to the lowest resonant transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. It is worth noting that ICD has been observed in molecular water clusters, suggesting that ICD may occur in waterabundant biological systems[4,5] and be an important source of genotoxic low-energy electrons and radical cations It has been shown theoretically and verified experimentally that ICD is not an isolated phenomenon, but might be part of complex cascade relaxation mechanisms, occurring for instance following an Auger decay process[6,7,8,9,10,11,12,13,14]. We note that similar processes have been studied in a completely different regime and form of matter, namely Rydberg gases, and shown to be responsible for the so-called avalanche ionization phenomenon a b
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