The Grotthuss mechanism

Femtosecond filamentation in transparent media

The field of laser-matter interaction traditionally deals with the response of atoms, molecules, and plasmas to an external light wave. However, the recent sustained technological progress is opening up the possibility of employing intense laser radiation to trigger or substantially influence physical processes beyond atomic-physics energy scales. Available optical laser intensities exceeding ${10}^{22}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ can push the fundamental light-electron interaction to the extreme limit where radiation-reaction effects dominate the electron dynamics, can shed light on the structure of the quantum vacuum, and can trigger the creation of particles such as electrons, muons, and pions and their corresponding antiparticles. Also, novel sources of intense coherent high-energy photons and laser-based particle colliders can pave the way to nuclear quantum optics and may even allow for the potential discovery of new particles beyond the standard model. These are the main topics of this article, which is devoted to a review of recent investigations on high-energy processes within the realm of relativistic quantum dynamics, quantum electrodynamics, and nuclear and particle physics, occurring in extremely intense laser fields.

Extremely high-intensity laser interactions with fundamental quantum systems

A laser-driven particle accelerator, delivering a beam of electrons with a record-breaking energy of 4.2 giga-electron-volts, could lead to compact x-ray lasers or high-energy colliders.

https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.113.245002

Multi-GeV Electron Beams from Capillary-Discharge-Guided Subpetawatt Laser Pulses in the Self-Trapping Regime

Electron Transfer Past and Future (R Marcus) Electron Transfer Reactions in Solution: A Historical Perspective (N Sutin) Electron Transfer--From Isolated Molecules to Biomolecules (M Bixon & J Jortner) Charge Transfer in Bichromophoric Molecules in the Gas Phase (D Levy) Long--Range Charge Separation in Solvent--Free Donor--Bridge--Acceptor Systems (B Wegewijs & J Verhoeven) Electron Transfer and Charge Separation in Clusters (C Dessent, et al) Control of Electron Transfer Kinetics: Models for Medium Reorganization and Donor--Acceptor Coupling (M Newton) Theories of Structure--Function Relationships for Bridge--Mediated Electron Transfer Reactions (S Skourtis & D Beratan) Fluctuations and Coherence in Long--Range and Multicenter Electron Transfer (G Iversen, et al) Lanczos Algorithm for Electron Transfer Rates in Solvents with Complex Spectral Densities (A Okada, et al) Spectroscopic Determination of Electron Transfer Barriers and Rate Constants (K Omberg, et al) Photoinduced Electron Transfer Within Donor--Spacer--Acceptor Molecular Assemblies Studied by Time--Resolved Microwave Conductivity (J Warman, et al) From Close Contact to Long--Range Intramolecular Electron Transfer (J Verhoeven) Photoinduced Electron Transfers Through sigma Bonds in Solution (N--C Yang, et al) Indexes

Electron transfer : from isolated molecules to biomolecules

Rapid progress in the development of high-intensity laser systems has extended our ability to study light–matter interactions far into the relativistic domain, in which electrons are driven to velocities close to the speed of light. As well as being of fundamental interest in their own right, these interactions enable the generation of high-energy particle beams that are short, bright and have good spatial quality. Along with steady improvements in the size, cost and repetition rate of high-intensity lasers, the unique characteristics of laser-driven particle beams are expected to be useful for a wide range of contexts, including proton therapy for the treatment of cancers, materials characterization, radiation-driven chemistry, border security through the detection of explosives, narcotics and other dangerous substances, and of course high-energy particle physics. Here, we review progress that has been made towards realizing such possibilities and the principles that underlie them.

Principles and applications of compact laser–plasma accelerators

The localization and solvation of excess electrons in pure water have been resolved at the femtosecond time scale. Before it becomes solvated, the electron thermalizes and reaches in 110 fs a localized state absorbing in the infrared. This transient species with lifetime 240 fs has been postulated to exist but has not been observed previously in liquid water.

Excess electrons in liquid water: First evidence of a prehydrated state with femtosecond lifetime

Femtosecond dynamics of geminate pair recombination in pure liquid water

The elucidation of detailed mechanisms of primary events in molecular dynamics, charge transfer or reaction dynamics have been made possible by advances in spectroscopic techniques using ultrashort laser pulse generation. In this paper we will center on femtosecond investigations of the very primary processes occurring in pure liquid water following a photoionization of solvent molecules by ultraviolet femtosecond pulses. We have observed in the near ultraviolet region (460, 410 nm), an instantaneous transient absorption with ultrashort lifetime which appears during the initial energy deposition. This induced absorption rises within the pulse, i.e. in less than 100 fs and faster than the precursor of the fully hydrated electron. Its relaxation can be described by a monoexponential law. This ultrashort transient absorption is tentatively assigned to the water cation H2O+. The relaxation would then correspond to the ion-molecule reaction H2O+ + H2O → H3O+ + OH for which the cleavage rate constant is measured to be 1013 s−1 at 294 K. An H/D isotope effect on the dynamics of the ion-water molecule reaction has been observed. These results are analyzed considering the dynamical properties of the protic solvent. The influence of the local dynamical molecular structure of the fluid on the primary reactions involving an ultrafast geminate recombination (e−hyd…X3O+; e−hyd…OX with X = H or D) will be discussed.

Some evidence of ultrafast H2O+-water molecule reaction in femtosecond photoionization of pure liquid water: Influence on geminate pair recombination dynamics

Dear Editor,

In conventional cancer therapy or fundamental radiobiology research, the accumulated knowledge on the complex responses of healthy or diseased cells to ionizing radiation is generally obtained with low-dose rates. Under these radiation conditions, the time spent for energy deposition is very long compared with the dynamics of early molecular and cellular responses. The energy depositions occur concomitantly with primary radio-chemical events (radical reactions), multiple biomolecular damage (membrane and DNA lesions), and repair.1 Such interferences may significantly influence the efficiency of signalling channels and repair processes or the recruitment of transducer proteins for programmed cell death or senescence. They render more complex or uncertain (i) a precise understanding of time-dependent relationships between the initial ionization density profile and the integrated complex response of normal or malignant tumour cells, and (ii) a complete description of biomolecule modifications and genome alterations resulting from energy deposition.

The use of ultrashort pulsed radiation would offer new perspectives for exploring the ‘black box' aspects of long irradiation profiles and favouring the selective control of early damage in living targets. Several attempts were previously performed using nanosecond or picosecond pulsed irradiations on various mammalian cells and radiosensitive mutants at high dose rate.2, 3, 4, 5 The effects of single or multi-pulsed radiations on cell populations were generally analyzed in the framework of dose survival curves or characterized by 2D imaging of γ-H2AX foci and no increase in cytotoxicity was shown compared with a delivery at a conventional dose rate. Moreover, when multi-shot irradiations were performed, the overall time needed to obtain an integrated dose of several Grays again overlapped with the multi-scale dynamics of biomolecular damage–repair sequences and cell signalling steps.

Ideally, a single-shot irradiation delivering a well-defined energy profile, via a very short temporal window, would permit the approach of a real-time investigation of early radiation-induced molecular damage within the confined spaces of cell compartments. Owing to the potential applications of intense ultrashort laser for radiation therapy,6 the model of the A431 carcinoma cell line was chosen. An ultrafast single-shot irradiation strategy was carried out with these radio-resistant human skin carcinoma cells,7 using the capacity of an innovating laser-plasma accelerator to generate quasi mono-energetic femtosecond electron bunches in the MeV domain and to deliver a very high dose rate of 1013 Gy s−1 per pulse.8, 9 The alkaline comet assay,10, 11 which is commonly used to quantify global DNA damage in individual cells (single-, double-strand breaks, and alkali-labile sites), was applied to detect the impact of the 100 fs single-shot 1 Gy exposure with electrons of mean energy 95 MeV (Figure 1). The initial distribution of irradiated cells as a function of the comet tail moment, which reflects the level of DNA damage, shows a shift towards a population of more damaged cells, as compared with the sham-irradiated cells. The fraction of cells with damage above a control tail moment value of 4 exhibited an eightfold increase over that of the control cells. When carcinoma cells were maintained for 60 min at 37°C before the comet assay to allow DNA repair, the distributions of irradiated and non-irradiated cells became similar, indicating repair of the DNA lesions. The recovery of a near homogeneous distribution of low comet tail moments argues for the reparability of the global DNA lesions triggered by a single femtosecond irradiation shot at 1 Gy. To assess the consequences of ultrafast electron-induced damage, the cytotoxicity was characterized in the same experiment, using a novel survival assay at a single-cell level.12 Two weeks after the femtosecond 1 Gy irradiation, a 95% survival was observed from a panel of 300 cells seeded in clonal microcultures.



Figure 1

Induction of DNA damage in skin carcinoma cells irradiated at a very high dose rate by a single ultrashort bunch of high-energy electrons. (a) Image showing the overlap between the 2D dose deposition of a femtosecond quasi-monoenergetic electron bunch ...



This first investigation of a single-shot 1 Gy irradiation performed at high energy level and very high dose rate demonstrates that a measurable assessment of immediate and reversible DNA damage in carcinoma cells can be explored at the single-cell level. This breakthrough opens the possibility of a complete characterization of induced damage and repair, and notably of DNA double-strand breaks. In the framework of advanced spatio-temporal radiation biology concepts,13 one challenge of such a non-conventional irradiation concerns the complete understanding of the multi-scale events triggered by the initial energy deposition, starting from the production and amplification of the localized radical processes and the induction of the primary lesions. A second challenge is deciphering the integrated cell response to these primary events, including cell signalling, damage sensing and DNA repair, and characterizing their late effects in cells, such as cell death, gene mutation and genomic instability. The emergence of ultrafast high-energy radiation biology could foreshadow the time-dependent and nanometric spatially defined effects in biomolecular architectures, such as aqueous groove of DNA, nucleosomes, protein pockets and sub-cellular compartments. Establishing an innovating approach of real-time nanodosimetry represents a prerequisite for the control of irradiations of living cells at very high dose rates. Moreover, the influence of the quality of short-pulsed particle beams (electrons and protons) on the relative biological efficiency (RBE) needs to be carefully evaluated, in synergy with ultrafast dose-fractionating protocols. Such knowledge is a necessary step before medical applications of ultrashort laser-accelerated particle beams. Currently, X-rays in the few MeV energy range represent the majority of ionizing radiations used for cancer therapy. The dose deposited by very high-energy electron beams in the tissue depth is higher and could be beneficial to target deep tumors.14 Specific conditions afforded by very high dose rates and ultrashort dose fractionations would permit the real-time control of amplified radio-sensitivity during selective targeting protocols, in combination with the modern prodrug strategies developed in chemotherapy.15 Ultrafast radiation biology thus represents a newly emerging interdisciplinary field, in strong synergy with the most recent progresses of ultrashort radiation sources, high-energy bioradical femtochemistry, molecular biology and anti-cancer therapy.

/pdf/exploring-ultrashort-high-energy-electron-induced-damage-in-3936gfvl9y.pdf

Yann Gauduel

Papers

Principles and applications of compact laser–plasma accelerators

Excess electrons in liquid water: First evidence of a prehydrated state with femtosecond lifetime

Femtosecond dynamics of geminate pair recombination in pure liquid water

Some evidence of ultrafast H2O+-water molecule reaction in femtosecond photoionization of pure liquid water: Influence on geminate pair recombination dynamics

Exploring ultrashort high-energy electron-induced damage in human carcinoma cells