The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today’s lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration ($ϵ>500\mathrm{MeV}$) with an intense laser pulse ($a_0>10$). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons ($\gamma$ rays), consistent with a quantum description of radiation reaction. The generated $\gamma$ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy ${ϵ}_{\mathrm{crit}}>30\mathrm{MeV}$.

The description of the dynamics of an electron in an external electromagnetic field of arbitrary intensity is one of the most fundamental outstanding problems in electrodynamics. Remarkably, to date, there is no unanimously accepted theoretical solution for ultrahigh intensities and little or no experimental data. The basic challenge is the inclusion of the self-interaction of the electron with the field emitted by the electron itself—the so-called radiation reaction force. We report here on the experimental evidence of strong radiation reaction, in an all-optical experiment, during the propagation of highly relativistic electrons (maximum energy exceeding 2 GeV) through the field of an ultraintense laser (peak intensity of $4\times {10}^{20}\mathrm{W}/{\mathrm{cm}}^2$). In their own rest frame, the highest-energy electrons experience an electric field as high as one quarter of the critical field of quantum electrodynamics and are seen to lose up to 30% of their kinetic energy during the propagation through the laser field. The experimental data show signatures of quantum effects in the electron dynamics in the external laser field, potentially showing departures from the constant cross field approximation.

The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies. Whilst the evolving nature of laser-plasma interactions can limit the effectiveness of individual acceleration mechanisms, it can also enable the development of hybrid schemes, allowing additional degrees of control on the properties of the resulting ion beam. Here we report on an experimental demonstration of efficient proton acceleration to energies exceeding 94 MeV via a hybrid scheme of radiation pressure-sheath acceleration in an ultrathin foil irradiated by a linearly polarised laser pulse. This occurs via a double-peaked electrostatic field structure, which, at an optimum foil thickness, is significantly enhanced by relativistic transparency and an associated jet of super-thermal electrons. The range of parameters over which this hybrid scenario occurs is discussed and implications for ion acceleration driven by next-generation, multi-petawatt laser facilities are explored.

The amplification of laser light to generate powers large enough to affect the nucleus has been the desire of scientists since the invention of the laser 40 years ago. Many lasers, including tabletop varieties, now have pulse powers greater than the electrical power generated by all the world's power plants combined. When this power is focused to dimensions of a few microns, laser-driven nuclear phenomena can occur. Here we review the developments in this research field and describe the potential of laserproduced proton, neutron, and heavy ion beams, together with isotope and isomer production.

The acceleration of ions from ultrathin foils has been investigated by using 250 TW, subpicosecond laser pulses, focused to intensities of up to $3\times {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}$. The ion spectra show the appearance of narrow-band features for protons and carbon ions peaked at higher energies (in the $5–10\mathrm{MeV}/\mathrm{\text{nucleon range}}$) and with significantly higher flux than previously reported. The spectral features and their scaling with laser and target parameters provide evidence of a multispecies scenario of radiation pressure acceleration in the light sail mode, as confirmed by analytical estimates and 2D particle-in-cell simulations. The scaling indicates that monoenergetic peaks with more than $100\mathrm{MeV}/\mathrm{\text{nucleon}}$ are obtainable with moderate improvements of the target and laser characteristics, which are within reach of ongoing technical developments.