For many years, laser-driven ion acceleration, mainly proton acceleration, has been proposed and a number of proof-of-principle experiments have been carried out with lasers whose pulse duration was in the nanosecond range. In the 1990s, ion acceleration in a relativistic plasma was demonstrated with ultra-short pulse lasers based on the chirped pulse amplification technique which can provide not only picosecond or femtosecond laser pulse duration, but simultaneously ultra-high peak power of terawatt to petawatt levels. Starting from the year 2000, several groups demonstrated low transverse emittance, tens of MeV proton beams with a conversion efficiency of up to several percent. The laser-accelerated particle beams have a duration of the order of a few picoseconds at the source, an ultra-high peak current and a broad energy spectrum, which make them suitable for many, including several unique, applications. This paper reviews, firstly, the historical background including the early laser-matter interaction studies on energetic ion acceleration relevant to inertial confinement fusion. Secondly, we describe several implemented and proposed mechanisms of proton and/or ion acceleration driven by ultra-short high-intensity lasers. We pay special attention to relatively simple models of several acceleration regimes. The models connect the laser, plasma and proton/ion beam parameters, predicting important features, such as energy spectral shape, optimum conditions and scalings under these conditions for maximum ion energy, conversion efficiency, etc. The models also suggest possible ways to manipulate the proton/ion beams by tailoring the target and irradiation conditions. Thirdly, we review experimental results on proton/ion acceleration, starting with the description of driving lasers. We list experimental results and show general trends of parameter dependences and compare them with the theoretical predictions and simulations. The fourth topic includes a review of scientific, industrial and medical applications of laser-driven proton or ion sources, some of which have already been established, while the others are yet to be demonstrated. In most applications, the laser-driven ion sources are complementary to the conventional accelerators, exhibiting significantly different properties. Finally, we summarize the paper.

An approach for accelerating ions, with the use of a cluster-gas target and an ultrashort pulse laser of 150-mJ energy and 40-fs duration, is presented. Ions with energy 10–20 MeV per nucleon having a small divergence (full angle) of 3.4° are generated in the forward direction, corresponding to approximately tenfold increase in the ion energies compared to previous experiments using solid targets. It is inferred from a particle-in-cell simulation that the high energy ions are generated at the rear side of the target due to the formation of a strong dipole vortex structure in subcritical density plasmas.

We report the generation of 63 J of broadband pulse energies at 0.1 Hz from the J-KAREN-P laser, which is based on an OPCPA/Ti:sapphire hybrid architecture. Pulse compression down to 30 fs indicates a peak power of over 1 PW. High temporal contrast of ${10}^{12}$ prior to the main pulse has been demonstrated with 10 J output energy. High intensities of ${10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ on target by focusing a 0.3 PW laser with an $f/1.3$ off-axis parabolic mirror have been achieved. Fundamental processes of laser matter interaction at over ${10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ intensities belong to a new branch of science that will be the principal research task of our infrastructure.

In a plasma wake wave generated by a high power laser, modulations of the electron density take the shape of paraboloidal dense shells, moving almost at the speed of light. A counterpropagating laser pulse is partially reflected from the shells, acting as relativistic flying mirrors, producing a time-compressed frequency-multiplied pulse due to the double Doppler effect. The counterpropagating laser pulse reflection from the plasma wake wave accompanied by its frequency multiplication (with a factor from 50 to 114) was detected in our experiment.

Duration-controlled amplified spontaneous emission with an intensity of ${10}^{13}\mathrm{W}∕{\mathrm{cm}}^2$ is used to convert a $7.5\text{−}\mu \mathrm{m}$-thick polyimide foil into a near-critical plasma, in which the $p$-polarized, $45\text{−}\mathrm{fs}$, ${10}^{19}\text{−}\mathrm{W}∕{\mathrm{cm}}^2$ laser pulse generates $3.8\text{−}\mathrm{MeV}$ protons, emitted at some angle between the target normal and the laser propagation direction of 45°. Particle-in-cell simulations reveal that the efficient proton acceleration is due to the generation of a quasistatic magnetic field on the target rear side with magnetic pressure inducing and sustaining a charge separation electrostatic field.

We report the demonstrated irradiation effect of laser-accelerated protons on human cancer cells. In vitro (living) A549 cells are irradiated with quasimonoenergetic proton bunches of 0.8–2.4 MeV with a single bunch duration of 15 ns. Irradiation with the proton dose of 20 Gy results in a distinct formation of $\gamma$ -H2AX foci as an indicator of DNA double-strand breaks generated in the cancer cells. This is a pioneering result that points to future investigations of the radiobiological effects of laser-driven ion beams. Unique high-current and short-bunch features make laser-driven proton bunches an excitation source for time-resolved determination of radical yields.