We present measurements of a magnetic reconnection in a plasma created by two laser beams (1 ns pulse duration, $1\times {10}^{15}\mathrm{W}{\mathrm{cm}}^{-2}$) focused in close proximity on a planar solid target. Simultaneous optical probing and proton grid deflectometry reveal two high velocity, collimated outflowing jets and 0.7—1.3 MG magnetic fields at the focal spot edges. Thomson scattering measurements from the reconnection layer are consistent with high electron temperatures in this region.

Experiments were performed to investigate the propagation of a high intensity ($I\sim {10}^{21}\mathrm{W}{\mathrm{cm}}^{-2}$) laser in foam targets with densities ranging from $0.9n_c$ to $30n_c$. Proton acceleration was used to diagnose the interaction. An improvement in proton beam energy and efficiency is observed for the lowest density foam ($n_e=0.9n_c$), compared to higher density foams. Simulations show that the laser beam penetrates deeper into the target due to its relativistic propagation and results in greater collimation of the ensuing hot electrons. This results in the rear surface accelerating electric field being larger, increasing the efficiency of the acceleration. Enhanced collimation of the ions is seen to be due to the self-generated azimuthal magnetic and electric fields at the rear of the target.

The generation of quasimonoenergetic electron beams, with energies up to 200 MeV, by a laser-plasma accelerator driven in a hydrogen-filled capillary discharge waveguide is investigated. Injection and acceleration of electrons is found to depend sensitively on the delay between the onset of the discharge current and the arrival of the laser pulse. A comparison of spectroscopic and interferometric measurements suggests that injection is assisted by laser ionization of atoms or ions within the channel.

The effect of laser-focusing conditions on the evolution of relativistic plasma waves in laser-wakefield accelerators is studied both experimentally and with particle-in-cell simulations. For short focal-length ($w_0<{\lambda }_p$) interactions, beam breakup prevents stable propagation of the pulse. High field gradients lead to nonlocalized phase injection of electrons, and thus broad energy spread beams. However, for long focal-length geometries ($w_0>{\lambda }_p$), a single optical filament can capture the majority of the laser energy and self-guide over distances comparable to the dephasing length, even for these short pulses ($c\tau \approx {\lambda }_p$). This allows the wakefield to evolve to the correct shape for the production of the monoenergetic electron bunches, as measured in the experiment.

Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of $I\sim 1\times {10}^{15}\text{W}{\text{cm}}^{-2}$ . Through the well known $\nabla n_e\times \nabla T_e$ mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be $\approx 400\pm 100\mu \text{m}$ . Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique conditions and have possible implications for multiple beam applications such as inertial confinement fusion experiments.

High harmonic generation (HHG) is a central driver of the rapidly growing field of ultrafast science. We present a novel quasiphase-matching (QPM) concept with a dual-gas multijet target leading, for the first time, to remarkable phase control between multiple HHG sources ($>2$) within the Rayleigh range. The alternating jet structure with driving and matching zones shows perfect coherent buildup for up to six QPM periods. Although not in the focus of the proof-of-principle studies presented here, we achieved competitive conversion efficiencies already in this early stage of development.