Nuclear fusion is regularly created in spherical plasma compressions driven by multi-kilojoule pulses from the world’s largest lasers. Here we demonstrate a dense fusion environment created by irradiating arrays of deuterated nanostructures with joule-level pulses from a compact ultrafast laser. The irradiation of ordered deuterated polyethylene nanowires arrays with femtosecond pulses of relativistic intensity creates ultra-high energy density plasmas in which deuterons (D) are accelerated up to MeV energies, efficiently driving D–D fusion reactions and ultrafast neutron bursts. We measure up to 2 × 106 fusion neutrons per joule, an increase of about 500 times with respect to flat solid targets, a record yield for joule-level lasers. Moreover, in accordance with simulation predictions, we observe a rapid increase in neutron yield with laser pulse energy. The results will impact nuclear science and high energy density research and can lead to bright ultrafast quasi-monoenergetic neutron point sources for imaging and materials studies.

We show that ultradense Z pinches with nanoscale dimensions can be generated by irradiating aligned nanowires with femtosecond laser pulses of relativistic intensity. Using fully three-dimensional relativistic particle-in-cell simulations, we demonstrate that the laser pulse drives a forward electron current in the area around the wires. This forward current induces return current densities of ∼0.1  GA per μm^{2} through the wires. The resulting strong, quasistatic, self-generated azimuthal magnetic field pinches the nanowires into hot plasmas with a peak electron density of >9×10^{24}  cm^{-3}, exceeding 1000 times the critical density. Arrays of these new ultradense nanopinches can be expected to lead to efficient microfusion and other applications.

Nanowire arrays heated by laser pulses of relativistic intensity open a path to extreme energy densities and pressures.

We report on improved proton acceleration from the interaction of a short pulse high intensity laser (>10 20 Wcm −2 ) with nano-engineered targets. Planar targets (from 7 to 20 μm) with protruding gold nanowires having different total areal densities, lengths, and diameters, ranging from 3% to 60% of the size of the laser focal spot were used during an experimental campaign at the 3 J, 30 fs HERCULES laser facility. The results show the importance of the average number of nanowires per focal spot, N, on laser energy absorption. We show that the proton acceleration is significantly improved by using 1 nanowires per focal spot. Detailed analysis indicates that 1 nanowire per focal spot optimizes the interaction between laser pulse and nanowires, in which the wings of the pulse pull out electrons from the wires forming a plasma with density that allows for deep penetration of the laser pulse into the array. When moving away from this optimum in both directions, N=1 and N?1, the laser pulse-nanowire coupling is either too weak or unfavorable for obtaining maximum proton energy. Proton spectra are compared to simulations using 2D-3V particle-in-cell code which reproduces the experimental data with good agreement.

The efficient conversion of optical laser light into bright ultrafast x-ray pulses in laser created plasmas is of high interest for dense plasma physics studies, material science, and other fields. However, the rapid hydrodynamic expansion that cools hot plasmas has limited the x-ray conversion efficiency (CE) to 1% or less. Here we demonstrate more than one order of magnitude increase in picosecond x-ray CE by tailoring near solid density plasmas to achieve a large radiative to hydrodynamic energy loss rate ratio, leading into a radiation loss dominated plasma regime. A record 20% CE into hν > 1 keV photons was measured in arrays of large aspect ratio Au nanowires heated to keV temperatures with ultrahigh contrast femtosecond laser pulses of relativistic intensity. The potential of these bright ultrafast x-ray point sources for table-top imaging is illustrated with single shot flash radiographs obtained using low laser pulse energy. These results will enable the deployment of brighter laser driven x-ray sources at both compact and large laser facilities.