We measured, using Petawatt-level pulses, the average ion energy and neutron yield in high-intensity laser interactions with molecular clusters as a function of laser intensity. The interaction volume over which fusion occurred (1-10 mm 3 ) was larger than previous investigations, owing to the high laser power. Possible effects of prepulses were examined by implementing a pair of plasma mirrors. Our results show an optimum laser intensity for the production of energetic deuterium ions both with and without the use of the plasma mirrors. We measured deuterium plasmas with 14 keV average ion energies, which produced 7.2×10 6 and 1.6×10 7 neutrons in a single shot with and without plasma mirrors, respectively. The measured neutron yields qualitatively matched the expected yields calculated using a cylindrical plasma model.

We measured the average deuterium cluster size within a mixture of deuterium clusters and helium gas by detecting Rayleigh scattering signals. The average cluster size from the gas mixture was comparable to that from a pure deuterium gas when the total backing pressure and temperature of the gas mixture were the same as those of the pure deuterium gas. According to these measurements, the average size of deuterium clusters depends on the total pressure and not the partial pressure of deuterium in the gas mixture. To characterize the cluster source size further, a Faraday cup was used to measure the average kinetic energy of the ions resulting from Coulomb explosion of deuterium clusters upon irradiation by an intense ultrashort pulse. The deuterium ions indeed acquired a similar amount of energy from the mixture target, corroborating our measurements of the average cluster size. As the addition of helium atoms did not reduce the resulting ion kinetic energies, the reported results confirm the utility of using a known cluster source for beam-target-fusion experiments by introducing a secondary target gas.

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We have designed, built, and calibrated an ultrafast streaked optical pyrometer (SOP) with ∼5 ps resolution for measuring the time-resolved surface blackbody temperature of an isochorically heated plasma. The pyrometer is calibrated to measure temperatures from 0.5 eV to 25 eV, with the option of adding calibrated neutral density filters to observe hotter plasmas. We demonstrated the use of this pyrometer on isochoric heating experiments using laser-accelerated proton beams as an energy source at the f/40 beamline of the Texas Petawatt Laser. We used the large focal spot size (∼80 μm radius) of the f/40 pulses to accelerate high numbers of ∼MeV protons off 5 μm thick solid gold targets. During our experimental campaign, we heated 10 µm thick aluminum foil targets to 1–10 eV over a duration of 50 ps and also observed heating to ∼2 eV in 100 µm thick 60 mg/cm3 carbon foams using the SOP to measure both the temperature and heating timescale.