Using a compact “homebuilt” ultrafast laser to heat arrays of ordered nanowires, scientists at Colorado State University (CSU; Fort Collins, CO) and collaborators have demonstrated microscale nuclear fusion in the lab. They have achieved record-setting efficiency for the generation of neutrons (which result from the fusion process). Laser-driven controlled fusion experiments are typically done via inertial confinement, for example, at the National Ignition Facility (NIF; Livermore, CA), requiring multi-hundred-million-dollar, multikilojoule lasers. Such experiments are geared either toward harnessing nuclear fusion for clean energy applications, or to materials studies. In contrast, the CSU-led team of students, research scientists, and collaborators work with an ultrafast tabletop laser.
Pulses with 60 fs duration, energies up to 1.65 J, and a center wavelength of 400 nm were produced, with the laser light focused with an f/1.7 parabolic mirror. The target was an array of 200- or 400-nm-diameter deuterated polyethylene (CD2) nanowires. The short pulses coupled very well to the volume deep within the nanowire array, turning a several-micron-deep layer of the CD2 into plasma and leading to deuteron-deuteron (D-D) fusion. The maximum number of neutrons per shot was about 3.6 × 106 for a laser pulse energy of 1.64 J, corresponding to 2.2 × 106 neutrons per joule. This is the largest fusion neutron yield obtained to date for joule-level laser pulse energies, the researchers say. In addition, this yield is about 500X higher than experiments that use conventional flat targets from the same material. Making fusion neutrons efficiently at a small scale could lead to advances in neutron-based imaging and neutron probes to gain insight on the structure and properties of materials. Reference: A. Curtis et al., Nat. Commun. (2018); doi:10.1038/s41467-018-03445-z.