Fusion yield enhancement via secondary beam-target reactions in laser-cluster experiments

Laser-cluster fusion offers a unique compact platform for studying nuclear reactions in the sub-100 keV regime. Here we report the first experimental demonstration of secondary beam-target DD fusion reactions in laser-cluster fusion experiments by surrounding a CD₄ cluster jet with a CD₂ foil. Deuterons accelerated to high ion temperatures of 60-100 keV through Coulomb explosion interacted with the surrounding CD₂ target, enhancing neutron yields by up to a factor of 3.5 compared with the cluster-only case. This enhancement was quantitatively reproduced by a time-resolved model, confirming the effectiveness of the additional target. Our results demonstrate a practical route to boost neutron production and to establish laser-cluster fusion as a compact platform for investigating a wider range of fusion reactions and cross-sections relevant to astrophysics.