We have made experimental studies on the generation of deuterium-deuterium fusion neutrons from intense Coulomb explosions (CE) of large-size (CD_4)_N cluster jets under the irradiation of intense femtosecond laser pulses. By optimizing the propagation of a laser pulse in the cluster gas and the time delay between the laser pulse and the gas flow, the maximum neutron yield of 2.5 × 10~5, which corresponds to a conversion efficiency of 2.1 × 10~6 fusion neutrons per joule of incident laser energy, has been obtained with a 120-mJ, 60-fs laser pulse and cluster jets with an average molecular density of 3.6 × 10~(18) cm~(-3) and cluster radius of 7 nm. We have demonstrated that the neutron yields can be dramatically increased by using heteronuclear (CD_4)_N clusters as compared with the similar sized homonuclear (D_2)_N clusters. This enhancement is attributed to the significant increase in the deuteron kinetic energies due to energetic boosting and overrun effects during CE of heteronuclear clusters.
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