High Repetition-Rate Neutron Generation by Several-mJ, 35 fs pulses interacting with Free-Flowing D$_{\mathrm{2}}$O.

Recent advance in ultra-high power laser technology allows a development of laser-based neutron sources. Here we demonstrate heavy-water based neutron source. Using several-mJ energy pulses from a high-repetition rate ( \textonehalf kHz), ultrashort (35 fs) pulsed laser interacting with a $\sim $ 10 $\mu $m diameter stream of free-flowing heavy water (D$_{\mathrm{2}}$O), we get a 2.45 MeV neutron flux of 10$^{\mathrm{5}}$/s. In the intentionally generated pre-plasma, laser pulse energy is efficiently absorbed, and energetic deuterons are generated. As a convertor, the bulk heavy water stream target and the large volume of low density D$_{\mathrm{2}}$O vapor near the target are collided with accelerated deuterons, generating neutron through d(d,n)$^{\mathrm{3}}$He reactions. As laser pulse energy increased from 6mJ to 12mJ, the neutron flux increased. From the 2D particle-in-cell simulation, comparable neutron fluxes are shown at the similar laser characteristics to the experiment. Also, simulation shows forward and backward moving deuterons, which are main distributing ions impinging upon D$_{\mathrm{2}}$O stream and vapor, respectively.