title: Explosion characteristics of intense femtosecond-laser-driven water droplets.
abstract: An efficient acceleration of energetic ions is observed when small heavy-water droplets of approximately 20 microm diameter are exposed to ultrafast (approximately 40 fs) Ti:sapphire laser pulses of up to 10(19) W/cm2 intensity. Quantitative measurements of deuteron and neutron spectra were done, allowing one to analyze the outward and inward directed deuteron acceleration from the droplet. Neutron spectroscopy based on the D (d,n) fusion reaction was accomplished in four different spatial directions. The energy shifts of those fusion neutrons produced inside the exploding droplet reflect a remaining deuteron acceleration inside the irradiated droplet along the axis of the incident laser beam. The overall neutron yield of the microdroplets is relatively small as a result of the dominant outward directed acceleration of the deuterons with 1200 neutrons/shot. Relying on the "explosion-like" acceleration of such spherical droplet targets we have developed a spray target consisting of heavy-water microspheres with diameters of 150 nm . Both the high deuteron energies of up to 1 MeV resulting from the irradiation intensity of approximately 10(19) W/cm2 as well as the collisions between the deuterons and the surrounding spray delivered about one order of magnitude more neutrons than the single-droplet system. The approximately 6 x 10(3) neutrons per laser pulse from the spray can be attributed to an efficient deuteron release from a significantly smaller laser excited volume as from deuterium-cluster targets.
authors.affiliation: Max-Born-Institut, Max-Born-Strasse 2a, D-12489 Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schnürer
authors.forename: D
authors.initials: D
authors.lastname: Hilscher
authors.forename: U
authors.initials: U
authors.lastname: Jahnke
authors.forename: S
authors.initials: S
authors.lastname: Ter-Avetisyan
authors.forename: S
authors.initials: S
authors.lastname: Busch
authors.forename: M
authors.initials: M
authors.lastname: Kalachnikov
authors.forename: H
authors.initials: H
authors.lastname: Stiel
authors.forename: P V
authors.initials: PV
authors.lastname: Nickles
authors.forename: W
authors.initials: W
authors.lastname: Sandner