Angular distribution of neutrons from deuterated cluster explosions driven by femtosecond laser pulses.

We have studied experimentally the angular distributions of fusion neutrons from plasmas of multi-keV ion temperature, created by 40 fs, multi-TW laser pulses in dense plumes of D2 and CD4 clusters. A slight anisotropy in the neutron emission is observed. We attribute this anisotropy to the fact that the differential cross section for DD fusion is anisotropic even at low collision energies, and this, coupled with the geometry of the gas jet target, leads to beam-target neutrons that are slightly directed. The qualitative features of this anisotropy are confirmed by Monte Carlo simulations.

Dynamic acceleration effects in explosions of laser-irradiated heteronuclear clusters.

Intense, femtosecond irradiation of atomic and molecular clusters can initiate Coulomb explosions, generating particle energies sufficient to drive nuclear fusion. Last and Jortner have proposed, based on particle dynamics simulations, that heteronuclear clusters with a mixture of heavy and light ions will not explode by the simple, equilibrium Coulomb model but that dynamic effects can lead to a boosting of energy of the lighter ejected ions [Phys. Rev. Lett. 87, 033401 (2001)]. We present experimental confirmation of this theoretically predicted ion energy enhancement in methane clusters.

Transverse breathing mode of an elongated Bose-Einstein condensate.

We study experimentally the transverse monopole mode of an elongated rubidium condensate. Because of the scaling invariance of the nonlinear Schrödinger (Gross-Pitaevskii) equation, the oscillation is monochromatic and sinusoidal at short times, even under strong excitation. For ultralow temperatures, the quality factor Q = omega(0)/gamma(0) can exceed 2000, where omega(0) and gamma(0) are the mode angular frequency and damping rate. This value is much larger than any previously reported for other eigenmodes of a condensate. We also present the temperature variation of omega(0) and gamma(0).

Stationary states of a rotating Bose-Einstein condensate: routes to vortex nucleation.

Using a focused laser beam we stir a 87Rb Bose-Einstein condensate confined in a magnetic trap. We observe that the steady states of the condensate correspond to an elliptic cloud, stationary in the rotating frame. These steady states depend nonlinearly on the stirring parameters (amplitude and frequency), and various solutions can be reached experimentally depending on the path followed in this parameter space. These states can be dynamically unstable and we observe that such instabilities lead to vortex nucleation in the condensate.