Highly anisotropic, beam-like neutron emission with peak flux of the order of 10 9 n/sr was obtained from light nuclei reactions in a pitcher-catcher scenario, by employing MeV ions driven by a subpetawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of~ 70 , with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitchercatcher materials indicates the dominant reactions being d(p, n+p) 1 H and d(d,n) 3 He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles is most likely related to the directionality and high energy of the projectile ions.

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An enclosing "box" calorimeter has been used to measure the polarization and angular dependence of 1.06-pm laser-light absorption under experimental conditions approximating those assumed by Estabrook, Valeo, and Kruer in their simulations; i.e., -10'~W /cm plane waves incident on a planar plasma. A clea~resonance absorption'maximum was observed for pbut not for s-polarized incident radiation as predicted.

The detection of -100-keV x radiation and of directly back-scattered light is described for neodymium-glass-laser light pulses focused on a polyethylene target. These observations can be explained in terms of the nonlinear excitation of plasma waves by the laser light.We recently made some measurements of x rays and light reflection from a laser-produced plasma which suggest that plasma instabilities have been produced. Our neodymium laser, which includes a multipass glass-disk system, has been described elsewhere. ' 3 The 1.06pm-wavelength neodymium-laser light was focused by means of an f/7 lens to an irregular-shaped spot with a mean diameter of approximately 80 pm. s The pulse energy ranged from 20 to 7P J; the pulse length ranged from 2 to 5 nsec. The maximum power during the pulse was 10 GW, corresponding to an intensity at the target of = 2x 10'4 W/cm~. The laser pulse was focused on flat targets of "deuterated" and ordinary polyethylene, (CD&)" and (CH2)", respectively. The targets were tilted about 5' to prevent back reflections from causing spontaneous oscillations in the laser amplifier chain. After each shot the target was moved to expose a fresh new surface. It was found necessary to wait 1 h between shots to allow the disk laser to cool. Failure to allow ample cooling resulted in a larger focal spot and a decrease or an absence of neutrons and hard x rays.Diagnostics for the first set of experiments included a large plastic scintillation counter, intended for neutron detection and located in close proximity to the laser target. The detector was initially shielded with 9. 5 mm of aluminum plus 6. 3 mm of lead. Nevertheless, when the laser was fired, scintillation pu1. ses were seen from the (CHz)" target as well as from (CD&)". When the shielding thickness was increased to 9. 5 mm of aluminum plus 12. 7 mm of lead, no pulses were seen when the (CH~)" target was in place, but small pulses corresponding to 103 and 104 neutrons were seen when the (CD&)" target was used. s ' The fact that large pulses were seen from a (CHz)" target with a scintillation detector shielded by 6. 3 mm of lead was interpreted as evidence that considerable quantities of hard x rays were being produced in these experiments.Similar hard x radiation has been reported recently by the I ebedev group in the USSR.To measure the x-ray spectrum more accurately, additional measurements were taken with four scintillation detectors using a target of polyvinyl chloride. One pair of detectors used europium-activated calcium fluoride fluors in conjunction with aluminum absorbers; the other pair used thalliumactivated sodium iodide fluors and nickel absorbers. To minimize background corrections, the nickelabsorber pair was shielded from scattered hard x rays by at least 6 mm of lead on all sides, except for a narrow cone pointed at the focal spot. The aluminum-absorber pair did not need such shielding, because the soft-x-ray signal was much greater than the hard-x-ray background. The absorption ratios for a given absorber pair were normalized...