[en] Time resolved dynamics of high intensity laser interactions with atomic clusters have been studied with both theoretical analysis and experiment. A short-pulse Ti:sapphire laser system, which could produce 50 mJ of energy in a 50 fs pulse, was built to perform these experiments. The laser used a novel single grating stretcher and was pumped, in part, by a custom Nd:YLF laser system, including 19 mm Nd:YLF amplifiers. It was found that there is an optimal pulse width to maximize absorption for a given cluster size. This optimal pulse width ranged from 400 fs for 85 A radius xenon clusters to 1.2 ps for 205 angstrom radius xenon clusters. Using a pump-probe configuration, the absorption of the probe radiation was observed to reach a maximum for a particular time delay between pump and probe, dependent on the cluster size. The delay for peak absorption was 800, 1400, and 2100 fs for 85 angstrom, 130 angstrom, and 170 angstrom radius xenon clusters respectively. Model calculations suggest that these effects are due to resonant heating of the spherical plasma in agreement with the hydrodynamic interpretation of cluster interactions. While this simple hydrodynamic code produces reasonable agreement with data, it does not include bulk plasma or non-linear propagation effects and is limited to the regime where resonant behavior dominates. We also measured the scattered laser light from the laser-cluster interaction. Similar to the absorption measurements, there is an optimal pulse width which maximizes the scattered signal. This pulse width is larger than the optimal pulse width for absorption. This disagrees with model calculations which show both pulse widths being similar. Further experiments measuring the scattered light in a pump-probe configuration should help to resolve this disagreement

[en] An intense ultrafast laser pulse can be very strongly absorbed in a moderate density gas composed of van der Waals bonded clusters. In this paper, the deposition of the energy of intense 30 fs light pulses in a gas of deuterium clusters has been diagnosed using a technique based on analysis of the trajectories of the resulting cylindrically symmetric blast waves. Using the well-known relation between blast wave velocity and energy deposition in gas, the laser energy deposited per unit length as a function of distance in gas jet plume was measured. These measurements were conducted in jets containing either deuterium clusters or simple deuterium molecules

[en] We have resolved the expansion of intensely irradiated atomic clusters on a femtosecond time scale. These data show evidence for resonant heating, similar to resonance absorption, in spherical cluster plasmas

[en] Recent experiments on the interaction of intense, ultrafast pulses with large van der Waals bonded clusters have shown that these clusters can explode with substantial kinetic energy. Producing explosions in deuterium clusters with a 35 fs laser pulse, we have accelerated ions to sufficient kinetic energy to drive DD nuclear fusion. By diagnosing the fusion yield through measurements of 2.45 MeV fusion neutrons, we have measured the production of over 10⁴ neutrons per laser shot when 100 mJ of laser energy is used. (authors)

[en] We have examined the interaction of deuterium clusters with high intensity, ultrafast laser radiation. Upon irradiation a hot plasma is created with a sufficient temperature to produce nuclear fusion. We have seen that larger clusters produce more fusion neutrons than smaller clusters, consistent with a Coulomb explosion model. Fusion yield is currently limited by propagation effects. Using inter ferometric imaging we have examined the laser propagation and found that the laser energy is absorbed before it penetrates to the center (highest density region) of the gas jet

[en] In conclusion, we have observed the production of 2.45 MeV deuterium fusion neutrons when a gas of deuterium clusters is irradiated with a 120 mJ, 35 fs laser pulse. When the focal position is optimized, we have observed as many as 10⁴ neutrons per laser shot. This yield is consistent with some simple estimates for the fusion yield. We also find that the fusion yield is a sensitive function of the deuterium cluster size in the target jet, a consequence of the Coulomb explosion origin of the fast deuterons. We also find that the neutron pulse duration is fast, with a characteristic burn time of well under 1 ns. This experiment may represent a means for producing a compact, table-top source of short pulse fusion neutrons for applications. Furthermore, we have measured hard x-ray yield from femtosecond laser interactions with both solid and micron scale droplet targets. Strong hard x-ray production is observed from both targets. However, the inferred electron temperature is somewhat higher in the case of irradiation of the droplets. These data are consistent with PIC simulations. This finding indicates that quite unique hot electron dynamics occur during the irradiation of wavelength scale particles by an intense laser field and likely warrants further study

[en] We have examined the dynamics of noble-gas clusters, heated with high-intensity laser radiation, using pump-probe experiments to temporally resolve the expansion of the clusters. Absorption of the probe radiation is observed to reach a maximum for a particular time delay between pump and probe, dependent on the cluster size. For single-pulse experiments, we find that there is an optimal pulse width to maximize absorption for a given cluster size. Model calculations suggest that these effects are due to resonant heating of the spherical cluster plasma in full support of a hydrodynamic interpretation of cluster interactions. copyright 1999 The American Physical Society

[en] We present theoretical and experimental evidence that nonionizing prepulses with intensities as low as 10⁸--10⁹ W/cm² can substantially alter high intensity laser-solid interactions. We show that prepulse-heating and vaporization of the target can lead to a preformed plasma once the vapor is ionized by the rising edge of the high-intensity pulse. Our results indicate that peak prepulse intensity is not the only important parameter to consider in determining preformed plasma thresholds, and that a more comprehensive analysis of the prepulse duration and the target material is required

[en] We have examined the evolution of cylindrically symmetric blast waves produced by the deposition of femtosecond laser pulses in gas jets. In high-Z gases radiative effects become important. We observe the production of an ionization precursor ahead of the shock front and deceleration parameters below the adiabatic value of 1/2 (for a cylinder), an effect expected when the blast wave loses energy by radiative cooling. Despite significant radiative cooling, the blast waves do not appear to develop thin shell instabilities expected for strongly radiative waves. This is believed to be due to the stabilizing effect of a relatively thick blast wave shell resulting in part from electron thermal conduction effects

[en] The increasing proliferation of 100 TW class ultrashort pulse lasers and the near completion of a number of petawatt class lasers world wide is opening many frontiers in laser science. Some of the most exciting frontiers rest in high energy-density science and high field physics. A multi-TW laser can create heated matter with pressure in excess of a Gbar and can create electric fields of ten to one hundred atomic units. In this paper some of the recent advances in high energy density science and high field physics made using high intensity short pulse lasers will be reviewed with illustrative examples from work performed at the University of Texas and Lawrence Livermore National Laboratory