When a large piece of space debris forced a change of flight plan for arecent U.S. Space Shuttle mission, the concept that we are trashing space as well as Earth finally attained broad public awareness. Almost a million pieces of debris have been generated by 35 years of spaceflight, and now threaten long-term space missions. The most economical solution to this problem is to cause space debris items to reenter and burn up in the atmosphere. For safe handling of large objects, it is desired to do this on a precomputed trajectory. Due to the number, speed, and spacial distribution of the objects, a highly agile source of mechanical impulse, as well as a quantum leap in detection capability are required. For reasons we will discuss, we believe that the best means of accomplishing these goals is the system we propose here, which uses a ground-based laser system and active beam phase error correcting beam director to provide the impulse, together with a new, computer-intensive, very high-resolution optical detection system to locate objects as small as 1 cm at 500-km range. Illumination of the objects by the repetitively pulsed laser produces a laser-ablation jet that gives the impulse to de-orbit the object. A laser of just 20-kW average power and state-of-the-art detection capabilities could clear near-Earth space below 100-km altitude of all space debris larger than 1 cm but less massive than 100 kg in about 4 years, and all debris in the threatening 1–20-cm size range in about 2 years of continuous operation. The ORION laser would be sited near the Equator at a high altitude location (e.g., the Uhuru site on Kilimanjaro), minimizing turbulence correction, conversion by stimulated Raman scattering, and absorption of the 530-nm wavelength laser beam. ORION is a special case of Laser Impulse Space Propulsion (LISP), studied extensively by Los Alamos and others over the past 4 years.

Weakly nonlinear stage of the ablative Rayleigh-Taylor instability has been studied by the perturbation theory. Mode coupling of linear growing waves with wave numbers kA and kB drives new excited waves with wave numbers k0 (= kA ± kB, 2kA, 2kB). We have investigated time evolution of the excited waves and found that the ablation effect plays an important role even in the nonlinear stage to reduce amplitude of the excited waves. Differences between an ablation surface and a classical contact surface have been discussed. Dependence of the excited wave amplitude on the wavenumber k0, the ablation velocity va, and the effective gravity g is also investigated.

The theory of magnetic field generation due to the interaction of short relativistic laser pulses with underdense plasmas has been developed. The magnetic field is generated due to the inverse Faraday effect occurring witha circularly polarized laser pulse. The spatial distribution of the magnetic field is investigated. It is shown that the magnetic field magnitude depends on the relationship between the laser beam radius and the plasma skin-depth.

The spatial profile, as well as ion-velocity distribution of laser-produced plasmas can be controlled experimentally by varying the time-form of laser pulse. A compression of nearly all produced plasma into a thin monovelocity spherical shell has been observed for the first time. A hydrodynamic numerical simulation shows that the shell generates due to special dynamics of ion ablation and geometry of experiment.

Recombining plasmas produced by picosecond laser pulses are characterized by measuring ratio of intensities of resonance lines of H- and He-like ions in the plasmas. It is found that the rapidly recombining plasmas produced by picosecond laser pulses are suitable for highgain operation.

The X-ray image of a compressed shell (enhanced by high-Z doping) was used in recent experiments to diagnose the effect of shell-fuel mixing. The emission ring (due to the limb effect) moves toward smaller radii due to mixing. We show here that using backlighting imaging can greatly enhance future imaging experiments. In addition to the emission ring, a backlighting absorption ring can appear around it. The absorption ring is virtually unaffected by mixing. Thus, the relative position of the two rings constitutes a mixing signature. In other words, the absorption ring delineates the colder part of the shell and is a true signature of the compression, whereas the emission ring reflects the shell material motion due to mixing.

We discuss two different approaches for observing induced gamma-ray emission of nuclei, departing from known attempts to use the Moessbauer transitions that have so far proven unsuccessful. Both approaches (presented at the 11th and 12th International Conferences on Laser Interaction and Related Plasma Phenomena) are based on the elimination of pernicious influence of Doppler line-broadening in ensembles of free nuclei, particularly in atom and ion beams.

Broad-band random-phase (BRP) irradiation is one of the beam smoothing techniques for KrF laser drivers. We have introduced this technique into the KrF laser system ASHURA. By one-dimensional (ID) BRP smoothing, the speckle pattern in conventional random-phase irradiation has been removed. Two BRP beams were overlap-focused on the target incoherently. Although the obtained profile is rather smooth, some low-frequency nonuniformity remains. To improve the uniformity, a new technique for two-dimensional (2D) smoothing has been proposed. In this technique, a wedged etalon is used to get angular dispersion to the orthogonal direction to the ID BRP effect. The preliminary experiment has been carried out.