The interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 10 19 W cm Ϫ2. The maximum ion energy cutoff E max ͑which is related to the hot electron temperature͒ is in the range 1.0-12.0 MeV and is shown to scale as E max ϷI 1/3. The hot electron temperatures were in the range 70-400 keV for intensities up to 5ϫ10 18 W cm Ϫ2 with an indication of a high absorption of laser energy. Measurements of x-ray/␥-ray bremsstrahlung emission suggest the existence of at least two electron temperatures. Collimation of the plasma flow has been observed by optical probing techniques.

No abstract

Protons with energies up to 18 MeV have been measured from high density laser-plasma interactions at incident laser intensities of 5x10(19) W/cm(2). Up to 10(12) protons with energies greater than 2 MeV were observed to propagate through a 125 &mgr;m thick aluminum target and measurements of their angular deflection were made. It is likely that the protons originate from the front surface of the target and are bent by large magnetic fields which exist in the target interior. To agree with our measurements these fields would be in excess of 30 MG and would be generated by the beam of fast electrons which is also observed.

Heavy ions with energies up to 430+/-40 MeV have been measured from laser-solid interactions at focused intensities of up to 5x10(19) W/cm(2). Observations of proton emission indicate significant structure in the energy spectrum as well as an angular emission profile which varies with energy. Two qualitatively different components of ion emission are observed: (i) a high-energy component which is likely generated by a combination of "Coulomb explosion" and acceleration by the space charge force from hot electrons which escape the plasma, and (ii) a lower-energy component which forms a ring likely created by magnetic fields in the ablated plasma.

We present measurements of a magnetic reconnection in a plasma created by two laser beams (1 ns pulse duration, 1 x 10(15) W cm(-2)) focused in close proximity on a planar solid target. Simultaneous optical probing and proton grid deflectometry reveal two high velocity, collimated outflowing jets and 0.7-1.3 MG magnetic fields at the focal spot edges. Thomson scattering measurements from the reconnection layer are consistent with high electron temperatures in this region.

Huge magnetic fields are predicted to exist in the high-density region of plasmas produced during intense laser-matter interaction, near the critical-density surface where most laser absorption occurs, but until now these fields have never been measured. By using pulses focused to extreme intensities to investigate laser-plasma interactions, we have been able to record the highest magnetic fields ever produced in a laboratory--over 340 megagauss--by polarimetry measurements of self-generated laser harmonics.

The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied by photoneutron activation in copper. We show that the gamma-ray beam moves from the target normal to the direction of the k(laser) vector as the scale length is increased. Similar behavior is found also in 2D particle-in-cell simulations.

Neutron fluxes of up to 7 × 10 7 neutrons/sr were measured when planar deuterated targets were irradiated with 1.3 ps FWHM (full width at half maximum) laser pulses at a wavelength of 1054 nm and focused intensities up to 10 19 W cm −2 . The neutron energy spectra are consistent with an angularly dispersed beam target interaction, whereas a thermonuclear source is considered unlikely.