Characterization of the preformed plasma for high-intensity laser-plasma interaction.

The interaction of a very intense, very short laser pulse is modified by the presence of a preformed plasma prior to the main short pulse. The preformed plasma is created by a small prepulse interacting with the target prior to the main pulse. The prepulse has been monitored using a water-cell-protected fast photodiode allowing on every shot a high dynamic measurement of the pulse profile. Simultaneously we have used time-resolved interferometry to look at the preformed plasma on a 300 TW, 700 fs laser. The two-dimensional density maps obtained have been compared with two-dimensional hydrodynamic simulations.

A picosecond time-resolved electron energy spectrometer based on Cerenkov radiation.

The energy spectrum of relativistic electrons is an important characterization of high intensity laser-matter interactions. We present a technique that utilizes Cerenkov radiation to measure the time-resolved energy distribution of electrons. Electrons escaping from targets irradiated by high-intensity laser pulses were measured, demonstrating the feasibility of such a novel diagnostic. Limitations on the time resolution of this diagnostic are also discussed.

High performance compact magnetic spectrometers for energetic ion and electron measurement in ultraintense short pulse laser solid interactions.

An ultraintense short pulse lasers incident on solid targets can generate relativistic electrons that then accelerate energetic protons and ions. These fast electrons and ions can effectively heat the solid target, beyond the region of direct laser interaction, and are important to realizing the fast ignition concept. To study these energetic ions and electrons produced from the laser-target interactions, we have developed a range of spectrometers that can cover a large energy range (from less than 0.1 MeV to above 100 MeV). They are physically compact, high performance, and low cost. We will present the basic design of these spectrometers and the test results from recent laser experiments.

Density measurement of shock compressed foam using two-dimensional x-ray radiography.

We have used spherically bent quartz crystal to image a laser-generated shock in a foam medium. The foam targets had a density of 0.16 g/cm(3) and thickness of 150 microm, an aluminum/copper pusher drove the shock. The experiment was performed at the Titan facility at Lawrence Livermore National Laboratory using a 2 ns, 250 J laser pulse to compress the foam target, and a short pulse (10 ps, 350 J) to generate a bright Ti K alpha x-ray source at 4.5 keV to radiograph the shocked target. The crystal used gives a high resolution (approximately 20 microm) monochromatic image of the shock compressed foam.

Direct experimental evidence of back-surface ion acceleration from laser-irradiated gold foils.

Au foils were irradiated with a 100-TW, 100-fs laser at intensities greater than 10(20) W/cm2 producing proton beams with a total yield of approximately 10(11) and maximum proton energy of >9 MeV. Removing contamination from the back surface of Au foils with an Ar-ion sputter gun reduced the total yield of accelerated protons to less than 1% of the yield observed without removing contamination. Removing contamination from the front surface (laser-interaction side) of the target had no observable effect on the proton beam. We present a one-dimensional particle-in-cell simulation that models the experiment. Both experimental and simulation results are consistent with the back-surface acceleration mechanism described in the text.