Data on the emission of energetic ions produced in laser–matter interactions have been analyzed for a wide variety of laser wavelengths, energies, and pulse lengths. Strong correlation has been found between the bulk energy per AMU for fast ions measured by charge cups and the x-ray-determined hot electron temperature. Five theoretical models have been used to explain this correlation. The models include (1) a steady-state spherically symmetric fluid model with classical electron heat conduction, (2) a steady-state spherically symmetric fluid model with flux limited electron heat conduction, (3) a simple analytic model of an isothermal rarefaction followed by a free expansion, (4) the lasnex hydrodynamics code [Comments Plasma Phys. Controlled Fusion 2, 85 (1975)], calculations employing a spherical expansion and simple initial conditions, and (5) the lasnex code with its full array of absorption, transport, and emission physics. The results obtained with these models are in good agreement with the experiments and indicate that the detailed shape of the correlation curve between mean fast ion energy and hot electron temperature is due to target surface impurities at the higher temperatures (higher laser intensities) and to the expansion of bulk target material at the lower temperatures (lower laser intensities).

The x-ray bremsstrahlung from 4 to 50 keV emitted by laser-produced plasmas has been measured using a Bragg crystal spectrometer. Direct spectral information was obtained in contrast to earlier filter spectroscopy. Measurements were made with focal spot powers of 1016 W/cm2 of 1.06-μm radiation and 1014 W/cm2 of 10.6-μm radiation. A definite suprathermal electron component was observed.

can make an order-of-magnitude estimate of r using a classical hard-sphere model for the collisions where the rotons are assumed to be stationary, and the He^ quasiparticles move with a mean speed {v) = {^kT/m^''Y''^, Thenwhere r'Ms the mean collision frequency, n is the number density of atoms, and m^'^-^2,Zm^ is the effective mass of the He^ quasiparticle. Using a value ofa = 1.6xl0"^^ cm^ measured by Herzlinger and King,^ this expression becomes r(°K) = 5.7X, in satisfactory agreement with our results.

The spectra and angular distributions of high-energy electrons emitted from laser-produced plasmas have been measured. The plasmas were produced using short pulses from both CO2 and Nd : glass lasers to irradiate polyethylene slabs. For a CO2 laser intensity of approximately 3×1014 W/cm2 we find at least an order of magnitude greater energy conversion to high-energy electrons than with a Nd : glass laser intensity of approximately 5×1015 W/cm2. The angular distribution of electron emission is strongly peaked along the target normal (i.e., density gradient) and fine angular structure is observed.

We have developed an experiment to study the propagation of laboratory synthesized fatigue cracks under various controlled conditions during Sonic IR inspection. The experiment provides for good repeatability in testing. The parameters of interest include the initial crack length, load history (stress intensity and load ratio) during crack generation, geometry of the crack, material and also the various conditions involving the ultrasonic excitation source. In general, we find that under typical sonic IR inspection conditions, the initial crack will propagate under sonic IR testing. The crack growth after each inspection event varies and exhibits a distribution in length of propagation. The results show that the average crack propagation decreases with increasing stress intensity factor, and we test two hypotheses about the cause of this. Furthermore, we find that crack propagation is affected by the initial crack length.