We present two laser driven shock wave loading techniques utilizing long pulse lasers, laser-launched flyer plate
and confined laser ablation, and their applications to shock physics. The full width at half maximum of the drive
laser pulse ranges from 100 ns to 10 μs, and its energy, from 10 J to 1000 J. The drive pulse is smoothed with
a holographic optical element to achieve spatial homogeneity in loading. We characterize the flyer plate during
flight and dynamically loaded target with temporally and spatially resolved diagnostics. The long duration
and high energy of the drive pulse allow for shockless acceleration of thick flyer plates with 8 mm diameter
and 0.1-2 mm thickness. With transient imaging displacement interferometry and line-imaging velocimetry, we
demonstrate that the planarity (bow and tilt) of the loading is within 2-7 mrad (with an average of 4±1 mrad),
similar to that in conventional techniques including gas gun loading. Plasma heating of target is negligible in
particular when a plasma shield is adopted. For flyer plate loading, supported shock waves can be achieved.
Temporal shaping of the drive pulse in confined laser ablation enables flexible loading, e.g., quasi-isentropic,
Taylor-wave, and off-Hugoniot loading. These dynamic loading techniques using long pulse lasers (0.1-10 μs)
along with short pulse lasers (1-10 ns) can be an accurate, versatile and efficient complement to conventional
shock wave loading for investigating such dynamic responses of materials as Hugoniot elastic limit, plasticity,
spall, shock roughness, equation of state, phase transition, and metallurgical characteristics of shock-recovered
samples, in a wide range of strain rates and pressures at meso- and macroscopic scales.
We present recent results of molecular dynamics simulations to illustrate the processes and mechanisms in
damages to silica glass, including densification, cavitation, fragmentation and agglomeration via photon, electron,
ion and neutron radiations and stresses. Radiation of glass creates point defects (vacancies and interstitials),
and subsequent structure relaxation induces densification. Nanovoid below a certain size and rapid-quenching
of silica liquid can also densify a glass. Hot spots due to photon-absorbing impurities in glass may cause local
densification and cavitation as well. Densification can also be induced by compressional stress, and spall, by
tensile stress. The densified glasses, regardless of the exact processes, share similar structural and vibrational
properties, for example, the five-fold coordinated Si atoms. Densification is essentially a kinetic frustration during
structure relaxation driven by excessive free energy, e.g., due to defects or stresses. The point-defect mechanism
is dominant for densification without compression and complemented by thermal spike mechanism in thermal
processes. Defects, thermal effects and stresses may interplay in a general damage process in silica glass.
Shocks extending across crystals' grain boundaries can nucleate and grow velocity fluctuations on the order of 5-10% when the shock speeds differ in the adjacent grains. Dynamic materials experiments at the Los Alamos National Laboratory Trident Laser Laboratory aim to examine this phenomenon by temporally- and spatially-resolving free surface velocity over a large region of interest. While line-imaged velocimetry can serve as a quantitative method for examining the velocity fluctuations across a single boundary, it is more desirable to resolve the velocity field around an entire embedded grain. We present a novel diagnostic design that utilizes a four-frame gated-optical-imaging interferometric velocimeter in combination with a streaked line-imaging interferometric velocimeter. This diagnostic will provide high-spatial resolution velocigraphs of a shock as it hits a free surface in multigrain crystals.