LLE Review 143

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Highlights

This volume of the LLE Review, covering April–June 2015, features “First-Principles Equation of State of Polystyrene and Its Effect on Inertial Confinement Fusion Implosions.” This article reports on obtaining an accurate first-principles equation of state (FPEOS) of polystyrene (CH), which is crucial to designing reliable inertial confinement fusion (ICF) capsules using CH/CH-based ablators. When compared with the widely used SESAME equation-of-state table, the FPEOS of CH has significant differences in the low-temperature regime, in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Simulations using the FPEOS of CH show better agreement with measurements of Hugoniot temperature and scattered lights from ICF implosions.

Additional highlights of research presented in this issue include the following:

• Hydrodynamic scaling of the deceleration phase of direct-drive inertial fusion implosions for OMEGA and equivalent National Ignition Facility (NIF)-size targets is presented. It is shown that the deceleration-phase Rayleigh–Taylor instability does not scale hydro-equivalently with implosion size. It is found that a minimum threshold for the no-α Lawson ignition parameter of χ_Ω ≈ 0.2 at the OMEGA scale is required to demonstrate hydro-equivalent ignition at the NIF scale for symmetric direct-drive implosions.
• Shock-wave equation-of-state measurements in fused silica are described on. The most-prevalent crystalline form, α-quartz, is extensively studied. Results extend the measured Hugoniot of fused silica to higher pressures, in the 200- to 1600-GPa range. These data are in very good agreement with those obtained with a different driver and standard material. A new shock velocity/particle relation is derived to fit the experimental data.
• Temporal-contrast measurements of a white-light–seeded noncollinear optical parametric amplifier are discussed on. Ultra-intense optical parametric chirped-pulse systems require front ends with broad bandwidth and high temporal contrast. Temporal cross-correlation measurements of a white-light–seeded noncollinear optical parametric amplifier (NOPA) show that its prepulse contrast exceeds the 120-dB dynamic range of the broadband NOPA-based cross-correlator.
• Computational methods based on the density functional theory and time-dependent density functional theory are employed to study the impact of molecular structure on optical switching properties in photoswitchable methacrylate and acrylamide polymers functionalized with azobenzene and spiropyran pendants. Using these new computational methods, materials can be efficiently designed with low switching energies, enhanced bistability, write/erase fatigue resistance, and high laser-damage thresholds.
• The temporal analog of reflection and refraction of optical beams is studied. It is shown numerically and analytically that when an optical pulse approaches a temporal boundary across which the refractive index changes, it undergoes a temporal equivalent of reflection and refraction of optical beams at a spatial boundary. The frequency dependence of the dispersion of the material in which the pulse is propagating plays a fundamental role in determining the frequency shifts experienced by the reflected and refracted pulses.
• The fabrication and optical characterization of novel semiconducting asymmetric nanochannel diodes (ANCD’s) are described on. It is demonstrated that ANCD’s can be operated as very sensitive, single-photon–level, visible-light photodetectors. The magnitude of the optical responsivity in ANCD’s with the conducting nanochannel increased linearly with a decrease in optical power over many orders of magnitude, reaching a value of almost 10,000 A/W at 1-nW excitation.