LLE Review 93

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Highlights

This volume of the LLE Review, covering October–December 2002, describes progress toward validating the predicted performance of direct-drive capsules that are hydrodynamically equivalent to the baseline direct-drive ignition design for the National Ignition Facility (NIF). These experiments measure the sensitivity of the direct-drive implosion performance to parameters such as the inner-ice-surface roughness, the adiabat of the cryogenic fuel during the implosion, the laser power balance, and the single-beam nonuniformity. Near 1-D hydrocode performance is measured with a high-adiabat drive pulse on a capsule containing a 100-µm-thick layer of D₂ ice, and near 2-D hydrocode performance is measured on a similar capsule with a low-adiabat drive.

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

• The growth of inner-surface modulations near peak compression in D³He-gas-filled spherical targets is probed using differential imaging of titanium-doped layers placed at various distances from the inner surface of the shell. Time histories of shell temperature and density are measured with titanium K-shell absorption spectroscopy and the shell areal density is estimated using 14.7-MeV D³3He proton spectra. These experiments provide a better quantitative understanding of the evolution of inner-shell modulations that grow due to the Rayleigh–Taylor instability and Bell–Plesset convergence effects in the deceleration phase of a spherical direct-drive implosion.
• Improved target performance in direct-drive implosions using adiabat shaping with a high-intensity picket in front of the main-drive pulse is described analytically. Experiments have demonstrated an improvement in target yields by a factor of up to 3 for the pulses with the picket compared to the pulses without the picket.
• A high-conversion-efficiency optical parametric chirped-pulse amplification (OPCPA) system is demonstrated using a spatiotemporally shaped pump pulse to maximize the conversion efficiency of the OPCPA process. This system is a test bed for a similar OPCPA design that will be used for injection of a short-pulse, petawatt-class laser.
• A new class of ultrafast, superconducting single-photon detectors for counting both visible and infrared photons is presented. Applications for these devices range from noncontact testing of semiconductor CMOS VLSI circuits to free-space quantum cryptography and communications.
• The temporal response characteristics of fast metal–semiconductor–metal ultraviolet photodiodes fabricated on GaN are measured. These detectors are attractive because they are relatively easy to fabricate and have no response in the visible region of the spectrum.
• Novel glassy liquid crystals with tunable spectral characteristics have been developed for photonic applications. The molecular design of photoresponsive systems that combine reversible spectral tunability with superior fatigue resistance and thermal stability is described.
• Near-field Raman spectroscopy and imaging of single-walled carbon nanotubes (SWNT) with unprecedented spatial resolution of less than 30nm is presented.