We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a "highfoot" laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10 16 neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel. In indirect-drive inertial confinement fusion (ICF) [1,2], laser energy, converted to thermal x rays inside a high-Z cavity (hohlraum), ablatively drives the implosion of a spherical capsule containing a deuterium-tritium (DT) fuel layer. A high-velocity, low-entropy, highly symmetric implosion is required to form a hot spot of sufficiently high density and temperature from a combination of PdV work and alpha particle deposition. Above the ignition threshold, a self-sustained nuclear burn wave is launched igniting the surrounding compressed fuel layer. Ignition and burn is predicted for stagnation pressures above 300 Gbar [3].Experiments during the National Ignition Campaign (NIC) [4] demonstrated high implosion velocities (∼360 km=s) [5], and high areal mass densities of 1.3 AE 0.1 g=cm 2 [6], which were predicted to be sufficient to reach ignition [7]. However, some of them showed evidence for significant amounts of CH ablator material mixing into the hot spot [8,9], degrading the implosion performance. To increase the resistance to hydrodynamic instabilities [10], the "high-foot" drive design was developed [11,12], which has demonstrated an order-of-magnitude improvement in neutron yields with first evidence for additional heating from alpha particle stopping [13]. The high-foot drive raises the hohlraum temperature to 90 eV during the foot, launching a stronger first shock and sets the implosion on a higher adiabat. Among the benefits are a larger ablator density scale length (reducing susceptibility to ablation front RayleighTaylor growth [14]), and a shorter, simplified laser drive (three shocks rather than four). These benefits come at the price of lower fuel areal density, which requires higher implosion velocity compared to the low-entropy design [7] to achieve ignition.The first high-foot DT implosions [12,13,15] were done in gold (Au) hohlraums. These experiments incrementally increased laser peak power P laser and thus total laser energy from 351 TW=1.3 MJ on N13...

Single-crystal, n-type, undoped CdS and Te-doped CdS (100 and 1000 ppm CdS:Te) electrodes exhibit electroluminescence (EL) in aqueous, alkaline peroxydisulfate electrolyte. Addition of Te to CdS introduces intraband gap states which drastically alter the EL spectral distribution. The EL spectrum of undoped CdS consists of a sharp band near the band gap energy (~2.4 eV) with Xmax ~510 nm and a weaker, broader band at lower energy; the EL spectra of 100 and 1000 ppm CdS:Te also exhibit a sharp band at ~510 nm but are dominated by broad bands with uncorrected Xmax ~600 and ~620 nm, respectively. Photoluminescence (PL) spectra, obtained with 457.9-nm excitation, aid in the assignments of the emissive transitions; PL spectra are generally similar to their EL counterparts. The potential dependence of the EL spectra was examined between ~-1.2 V (onset) and -2.0 V vs. SCE, Changes in potential can affect both the relative and absolute intensities of the bands present in the EL spectra. Lower-limit, order-of-magnitude estimates of instantaneous EL efficiency, $el, have been made. Under steady-state conditions 0el is iílO-6 for undoped CdS and itlO""6 for CdS:Te. Results are discussed in terms of interfacial charge-transfer processes and the excited-state manifolds of CdS and CdS:Te.

Samples of single-crystal, n-type CdSe emit when excited with ultraband gap excitation. The emission band (Xmal =» 720 nm) is near the band gap of CdSe (~1 .7 eV); its energy, decay time, and temperature dependence are consistent with its description as edge emission. Photoluminescence (PL) spectra can be dependent on excitation wavelength and show evidence of self-absorption effects: PL spectra obtained with 457.9-nm excitation are broadened in the high-energy portion of the band relative to spectra obtained with more deeply penetrating 632.8-nm excitation. Measured PL efficiencies, , are ~10~4 in air at 295 K. When CdSe is used as the photoanode of photoelectrochemical cells employing aqueous polychalcogenide electrolytes, emission is quenched by the passage of photocurrent resulting from ultraband gap excitation. Electroluminescence (EL) can be observed from CdSe when the semiconductor is used as a dark cathode in aqueous, alkaline peroxydisulfate electrolyte.

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