Leslie J. Summers

Electrochemical Treatment of Mixed and Hazardous Wastes: Oxidation of Ethylene Glycol and Benzene by Silver (II)

In the future, mediated electrochemical oxidation (MEO) may be used for the ambient temperature destruction of hazardous waste and for the conversion of mixed waste to low-level radioactive waste. We have studied the MEO of ethylene glycol and benzene, two model compounds, in an electrochemical reactor. The reactor had a rotating-cylinder anode that was operated well below the limiting current for Ag(II) generation. Rates of CO 2 generation were measured and used to calculate both destruction and current efficiencies for the process. Gas chromatography with mass spectrometry (GC/MS) was used to identify several reaction intermediates

Diffractive Alvarez lens

A diffractive Alvarez lens is demonstrated that consists of two separate phase plates, each having complementary 16-level surface-relief profiles that contain cubic phase delays. Translation of these two components in the plane of the phase plates is shown to produce a variable astigmatic focus. Both spherical and cylindrical phase profiles are demonstrated with good accuracy, and the discrete surface-relief features are shown to cause less than lambda/10 wave-front aberration in the transmitted wave front over a 40 mm x 80 mm region.

Destruction of Chlorinated Organics by Cobalt(III)‐Mediated Electrochemical Oxidation

In the future, mediated electrochemical oxidation (MEO) may be used for the ambient temperature destruction of hazardous waste and for the conversion of mixed waste to low-level radioactive waste. In this paper, the authors study the Co(III) mediated electrochemical oxidation of ethylene glycol, 1,3-dichloro-2-propanol, 2-monochloro- 1-propanol, and isopropanol in sulfuric acid. The electrochemical reactor had a rotating cylinder anode that was operated well below the limiting current for Co(III) generation. Rates of CO[sub 2] generation were measured and used to calculate both destruction and current efficiencies for the process. The authors find that electrode separators can be eliminated in MEO processes based upon Co(III) and sulfuric acid. Electrodes must be separated by ion exchange membranes in classical Ag(II)-based processes.

Fabrication of large-aperture lightweight diffractive lenses for use in space

We describe the advantages of using diffractive (Fresnel) lenses on thin membranes over conventional optics for, among others, future space telescope projects. Fabrication methods are presented for lenses on two types of freestanding membrane up to 50 cm in size. The first is a Fresnel lens etched into a thin (380-microm) glass sheet, and the second is an approximately 50-microm-thick polymer membrane containing a Fresnel lens made by replication process from a specially made fused-silica master. We show optical performance analysis of all the lenses that are fabricated, including a diffraction-limited Airy spot from a 20-m- focal-length membrane lens in a diffractive telescope system.

Methods for mitigating surface damage growth in NIF final optics

We report a summary of the surface damage, growth mitigation effort at 3(omega) for fused silica optics at LLNL. The objective was to experimentally validate selected methods that could be applied to pre-initiated or retrieved-from- service optics, to stop further damage growth. A specific goal was to obtain sufficient data and information of successful methods for fused silica optics to select a single approach for processing NIF optics. This paper includes the test results and the evaluation thereof, for several mitigation methods for fused silica. The mitigation methods tested in this study are wet chemical etching, cold plasma etching, CO2 laser processing, and micro-flame torch processing. We found that CO2 laser processing produces the most significant and consistent results to halt laser-induced surface damage growth on fused silica. We recorded successful mitigation of the growth of laser-induced surface damage sites as large as 0.5-mm diameter, for 1000 shots at fluences in the range of 8 to 13 J/cm2. We obtained sufficient data for elimination of damage growth using CO2 laser processing on sub-aperture representative optics, to proceed with application to full- scale NIF optics.

Fabrication and testing of thermoelectric thin film devices

Two thin-film thermoelectric devices are experimentally demonstrated. The relevant thermal loads on the cold junction of these devices are determined. The analytical form of the equation that describes the thermal loading of the device enables us to model the performance based on the independently measured electronic properties of the films forming the devices. This model elucidates which parameters determine device performance, and how they can be used to maximize performance.

Chemical etch effects on laser-induced surface damage growth in fused silica

We investigated chemical etching as a possible means to mitigate the growth of UV laser-induced surface damage on fused silica. The intent of this work is to examine the growth behavior of existing damage sites that have been processed to remove the UV absorbing, thermo-chemically modified material within the affected area. The study involved chemical etching of laser-induced surface damage sites on fused silica substrates, characterizing the etched sites using scanning electron microscopy (SEM) and laser fluorescence, and testing the growth behavior of the etched sites upon illumination with multiple pulses of 351- nm laser light. The results show that damage sites that have been etched to depths greater than about 9 micrometers have about a 40% chance for zero growth with 1000 shots at fluences of 6.8-9.4 J/cm2. For the etched sites that grow, the growth rates are consistent with those for non-etched sites. There is a weak dependence of the total fluorescence emission with the etch depth of a site, but the total fluorescence intensity from an etched site is not well correlated with the propensity of the site to grow. Deep wet etching shows some promise for mitigating damage growth in fused silica, but fluorescence does not seem to be a good indicator of successful mitigation.

Multiscale, multifunction diffractive structures wet etched into fused silica for high-laser damage threshold applications

We combined functionalities of two diffractive optics with almost 100x lateral and vertical scale-length difference onto a single fused-silica surface. Fine-scale (2-mum-period) gratings for beam sampling were printed in photoresist by interference lithography and transferred to the substrate by a hydrofluoric acid etch. Subsequently, 115-mum-linewidth stairstep gratings for color separation at focus were proximity printed and wet etched in a two-mask process. Line shapes of the lamellar sampling grating are remarkably preserved following etching of the much deeper color separation grating structures with this nominally isotropic etch process. Model simulations of isotropic etching of topographical features show good agreement with the measured shape evolution of the sampling grating profiles, and the simulations reveal the sensitivity of the final feature shape to its initial aspect ratio. As a rule of thumb, lamellar grating profiles can be etched approximately 0.08A(-2) times their modulation depth, where A is their initial aspect ratio (height/width), before they evolve into a cusplike shape and begin to lose height.

Sputter deposition of multilayer thermoelectric films: An approach to the fabrication of two‐dimensional quantum wells

The relative efficiency of a thermoelectric material is measured in terms of a dimensionless figure of merit, ZT. Though all known thermoelectric materials are believed to have ZT≤1, recent theoretical results predict that thermoelectric devices fabricated as two‐dimensional quantum wells (2D QWs) or one‐dimensional (1D) quantum wires could have ZT≥3. Multilayers with the dimensions of 2D QWs have been synthesized by alternately sputtering Bi0.9Sb0.1 and PbTe0.8Se0.2 onto a moving single‐crystal sapphire substrate from dual magnetrons. These materials have been used to test the thermoelectric quantum‐well concept and gain insight into relevant transport mechanisms. If successful, this research could lead to thermoelectric devices that have efficiencies close to that of an ideal Carnot engine. Ultimately, such devices could be used to replace conventional heat engines and mechanical refrigeration systems.

Gratings for High-Energy Petawatt Lasers

To enable high-energy petawatt laser operation we have developed the processing methods and tooling that produced both the worlds largest multilayer dielectric reflection grating and the worlds highest laser damage resistant gratings. We have successfully delivered the first ever 80 cm aperture multilayer dielectric grating to LLNLs Titan Intense Short Pulse Laser Facility. We report on the design, fabrication and characterization of multilayer dielectric diffraction gratings.