Transparent Laser Ceramics at Lawrence Livermore National Laboratory (LLNL)

LLNL has been using the largest transparent laser ceramics for the last two years in the solid-state heat capacity laser (SSHCL). The lab is very interested in extending the use of transparent ceramics to other laser applications. In this talk we will discuss work at the laboratory aimed at better understanding the sintering and the criteria needed for good ceramic transparency, the application of transparent ceramics in the SSHCL laser and possible new applications of tailored ceramics

Densification and residual stress induced by CO2 laserbased mitigation of SiO2 surfaces

ABSTRACT Knowing the ultimate surface morphology resulting from CO 2 laser mitigation of induced laser damage is important both for determining adequate treatment protocols, and for preventing deleterious intensification upon subsequent illumination of downstream optics. Physical effects such as evaporation, viscous flow and densification can strongly affect the final morphology of the treated site. Evaporation is a strong function of temperature and will play a leading role in determining pit shapes when the evaporation rate is large, both because of material loss and redeposition. Viscous motion of the hot molten material during heating and cooling can redistribute material due to surface tension gradients (Marangoni effect) and vapor recoil pressure effects. Less well known, perhaps, is that silica can densify as a result of structural relaxation, to a degree depending on the local thermal history. The specific volume shrinkage due to structural relaxation can be mistaken for material loss due to evaporation. Unlike evaporation, however, local density change can be reversed by post annealing. All of these effects must be taken into account to adequately describe the final morphology and optical properties of single and multiple-pass mitigation protocols. We have investigated, experimentally and theoretically, the significance of such densification on residual stress and under what circumstances it can compete with evaporation in determining the ultimate post treatment surface shape. In general, understanding final surface configurations requires taking all these factors including local structural relaxation densification, and therefore the thermal history, into account. We find that surface depressions due to densification can dominate surface morphology in the non-evaporative regime when peak temperatures are below 2100K

An Assessment of Molecular Dynamic Force Fields for Silica for Use in Simulating Laser Damage Mitigation

We compare force fields (FF's) that have been used in molecular dynamic (MD) simulations of silica in order to assess their applicability for use in simulating IR-laser damage mitigation. Although pairwise FF?s obtained by fitting quantum mechanical calculations such as the BKS and CHIK potentials have been shown to reproduce many of the properties of silica including the stability of silica polymorphs and the densification of the liquid, we show that melting temperatures and fictive temperatures are much too high. Softer empirical force fields give liquid and glass properties at experimental temperatures but may not predict all properties important to laser mitigation experiments

The Use of Large Transparent Ceramics in a High Powered, Diode Pumped Solid State Laser

The advent of large transparent ceramics is one of the key enabling technological advances that have shown that the development of very high average power compact solid state lasers is achievable. Large ceramic neodymium doped yttrium aluminum garnet (Nd:YAG) amplifier slabs are used in Lawrence Livermore National Laboratory's (LLNL) Solid State Heat Capacity Laser (SSHCL), which has achieved world record average output powers in excess of 67 kilowatts. We will describe the attributes of using large transparent ceramics, our present system architecture and corresponding performance; as well as describe our near term future plans

Resonance transition 795-nm rubidium laser using He buffer gas

Abstract not provide

Identification of cell surface glycoprotein markers for glioblastoma-derived stem-like cells using a lectin microarray and LC-MS/MS approach

Despite progress in the treatment of glioblastoma, more than 95% of patients suffering from this disease still die within 2 years. Recent findings support the belief that cancer stem-like cells are responsible for tumor formation and ongoing growth. Here a method combining lectin microarray and LC-MS/MS was used to discover the cell surface glycoprotein markers of a glioblastoma-derived stem-like cell line. Lectin microarray analysis of cell surface glycans showed that two galactose-specific lectins Trichosanthes kirilowii agglutinin (TKA) and Peanut agglutinin (PNA) could distinguish the stem-like glioblastoma neurosphere culture from a traditional adherent glioblastoma cell line. Agarose-bound TKA and PNA were used to capture the glycoproteins from the two cell cultures, which were analyzed by LC-MS/MS. The glycoproteins were quantified by spectral counting, resulting in the identification of 12 and 11 potential glycoprotein markers from the TKA and PNA captured fractions respectively. Almost all of these proteins were membrane proteins. Differential expression was verified by Western blotting analysis of 6 interesting proteins, including the up-regulated Receptor-type tyrosine-protein phosphatase zeta, Tenascin-C, Chondroitin sulfate proteoglycan NG2, Podocalyxin-like protein 1 and CD90, and the down-regulated CD44. An improved understanding of these proteins may be important for earlier diagnosis and better therapeutic targeting of glioblastoma

Hydrocarbon-free resonance transition 795-nm rubidium laser

An optical resonance transition rubidium laser (5{sup 2}P{sub 1/2} {yields} 5{sup 2}S{sub 1/2}) is demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either the buffer gas or a buffer gas component to promote rapid fine-structure mixing. However, our experience suggests that the alkali vapor reacts with the ethane producing carbon as one of the reaction products. This degrades long term laser reliability. Our recent experimental results with a 'clean' helium-only buffer gas system pumped by a Ti:sapphire laser demonstrate all the advantages of the original alkali laser system, but without the reliability issues associated with the use of ethane

Resonance transition 795-nm Rubidium laser using 3He buffer gas

We report the first demonstration of a 795-nm Rubidium resonance transition laser using a buffer gas consisting of pure {sup 3}He. This follows our recent demonstration of a hydrocarbon-free 795-nm Rubidium resonance laser which used naturally-occurring He as the buffer gas. Using He gas that is isotopically enriched with {sup 3}He yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improving thermal management in high average power Rb lasers and enhancing the power scaling potential of such systems

Wikipedia as informal self-education for clinical decision-making in medical practice

Background For almost any topic, a Wikipedia page will appear among the first ten items of a search online. Wikipedia is also a site whose quality and reliability has been called into question. Methods In this paper, we aim to discuss medical practitioners’ use of Wikipedia, what this consists of and what it might be. We consider the context and history of Wikipedia before discussing the relationship between Wikipedia and the medical profession. In so doing, we will consider Wikipedia as a means of informal self-education and the extent to which it might inform clinical decision-making. We compare with the existing literature results from our two small-scale empirical studies of Wikipedia and clinical decision-making. Results Notwithstanding issues over quality and reliability, Wikipedia’s rules on verifiability are such that its articles are very heavily referenced, and this is just as true of health-related articles. The Cochrane/Wikipedia Initiative in improving the quality and reliability of medical and health pages in Wikipedia is significant in increasing reliability. Our respondents largely concurred with the results from earlier studies on the use of Wikipedia by medical practitioners. Conclusion Perhaps the very doubt over Wikipedia’s accuracy is its greatest strength as a means of informal education of doctors. That medical and health articles on Wikipedia can be so fully referenced and still be doubted is arguably a good thing and one whose effects may be spread into other, more trusted, publications. Hence, one might envisage a future where no one source is taken automatically on trust. Keywords Wikipedia, informal education, continued professional development, medical education