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Elimination of Platinum Inclusions in Phosphate Laser Glasses
Abstract
Results from small-scale glass melting experiments aimed at reducing the density of platinum particles in phosphate laser glasses are discussed. The platinum particles originate from the crucibles used to melt the laser glass and can cause optical damage in glasses used in high-peak-power lasers; this problem was particularly acute in the LLNL 120 kJ, 100 TW Nova laser. The melting experiments examine the effects of (i) N{sub 2}, O{sub 2}, and Cl{sub 2} gas atmospheres; (ii) temperature and temperature gradients; (iii) processing time; and (iv) platinum alloys on the formation and dissolution of platinum inclusions in LHG-8 and LG-750 phosphate laser glasses. Results show that most platinum inclusions originate early in the melt cycle, with thermal gradients within the melter being one of the major causes. By using oxidizing gas conditions (O{sub 2}, Cl{sub 2}, or O{sub 2} + Cl{sub 2}), the platinum inclusions can be dissolved into the glass during the course of the melt cycle. The dissolution rate of platinum under oxidizing conditions has been measured, and a model is used to quantify the description of the dissolution process. The effect of ionic platinum on the transmission spectra of the laser glasses produced under various oxidizing conditions has also been measured. Results from the above laboratory-scale melting experiments have been incorporated into proprietary laser-glass melting processes. The laser glasses prepared under these conditions have an average of less than 0.1 platinum inclusions/liter, which represents a 1000-fold reduction over the previously available phosphate laser glasses. 52 refs., 56 figs., 15 tabs.
... For HEHP laser systems it is essential to ensure that the concentration of platinum particles in the glass left over from the melting process is < 0.1 /L and any particles are < 5 µm in size, because of the damage that they could cause to the laser glass. The damage occurs when a metallic platinum particle experiences laser irradiation, causing a thin layer of Pt on the front of the inclusion to vaporize [28]. The ablated Pt causes a shock wave within the glass (a brittle material), which then fractures [28]. ...
... The damage occurs when a metallic platinum particle experiences laser irradiation, causing a thin layer of Pt on the front of the inclusion to vaporize [28]. The ablated Pt causes a shock wave within the glass (a brittle material), which then fractures [28]. The damage sites progressively grow with each laser shot, potentially growing to centimeter size and making the glass unusable [4]. ...
... Oxidizing conditions can be enhanced by bubbling gases through the glass melt. The rate of Pt dissolution as a function of different bubbling gases follows the following trend [26,28,29]: ...
Laser glass is a highly engineered optical material that enables the amplification of light in laser systems. It is known for being the heart of the largest laser facilities ever built, where thousands of neodymium-doped meter-sized slabs of laser glass create intense beams of near-infrared laser radiation used to study fusion reactions. Or if doped with ytterbium and erbium, laser glass can be made into millimeter-sized components empowering range-finders and dermatological lasers. Decades of development have poised laser glass for the next challenge on the horizon: amplifying light for sustainable inertial fusion energy power plants.
... Under Ar and dry-air atmospheres, the platinum concentrations were 4 ppm (P O2 ≒ 10 −5 atm) and 19 ppm (P O2 = 0.2 atm), respectively (also see Supplementary Table S1). These values almost correspond to the reported platinum solubility at 1723 K in lithium silicate melts of a similar composition 27,28 . Researchers have previously discussed the valence state of platinum ions in silicate glasses and melts 25,28,29 . ...
... This starting material has only 4 ppm platinum (see Supplementary Table S1). Since the melting time was short and liquid quantity (15 g) was large, the platinum concentration is much lower than platinum solubility (>15 ppm 27,28 ) under air at 1673 K. Platinum plates (99.95% purity) were used as solid substrates, which were cut into circular shapes with a thickness and diameter of 1 mm and 11 mm, respectively. The substrates were polished using SiC papers, and then ultrasonically cleaned in acetone. ...
Crystalline lithium disilicate (Li2Si2O5, LS2) materials, which have excellent mechanical properties with high transparency, should be obtained efficiently through the crystallization of supercooled liquid composed of LS2. However, in addition to LS2, a lithium monosilicate (Li2SiO3, LS) phase is also precipitated during the crystallization of the liquid. The precipitation of the LS phase renders it difficult to obtain a single-phase LS2 material. Here, we show that by altering the oxygen partial pressure, it is possible to change the selectivity of the precipitated phase by controlling the interfacial phenomena that occur between the liquid and platinum contact material. During cooling of the supercooled liquid, the type of precipitated phase can be controlled by optimizing the atmosphere and type of contact material. This methodology can be applied for the fabrication of other functional materials and does not require the use of other additives.
... at r 2 ar ar (3) where t = time (in s), r = radius (in cm), C = platinum concentration (in g/cm 3 ), and D = platinum ion diffusion coefficient (in cm 2 /s). ...
... To use the platinum-inclusion dissolution model described in section 2., one must first estimate the diffusion constant and Ptn+ solubility. Based on the experiments on LHG-8 glass reported in [5], the solubility limit, Cs, for Ptn+ in phosphate laser glass is about 1050 to 1100 ppm (1 ppm Ptn+ = = 1.46 . 1 o-s mole/cm 3 ) under typical processing conditions. In these calculations, a solubility limit of 1070ppm was assumed. ...
... al. (1997). On the other hand, small traces of platinum can be dissolved in the phosphate melt, which, depending on the glass composition and application, might result in an insigni cant additional absorption in the UV-Vis range due to absorption by Pt 2+ or Pt 4+ ions (Click et al. 2003); or be detrimental to laser glasses, if Pt-particles form which will scatter the light, and when heated by the laser energy, the mismatch of the coef cient of thermal expansion of the metallic particles and the glass might lead to the scattering of the laser glass itself (Hayden et al. 1988). Other crucible materials could be Al 2 O 3 or SiO 2 . ...
... al. (1997). On the other hand, small traces of platinum can be dissolved in the phosphate melt, which, depending on the glass composition and application, might result in an insignificant additional absorption in the UV-Vis range due to absorption by Pt 2+ or Pt 4+ ions (Click et al. 2003); or be detrimental to laser glasses, if Pt-particles form which will scatter the light, and when heated by the laser energy, the mismatch of the coefficient of thermal expansion of the metallic particles and the glass might lead to the scattering of the laser glass itself (Hayden et al. 1988). Other crucible materials could be Al 2 O 3 or SiO 2 . ...
OVERVIEW
In theory, any molten material can form a glass when quenched fast enough. Most natural glasses are based on silicates and for thousands of years only alkali/alkaline earth silicate and lead-silicate glasses were prepared by humankind. After exploratory glass experiments by Lomonosov (18th ct) and Harcourt (19th ct), who introduced 20 more elements into glasses, it was Otto Schott who, in the years 1879–1881, melted his way through the periodic table of the elements so that Ernst Abbe could study all types of borate and phosphate glasses for their optical properties. This research also led to the development of the laboratory ware, low alkali borosilicate glasses. Today, not only can the glass former silicate be replaced, partially or fully, by other glass formers such as oxides of boron, phosphorous, tellurium or antimony, but also the oxygen anions can be substituted by fluorine or nitrogen. Chalcogens, the heavier ions in the group of oxygen in the periodic table (S, Se, Te), on their own or when paired with arsenic or germanium, can function as glass formers. Sulfate, nitrate, tungstate and acetate glasses lack the conventional anion and cation classification, as do metallic or organic glasses. The latter can occur naturally—amber predates anthropogenic glass manufacture by more than 200 million years.
In this chapter, we are going to provide an overview of the different glass families, how the structure and properties of these different glass types differ from silicate glasses but also what similarities are dictated by the glassy state. Applications and technological aspects are discussed briefly for each glass family.
... Research on their formation and dissolution led to a redox-controlled process for minimizing the number and size of inclusions in the glass. [96][97][98][99][100] Specifically under oxidizing conditions and in the presence of chloride ions, which are formed in situ by the addition of chlorine containing gases such as Cl 2 or CCl 4 , the metallic (Pt 0 ) is oxidized and dissolves into the glass matrix. Spectroscopic evidence strongly suggests that this is due to the formation of the highly stable hexachloroplantinate anion, where each Pt 4ϩ ion is surrounded by six chloride (Cl Ϫ ) ions within an octahedrally symmetric coordination sphere. ...
The possibility of imploding small capsules to produce mini-fusion explosions was explored soon after the first thermonuclear explosions in the early 1950s. Various technologies have been pursued to achieve the focused power and energy required for laboratory-scale fusion. Each technology has its own challenges. For example, electron and ion beams can deliver the large amounts of energy but must contend with Coulomb repulsion forces that make focusing these beams a daunting challenge. The demonstration of the first laser in 1960 provided a new option. Energy from laser beams can be focused and deposited within a small volume; the challenge became whether a practical laser system can be constructed that delivers the power and energy required while meeting all other demands for achieving a high-density, symmetric implosion. The National Ignition Facility (NIF) is the laser designed and built to meet the challenges for study of high-energy-density physics and inertial confinement fusion (ICF) implosions. This paper describes the architecture, systems, and subsystems of NIF. It describes how they partner with each other to meet these new, complex demands and describes how laser science and technology were woven together to bring NIF into reality.
Research on Inertial Confinement Fusion (ICF) has progressed rapidly in the past several years. As a consequence, LLNL is developing plans to upgrade the current 120 kj solid state (Nd+3-phosphate glass) Nova laser to a 1.5 to 2 megajoule system with the goal of achieving fusion ignition. The design of the planned Nova Upgrade is briefly discussed.
Because of recent improvements in the damage resistance of optical materials it is now technically and economically feasible to build a megajoule-class solid state laser. Specifically, the damage threshold of Nd+3-doped phosphate laser glass, multilayer dielectric coatings, and non-linear optical crystals (e.g., KDP) have been dramatically improved. These materials now meet the fluence requirements for a 1.5–2 MJ Nd3+-glass laser operating at 1054 and 351 nm and at a pulse length of 3 ns. The recent improvements in damage thresholds are reviewed; threshold data at both 1064 and 355 nm and the measured pulse length scaling are presented.
The decomposition of raw materials during glass melting yields large quantities of gases [6.1]. Most of these gases, especially water vapour, sulphur dioxide, carbon dioxide, and air, are released into the furnace atmosphere, while a smaller portion either remains dissolved within the glass melt or forms bubbles. But this not the only bubble-forming mechanism.
The National Ignition Facility (NIF) laser with its 192 independent laser beams is not only the world's largest laser but also the largest optical system ever built. With its 192 independent laser beams, the NIF requires a total of 7648 large-Aperture (meter-sized) optics. One of the many challenges in designing and building NIF has been to carry out the research and development on optical materials, optics design, and optics manufacturing and metrology technologies needed to achieve NIF's high output energies and precision beam quality. This paper describes the multiyear, multisupplier development effort that was undertaken to develop the advanced optical materials, coatings, fabrication technologies, and associated process improvements necessary to manufacture the wide range of NIF optics. The optics include neodymium-doped phosphate glass laser amplifiers; fused-silica lenses, windows, and phase plates; mirrors and polarizers with multilayer, high-reflectivity dielectric coatings deposited on BK7 substrates; and potassium di-hydrogen phosphate crystal optics for fast optical switches, frequency conversion, and polarization rotation. Also included is a discussion of optical specifications and custom metrology and qualityassurance tools designed, built, and fielded at supplier sites to verify compliance with the stringent NIF specifications. In addition, a brief description of the ongoing program to improve the operational lifetime (i.e., damage resistance) of optics exposed to high fluence in the 351-nm (3Ω) is provided.
IntroductionIntrinsic Redox System of Oxidic Glass-Forming MeltsChoice of the Sensor SystemElectrochemical Cell for Measuring Oxygen Fugacities in Oxidic Glass-Forming MeltsApplicationsReferences
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