Richard A. Torres

The effect of impurities and supersaturation on the rapid growth of KDP crystals

Potassium orthophosphate (KDP) crystals were grown at the growth rates from 0.5 to 25 mm/day. The distribution of impurities connected with the vicinal and sectoral structure of the rapidly grown crystals is described. It has been shown that to decrease the effect of impurities and to obtain crystals of high homogeneity, rapid growth should be performed at high supersaturations outside the dead zone and the region of the sharp increase of the growth rate with supersaturation.

Depth profiling of polishing-induced contamination on fused silica surfaces

Laser-induced damage on optical surfaces is often associated with absorbing contaminants introduced by the polishing process. This is particularly the case for UV optics. In the present study, secondary ion mass spectroscopy (SIMS) was used to measure depth profiles of finishing-process contamination on fused silica surfaces. Contaminating detected include the major polishing compound components, Al present largely because of the use of Al2O3 in the final cleaning process, and other metals incorporated during the polishing step or earlier grinding steps. Depth profile data typically showed an exponential decay of contaminant concentration to a depth of 100-200 nm. This depth is consistent with a polishing redeposition layers formed during the chemo-mechanical polishing of fused silica. Peak contaminant levels are typically in the 10-10 pm range, except for Al which often exceeds 1000 ppm.

Effect of thermal annealing and second harmonic generation on bulk damage performance of rapid-growth KDP type-I doublers at 1064 nm

This paper discusses the results of thermal annealing and in-situ second harmonic generation (SHG) damage tests performed on six rapid growth KDP type 1 doubler crystals at 1064 nm (1(omega) ) on the Zeus automated damage test facility. Unconditioned (S/1) and conditioned (R/1) damage probability tests were performed before and after thermal annealing, then with and without SHG on six doubler crystals from the NIF-size, rapid growth KDP boule F6. The tests revealed that unannealed, last-grown material from the boule in either prismatic or pyramidal sectors exhibited the highest damage curves. After thermal annealing at 160 degree(s)C for seven days, the prismatic sector samples increased in performance ranging from 1.6 to 2.4X, while material from the pyramidal sector increased only modestly, ranging from 1.0 to 1.3X. Second harmonic generation decreased the damage fluence by an average of 20 percent for the S/1 tests and 40 percent for R/1 tests. Conversion efficiencies under test conditions were measured to be 20 to 30 percent and compared quite well to predicted behavior, as modeled by LLNL frequency conversion computer codes.

Low-temperature growth of DKDP for improving laser-induced damage resistance at 350 nm

A set of twenty-three 20-L crystallizer runs exploring the importance of several engineering variables found that growth temperature is the most important variable controlling damage resistance of DKDP over the conditions investigated. Boules grown between 45 degree(s)C and room temperature have a 50% probability of 3(omega) bulk damage that is 1.5 to 2 times higher than boules grown between 65 and 45 degree(s)C. This raises their damage resistance above the NIF tripler specification for 8 J/cm2 operation by a comfortable margin. Solution impurity levels do not correlate with damage resistance for iron less than 200 ppb and aluminum less than 2000 ppb. The possibility that low growth temperatures could increase damage resistance in NIF- scale boules was tested by growing a large boule in a 1000-L crystallizer with a supplemental growth solution tank. Four samples representing early and late pyramid and prism growth are very close to the specification as best it is understood at the present. Implications of low temperature growth for meeting absorbance, homogeneity, and other material specifications are discussed.

Solution thermodynamics of Europium−fluoride complexation

Abstract The enthalpy of formation of EuF 2+ in solution has been redetermined by titration calorimetry. Experiments at a constant ionic strength of μ = 1.0 M (NaClO 4 ), but at a variety of fluoride titrant concentrations, gave ΔH 101 =(9.61 ± 0.03) kJ/mol at 25 °C. This value is considerably lower than that previously reported in the literature. The corresponding entropy, however, is now consistent with an electrostatic model which has bcen shown to describe the behavior of a wide variety of metal-fluoride complexes.

Investigation of impurities and laser-induced damage in the growth sectors of rapidly grown KDP crystals

We report the experimental results of impurity contamination and laser-induced damage investigations on rapidly grown potassium dihydrogen phosphate (KDP) crystals. Using absorption spectroscopy and chemical analysis, we determined the impurity distribution in the different growing sectors of KDP single crystals. The level of impurity was dependent on the starting materials and growth rate. We also studied the influence of impurities on the laser-induced damage in fast grown KDP. The laser damage threshold in the impurity- rich prismatic sector is same as in the high purity pyramidal sector within the experimental error. Meanwhile, the laser damage threshold (LDT) at the boundary of the prismatic and pyramidal sectors is less than half of that in the bulk. Furthermore, we found that the thermal annealing of the crystal eliminated the weakness of this sector boundary and increased its LDT to the same level as in the bulk of the crystal. Our result suggests that laser damage occurred in the vicinity of a high, localized strain field.

High-temperature spectroscopy for nuclear waste applications

Instrumentation has been developed to perform uv-vis-nir absorbance measurements remotely and at elevated temperatures and pressures. Fiber-optic spectroscopy permits the interrogation of radioactive species within a glovebox enclosure at temperatures ranging from ambient to >100 °C. Spectral shifts as a function of metal-ligand coordination are used to compute thermodynamic free energies of reaction by matrix regression analysis. Pr3+ serves as a convenient analog for trivalent actinides without attendant radioactivity hazards, and recent results obtained from 20–95 °C with the Pr-acetate complexation system are presented. Preliminary experimentation on Am(III) hydrolysis is also described.

A case study in plutonium radiochronometry using multiple isotope systems

Radiochronometry analyses of two Pu metals were performed using the 237Np–241Am–241Pu, 234U–238Pu, 235U–239Pu, and 236U–240Pu decay series. For one sample, all radiochronometers yield concordant model dates in 1959–1960, indicating that the aqueous processing method used to purify Pu effectively removed U, Am and Np decay products from the bulk Pu. The second sample yields discordant model dates that are also older than the known production date in 1982. The excess U, Am and Np present in the sample indicate that the sample was purified during at least two different episodes, using a combination of aqueous methods and molten salt extraction.

Impurity contamination in fast-grown KDP

Potassium dihydrogen phosphate (KDP) has traditionally been used as a nonlinear optical material for frequency conversion to produce second and third harmonic radiation. A high laser induced damage threshold for KDP crystals is required for high power laser applications, such as laser fusion. High quality KDP crystals for such applications can be produced by a recently developed rapid crystal growth method. We report the results of an impurity contamination study in raidlygrown KDP crystals. Using absorption spectroscopy, we identified the impurity contamination in the different growth sectors of the crystals. We show that the level of contamination depends on the growth rate achieved during the rapid growth. The impurities observed by absorption spectroscopy are identified as the origin of lattice distortion and optical birefringence in the KDP crystals. The study of impurity incorporation during crystal growth is important for understanding the damage mechanism of KDP.

Development of High-Temperature Uv-Vis-Nir Spectroscopy for the Measurement of Free Energies of Complexation at Elevated Temperatures

We have developed instrumentation capable of measuring optical absorption spectra over a wavelength range of 200--1200 nm and a temperature range of 20--100{degree}C. This fiber-optic based spectrometer generates data which allow the computation of metal-ligand equilibrium constants. Studies at five temperatures have been completed using praseodymium-diglycolate as a model system. Fundamental thermodynamic values (free energies, enthalpies, entropies) were obtained from the experimentally-determined stability constants. Thermodynamic data pertinent to the interactions of actinides and long-lived fission products with groundwater, waste package components, and geologic media are critical input to modeling programs. 9 refs., 1 fig., 2 tabs.