8 Matching Results

Search Results

Advanced search parameters have been applied.

Laser conditioning study of KDP on the optical sciences laser using large area beams

Description: Considerable attention has been paid over the years to the problem of growing high purity KDP and KD*P to meet threshold requirements on succeeding generations of inertial confinement fusion lasers at LLNL. While damage thresholds for these materials have increased over time, the current National Ignition Facility (NIF) maximum fluence requirement (redline) for KD*P frequency triplers of 14.3 J/cm{sup 2} at 351 nm, 3 ns has not been reached without laser (pre)conditioning. It is reasonable to assume that, despite the rapid increase in damage thresholds for rapidly grown crystals, -a program of large scale conditioning of the 192 NIF triplers will be required. Small area ramp (R/1) tests on single sites indicate that KDP damage thresholds can be raised on average up to 1.5X the unconditioned values. Unpublished LLNL 3{omega} raster conditioning studies on KDP, however, have not conclusively shown that off-line conditioning is feasible for KD*P. Consequently, investigating the feasibility of on-line conditioning of NIF triplers at 3{omega} has become a high priority for the KDP damage group at LLNL. To investigate the feasibility of on-line conditioning we performed a series of experiments using the Optical Sciences Laser (OSL) on numerous samples of conventional and rapid growth KDP and KD*P. The experiment entailed exposing sites on each sample to a range of ramped shot (N/l) sequences starting at average fluences of -2 J/cm{sup 2} (in a 7 mm ``top hat`` beam @ 351 nm, 3 ns) up to peak fluences of approximately 13 J/cm{sup 2}. Test results indicated that the most effective conditioning procedure entailed a 7-8 shot ramp starting at 2 J/cm{sup 2} and ending at 12-13 J/cm{sup 2}. The pinpoint onset fluence for the 8/1 tests was 1.4 times that of the unconditioned site. Damage evolution appears to be exponential as a function of increasing fluence. When ...
Date: December 20, 1997
Creator: Runkel, M.; DeYoreo, J.; Sell, W. & Milam, D.
Partner: UNT Libraries Government Documents Department

Photothermal mapping of defects in the study of builk damage in KDP

Description: Interest in producing high-damage-threshold KH{sub 2}PO{sub 4} (KDP) and (D{sub x}H{sub 1-x}){sub 2}PO{sub 4} (DKDP) for frequency conversion and optical switching applications is driven by the requirements of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL). At present only the best crystals meet the NIF system requirements at the third harmonic (351 nm) and only after a laser conditioning process. Neither the mechanism for damage in bulk KDP nor the mechanism for conditioning is understood. As part of a development effort to increase the damage thresholds of KDP and DKDP, we have been developing a diagnostic tool that will find these locations, we will use other measurement techniques to determine how these locations differ from the surrounding material and why they cause damage. This will allow crystal growers to focus their efforts during the growth process in improving damage thresholds.
Date: December 20, 1997
Creator: Woods, B.; Yan, M.; DeYoreo, J.; Kozlowski, M.; Radouski, H. & Wu, Z.
Partner: UNT Libraries Government Documents Department

Plasma Electrode Pockels Cells for the Beamlet and NIF lasers

Description: We describe Plasma Electrode Pockels Cells (PEPC) for the Beamlet laser and the proposed National Ignition Facility (NIF) laser. These PEPCs, together with passive polarizers, function as large aperture (> 35 {times} 35 cm{sup 2}) optical switches enabling the design of high-energy (> 5 kJ), multipass laser amplifiers. In a PEPC, plasma discharges form on both sides of a thin (1 cm) electro-optic crystal (KDP). These plasma discharges produce highly conductive and transparent electrodes that facilitate rapid (< 100 ns) and uniform charging of the KDP up to the half-wave voltage (17 kV) and back to zero volts. We discuss the operating principles, design, and optical performance of the Beamlet PEPC and briefly discuss our plans to extend PEPC technology for the NIF.
Date: May 1, 1994
Creator: Rhodes, M. A.; Woods, B.; DeYoreo, J. & Atherton, J.
Partner: UNT Libraries Government Documents Department

Evaluation of materials proposed for the construction of the plasma electrode Pockels cell (PEPC) on beamlet

Description: The proposed upgrade of the NOVA laser system at Lawrence Livermore National Laboratory employs a multipass architecture that requires an optical switch to emit the laser light at the appropriate fluence. This Pockels cell-based optical switch does not use traditional ring or thin-film electrodes because of the large aperture and high fluence of the laser system. Rather, it uses a plasma electrode Pockels cell with a KD*P crystal as the electro-optical medium. A discharge plasma is formed on each side of the electro-optic crystal and high voltage is applied across the crystal through the plasma electrode to initiate optical switching. In October 1991 we began evaluating materials suggested for the large aperture plasma electrode optical switch. Previous experiments suggested that switching performance could be significantly affected by the deterioration of cell materials. The final prototype switch tested used polyethylene for the switch body, Mykroy for the mid-plane and a silicone vulcanite to encapsulate the KD*P crystal. The encapsulant easily compensated for the effect of assembling the optical switch and we measured no strain-induced birefringence in the crystal after encapsulation. Oxygen was eventually added to the plasma to react with the sputtered carbon from the cathode and produce a gaseous effluent. As an added benefit, the production of ozone absorbed most of the ultra violet radiation affecting the encapsulant. All the materials tested decomposed and produced volatiles, although we have seen no change in the damage threshold of exposed optical surfaces tested to date. The following is an evaluation of the recommended materials for major cell components using published manufacturers data, experimental results from our Material Evaluation Apparatus, and outgassing performance and sputtering data produced at the Laboratory`s Vacuum Process Lab.
Date: November 1, 1992
Creator: Roberts, D.; Robb, C.; DeYoreo, J. & Atherton, J.
Partner: UNT Libraries Government Documents Department

Impurity and laser-induced damage in the growth sectors of rapidly grown DKP crystals

Description: 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 starting materials and growth rate. We also studied influence of impurities on laser-induced damage in fast grown KDP. The laser damage threshold (LDT) in the impurity-rich prismatic sector is same as in the high purity pyramidal sector within experimental error. Meanwhile, the 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. Result suggests that the laser damage occurred in the vicinity of a high; localized strain field.
Date: February 13, 1997
Creator: Yan, M.; Torres, R.; Runkel, M.; Woods, B.; Hutcheon, I.; Zaitseva, N. et al.
Partner: UNT Libraries Government Documents Department

Rapid growth of large-scale (40-55 cm) KDP crystals

Description: KDP (KH{sub 2}PO{sub 4}) single crystals up to 47 cm in size have been grown by the rapid growth technique on the point seed in glass recrystallizers of 1000 L in volume at growth rates of 10 to 25 mm/day in both the [001] and [100] directions. Measurements of the optical quality of 41 x 41 cm single crystal plates are presented.
Date: February 13, 1997
Creator: Zaitseva, N.P.; DeYoreo, J.J.; Dehaven, M.R.; Vital, R.L.; Carman, L.M. & Spears, H.R.
Partner: UNT Libraries Government Documents Department

Large-aperture, high-damage-threshold optics for beamlet

Description: Beamlet serves as a test bed for the proposed NIF laser design and components. Therefore, its optics are similar in size and quality to those proposed for the NIF. In general, the optics in the main laser cavity and transport section of Beamlet are larger and have higher damage thresholds than the optics manufactured for any of our previous laser systems. In addition, the quality of the Beamlet optical materials is higher, leading to better wavefront quality, higher optical transmission, and lower-intensity modulation of the output laser beam than, for example, that typically achieved on Nova. In this article, we discuss the properties and characteristics of the large-aperture optics used on Beamlet.
Date: February 23, 1995
Creator: Campbell, J.H.; Atherton, L.J.; DeYoreo, J.J.; Kozlowski, M.R.; Maney, R.T.; Montesanti, R.C. et al.
Partner: UNT Libraries Government Documents Department

Frequency converter development for the National Ignition Facility

Description: The design of the National Ignition Facility (NIF) incorporates a type I/type II third harmonic generator to convert the 1.053-{micro}m fundamental wavelength of the laser amplifier to a wavelength of 0.351 {micro}m for target irradiation. To understand and control the tolerances in the converter design, we have developed a comprehensive error budget that accounts for effects that are known to influence conversion efficiency, including variations in amplitude and phase of the incident laser pulse, temporal bandwidth of the incident laser pulse, crystal surface figure and bulk non-uniformities, angular alignment errors, Fresnel losses, polarization errors and crystal temperature variations. The error budget provides specifications for the detailed design of the NIF final optics assembly (FOA) and the fabrication of optical components. Validation is accomplished through both modeling and measurement, including full-scale Beamlet tests of a 37-cm aperture frequency converter in a NIF prototype final optics cell. The prototype cell incorporates full-perimeter clamping to support the crystals, and resides in a vacuum environment as per the NIF design.
Date: October 30, 1998
Creator: Auerbach, J M; Barker, C E; Burkhart, S C; Couture, S A; DeYoreo, J J; Hackel, L A et al.
Partner: UNT Libraries Government Documents Department