Publications by authors named "Rigatti A"

Article Synopsis
  • High-energy laser facilities need specialized multilayer coatings on large surfaces, requiring strict control over deposition parameters to achieve desired optical and mechanical qualities.
  • The study expands the understanding of how relative humidity affects these coatings, causing shifts in their optical spectra, which are usually limited to a narrow wavelength range.
  • Validation of the spectral shift method involved comparing the effects of humidity on single layers with simulated changes due to thickness or refractive index, revealing that humidity primarily influences the refractive index, with SiO being more responsive than HfO.
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Monolayers containing subnanometer striations of silica and hafnia to form composite materials at varying ratios are explored as a method to develop high-index dielectric layers with increased laser-induced-damage thresholds (LIDTs). These layers can then be used in multilayer dielectric coatings for short-pulse, high-peak-power laser applications, particularly in regions of the highest electric-field intensity. Fabrication is achieved by means of exposure to two different evaporant vapor plumes, where local exposure to each plume is controlled via shielding to prevent simultaneous exposure.

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  • * This experiment produced 2.05 MJ of laser energy, resulting in 3.1 MJ of total fusion yield, which exceeds the Lawson criterion for ignition, demonstrating a key milestone in fusion research.
  • * The report details the advancements in target design, laser technology, and experimental methods that contributed to this historic achievement, validating over five decades of research in laboratory fusion.
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Contamination of pulse compression gratings during the manufacturing process is known to give rise to reduced laser damage performance and represents an issue that has not yet been adequately resolved. The present work demonstrates that the currently used etching methods introduce carbon contamination inside the etched region extending to a 50- to 80-nm layer below the surface. This study was executed using custom samples prepared in both, a laboratory setting and by established commercial vendors, showing results that are very similar.

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Article Synopsis
  • * In inertially confined fusion, ignition allows the fusion process to spread into surrounding fuel, potentially leading to higher energy output.
  • * Recent experiments at the National Ignition Facility achieved capsule gains of 5.8 and approached ignition, even though "scientific breakeven" has not yet been fully realized.
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A transmitted-beam diagnostic (P9TBD) was developed as part of a new experimental platform used to study laser-plasma interactions on OMEGA. Located in the opposing port to the wavelength-tunable (350 nm to 353 nm) UV drive beam, the P9TBD characterizes the beam after it propagates through an undersense plasma. The instrument consists of a large-aperture window that allows light to exit the target chamber and project onto a thin sheet of semi-transparent diffuser material.

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The modifications of multilayer dielectric (MLD) gratings arising from laser-induced damage using 0.6-ps and 10-ps laser pulses at 1053 nm are investigated to better understand the damage-initiation mechanisms. Upon damage initiation, sections of the affected grating pillars are removed, thereby erasing the signature of the underlying mechanisms of laser damage.

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Optical coatings for fusion-class laser systems pose unique challenges, given the large substrate sizes, the high intensities incident on the coatings, and the system-focusing requirements, necessitating a well-controlled optical wavefront. Significant advancements have taken place in the past 30 years to achieve the coating capabilities necessary to build laser systems such as the National Ignition Facility, Laser Mégajoule, OMEGA EP, and OMEGA. This work summarizes the coating efforts and advancements to support such system construction and maintenance.

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This work aimed to determine variance components and genetic parameters, as well as phenotypic, genetic and environmental correlations among black oat (Avena strigosa) families grown in different crop season. Seventy-six black oat families and three controls (BRS Madrugada, BRS Centauro, BRS 139 Neblina) were evaluated in two crop seasons (2016 and 2017), using families with intercalary controls experimental design. The results reveled high potential of black oat families to compose a breeding program, due to families and controls variance were similar, variance components expressed greater genetic variance origin for crop season.

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Multibeam lasers often require an output beam balance that specifies the degree of simultaneity of the laser output energy, instantaneous power, or instantaneous irradiance (power per unit area). This work describes the general problem of balancing a multibeam laser. Specific techniques used to balance the output power of the 60-beam pulsed OMEGA Laser System are discussed along with a measured reduction of beam-to-beam imbalance.

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We investigate the role of defects in laser-induced damage of fused silica and of silica coatings produced by e-beam and PIAD processes which are used in damage resistant, multi-layer dielectric, reflective optics. We perform experiments using 1053 nm, 1-60 ps laser pulses with varying beam size, number of shots, and pulse widths in order to understand the characteristics of defects leading to laser-induced damage. This pulse width range spans a transition in mechanisms from intrinsic material ablation for short pulses to defect-dominated damage for longer pulses.

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Article Synopsis
  • Laser-induced damage from picosecond (ps) pulses shows a transition between multi-photon ionization and thermal-based damage mechanisms typical of nanosecond (ns) pulses.
  • Research on fused silica and silica coatings revealed three damage types: ablation craters, ultra-high density pits, and smooth circular depressions, with increasing damage performance limitations at pulse lengths of 10 ps and longer.
  • The study emphasizes that factors such as surface defects significantly influence the onset of laser-induced damage, indicating that simply considering pulse width is insufficient for understanding damage processes, particularly for pulses shorter than 60 ps.
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High dielectric constant multilayer coatings are commonly used on high-reflection mirrors for high-peak-power laser systems because of their high laser-damage resistance. However, surface contaminants often lead to damage upon laser exposure, thus limiting the mirror's lifetime and performance. One plausible approach to improve the overall mirror resistance against laser damage, including that induced by laser-contaminant coupling, is to coat the multilayers with a thin protective capping (absentee) layer on top of the multilayer coatings.

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Large-aperture deposition of high-laser-damage-threshold, low-dispersion optical coatings for 15 femtosecond pulses have been developed using plasma-ion-assisted electron-beam evaporation. Coatings are demonstrated over 10 in. aperture substrates.

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A low-temperature chemical cleaning approach has been developed to improve the performance of multilayer dielectric pulse-compressor gratings for use in the OMEGA EP laser system. X-ray photoelectron spectroscopy results guided the selection of targeted cleaning steps to strip specific families of manufacturing residues without damaging the grating's fragile 3D profile. Grating coupons that were cleaned using the optimized method consistently met OMEGA EP requirements on diffraction efficiency and 1054 nm laser-damage resistance at 10 ps.

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Plasma-assisted electron-beam evaporation leads to changes in the crystallinity, density, and stresses of thin films. A dual-source plasma system provides stress control of large-aperture, high-fluence coatings used in vacuum for substrates 1m in aperture.

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A task force approach to resolving radiology problems has been used successfully at Hartford Hospital. The involvement of nursing, medical staff, and other ancillary personnel has resulted in the solution of issues common to all hospitals and imaging departments, including problems in patient scheduling, transportation, monitoring, and preparation. Sharing of issues and ideas and the development of direct lines of communication have brought about beneficial change and contributed to quality patient care.

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