Technical challenges for the future of high energy lasers

The Solid-State, Heat-Capacity Laser (SSHCL) program at Lawrence Livermore National Laboratory is a multi-generation laser development effort scalable to the megawatt power levels with current performance approaching 100 kilowatts. This program is one of many designed to harness the power of lasers for use as directed energy weapons. There are many hurdles common to all of these programs that must be overcome to make the technology viable. There will be a in-depth discussion of the general issues facing state-of-the-art high energy lasers and paths to their resolution. Despite the relative simplicity of the SSHCL design, many challenges have been uncovered in the implementation of this particular system. An overview of these and their resolution are discussed. The overall system design of the SSHCL, technological strengths and weaknesses, and most recent experimental results will be presented

Plasma electrode pockels cell for the National Ignition Facility

The National Ignition Facility (NIF), now under construction at Lawrence Livermore National Laboratory, will be the largest laser fusion facility ever built. The NIF laser architecture is based on a multi-pass power amplifier to reduce cost and maximize performance. A key component in this laser design is an optical switch that closes to trap the optical pulse in the cavity for four gain passes and then opens to divert the optical pulse out of the amplifier cavity. The switch is comprised of a Pockels cell and a polarizer and is unique because it handles a beam that is 40 cm x 40 cm square and allows close horizontal and vertical beam spacing. Conventional Pockels cells do not scale to such large apertures or the square shape required for close packing. Our switch is based on a Plasma-Electrode Pockels Cell (PEPC). In a PEPC, low-pressure helium discharges (1-2 kA) are formed on both sides of a thin slab of electro-optic material. Typically, we use KH{sub 2}PO{sub 4 } crystals (KDP). The discharges form highly conductive, transparent sheets that allow uniform application of a high-voltage pulse (17 kV) across the crystal. A 37 cm x 37 cm PEPC has been in routine operation for two years on the 6 k.J Beamlet laser at LLNL. For the NIF, a module four apertures high by one wide (4x1) is required. However, this 4x1 mechanical module will be comprised electrically of a pair of 2x1 sub-modules. Last year (FY 97), we demonstrated full operation of a prototype 2x1 PEPC. In this PEPC, the plasma spans two KDP crystals. A major advance in the 2x1 PEPC over the Beamlet PEPC is the use of anodized aluminum construction that still provides sufficient insulation to allow formation of the planar plasmas

Sub-50 femtosecond, multiterwatt Ti:sapphire laser system

We discuss a Ti:sapphire laser system based on chirped pulse amplification which produces over 750 mJ in sub-50 femtosecond pulses. We also describe a novel, all-reflective stretcher with a stretching ratio of 30,000

Interaction of a High-Power Laser Beam with Metal Sheets Interaction of a high-power laser beam with metal sheets

Experiments with a high-power laser beam directed onto thin aluminum sheets, with a large spot size, demonstrate that airflow produces a strong enhancement of the interaction. The enhancement is explained in terms of aerodynamic effects. As laser heating softens the material, the airflow-induced pressure difference between front and rear faces causes the metal to bulge into the beam. The resulting shear stresses rupture the material and remove it at temperatures well below the melting point. The material heating is shown to conform to an elementary model. We present an analytic model of elastic bulging. Scaling with respect to spot size, wind speed, and material parameters is determined

Longitudinal analysis of functional capacity in nursing home residents during the COVID-19 pandemic

Background and Purpose: The COVID-19 pandemic has raised concerns about nursing home residents’ well-being, with recent studies indicating a significant increase in functional decline rate during this critical period. However, a comprehensive exploration of functional capacity trajectories in nursing home residents during the pandemic remains unexplored. This study aims to address this research gap by conducting an in-depth analysis of the impact of the COVID-19 pandemic on nursing home residents’ functional capacity. Methods: A 24-month multicenter prospective study involving 123 nursing home residents from Spain, with data collected at six-month intervals over 5 waves, beginning just before the pandemic's onset. Functional capacity was assessed using the Modified Barthel Index, and data were analyzed employing the actuarial method, log-rank test, and Cox's regression. Results and Discussion: The likelihood of maintaining functional capacity were unfavorable, with only a 19.3% chance of preservation for a 1-point decline (FD-1) in Barthel scores and a 50.5% probability for a 10-point decline (FD-10). Personal hygiene, eating, and toilet use were identified as the most affected activities of daily living. Urinary continence decline emerged as a risk factor for FD-1, while fecal continence decline was associated with FD-10. The probability of maintaining functional capacity in the initial 6 months of a pandemic was comparable to a 2-year non-pandemic follow-up. Pandemic-induced isolation strategies significantly impacted toileting and personal hygiene. Urinary decline was associated with minor functional decline (FD-1), while fecal decline correlated with major functional decline (FD-10). Notably, the number of days spent in room confinement did not significantly contribute to the observed decline.Conclusions: A substantial increase in the risk of FD among NH residents during the COVID-19 pandemic compared to the pre-pandemic period was found. It is crucial to implement urgent, targeted interventions that prioritize promoting physical activity and the implementation of mobility and toileting programs. These measures are pivotal for mitigating functional decline and enhancing the overall health and well-being of nursing home residents in a pandemic context