Stages of Ion Acceleration Ultrashort Laser Target Production of Directed Neutrons

The purpose of the research is to provide the tools to combat the GWOT by developing a radiation source to detect special nuclear materials (SNM). Neutrons have been shown to produce identifiable signatures in SNM materials. However, the effect range for active detection techniques is limited by the lack of directionality in the neutron beam used to probe the material.

Three-dimensional graphic of the total electron content (TEC) showing the impact of equatorial spread F bubbles, the large meridional structures in the equatorial region Equatorial Spread F Modeling

The Naval Research Laboratory has developed a comprehensive three-dimensional ionosphere model SAMI3 to study the evolution of equatorial spread F (ESF). The model follows the dynamical and chemical evolution of seven ion species (H+ , He+ , N+, O+ , N+2 , NO+, and O+2). The complete ion temperature equation is solved for three ion species (H+ , He+ and O+) as well as the electron temperature equation. The SAMI3 code has been modified to capture the onset and evolution of small-scale equatorial bubbles (L ~ 10 km) within the framework of a self-consistent global model (L ~ 1000s km) which is unprecedented.

Time snapshots of three communicating robots (black) tracing the coherent structures in time dependent double gyre flow. The bright red signatures shown are ridges that contain the coherent structures of the flow. The coherent structures are unstable; i.e., if one starts a single tracer near the red structures, it is quickly swept away into some basin of attraction. Even though the coherent structures are unstable, the trio of autonomous robots shown track the most unstable regions throughout the phase spac Autonomous Robots Designed to Track Coherent Structures in Ocean Models

Dr. Ira B. Schwartz and colleagues have derived and implemented a novel autonomous communicating robot architecture to track coherent structures in ocean flows, such as those structures which separate large eddy flows in the Gulf of Mexico. Coherent structures are time evolving unstable objects in the ocean that play a large role in the determination of transport. These structures, therefore, play an important role in temperature distribution, algae bloom development, and climate and weather prediction. The multi-robot design uses communication and local velocity measurement information to control the robot positions along the coherent structures. The technique has been applied to time dependent flows modeling double gyres, and has been verified in experiments.

Plasma density profiles obtained from interferometry measurements (data points) and SPARC simulations (solid lines). Curves are offset in order of the scale of the vacuum-plasma transition. For the cyan curve (no shock), the transition region is 100 microns long, while for the green curve (strong shock), the transition region is only 20 microns long. The spike in density representing the shock front could not be directly resolved, but the appearance of accelerated electrons was correlated with strong shocks Optically Shaped Gas Targets for Laser Accelerators

An optically shaped gas target was developed at NRL for producing high-energy electron beams. The gas target is initially formed using a simple gas jet, which consists of a nozzle and valve arranged so that when the valve is opened, a supersonic jet of gas is produced. The jet of gas is then optically shaped, i.e., a high-energy laser pulse is used to create a shock wave in the gas, altering its density profile. As the optically induced shock wave evolves, a density profile is created that is favorable for laser acceleration of electrons. At the right instant, another laser pulse, more intense than the first, is focused into the shaped gas jet. This laser produces a high-quality, high-energy, electron beam. Because of the optical shaping, the reliability and quality of the electron beam are improved.

Typical spectral signals obtained from NaNO3 in ULIBS using 10mJ, 100 fsec laser pulses at different laser diameters on target: A) 0.608 mm, B) 0.628 mm, C) 0.740 mm, and D) 0.896 mm. The prominent broadband feature between 400 nm to 420 nm for both NaNO3 and KNO3 for various laser energies, pulse lengths, and spot diameters. Identifying Explosive Surrogates with Ultrashort Pulse Laser Induced Breakdown Spectroscopy (ULIBS)

Ultrashort Laser Induced Breakdown Spectroscopy (ULIBS) was used to detect the emission radiation from the breakdown of surface contaminants by an ultrashort laser pulse. This study focused on the detection of radiation signatures from molecular fragments of the Nitro (NO) group present in the breakdown plasma, where target chemicals of Potassium Nitrate (KNO3) and Sodium Nitrate (NaNO3) were used. The results of this study could lead to the early detection of residues of nitro-group explosive materials at standoff distances. Spectral signatures at a wavelength region around 410 nm were observed for both KNO3 and NaNO3, and were identified as the fluorescence transitions of the NO-molecular structures. The signatures obtained were systematically analyzed and studied as functions of laser parameters. It is shown that for laser parameters used in this study, laser pulse durations ≥1 psec were not as effective as shorter pulses in generating these signatures.

Laser fluence distribution (arbitrary units) of a megawatt-class beam in target plane at 5 km range after propagating through a maritime environment. Insets show spatial wander of the laser centroid in time for various power levels. Atmospheric Propagation of High-Energy Laser Beams

The propagation of high-energy laser (HEL) beams in the atmosphere is rich in fundamental physics and of paramount importance to the Navy’s directed energy research program. Laser beams with hundreds of kilowatts to megawatts of average power are affected by numerous interrelated linear and nonlinear phenomena such as molecular and aerosol absorption and scattering, atmospheric turbulence, and thermal blooming. Aerosol scattering and absorption are often the major limiting factors in HEL propagation. In particular, aerosol absorption has been shown to be a major factor leading to thermal blooming.

Nike Laser The Nike Laser Facility

The Nike laser facility is the world’s largest krypton fluoride laser facility that is utilized to study laser matter interactions under conditions expected for laser fusion. Nike’s capability to provide extremely uniform focal profiles and its deep UV wavelength facilitate the conducting of experiments with laser-produced shocks with negligible effects from laser imperfections and laser plasma instability.