K. Flippo

Laser-triggered ion acceleration and table top isotope production

We have observed deuterons accelerated to energies of about 2 MeV in the interaction of relativistically intense 10 TW, 400 fs laser pulse with a thin layer of deuterated polystyrene deposited on Mylar film. These high-energy deuterons were directed to the boron sample, where they produced ∼105 atoms of positron active isotope 11C from the reaction 10B(d,n)11C. The activation results suggest that deuterons were accelerated from the front surface of the target.

High-energy ion generation by short laser pulses

This paper reviews the many recent advances at the Center for Ultrafast Optical Science (CUOS) at the University of Michigan in multi-MeV ion beam generation from the interaction of short laser pulses focused onto thin foil targets at intensities ranging from 1017 to 1019 W/cm2. Ion beam characteristics were studied by changing the laser intensity, laser wavelength, target material, and by depositing a well-absorbed coating. We manipulated the proton beam divergence using shaped targets and observed nuclear transformation induced by high-energy protons and deuterons. Qualitative theoretical approaches and fully relativistic two-dimensional particle-in-cell simulations modeled energetic ion generation. Comparison with experiments sheds light on ion energy spectra for multi-species plasma, the dependences of ion-energy on preplasma scale length and solid density plasma thickness, and laser-triggered isotope yield. Theoretical predictions are also made with the aim of studying ion generation for high-power lasers with the energies expected in the near future, and for the relativistic intensity table-top laser, a prototype of which is already in operation at CUOS in the limits of several-cycle pulse duration and a single-wavelength spot size.

Pulse radiolysis of liquid water using picosecond electron pulses produced by a table-top terawatt laser system

A laser based electron generator is shown, for the first time, to produce sufficient charge to conduct time resolved investigations of radiation induced chemical events. Electron pulses generated by focussing terawatt laser pulses into a supersonic helium gas jet are used to ionize liquid water. The decay of the hydrated electrons produced by the ionizing electron pulses is monitored with 0.3 μs time resolution. Hydrated electron concentrations as high as 22 μM were generated. The results show that terawatt lasers offer both an alternative to linear accelerators and a means to achieve subpicosecond time resolution for pulse radiolysis studies.

Mechanism and Control of High-Intensity- Laser-Driven Proton Acceleration

We discuss the optimization and control of laser‐driven proton beams. Specifically, we report on the dependence of high‐intensity laser accelerated proton beams on the material properties of various thin‐film targets. Evidence of star‐like filaments and beam hollowing (predicted from the electrothermal instability theory) is observed on Radiochromic Film (RCF) and CR‐39 nuclear track detectors. The proton beam spatial profile is found to depend on initial target conductivity and target thickness. For resistive target materials, these structured profiles are explained by the inhibition of current, due to the lack of a return current. The conductors, however, can support large propagating currents due to the substantial cold return current which is composed of free charge carriers in the conduction band to neutralize the plasma from the interaction. The empirical plot shows relationship between the maximum proton energy and the target thickness also supports the return current and target normal sheath accel...

A spatially resolved optical emission sensor for plasma etch monitoring

A spatially resolved optical emission spectroscopy sensor has been developed, and the resulting reconstructed radial emission profiles from an ArI and ArII line compare well with Ar sputter etch uniformity profiles. The new sensor collects light from a wedge shaped field of view, and is rotated around a single collection point in order to observe the entire plasma through a relatively small viewpoint.

Laser accelerated plasma propulsion system (LAPPS)

Recently conducted experiments at the University of Michigan and elsewhere have shown that ultrashort pulse (ultrafast) lasers could accelerate charged particles to relativistic speeds. For example a picosecond laser pulse with only one joule of energy can accelerate an electron to MeV energy in just a few microns distance. This takes place through the high gradient potential that manifests itself in an electric field of a gigavolt per cm which in turn accelerates the electron to a megavolt energy over a distance of 10 microns. Current achievable laser peak power of 10 watts has been utilized in the study of relativistic non-linear optics in plasmas, and it is expected that laser power values will be reached in the near future that will accelerate protons to energies equal to their rest mass energy. That readily means that when such particles are ejected from a system at 0.866 the speed of light they will produce a specific impulse of 26 million seconds. Current experiments have also demonstrated that a beam of one MeV protons containing more than 10 particles has been accelerated by an electric field of 10 GeV/cm corresponding to a laser power of about 100 TW. On the basis of these accomplishments it is reasonable to project that accelerating 100 MeV proton beams containing 10 particles will be quite achievable in the near future. If utilized as a propulsion device such a system will make distant planets in the solar system and some Copyright

High contrast 150-terawatt laser for high field laser-plasma interaction studies

Summary form only given. High power chirped pulse amplification (CPA) lasers are capable of providing enough power to study relativistic regime-of laser-plasma interaction, including effects such as high-energy particle acceleration, relativistic self-focusing and nonlinear Thomson scattering. To achieve this regime focused laser intensity must be over 10/sup 18/ W/cm/sup 2/ (typically-10/sup 19/-10/sup 20/ W/cm/sup 2/). If solid metal target is irradiated the laser intensity contrast on the nanosecond timescale must be better than 12 orders of magnitude to ensure that the target does not disintegrate before the pulse arrives. To improve the pulse contrast in the 25 fs CPA laser system, we are currently building for high field laser-plasma studies at CUOS, we pursue an approach, originally developed at CUOS for longer pulses (/spl sim/100 fs). We pre-amplify the oscillator output pulse to submicrojoule energy level without stretching the pulse, improve the pulse contrast by using a saturable absorber and stretch the pulse thereafter for further amplification.

A Field-Reversed Gasdynamic Mirror Fusion Propulsion System

Previous studies have shown that the gasdynamic mirror (GDM) fusion propulsion system is capable of producing specific impulses in excess of 105 seconds and thrusts in the tens of kilonewtons. These propulsive capabilities arise from the ability of this magnetic fusion system to confine a hot plasma long enough to produce fusion energy while allowing a certain fraction of its charged particle population to escape through one end (a magnetic nozzle) to generate thrust. Earlier investigations have revealed that the optimum performance arises from the use of large mirror ratios which require large magnets and result in very massive vehicles. Major contributors to the large mass, in addition to the magnetic fields, are the large radiators required to dispose of waste heat. In this paper we address the question of mass reduction by investigating the role of magnetic field reversal near the mirror region, on the one hand, and the utilization of the liquid droplet radiator design on the other. We find that signi...

Developments in Relativistic Nonlinear Optics

We report recent results of experiments and simulations in the regime of peak laser intensities above 1019 W/cm2, including the following topics: (1) electron and proton acceleration to energies in excess of 10 MeV in well collimated beams; (2) use of laser chirp to control the growth of plasma waves and acceleration of electrons by the Raman instability; (3) all optical injection and acceleration of electrons; (4) relativistic self-focusing by means of the mutual index of refraction of two overlapping laser pulses; (5) creation of a radioisotope by the reaction 10B(d,n)11C; (6) high-order harmonic generation from relativistic free electrons in an underdense plasma.

Study of Energetic Ion Generation from High-Intensity-Laser Dense-Plasma Interactions

We report on the characteristics of an ultrafast‐laser driven proton beam from thin‐film targets. The difference in proton beam profiles, beam energies, and laser induced back ablation plumes between a dielectric (Mylar) and a conductor (aluminum) are discussed. Evidence for front‐side acceleration and a method for beam manipulation are also presented.