Fred Hartemann

PLEIADES: A picosecond Compton scattering x-ray source for advanced backlighting and time-resolved material studies

The PLEIADES (Picosecond Laser-Electron Inter-Action for the Dynamical Evaluation of Structures) facility has produced first light at 70 keV. This milestone offers a new opportunity to develop laser-driven, compact, tunable x-ray sources for critical applications such as diagnostics for the National Ignition Facility and time-resolved material studies. The electron beam was focused to 50 μm rms, at 57 MeV, with 260 pC of charge, a relative energy spread of 0.2%, and a normalized emittance of 5 mm mrad horizontally and 13 mm mrad vertically. The scattered 820 nm laser pulse had an energy of 180 mJ and a duration of 54 fs. Initial x rays were captured with a cooled charge-coupled device using a cesium iodide scintillator; the peak photon energy was approximately 78 keV, with a total x-ray flux of 1.3×106 photons/shot, and the observed angular distribution found to agree very well with three-dimensional codes. Simple K-edge radiography of a tantalum foil showed good agreement with the theoretical divergence-...

Laser Technology for Compact, Narrow-bandwidth Gamma-ray Sources

Compton-scattering is a well-known process, observed and described by Arthur H. Compton in 1924, where the energy of an incident photon is modified by an inelastic scatter with matter (Compton, 1923). In 1948, Feenberg and Primakoff presented a theory of Compton backscattering, where photons can gain energy through collisions with energetic electrons (Feenberg & Primakoff, 1948). In 1963, Milburn and Arutyanyan and Tumanyan developed a concept for Compton-scattering light sources based on colliding an accelerated, relativistic electron beam and a laser (Arutyunyan & Tumanyan, 1964; Milburn, 1963). When an infrared photon scatters off a relativistic electron beam, its wavelength can be Doppler-upshifted to X-rays. Under properly designed conditions, we can generate high brightness, high flux, MeV-scale photons by colliding an intense laser pulse with a high quality, electron beam accelerated in a Linac. Despite being incoherent, the Compton-generated gamma-rays sharemany of the laser light characteristics: low divergence, high flux, narrow-bandwidth, and polarizability. Traditional laser sources operate in a 0.1−10 eV range, overlapping most of the molecular and atomic transitions. Transitions inside the nucleus have energies greater than 0.1MeV. Bymatching the gamma-ray energy to a particular nuclear transition, we can target a specific isotope, akin to using a laser to excite a particular atomic or molecular transition. Narrow-bandwidth gamma-ray sources enable high impact technological and scientific missions such as isotope-specific nuclear resonance fluorescence (NRF) (Bertozzi & Ledoux, 2005; Pruet et al., 2006), radiography of low density materials (Albert et al., 2010), precision nuclear spectroscopy (Pietralla et al., 2002), medical imaging and treatment (Carroll et al., 2003; Bech et al., 2009), and tests of quantum chromodynamics (Titov et al., 2006). In traditional X-ray radiography, the target must have a higher atomic number than the surrounding material. Hence, one could conceal an object by shielding with a higher Z-number material. In NRF gamma-ray imaging, the MeV class photons have very long absorption lengths and will transmit through meter lengths of material unless resonantly absorbed by a specific isotope. Some applications of NRF tuned gamma-rays include nuclear waste imaging and assay, monitoring of special nuclear material for homeland security, and tumor detection for medical treatment. Compton-based sources are attractive in the 100 keV and higher energy regime because they are highly compact and can be more than 15 orders of magnitude brighter than alternative methods for producing photons in this energy regime: Bremsstrahlung radiation 3

Characterization and applications of a bright, tunable, MeV class Compton scattering γ-ray source

We report detailed spectral and spatial characterization of a 0.1-MeV-0.8 MeV tunable ultra-bright laser-based Compton scattering source. Nuclear Resonance Fluorescence experiments with the source are also presented.

High Power Picosecond Laser Pulse Recirculation

We designed and constructed a nonlinear crystal-based short pulse recirculation cavity that traps the second harmonic of an incident high power laser. This scheme aims to increase the efficiency of Compton-scattering based light sources.