We demonstrate a <1 mrad, 10-75 MeV, inverse-Compton photon source capable of penetrating several centimeters of Pb. First a petawatt pulse is focused into a gas cell, driving a laser wakefield that injects and accelerates electrons to >GeV energies with <0.6 mrad divergence. Upon exiting the gas cell, the same pulse forms a retro-reflecting Plasma Mirror on a thin substrate downstream which stimulates Compton Backscatter from the closely trailing, copropagating electrons.
We report the generation of a Compton backscatter (CBS) source with photon energies prominently peaked in the range of 10-75 MeV and capable of penetrating several centimeters of lead. The Texas Petawatt laser drives a laser wakefield which injects and accelerates electrons up to 2 GeV in a 7 cm, low density, helium gas cell . A plasma mirror (PM) retro-reflects the wakefield-driving laser, at a small angle, into the closely following electrons. The plasma mirror substrate, a 100 micron thick, glass coverslip, was placed 3 centimeters after the gas cell exit to allow its interrogation by a probe beam to verify the PM reflectivity. This scheme consistently generated a CBS source exhibiting sub-milliradian divergence. The CBS beam qualities were evaluated using: two pixelated-CsI(Tl) scintillators placed at 3 m and 5.5 m from the source; a modular array of metal attenuators comprised of aluminum, copper, tungsten, tungsten carbide, and lead; Fujifilm image plates; and simulations using GEANT4. A shot-to-shot comparative analysis on the accelerated electron bunch, subsequent betatron x-ray, and CBS gamma-ray signals reveals strong agreement in their pointing and divergence properties, suggesting a reliable and non-invasive extension for GeV-beam metrology. Furthermore the use of on-axis image plates facilitated the observation of secondary particles emitted by multi-MeV photon absorption within the metal attenuators, offering a corroborating, indirect measurement of photon number.
 Wang, X. et al. Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV. Nat Commun. 4:1988 doi: 10.1038/ncomms2988 (2013).
|Are you a student?||Yes|