In this Colloquium, Prof. Banerjee will discuss our recent work on the
development of an all-laser-driven, tunable x-ray source based on inverse
Compton scattering. This source produces highly collimated beams of
high-energy x-rays that span the energy range 10 keV to 20 MeV. Unlike
conventional bremsstrahlung the x-rays have low energy spread and a
bandwidth as low as 10% has been reported. This breakthrough device uses
two high-power laser pulses obtained from the PW-class Diocles laser
system. One pulse accelerates electrons to high-energy by the process of
laser-wakefield acceleration and the second pulse scatters off the electron
beam to produce x-rays. High-brightness is achieved on account of the fact
that the electron and laser pulse are both micron size and femtosecond
duration and can be made to interact optimally in the counterpropagating
configuration. The system can operate in a repetitive mode with photon
output of 108 photons s-1. The peak brightness approaches 1021 photons
mm-2 mrad-2 s-1 (0.1% bandwidth) and this is three orders of magnitude
higher than for conventional Compton sources. We have used this source to
demonstrate a number of proof-of-concept applications such as radiography
through dense shielded structures, photonuclear activation, and diffractive
imaging using single photon spectroscopy. In addition the scattering
process can be used to infer the characteristics of high-energy electron
beams and has been used to measure the intrinsic emittance in a regime where
the electron beam is strongly influenced by space-charge induced forces.
More recently we demonstrated for the first time, high-order multiphoton
scattering by the use of laser intensity approaching 1021 W cm-2, and
our experimental results indicate that >500th order harmonic is produced in
the interaction of free electrons with intense laser light.