Here we explore ways of transforming laser radiation into incoherent and coherent electromagnetic radiation using laserdriven plasma waves. We present several examples based on the laser wakefield accelerator (LWFA) and show that the electron beam and radiation from the LWFA has several unique characteristics compared with conventional devices. We show that the energy spread can be much smaller than 1% at 130-150 MeV. This makes LWFAs useful tools for scientists undertaking time resolved probing of matter subject to stimuli. They also make excellent imaging tools. We present experimental evidence that ultra-short XUV pulses, as short as 30 fs, are produced directly from an undulator driven by a LWFA, due to the electron bunches having a duration of a few femtoseconds. By extending the electron energy to 1 GeV, and for 1-2 fs duration pulses of 2 nm radiation peak powers of several MW per pC can be produced. The increased charge at higher electron energies will increase the peak power to GW levels, making the LWFA driven synchrotron an extremely useful source with a spectral range extending into the water window. With the reduction in size afforded by using LWFA driven radiation sources, and with the predicted advances in laser stability and repletion rate, ultra-short pulse radiation sources should become more affordable and widely used, which could change the way science is done.
The ion-channel laser (ICL) has been proposed as an alternative to the free-electron laser (FEL), replacing the deflection of electrons by the periodic magnetic field of an undulator with the periodic betatron motion in an ion channel. Ion channels can be generated by passing dense energetic electron bunches or intense laser pulses through plasma. The ICL has potential to replace FELs based on magnetic undulators, leading to very compact coherent X-ray sources. In particular, coupling the ICL with a laser plasma wakefield accelerator would reduce the size of a coherent light source by several orders of magnitude. An important difference between FEL and ICL is the wavelength of transverse oscillations: In the former it is fixed by the undulator period, whereas in the latter it depends on the betatron amplitude, which therefore has to be treated as variable. Even so, the resulting equations for the ICL are formally similar to those for the FEL with space charge taken into account, so that the well-developed formalism for the FEL can be applied. The amplitude dependence leads to additional requirements compared to the FEL, e.g. a small spread of betatron amplitudes. We shall address these requirements and the resulting practical considerations for realizing an ICL, and give parameters for operation at UV fundamental wavelength, with harmonics extending into X-rays.
The ion-channel laser (ICL) has been proposed as an alternative to the free-electron laser (FEL), replacing the
deflection of electrons in an undulator by betatron oscillations in an ion channel. The aim of this study is to
describe the ICL in terms of the well-developed formalism for the FEL in the steady-state, while taking into
account the dependence of the resonance between oscillations and emitted field on the oscillation amplitude. Numerical
solutions for experimentally relevant parameters show similarities and differences between both devices.
The ICL has potential to replace FELs based on magnetic undulators, leading to very compact coherent X-ray
sources. Furthermore, coupling the ICL with a laser plasma wakefield accelerator would reduce the size of a
coherent light sources by several orders of magnitude.
Electron acceleration using plasma waves driven by ultra-short relativistic intensity laser pulses has
undoubtedly excellent potential for driving a compact light source. However, for a wakefield accelerator to
become a useful and reliable compact accelerator the beam properties need to meet a minimum standard. To
demonstrate the feasibility of a wakefield based radiation source we have reliably produced electron beams
with energies of 82±5 MeV, with 1±0.2% energy spread and 3 mrad r.m.s. divergence using a 0.9 J, 35 fs 800
nm laser. Reproducible beam pointing is essential for transporting the beam along the electron beam line. We
find experimentally that electrons are accelerated close to the laser axis at low plasma densities. However, at
plasma densities in excess of 1019 cm-3, electron beams have an elliptical beam profile with the major axis of
the ellipse rotated with respect to the direction of polarization of the laser.