Relativistic laser plasmas for electron acceleration and short wavelength radiation generation

Abstract

We consider here a few options to use relativistic laser plasmas for novel sources of short wavelength radiation. Electrons accelerated in underdense plasmas in the bubble regime wiggle in an ion channel. This leads to broadband incoherent synchrotron-like radiation bursts which are of femtosecond duration. The photon energies are in the kiloelectronvolt to megaelectronvolt energy range. However, this radiation is not coherent. To reach coherency, the electron bunch must have structure at the wavelength of the emitted x-rays. This can be achieved in principle by sending the laser-accelerated electron bunch through an external wiggler. However, to reach free electron lasing in the x-ray regime, the energy spread of the laser-accelerated electrons must be reduced dramatically. Another option is to use high harmonic generation at overdense plasma boundaries. The high harmonics are emitted in coherent sub-femtosecond flashes. The harmonic spectra decay as a power of the harmonic number, with an exponent that can be as low as −6/5. This can make the high harmonics potentially the brightest laser-driven short wavelength sources with unique properties.