Relativistic Laser Plasmas for Electron Acceleration and Short Wavelength Radiation Generation

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 kilo electron volt (keV) to mega electron volt (MeV) 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 laser-driven plasma surface oscillates at relativistic velocities and severely alters the frequency of the reflected laser light. The high harmonics are emitted in coherent subfemtosecond flashes. The theory of harmonics generation in the relativistic regime predicts a power law energy spectrum with an exponent \(-8/3\). However, for short laser pulses and high intensities, the electrons self-organize in nanobunches that lead to coherent12pc]First author has been considered as corresponding author. Please check. synchrotron emission. The power law harmonic spectrum can become very flat in this case with the exponent as low as \(-6/5\). This can make the high harmonics potentially the brightest laser-driven short wavelength sources with unique properties.