Robust relativistic high harmonic generation from 400 nm laser matter interactions*

Relativistically intense laser solid density plasma interactions are capable of upshifting the laser frequency into the soft and hard x-ray wavelengths via high order harmonic generation. Experiments were performed at the ALEPH laser system at 10²¹ Wcm^-2 and at a wavelength of 400 nm. Results from conductive and dielectric targets at a variety of thicknesses will be shown. The second harmonic generation process that produces the 400 nm laser pulses greatly increases laser contrast and enables highly consistent harmonic production. Mechanisms of attosecond pulse generation were identified, including Relativistic Oscillating Mirror (ROM) and Coherent Wake Emission (CWE). Numerical modeling was performed as well.