Abstract

We survey the problem of high harmonic generation at overdense plasma surfaces. It is shown that the harmonics appear as a train of sub-attosecond pulses because of the Doppler effect. [1] These pulses promise to become a unique experimental and technological tool since their length is of the order of the Bohr radius and the intensity is extremely high, on the order of 10¹⁹ W/cm². We present the physical mechanism, analytical theory, and direct particle-in-cell simulations. The harmonics are phase-locked, coherent and have a universal power-law spectrum. Reflection from concave plasma surfaces can lead to coherent harmonics focusing reaching extremely high intensities [2].

© 2005 Optical Society of America