Relativistic High Harmonic Generation

In recent advance, laser atom interaction has made significant progress in theoretical and experimental method. This article is devoted to a review of recent relativistic High Harmonic Generation (HHG) and Above Threshold Ionization (ATI) in intense laser field is investigated via the Klein-Gordon equation with ponderomotive approach. Thus, in relativistic effects at higher intensity are discussed within strong field approximation (SFA). Moreover, with this relativistic effect shows the simple representation in harmonic spectrum for Ar
⁸⁺
ion exposed to 800 nm laser field and will be given current information on how the harmonic spectrum changes and how it will be affected attosecond pulse production in ultra-fast dynamic.