Nonlinear beat noise in optical parametric chirped-pulse amplification.

The pulse contrast of state-of-the-art petawatt lasers is limited by coherent noise. This paper reports on a new family of noise, termed nonlinear beat noise, which is generated by the nonlinear mixing of two kinds of coherent noise in optical parametric chirped-pulse amplification (OPCPA). We theoretically study the various nonlinear beat noises and reveal their intensity evolutions in an OPCPA amplifier. The results suggest that nonlinear beat noise will be destructive to the future hundred-petawatt lasers.