Time correlation inside a laser pulse

Looking inside a laser pulse by detecting an instantaneous ionization rate (IIR) has been a useful instrument for characterizing subcycle ionization dynamics [Phys. Rev. A 64, 013409 (2001)PLRAAN1050-294710.1103/PhysRevA.64.013409]. However, this instrument relies entirely on IIR being a deterministic function of time. By introducing an IIR operator and studying its autocorrelation function, we show that electron ionization dynamics is more complex and the ionization rate depends on the "prehistory," i.e., the IIRs at the two instants of time are, in fact, correlated. The pattern of this correlation changes dramatically between the multiphoton and tunneling ionization regimes. These findings have wide implications for strong-field atomic physics and providing new possibilities for quantum local realism tests.