High order harmonic generation for study of atomic and molecular dynamics

We present a pump-probe experiment based on the use of a second electrical field to modulate the intensity and the spatial profile of the phase-matched high-order harmonics radiation generated by the first strong driving field. The modification is caused by the variation of the phase-matching condition, e.g., change of electron trajectory and the effect of field gradient forces on the electron that reflect the dynamics of atomic and molecular gases. Atomic argon and molecular oxygen gases are used to demonstrate the feasibility of the technique.