Non-perturbative generation of above-threshold harmonics from pre-excited argon atoms in intense mid-infrared laser fields

摘要

We experimentally investigate the generation of above-threshold harmonicscompletely from argon atoms on an excited state using mid-infrared femtosecondlaser pulses. The highly nonlinear dependences of the observed signal on thepulse energy and polarization of the driver laser pulses indicate itsnon-perturbative characteristic.