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

TL;DR

This paper demonstrates the experimental generation of above-threshold harmonics from pre-excited argon atoms using intense mid-infrared femtosecond laser pulses, highlighting the non-perturbative nature of the process.

Contribution

It presents the first experimental evidence of non-perturbative above-threshold harmonic generation from excited argon atoms in mid-infrared fields.

Findings

Harmonic signals depend strongly on pulse energy and polarization.

Generation occurs from atoms initially in an excited state.

Process exhibits non-perturbative nonlinear characteristics.

Abstract

We experimentally investigate the generation of above-threshold harmonics completely from argon atoms on an excited state using mid-infrared femtosecond laser pulses. The highly nonlinear dependences of the observed signal on the pulse energy and polarization of the driver laser pulses indicate its non-perturbative characteristic.