Frequency shift in high order harmonic generation from isotopic molecules

TL;DR

This paper reports the first experimental observation of a frequency red shift in high order harmonic generation from isotopic molecules H2 and D2, attributed to laser-driven nuclear motion, and demonstrates manipulation of this shift via laser chirp.

Contribution

It introduces the first experimental detection of frequency shifts in HHG from isotopic molecules and links it to nuclear motion, also showing control through laser chirp.

Findings

Harmonics from isotopic molecules show a spectral red shift.

The red shift results from laser-driven nuclear motion.

Frequency shift can be manipulated by laser chirp.

Abstract

We report the first experimental observation of frequency shift in high order harmonic generation (HHG) from isotopic molecules H2 and D2 . It is found that harmonics generated from the isotopic molecules exhibit obvious spectral red shift with respect to those from Ar atom. The red shift is further demonstrated to arise from the laser-driven nuclear motion in isotopic molecules. By utilizing the red shift observed in experiment, we successfully retrieve the nuclear vibrations in H2 and D2, which agree well with the theoretical calculations from the time-dependent Schrodinger equation (TDSE) with Non-Born-Oppenheimer approximation. Moreover, we demonstrate that the frequency shift can be manipulated by changing the laser chirp.