All-optical measurement of high-order fractional molecular echoes by high-order harmonic generation

TL;DR

This paper demonstrates an all-optical method using high-order harmonic generation to measure high-order fractional molecular echoes, revealing rapid dephasing and enabling ultrashort-time molecular dynamics studies.

Contribution

It introduces a novel HHG-based approach to observe and analyze high-order fractional molecular echoes, expanding the capabilities of ultrafast molecular measurement techniques.

Findings

High-order fractional echoes (1/2, 1/3, 1/4) observed in HHG signals.

High-order echoes dephase more rapidly than traditional revivals.

Method enables access to ultrashort-time molecular dynamics.

Abstract

An all-optical measurement of high-order fractional molecular echoes is demonstrated by using high-order harmonic generation (HHG). Excited by a pair of time-delayed short laser pulses, the signatures of full and high order fractional (1/2 and 1/3) alignment echoes are observed in the HHG signals measured from CO2 molecules at various time delays of the probe pulse. By increasing the time delay of the pump pulses, much higher order fractional (1/4) alignment echo is also observed in N2O molecules. With an analytic model based on the impulsive approximation, the spatiotemporal dynamics of the echo process are retrieved from the experiment. Compared to the typical molecular alignment revivals, high-order fractional molecular echoes are demonstrated to dephase more rapidly, which will open a new route towards the ultrashort-time measurement. The proposed HHG method paves an efficient way for accessing the high-order fractional echoes in molecules.