Comparative investigation of third and fifth harmonic generation in atomic and molecular gases driven by mid-infrared ultrafast laser pulses

TL;DR

This study compares third and fifth harmonic generation in atomic and molecular gases driven by mid-infrared ultrafast laser pulses, revealing saturation behaviors and the role of high-order Kerr effects.

Contribution

It provides the first comparative experimental analysis of THG and FHG efficiencies and their saturation in different gases at mid-infrared wavelengths.

Findings

Conversion efficiencies saturate near 1.5×10^14 W/cm^2 for all gases.

FHG yields are about 10% of THG yields at saturation.

High-order Kerr effects are present but insufficient alone to prevent self-focusing.

Abstract

We report on the comparative experimental investigation on third and fifth harmonic generation (THG and FHG) in atomic and molecular gases driven by mid-infrared ultrafast laser pulses at a wavelength of ~1500 nm. We observe that the conversion efficiencies of both the THG and FHG processes saturate at similar peak intensities close to ~1.5\times1014 W/cm2 for argon, nitrogen, and air, whose ionization potentials are close to each other. Near the saturation intensity, the ratio of yields of the FHG and THG reaches ~10-1 for all the gases. Our results show that high-order Kerr effects do exist, whereas they are insufficient to balance the Kerr self-focusing without the assistance of plasma generation.