Third and fifth harmonics generation by tightly focused femtosecond pulses at 2.2 {\mu}m wavelength in air

TL;DR

This paper reports experimental results on third and fifth harmonic generation using femtosecond laser pulses at 2.2 μm in air, showing a specific harmonic yield ratio that challenges previous theories about Kerr effect saturation.

Contribution

The study provides new experimental data on high-order harmonic generation in air at mid-infrared wavelengths, contradicting recent claims about Kerr effect saturation.

Findings

Harmonic yield ratio of about 2 x 10^-4 for third and fifth harmonics.

Results challenge the idea of Kerr effect saturation and sign change in ultra-intense fields.

Experimental setup with millijoule-level femtosecond pulses at 2.2 μm.

Abstract

We report experiments on the generation of third and fifth harmonics of millijoule-level, tightly focused, femtosecond laser pulses at 2.2 {\mu}m wavelength in air. The measured ratio of yields of the third and fifth harmonics in our setup is about 2 \cdot 10-4. This result contradicts the recent suggestion that the Kerr effect in air saturates and changes sign in ultra-intense optical fields.