Ab-initio calculations of the linear and nonlinear susceptibilities of N$_2$, O$_2$, and air in the mid-infrared

TL;DR

This paper uses first-principles calculations to determine the linear and nonlinear optical susceptibilities of N$_2$, O$_2$, and air in the mid-infrared range, aiding accurate modeling of laser pulse propagation.

Contribution

It provides ab-initio calculations of susceptibilities in the mid-infrared, validated against experimental data, and shows insensitivity to laser intensity up to high fields.

Findings

Good agreement with experimental linear susceptibility data.

Nonlinear susceptibility matches measurements up to 2.4 μm.

Susceptibilities are insensitive to laser intensities up to 5×10^{13} W/cm².

Abstract

We present first-principles calculations of the linear and nonlinear susceptibilities of N$_2$, O$_2$, and air in the mid-infrared wavelength regime, from $1-4$ $\mu$m. We extract the frequency-dependent susceptibilities from the full time-dependent dipole moment that is calculated using time-dependent density functional theory. We find good agreement with curves derived from experimental results for the linear susceptibility, and with measurements for the nonlinear susceptibility up to 2.4 $\mu$m. We also find that the susceptibilities are insensitive to the laser intensity even in the strong field regime up to $5\times 10^{13}$ W/cm$^2$. Our results will allow accurate calculations of the long-distance propagation of intense MIR laser pulses in air.