Measurements of Optical Kerr Nonlinearity n2 in Compressed Gases

TL;DR

This study experimentally measures the Kerr nonlinearity coefficient n2 in various gases under different pressures and pulse durations, revealing its dependence on these parameters and providing new data for CO2 at atmospheric pressure.

Contribution

First experimental determination of n2 in CO2 at atmospheric pressure and analysis of its dependence on pressure and pulse duration in gases.

Findings

n2 in CO2 at atmospheric pressure is approximately 10.0×10⁻²⁴ m²/W

Effective n2 increases with gas pressure due to self-focusing effects

Inertial component of nonlinearity increases with pulse duration and pressure

Abstract

High-power optical pulses experience self-focusing when propagating in a gaseous medium due to the manifestation of the cubic (Kerr-like) nonlinearity. The magnitude of this effect depends on the Kerr nonlinearity coefficient n2, which in turn may depend on the parameters of laser radiation and the propagation medium. We present experimental data on the coefficient n2 for atomic Ar, molecular N2 and CO2 with a pressure change from 1 to 11 bar and optical pulse duration from 50 to 500 fs of propagating femtosecond near-IR laser radiation (800 nm). Importantly, all three gases under study possess close n2-values in the short pulse limit (50 fs) over the entire pressure range. According to our data, for the first time, as far as we know, the Kerr nonlinearity in CO2 is obtained at atmospheric pressure equal to n2(CO2) = 10.0x1.1x10-24 m2/W. Meanwhile, with increasing gas pressure, effective n2 also increases due to the manifestation of aberrational pulse self-focusing caused by the development of modulation instability. In addition, according to our approximate estimate, the magnitude of the inertial component in the cubic nonlinearity of molecular gases (N2, CO2) is substantial and increases with both pulse duration and gas pressure.