Abstract

The measurement of the pure electronic nonlinear optical refractive index of gases, n₂, is not an easy task because gases have low density and n₂ are small. In this way, one important method is based on the self-induced spectral broadening using long interaction length and high laser peak intensity [1]. In Ref. 1, using hollow-core fiber (HCF) it was possible to measure n₂ by spectral broadening. Here we propose a new method that also uses a gas filled HCF to measure n₂ at lower laser power. In fact, it was possible to measure the nonlinearity before any macroscopic spectral broadening is observed. This sensitivity was possible due to use of the recently introduced nonlinear ellipse rotation (NER) method that’s use a dual-phase lock-in amplifier [2]. We did measurements in argon, nitrogen, oxygen, air and helium gases to demonstrate our method.

© 2015 IEEE