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arXiv · 1105.6334

Optical nonlinearity in Ar and N$_2$ near the ionization threshold

J. K. Wahlstrand·Y. -H. Cheng·Y. -H. Chen·H. M. Milchberg
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Abstract

We directly measure the nonlinear optical response in argon and nitrogen in a thin gas target to laser intensities near the ionization threshold. No instantaneous negative nonlinear refractive index is observed, nor is saturation, in contrast with a previous measurement [Loriot et al., Opt. Express v. 17, 13429 (2009)] and calculations [Brée et al., Phys. Rev. Lett. v. 106, 183902 (2011)]. In addition, we are able to cleanly separate the instantaneous and rotational components of the nonlinear response in nitrogen. In both Ar and N$_2$, we observe the peak instantaneous index response scale linearly with the laser intensity until the point of ionization, whereupon it turns abruptly negative and ~constant, consistent with plasma generation.

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J. K. Wahlstrand, Y. -H. Cheng, Y. -H. Chen, H. M. Milchberg. 2011-08-15. Optical nonlinearity in Ar and N$_2$ near the ionization threshold. https://doi.org/10.1103/physrevlett.107.103901

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