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Transient mid-IR nonlinear refraction in air.

Salimeh Tofighi, Natalia Munera, Matthew Reichert

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    Summary

    We measured the nonlinear refractive index of air using mid-IR light, finding no dispersion. The effective nonlinear refractive index peaks at 0.5 ps pulsewidths, with implications for atmospheric modeling.

    Area of Science:

    • Nonlinear optics
    • Atmospheric optics
    • Laser physics

    Background:

    • Nonlinear refractive index (n2) is crucial for understanding light-matter interactions in gases.
    • Previous studies have investigated air's nonlinear refraction, but comprehensive mid-IR measurements are lacking.

    Purpose of the Study:

    • To measure the nonlinear refraction of air using mid-IR excitation and probing.
    • To investigate the dispersion of the bound-electronic nonlinear refractive index (n2,el).
    • To model the pulsewidth dependence of the effective nonlinear refractive index (n2,eff) and predict atmospheric behavior.

    Main Methods:

    • Utilized polarization-sensitive, time-resolved Beam-Deflection technique.
    • Employed near- and mid-infrared excitation, with mid-infrared probing.

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  • Measured nonlinear refraction across various pressures and temperatures.

    • Main Results:

    • First measurements of air's nonlinear refraction with both mid-IR excitation and probe.
    • Observed no dispersion in the bound-electronic nonlinear refractive index (n2,el).
    • Found the effective nonlinear refractive index (n2,eff) is maximized at ~0.5 ps pulsewidth, decreasing with pressure and temperature.

    Conclusions:

    • The bound-electronic nonlinear refractive index of air shows no significant dispersion in the mid-IR.
    • The pulsewidth dependence of n2,eff has implications for high-intensity laser propagation in the atmosphere.
    • Predicted nonlinear refraction behavior at various atmospheric altitudes based on experimental data and modeling.