Noncollinear six-wave mixing of femtosecond light pulses in air by two crossed laser beams has been demonstrated. It was shown that within a wide range of laser intensities this process leads to efficient third-order-harmonic generation, which indicates the importance of higher-order optical nonlinearities in intense light-matter interactions. A direct comparison of the experiment and theory allowed us to estimate unambiguously the magnitude of the quintic optical nonlinearity ${\chi }_{xyyyyx}^{\left(5\right)}(-3\omega ;\omega ,\omega ,\omega ,\omega ,-\omega )$ of air as $2\times {10}^{-49}$ (m/V)${}^4$. We expect that this technique could be useful for multiphoton spectroscopy and laser frequency conversion, as well as for ultrashort light-pulse characterization and verification of theoretical models describing propagation of powerful laser pulses in gaseous media.

• Received 29 March 2013

DOI:https://doi.org/10.1103/PhysRevA.87.063825