Stuttgart 2012 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 59: Ultrakurze Laserpulse

Q 59.5: Talk

Friday, March 16, 2012, 11:30–11:45, V38.04

Saturation of the all-optical Kerr effect in solids — •Bastian Borchers¹, Carsten Brée², Simon Birkholz¹, and Günter Steinmeyer¹ — ¹Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2a, 12489 Berlin, Germany — ²Weierstraß Institute for Applied Analysis and Stochastics, Mohrenstraße 39, 10117 Berlin, Germany

Nonlinear Optics is based on a perturbative expansion of the relation between the polarization and the electric field: P=є₀(χ⁽¹⁾E + χ⁽²⁾E²+ χ⁽³⁾E³+…). Normally it is sufficient to consider terms up to third order in this expansion. Recently, a controversial debate started whether or not higher order terms contribute to the formation of filaments in gases. Little is known, however, on the appearance of similar effects in solid dielectrica. In fact, their appearance would have severe consequences for our understanding of, e.g., Kerr lens mode-locking or supercontinuum generation in photonic crystal fibers.

We used multiphoton absorption rates provided by different theoretical models to compute a) the nonlinear refractive index via Kramers-Kronig transform and b) the plasma contribution predicted by the Drude model. Within this theoretical framework we observe the onset of the two different effects at nearly the same intensity, indicating that Kerr-saturation must not be neglected at intensities where plasma formation comes into play. These theoretical findings are discussed for the scenarios mentioned above along with the result of a four-wave mixing experiment in BaF₂ supporting the appearance of HOKE.