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Q: Fachverband Quantenoptik und Photonik
Q 31: Laseranwendungen: Optische Messtechnik
Q 31.8: Vortrag
Mittwoch, 4. März 2009, 15:45–16:00, Audi-A
Sensitive method for measurement of weak nonresonant third-order optical nonlinearities — •Anatoly Sherman, Erik Benkler, and Harald Telle — Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
A sensitive method for measurement of weak nonresonant third-order optical nonlinearities (n2) in waveguides is demonstrated. Its value is referenced to the nonlinearity of a thin bulk sample with well-known optical properties. The contribution of this bulk sample to the total nonlinear signal is switched on and off by scanning it across the focal plane of the waveguide output without changing the beam geometry. Thus, the measurement becomes independent of mode field parameters and laser parameters like pulse length, shape, chirp and peak power.
The experimental scheme combines nearly degenerate four-wave mixing of short pulses at 1.5 µ m (duration ≈ 100 fs) with heterodyne detection for ultra-high sensitivity. As a first experimental demonstration of this method, we measure the nonresonant nonlinearity of a 21 mm short strand of air-filled hollow-core photonic crystal fiber. The measured value which is more than 1000 times smaller than in standard optical fiber (SMF-28) is in good agreement with theoretical calculations. Possible limitations e. g. due to noise contributions and parasitic nonlinear effects in the photodetector will be discussed.
As a universal method, the presented scheme also allows the measurement of third-order optical nonlinearities of highly asymmetric waveguides or bulk samples as well.