Erlangen 2018 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 3: Ultrashort Laser Pulses

Q 3.7: Talk

Monday, March 5, 2018, 12:00–12:15, K 0.023

Long-Lived Index Changes Induced by Femtosecond Ionization in Ar-Filled Hollow-Core PCF — •Johannes R. Köhler, Francesco Tani, Barbara M. Trabold, Felix Köttig, Mallika I. Suresh, and Philip St.J. Russell — Max-Planck-Institut für die Physik des Lichts, Erlangen, Deutschland

Gas-filled hollow-core photonic crystal fibre (HC-PCF) is finding important applications in ultrafast nonlinear optics, for example for pulse compression down to single cycles and for generation of broadband tunable radiation in the deep and vacuum ultraviolet. Scaling these novel light sources to MHz repetition rates is enabled by exploiting the large damage threshold in HC-PCFs that guide light by anti-resonant reflection (ARR) in the cladding. At the same time, they offer small core diameters, making it possible to access strongly nonlinear effects such as gas ionisation, using femtosecond pulses with energies of only a few µJ. When a plasma forms, each pulse causes a transient refractive index change that, if sufficiently long-lived, may affect the propagation of subsequent pulses. Here we investigate the effects of ionization, caused by self-compressed femtosecond pulses, on the temporal refractive index evolution in an argon-filled ARR-PCF. To this end we focus CW probe light transversely through the fiber cladding into the core and follow its transient phase-shifts over time using a fibre-based Mach-Zehnder interferometer. The results reveal long-lived ionisation-induced refractive index changes decaying over ∼25 µs and indicate that interactions among pulses, so far disregarded in HC-PCFs, will occur at repetition rates as low as 40 kHz.