title: Observation of Geometric Parametric Instability Induced by the Periodic Spatial Self-Imaging of Multimode Waves.
abstract: Spatiotemporal mode coupling in highly multimode physical systems permits new routes for exploring complex instabilities and forming coherent wave structures. We present here the first experimental demonstration of multiple geometric parametric instability sidebands, generated in the frequency domain through resonant space-time coupling, owing to the natural periodic spatial self-imaging of a multimode quasi-continuous-wave beam in a standard graded-index multimode fiber. The input beam was launched in the fiber by means of an amplified microchip laser emitting sub-ns pulses at 1064 nm. The experimentally observed frequency spacing among sidebands agrees well with analytical predictions and numerical simulations. The first-order peaks are located at the considerably large detuning of 123.5 THz from the pump. These results open the remarkable possibility to convert a near-infrared laser directly into a broad spectral range spanning visible and infrared wavelengths, by means of a single resonant parametric nonlinear effect occurring in the normal dispersion regime. As further evidence of our strong space-time coupling regime, we observed the striking effect that all of the different sideband peaks were carried by a well-defined and stable bell-shaped spatial profile.
authors.affiliation: Université de Limoges, XLIM, UMR CNRS 7252, 123 Avenue A. Thomas, 87060 Limoges, France.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Krupa
authors.affiliation: Université de Limoges, XLIM, UMR CNRS 7252, 123 Avenue A. Thomas, 87060 Limoges, France.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Tonello
authors.affiliation: Université de Limoges, XLIM, UMR CNRS 7252, 123 Avenue A. Thomas, 87060 Limoges, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Barthélémy
authors.affiliation: Université de Limoges, XLIM, UMR CNRS 7252, 123 Avenue A. Thomas, 87060 Limoges, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Couderc
authors.affiliation: Physics Department, Faculty of Science, Tanta University, Egypt and Université de Limoges, XLIM, UMR CNRS 7252, 123 Avenue A. Thomas, 87060 Limoges, France.
authors.forename: Badr Mohamed
authors.initials: BM
authors.lastname: Shalaby
authors.affiliation: Université de Bourgogne Franche-Comté, ICB, UMR CNRS 6303, 9 Av. A. Savary, 21078 Dijon, France.
authors.forename: Abdelkrim
authors.initials: A
authors.lastname: Bendahmane
authors.affiliation: Université de Bourgogne Franche-Comté, ICB, UMR CNRS 6303, 9 Av. A. Savary, 21078 Dijon, France.
authors.forename: Guy
authors.initials: G
authors.lastname: Millot
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università di Brescia, and INO-CNR, via Branze 38, 25123, Brescia, Italy.
authors.forename: Stefan
authors.initials: S
authors.lastname: Wabnitz