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. DOI: 10.1103/PhysRevLett.116.183901 Pattern formation as the result of parametric instability (PI) is a universal phenomenon that is widely encountered in many branches of physics [1]. PIs emerge in wave propagation thanks to the interplay between nonlinearity and the dispersion of the medium, when one of the medium parameters is periodically modulated along the longitudinal direction. In the case of externally forced systems, PI is commonly referred to as the Faraday instability, following its initial observation in hydrodynamics under the external modulation of the vertical position of an open fluid tank [2]. Besides fluid mechanics, Faraday-like patterns were subsequently reported in a variety of physical contexts such as crystallization dynamics, chemical systems, or laser physics [3–7]. In addition to parametrically forced systems, many physical systems naturally exhibit collective oscillations that may lead to a so-called geometric-type of parametric instability

Observation of Geometric Parametric Instability Induced by the Periodic Spatial Self-Imaging of Multimode Waves

WABNITZ, Stefan
2016-01-01

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. DOI: 10.1103/PhysRevLett.116.183901 Pattern formation as the result of parametric instability (PI) is a universal phenomenon that is widely encountered in many branches of physics [1]. PIs emerge in wave propagation thanks to the interplay between nonlinearity and the dispersion of the medium, when one of the medium parameters is periodically modulated along the longitudinal direction. In the case of externally forced systems, PI is commonly referred to as the Faraday instability, following its initial observation in hydrodynamics under the external modulation of the vertical position of an open fluid tank [2]. Besides fluid mechanics, Faraday-like patterns were subsequently reported in a variety of physical contexts such as crystallization dynamics, chemical systems, or laser physics [3–7]. In addition to parametrically forced systems, many physical systems naturally exhibit collective oscillations that may lead to a so-called geometric-type of parametric instability
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11379/476782
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