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Register a new userAnalytical study of coherence in seeded modulation instability
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We derive analytical expressions for the coherence in the onset of modulation instability, in excellent agreement with thorough numerical simulations. As usual, we start by a linear perturbation analysis, where broadband noise is added to a continuous wave (CW) pump; then, we investigate the effect of adding a deterministic seed to the CW pump, a case of singular interest as it is commonly encountered in parametric amplification schemes. Results for the dependence of coherence on parameters such as fiber type, pump power, propagated distance, seed signal-to-noise ratio are presented. Finally, we show the importance of including higher-order linear and nonlinear dispersion when dealing with generation in longer wavelength regions (mid IR). We believe these results to be of relevance when applied to the analysis of the coherence properties of supercontinua generated from CW pumps.
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In optical second harmonic generation with normal dispersion, the virtually infinite bandwidth of the unbounded, hyperbolic, modulational instability leads to quenching of spatial multi-soliton formation and to the occurrence of a catastrophic spatio-temporal break-up when an extended beam is let to interact with an extremely weak external noise with coherence time much shorter than that of the pump.
We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of a long proton bunch in plasma. We show experimentally that, with sufficient initial amplitude ($ge(4.1pm0.4)$ MV/m), the phase of the modulation along the bunch is reproducible from event to event, with 3 to 7% (of 2$pi$) rms variations all along the bunch. The phase is not reproducible for lower initial amplitudes. We observe the transition between these two regimes. Phase reproducibility is essential for deterministic external injection of particles to be accelerated.
We present a novel approach to the analysis of a full model of scalar modulation instability (MI) by means of a simple geometrical description in the power vs. frequency plane. This formulation allows to relate the shape of the MI gain to any arbitrary dispersion profile of the medium. As a result, we derive a straightforward explanation of the non-trivial dependence of the cutoff power on high-order dispersion and obtain explicitly the power that maximizes the gain. Our approach puts forth a powerful tool to synthesize a desired MI gain with the potential application to a vast number of parametric-amplification and supercontinuum-generation devices whose functioning relies upon modulation instability.
We revisit the problem of modulation instability (MI) in optical fibers, including higher-order dispersion terms, self-steepening, and Raman response. We derive expressions for the MI gain and use them to explore the role of self-steepening towards a high-power limit. We show that, contrary to common wisdom, there is a pump power level that maximizes the MI gain. Further increasing the power not only diminishes the gain, but eventually makes it disappear. We believe these findings to be of special relevance, for instance, when applied to the generation of supercontinuum in the mid and far infrared bands. Finally, numerical simulations confirming our analytical results are presented.
We investigate multi-wave mixing associated with the strongly pump depleted regime of induced modulation instability (MI) in optical fibers. For a complete transfer of pump power into the sideband modes, we theoretically and experimentally demonstrate that it is necessary to use a much lower seeding modulation frequency than the peak MI gain value. Our analysis shows that a record 95 % of the input pump power is frequency converted into the comb of sidebands, in good quantitative agreement with analytical predictions based on the simplest exact breather solution of the nonlinear Schrodinger equation.
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