Abstract
<p> <a href="http://oe.osa.org/virtual_issue.cfm?vid=36">Focus Serial: Frontiers of Nonlinear Optics</a> </p>We investigate ultrashort laser pulse filamentation within the framework of spontaneous X Wave formation. After a brief overview of the filamentation process we study the case of an intense filament co-propagating with a weaker seed pulse. The filament is shown to induce strong Cross-Phase-Modulation (XPM) effects on the weak seed pulse: driven by the pump, the seed pulse undergoes pulse splitting with the daughter pulses slaved to their pump counterparts. They undergo strong spatio-temporal reshaping and are transformed into XWaves traveling at the same group velocities as the pump split-off pulses. In the presence of a gain mechanism such as Four-Wave-Mixing or Stimulated Raman Scattering, energy is then transferred from the pump filament leading to amplification of the seed X Wave and formation of a temporally compressed intensity peak.
Highlights
Ultrashort laser pulse filamentation is an extremely rich branch of nonlinear optics that has been attracting interest for many years [1] due to both the fundamental physical implications and the potential applications ranging from spectral superbroadening [2] and remote sensing [3], lightning protection [4] and, more recently, frequency conversion [5, 6, 7]
All these approaches agree on the fact that the nonlinear dynamics are dominated by a pulse splitting event, i.e. a generation of two daughter X Waves that travel with opposite group velocities
We underline that the description of ultrashort laser pulse filamentation in terms of X Wave formation goes beyond the over-simplified idea that single, stationary, X Waves are formed and is based on the observation that, due to the extremely high intensities involved, the X Waves continuously interact within the filament leading to a highly dynamical propagation
Summary
Ultrashort laser pulse filamentation is an extremely rich branch of nonlinear optics that has been attracting interest for many years [1] due to both the fundamental physical implications and the potential applications ranging from spectral superbroadening [2] and remote sensing [3], lightning protection [4] and, more recently, frequency conversion [5, 6, 7]. We underline that the description of ultrashort laser pulse filamentation in terms of X Wave formation goes beyond the over-simplified idea that single, stationary, X Waves are formed and is based on the observation that, due to the extremely high intensities involved, the X Waves continuously interact within the filament leading to a highly dynamical propagation. The above described dynamics typically do not involve the whole input pulse but the only a small portion of the overall energy corresponding to the higher intensity regions while the weaker outer regions of the pulse will continue to propagate in a linear fashion This immediately implies that a direct spatio-temporal characterization of the near-field reveals complicated interference patterns between the two regions [37] and to date, a clear space-time measurement of the X Waves contained within the filament is still lacking. Emphasis will be given in this last section on the formation of temporally compressed pulses
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