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Spectrogram representation of pulse self compression by filamentation.

Selcuk Akturk¹, Arnaud Couairon, Michel Franco

¹Laboratoire d'Optique Appliquée, Ecole Nationale Supérieure des Techniques Avancées, Ecole Polytechnique, CNRS UMR 7639, Palaiseau Cedex, France. selcuk.akturk@ensta.fr

|October 30, 2008

Summary

This summary is machine-generated.

Pulse self-compression via filamentation is visualized using spectrograms, revealing spectral broadening and pulse shortening. Simulations show negative chirp arises from self-phase modulation and group velocity dispersion, not plasma effects.

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Area of Science:

Nonlinear Optics
Ultrafast Laser Science
Computational Physics

Background:

Ultrashort laser pulses undergo complex spectral and temporal evolution during nonlinear propagation.
Filamentation is a key phenomenon in high-intensity laser-matter interactions, leading to pulse dynamics like self-compression.
Understanding spectral phase evolution is crucial for controlling pulse shortening.

Purpose of the Study:

To investigate and visualize the mechanisms of pulse self-compression during laser filamentation.
To analyze the spectral phase evolution and its contribution to pulse shortening.
To differentiate the roles of nonlinear effects and plasma dispersion in self-compression.

Main Methods:

Numerical simulations of ultrashort pulse propagation and filamentation.
Experimental validation of simulation results.
Spectrogram analysis to visualize spectral and temporal dynamics.
Analysis of spectral phase during nonlinear propagation.

Main Results:

Spectrograms intuitively represent spectral broadening and pulse shortening during filamentation.
Simulations reveal the occurrence of negative chirp preceding pulse shortening.
Negative chirp is attributed to the interplay of self-phase modulation and group velocity dispersion.
Plasma-induced dispersion was found to have a minimal impact on negative chirp generation.

Conclusions:

Spectrograms offer a powerful tool for understanding pulse self-compression in filamentation.
Spatio-temporal reshaping driven by nonlinear effects is the primary mechanism for negative chirp and self-compression.
The findings provide a deeper insight into the physics of ultrashort pulse self-compressed filaments.