Filamentation femtoseconde dans les solides

Filamentation dans les solides transparents

The self guided propagation can also be observed in a transparent solid like fused silica. A filament of 20 microns propagates over distances longer than one centimeter (see picture below). We caracterized its spatial, temporal and spectral profile. 3D simulations were also performed using a non-linear propagation code in collaboration with A. Couairon. The good agreement between simulations and measurments allowed us to know the physical caracteristics of the system on the microscopic scale [1].

Left: Self-guided propagation of IR femtosecond laser pulse in fused silica. The laser is focused on the entrance window of the sample. The propagating beam diameter for low incident power is shown as dashed lines. Right: Beam intensity as a function of the radial and the propagation distances in the sample of amorphous SiO2, resulting from our simulations.

Damages in fused silica created by femtoseconde laser pulses.

Femtosecond laser pulses allow the modification, in a controlled and permanent way, of the optical properties of transparent materials such as glasses or silica, in microscopic dimensions. This property can lead to new applications (optical waveguides, high density optical memories, micro-optics, etc.) We have recently started an activity in this domain in our laboratory. When the incident laser power is higher than a critical threshold we have observed in silica the appearance of a birefringence localized in volume. This allow for the fabrication of transmission diffraction gratings (see figure on the left). These gratings are polarization dependent. We also observe the formation of damages in the form of filaments with sub-microscopic dimensions over distances that are many times the Rayleigh distance (see figure on the right). Experiments are actually under the way for the better understanding of the physical mechanisms responsible for those effects.

Left: detail of a polarization grating written in the bulk of a silica plate. Right: filamented damages with sub-micron transverse dimensions and lengths of several tens of microns.

References:

[1] Self-guided propagation of ultrashort IR laser pulses in fused silica
Tzortzakis et al., Phys. Rev. Lett. 87, 213902 (2001) [link]

[2] Writing of permanent birefringent microlayers in bulk fused-silica with femtosecond laser pulses
Sudrie et al., Optics Comm. 171, 279 (1999) [link]

[3] Study of damage in fused silica induced by ultra-short IR laser pulses
Sudrie et al., Opt. Commun. 191, 333 (2001) [link]

[4] Amplification of femtosecond laser filament in Ti:Sapphire.
Philip et al., Phys. Rev. Lett. 95, 163901 (2005) [link]

[5] Femtosecond filamentation in transparent media.
A. Couairon and A. Mysyrowicz
Physics Reports, Vol. 441, p 47 (2007) [link]

 

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