Jullien, Aurélie (2006) Generation of ultra-intense and ultra-short laser pulses with high temporal contrast. PhD thesis Physique, ENSTA / EP / LOA - Laboratoire d'Optique Appliquée UMR 7639, EP/X.
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Abstract
The topic of this thesis work concerns the design and the characterization of an efficient device devoted to the temporal contrast improvement for ultra-intense femtosecond laser pulses. The contrast is defined as the intensity ratio between the main femtosecond pulse and its nanosecond pedestal. This pedestal is the amplified spontaneous emission (ASE), inherent with laser amplification mechanism. The ASE background has dramatic effects for laser-matter interactions on a solid target.
The presented work consists in the theoretical and experimental study of a temporal filter based on a third order nonlinear effect acting on the pulse polarization. We have studied several kinds of nonlinear filters. The selected device is based on the process of cross-polarized wave generation (XPW) in crystals with an anisotropic third-order nonlinear susceptibility. This nonlinear filter has been experimented on various femtosecond systems. It allows a contrast improvement of several orders of magnitude, as demonstrated by temporal profiles measurements on a large intensity dynamic. A device to improve the nonlinear process conversion efficiency, it means the filter transmission, has also been achieved. This method is based on constructive interferences between XPW signals generated in different crystals. This setup has made it possible to reach experimentally the maximum theoretical efficiency ( >20%) and in the same time ensures the system stability. At least, we have demonstrated that the filter preserves, or even improves, spectral and spatial qualities of the laser pulse.
These results are thus particularly promising and allow contemplating the implementation of the filter in current femtosecond systems.
| Item Type: | PhD Thesis (PhD) |
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| Thesis Supervisor: | Chériaux, Gilles |
| Date: | March 2006 |
| Board of examiners: | Etchepare, Jean and Falcoz, Franck and Kieffer, Jean-Claude and Reitze, David and Segonds, Patricia |
| Ecole Doctorale: | ED 447 ECOLE DOCTORALE DE L'ECOLE POLYTECHNIQUE |
| Discipline: | Physique |
| Collection (Fonds): | EP/X ENSTA |
| Institution: | EP/X |
| Department: | ENSTA / EP / LOA - Laboratoire d'Optique Appliquée UMR 7639 |
| Subjects: | 3. Physics, Optics |
| Uncontrolled Keywords: | Laser, Femtosecond pulse, Temporal contrast, Amplified spontaneous emission, Nonlinear filter, Third-order nonlinearities, Anisotropy, Cross-Polarized Wave generation, Laser, Impulsions femtoseconde, Contraste temporel, Emission spontanée amplifiée, Filtre non linéaire, Non linéarités d’ordre trois, Anisotropie, Génération de polarisation orthogonale |
| ID Code: | 1756 |
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| Deposited By: | Julien Karachehayas |
| Deposited On: | 01 June 2006 |
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