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Project ID: HPRI-CT-2001-50037
Finanziato nell'ambito di: FP5-HUMAN POTENTIAL
Paese: France

Double CPA concept with non linear filtering

Double CPA concept with non linear filtering :
The principle of the double CPA concept is to build a first CPA laser system in order to obtain femtoseconde pulses at a millijoule level. Those pulses are filtered thanks to a nonlinear filter in order to obtain pulses of a few hundred of microjoules with a high contrast. The laser beam is then amplified again in a second CPA laser chain.

The nonlinear filter presented here is based on a sagnac interferometer. On one arm of the interferometer, a non linear medium is introduced (a block of BK7 in our case).

The femtosecond part of the laser pulse generate strong nonlinear effets in the medium which change the phase of this part of the pulse whereas it is not the case of the ASE part and of the satellite pulses of the laser beam (there are few nonlinear effets).

The value of the phase difference is a fonction of the laser beam diameter, the pulse energy and the length of the nonlinear medium. When those parameters are well suited, it is possible to obtain a very clean pulse at the output of the interferometer.

The best results obtained were 200µJ, 50fs pulses with a contrast improvement around 4 order of magnitude. Unfortunately, due to the important B integration inside the interferometer, the spatial profile of the output beam is disturbed. During the filtering, the spatial defaults of the input beam are amplified and some hot spots could appear.

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laboratoire d'optique appliquee
chemin de la huniere, batterie de l'yvette
91761 Palaiseau cedex