The peak power handling capability of ultra-short pulse lasers is main concern for new facilities, like those for the French Apollon 10P, and European Extreme Light Infrastructure (ELI) projects. Indeed, these last generation lasers require complex, large (Ø1m) and resistant optical components with optimized thin-film coatings. Using on one hand the recent development of high laser resistant broadband high reflective coatings through a joint project with the Laboratoire d’Optique Appliquée and Fresnel Institute, and on the other hand its long time experience with polishing and measuring large and complex optical components, Reosc decided to demonstrate the feasibility of a Ø500mm aperture, 90° deviation, F/2.5 high output NA Off-Axis Parabola (OAP) dedicated to focus fs ultra-intense laser beams.
The prototype of the 90° OAP has a concave surface with 20mm of aspherisation for focal length of F1250mm. The OAP is coated with a hybrid Metal/Multi-Layer-Dielectric coating. It provides a reflectivity up to 98%, an absolute Group Delay Dispersion (GDD) below 100fs² and a Laser-Induced Damage Threshold (LIDT) up to 0.5J/cm², at 15fs and under vacuum. These performances are achieved on the whole surface and on the 200nm spectral range required by the sub 20fs PW-systems.
In this paper, Reosc report the developments required for the polishing, the coating and the measurements of the OAP and we will show the performances achieved on the prototype.