More than 50 large aperture optics coated by Safran Reosc have been delivered to LULI for the APOLLON laser facility. Coating designs, processes and measurements are discussed with regard to the requirements. As a part of these optics is mounted on the beam line, we present operational performances with a specific focus on LIDT. This paper also relates the challenge to give a reliable LIDT value within a specific application toward the coatings of those component that have been tested by several LIDT-testing facilities. This test results are discussed and compared with LIDT test performed with the APOLLON laser beam.
In order to transport multi-petawatt (PW) femtosecond laser beams with large spectral bandwidth, specific mirrors have to be designed and manufactured. We report on an experimental study of the laser-damage resistance and other optical properties of coating materials deposited in a 1-m class coating chamber. The study is conducted on single-layer coatings deposited by electron beam evaporation at 500 fs. Based on the experience of large optics for nanosecond applications, hafnia and silica are particularly investigated. However, in the case of sub-15 fs, the spectral specifications for PW beam transport mirrors cannot be reached by classical high laser-resistant quarter-wave SiO2/HfO2 stacks. Therefore, we investigate the laser resistance of different dielectrics of interest deposited with electron-beam processes: Al2O3, Y2O3, Sc2O3, HfO2, Ta2O5, TiO2. The influence of multiple pulse irradiations and environmental conditions, such as vacuum and temperature, is studied. With the investigation of multilayer stacks, we also show that there is no difference in behavior when a film is studied as a single layer or embedded in a stack. Based on these results, we were able to optimize high reflective (>99.5%), broadband (300 nm) and high laser-induced damage threshold (2.5 J/cm2) mirrors for PW applications.
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.
Dielectrics as single layers and broadband high-reflective stacks were deposited by electron beam deposition
processes compatible with 1-meter class optics. After being physically and optically characterized, samples were
irradiated with several ultrafast lasers (KYW:Yb 500fs, Ti:Sa 40fs and Ti:Sa 11fs) with single and multi-pulses.
The setups of the test platforms, laser-induced damage threshold investigations of intrinsic materials, dielectric
multilayers and hybrid metal/dielectric multilayers and electric field intensity distributions are described.
Laser induced damage threshold is a key parameter for all components in high-power laser system, establishing limits of
maximum achievable energy, and consequently average power. To provide reliable and stable laser sources, desirable
both in academic and industrial area, involved components has to be tested and meet certain quality criteria. To provide
such laser source is the goal of HiLASE project, where the development of scalable kW-class laser delivering ps pulses
in kHz repetition rate is taking place. Broadband, high damage threshold mirrors are one of the key components for
future installations and their development is carried out synergistically with laser system and LIDT station.
In new laser facilities, broadband ultra-short pulses need to be transported in large and energetic beams to the experiment chambers through high performance optical components. We studied laser resistance of electronbeam- deposited materials in order to design meter scale high reflective optics according to petawatt-system requirements. We report intrinsic laser resistance of several dielectric materials, spectral performances of high reflective coatings and their laser induced damage threshold at different pulse durations from 150ps to 11fs.
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