With the aim of constantly reducing the prices and manufacturing times of space optical instruments, CNES has carried out research and development activities to evaluate new optical concepts for medium-resolution imaging applications. In reality, this study had two objectives. The first consisted of defining a disruptive optical architecture to significantly improve the compactness of telescopes. For this, we decided to target annular telescopes, which offer great compactness with a large numerical aperture, very interesting characteristics for small instruments. The second objective sought was to test a new manufacturing process, which will speed up production times. This is why the diamond turning point was chosen to create the prototype. We will therefore first present the optical design compromise between two interesting solutions for imaging applications. Detailed analyses were performed with optical software tools to prepare manufacturing files. In a second part, a description of the finalized prototype will be provided. It will focus on the opto-mechanical principle but also on the manufacturing quality obtained with diamond machining. Finally, we will detail all the characterizations on the prototype with and without sensor: optical performances evaluated in the laboratory as well as a set of images acquired on different realistic scenes. We will conclude and present perspectives for future versions.
The BepiColombo Spacecraft can’t tolerate to absorb a major fraction of the off-axis sunlight through larger payload apertures. Fortunately, there are solutions to design baffles such that they reflect the incoming radiation back through the front aperture rather than absorbing it. A Design Study, sponsored by ESA and performed by Contraves Space together with SAGEM Défense Securité, has analysed the potential of various solutions and assessed the options to manufacture them. The selected configuration has been analysed in detail for the optical, mechanical and thermal performance as well as the impact on mass and power dissipation. The size of the baffle was adapted to the needs of the BepiColombo Laser Altimeter (BELA) payload.
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.
High end applications in infrared may benefit from infrared colorimetry. Actual systems are designed using filter wheel, gratings or dichroic components. Those systems are bulky, do not allow real-time acquisition and are sensitive to stray light.
Sagem & Reosc recently developed technologies to pixelate infrared coating filters at detector level. It allows designing very compact systems, easy to cool down and to significantly reduce ghost images. Optical systems are simplified and can achieve fast acquisition of multi-spectral video.
Numerical simulations have been performed in order to quantify the pattern shape influence on the optical performances at the microscopic scale. The etching processes of multilayer stacks have been developed. Finally, prototypes have been manufactured and tested.
This technology opens up new perspectives in the field of infrared filtering.
For the most demanding infrared applications, fine knowledge of system performance under operational temperature is required. Management of thin film spectral and mechanical behaviour at cryogenic temperature is a key factor to improve infrared system performances.
Reosc recently investigated models and methods to anticipate measure and control effects of low temperature on coated optical components. Solutions have been developed in order to maximize highest performances under operational conditions. Effects of temperature on spectral transmission and flatness have been studied.
This work has been applied to narrow band pass filters and dichroic coatings working in the range 55K to 90K. Measurements show satisfying correspondence with model. On the basis of model prediction, process and design have then been adapted to improve performances at operational temperature. It has been applied to manufacturing of optics for MTG satellites and IASI NG instrument.
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.
The Spectral Separation Assembly is a key component of the Flexible Combined Imager, an instrument that will be on-board Meteosat Third Generation. It splits the input beam coming from the telescope into five spectral groups, for a total of 16 channels, from 0.4 to 13.3 μm. It comprises a set of four dichroics separators followed by four collimating optics for the infrared spectral groups, which feed the cold imaging optics. The visible spectral group is directly imaged on a detector. This paper presents the optical design of the assembly, the mechanical mounting of the optical components, and the coatings developed for the dichroics, mirrors and lenses.
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.
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.
SAGEM has developed a line of product specific to the large-sized parts. The
means available make it possible today to coat substrates of dimensions going
until 1m50. Current developments address coating of substrate up to 2m20. A
specific focus has been held on the wavefront deformation due to the coating.
Principle contributors of this deformation are introduced and analyzed as well
as some experimental results.
REOSC has developed a new hard multispectral coating on ZnS compatible with military environment conditions. In extreme conditions the coating exhibit a pretty good behavior. Developed on ZnS, other substrates can be used. The coating itself can be tuned from UV up to 10micrometers . High transmission in visible spectrum >= 90 percent is achievable for an antireflection coating tuned around 8-10 micrometers on ZnS. The coating is laser compatible.
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