Thin films

Safran Reosc offers state of the art optical thin films for DUV, Vis or IR spectral domains as a separate service to its customers or included within the products we deliver for space, laser, cryogenic or defense environment.
Space qualification, resistance to cryogenic environment, high laser fluence level, 2D linear or pixelated structuration are our key differentiation factors and value offered to our customers. 

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Thin films

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Design: Our thin film design team holds several decades of expertize in designing and simulating thin films performance and to defining and developing the required deposition process parameters as well as the characterization methodologies.
Our team maintains tight relations with all other thin film specialists within Safran Electronics & Defense working on IR, Vis and laser-gyro equipment.

Beyond the spectral characteristics, we precisely engineer the various other aspects of uniformity of the coating over large or strongly curved components, stresses within the layers, substrate bending, long term stability of the coating, micro-structure of the layers, etc… thanks to proper selection of the materials involved in the thin film stack and the deposition technology used.
In addition the thin film team can exchange data with the lens-design and Finite Element team of the design office in order to evaluate at higher level the impact of the thin films to the global performance of the equipment.

Deposition techniques: We have 8 coating machines ranging from 0.55-m to 1.7-m cubic size where we apply thermal, e-beam and Ion-assisted deposition technologies.
One machine is dedicated to DUV coatings, several machines are dedicated to IR coatings. The largest 1.7-m machine is specialized in high energy laser coatings on large optics and is also dedicated to the reflective coating of large space mirrors.

Characterization: Our characterization lab is equipped with 10 spectrophotometers allowing to perform spectral measurements from 120 to 50.000 nm, from ambiant temperature to 19K. Other instruments are dedicated to absorption measurement, laser damage threshold evaluation at 1064 nm and sample flatness for stress level evaluation. Environment chambers aloow us to simulate various temperature, hygrometry and vacuum conditions 

Structuration: Through photolithography with a mask aligner we perform 2D structuration of the coatings for creating photonic devices and spatial filters like stripe filters for space camera or cryostat windows for IR detector modules. Specific process are deployed for facbrication of pixelated coatings.     

Space mirrors coatings

Safran Reosc undertakes the coating of all its produced space optics. We apply enhanced silver coating with due protective layers or ‘boosting' layers providing improved reflectivity over a specific spectral range.

For IR applications we gold is the material of choice. It can be protected too with some layers without too much sacrifice on the IR reflectivity.

Our space mirror coating offer superior durability and resistance to humidity as well as lower stress level, thus minimizing deformations of large lightweight or ultra-lightweight mirrors. 

Such coatings can be applied on glass, glass ceramic, Silicon carbide or metal optics. 

Laser coatings: from ns to fs regime

Safran Reosc has gained solid background and reputation in precision thin films for laser applications thanks to long collaboration with the Centre d'Etude Atomique (CEA) and Laboratoire d'Optique Appliquée (LOA) on the development of high fluence coatings on large optics for MEGAJOULE and APOLLON projects.

We have various strategies to control the stresses within the layers which impact the flatness of the optics and can adapt the coating to Vacuum, Nitrogen or air environment. 

Ns regime : In 1.7-m large coating chamber we deposit unique high performance thin film stacks on meter-class optics with unique performances for 1.06 µm – 3 ns pulses:

   Anti-reflective       : R < 0.15%                           8 J/cm²  

   Mirrors                : R > 99.5% for s & p           40-70 J/cm²          i = 0° to 45° @ 1.06 µm

   Polarizers           : T°p > 97%  /  T°s < 1%       10 J/cm²                over 750 x 450 mm

Fs regime : More recently Safran Reosc has developed strong efforts in the development of highest performance thin film solution for ultrafast laser systems operating in picosecond and femtosecond regime. We achieve world record performance on large optics as follows:

  R > 99%  /  GDD > 200 fs²  /  1J/cm²  /  l=800 nm  /  200 nm spectral range.

The subject is complex, do not hesitate to contact our technical team for more details. 

Infrared optics coating

High performance IR coatings are one of Safran Reosc key specialty, especially for demanding space applications. Thin films for infrared are much thicker than in visible; this makes the job much more difficult alongs the various aspects of quality of the layers, adhesion onto the substrate, prevention of development of internal stresses during deposition or during exposition to cryogenic temperatures.

Safran Reosc developed unique expertise in the domain and supplied major customers with advanced IR coatings and filter element like :

  • Infrared Atmospheric Sounding Instrument (IASI) Fourier Transform Interferometer with the separator and compensating plates working from Vis to 14 µm wavelength. IASI NG project with KBr optics is now on-going.
  • Meteosat Second Generation (MSG) and presently Meteosat Third Generation (MTG) with spectral separation optics and dichroics as well as detector filters

Recent achievements are conducted inthe domainof AR coatings and 2D structured coatings applied directly onto the detector itself. This new technology is enables new IR optronics concepts and significantly enhances the performance of IR optical systems.