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OptiLayer:  Your Partner in Design and Post-Production Characterization of Optical Coatings

 

Antireflection Coatings

antireflection coating

 

Antireflection coatings (AR) are used to reduce the Fresnel reflectance of optical components. In imaging systems, AR coatings improve the efficiency because they provide less light lost. In complex optical systems, the reduction in reflections also improves the contrast of the image by elimination of stray light.

OptiLayer allows designing all types of AR coatings:

  • Narrow-band and broadband AR coatings;
  • Single-band, dual-band, multiple-band AR coatings; 
  • AR coatings at normal and oblique incidence;
  • AR operating in all spectral ranges;
  • AR coatings formed from two, three and more materials;
  • AR coatings using absorbing layers;
  • AR coatings with specified color properties;
  • AR coatings in stacks

It follows from the theory that, at normal angle of incidence and at oblique incidence case (s-polarization), two-component AR designs with the highest and lowest available refractive indices form an optimal class of AR designs.

Residual reflectance of broadband AR coatings is decreasing with increase of optical thickness of the coating and with growing the number of layers. At the same time, there is a lower limit of the residual reflectance. 

We present a video example of the designing broadband AR coating at YouTube YouTube

It has been shown that there exists the minimum achievable residual reflectance of broadband AR coatings.

This limit depends on:

  • Relative width of the antireflection spectral range;
  • Ratio between high and low refractive indices;
  • Ratio between low index material and refractive index of the incidence medium;
  • Ratio between substrate refractive index and refractive index of the incidence medium.

You can estimate residual reflectance for your design problem here. This formula gives accurate estimations for broadband AR design problems when relative width of AR range is more than 2.

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Example: two-octave AR coating operating in the spectral range from 450nm to 1800 nm. Layer materials are Ta2O5 and SiO2, refractive indices are specified by Cauchy formulas. Substrate is Suprasil. Minimum achievable reflectance can be calculated with the help of this formula with: 

  • nH=2.1 (Average index)
  • nL=1.46 (Average index)
  • ns=1.46 (Average index)
  • λl=450 nm
  • λu=1800 nm

The formula estimates minimum achievable reflectance as 1.1%

The simplest AR coating contains 10 layers and achieves reflectance equal to 1.6%.

This coating was produced at Helios deposition plant. See comparison of the theoretical and experimental data at this picture. The substrate is covered from one side.

See the details in our publications on AR coatings:

broadband antireflection coating
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Easy to start

Icons 100x100 1OptiLayer provides user-friendly interface and a variety of examples allowing even a beginner to effectively start to design and characterize optical coatings.        Read more...

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Icons 100x100 2Comprehensive manual in PDF format and e-mail support help you at each step of your work with OptiLayer.

 

Advanced

Icons 100x100 3If you are already an experienced user, OptiLayer gives your almost unlimited opportunities in solving all problems arising in design-production chain. Visit our publications page and challenge page.

 

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