The coating is crucial

Mr. Bernitzki, you have been working with optical coatings for almost four decades. What do you find particularly exciting?

One of the best parts of my job is when we create something that others can't manage to do. And it is always a challenge but also very interesting to understand and use interfaces to optics manufacturing, cleaning and measurement technology.

Does one special order come to mind?

There have been quite a lot because, as OEM-partner, we generally offer customized solutions.
Our deep ultraviolet (DUV) coatings are pretty special. They are very complex and the solutions we've implemented, for example in 193-nanometer mirrors, are world class. The development of the basic technology for DUV coatings was also outstanding. It enabled us to generate a number of key customers.

What types of surfaces and geometries do you coat and how long does the process take?

We coat plano optics, spheres or aspheres – for example cylindrical lenses. It is possible to coat optics up to a maximum length of approximately 900 mm. Our coating cycles range from under two up to 24 hours at temperatures between 100 and 300 degrees.

What are your greatest challenges in optical coatings?

Above all, knowing what materials are best suited for specific applications, and of course an understanding of the best technology to use. Among other things, we coat crystals and optical glasses made from calcium fluoride, crystalline quartz, silicon, germanium, zinc sulfide, sapphire, quartz glass, BK7 with fluorides, oxides, germanium, zinc sulfide and metals.

We work with up to 100 coatings on one substrate side for some applications for semiconductor equipment, medical technology and analytics. This number makes it clear that knowledge about design is crucial, as well as knowing which layer offers which solution. Among other things, this also includes monitoring and documentation. The results we achieve are transferred to the complete series production.

Which application areas and wavelengths do we offer?

Our most important objective is to meet the requirements of our customers. These include suppliers to the semiconductor industry, machine builders for laser material processing and system vendors that require infrared components. We therefore coat from DUV (deep ultraviolet) through VIS (visible) up to IR (infrared) – from 193 nanometers to 20 micrometers.
In addition to this, we also manufacture coatings for special broadband applications, from DUV to NIR (deep ultraviolet to near infrared).

What does "broadband" mean?

Applications are broadband or even multispectral if more than one wavelength plays a role. This is the case in the semiconductor industry, for example. Here, broadband light sources and sensors are used to control technologies in wafer processing or also to precisely adjust wafers. These are based on highly accurate measuring methods.

In which order are the optical coatings "vapor deposited" one on top of the other?

First and foremost, the order depends on the component and the requirements of the application. We rely on our experience and understanding of which layer follows which layer – this is part of our skill set.

How do you measure and test the properties of the coatings and ensure quality?

Our quality assurance process also includes an in-house developed DUV photometer, which measures the transmission on moving substrates down to a measuring wavelength of 200 nanometers during the coating process. The increased measuring accuracy of this device gives us a unique competitive edge. We have instrument technicians on board who can check the performance of each individual component.

We measure more complex components using in-house developed laser-based measuring instruments in high purity nitrogen under clean room conditions. Furthermore, we can perform lifecycle tests. We shoot components and lenses with 20 to 50 million laser pulses – in one case even with 7 billion "shots", enabling us to simulate ten years of use under real-life conditions.

We obtain approval for start of series production from customers themselves as soon as they have successfully tested the prototype in use.

Thank you for the interesting interview, Mr Bernitzki.