Measurement Technology for Production

Anyone who has ever painted a wall as a do-it-yourself handyman is all too familiar with the following scenario: The paint is on the wall, and somehow everything is colorful. Upon closer inspection, however, it appears that the result did not turn out quite as intended. Too much paint in some spots, not enough in other spots: the whole wall is more like a patchwork carpet than a uniform, colored surface.

Uniform coating is also important for laser optics. But unlike painting your home, irregularities cannot simply be masked by hanging up a picture to cover it up. If the dielectric layers are not homogeneous, this has an effect on the beam shape and the imaging properties of the optics. The coating is then useless and must be disposed of. But nobody can afford this because a dielectric coating system is much more expensive than a bucket of paint. Precise control of the coating thickness is therefore essential in our industry.

A further complicating factor is the fact that experts do not speak of “thin layers” for no reason: While a layer of wall paint measures approximately 100 µm on average, the layer thicknesses of laser optics typically range between 100 nm and 6 µm for the visual spectral range. A layer design can consist of 20 or more layers. A standard coating of paint is therefore around a thousand times thicker than the individual coating thicknesses. That’s about the difference in height between a man and a flea.