Laser Window

Lately we’ve been busy with building sapphire laser windows for the industry. Second to only diamonds in mechanical strength sapphire is the choice for not-so-easy-on-it applications. Sapphire laser windows are scratch resistant, have a wide transmission spectrum of light, (from 200nm to 6µm) and inert virtually to all chemicals, except molten salts (salts in liquid phase), and Hydrogen Fluoride above ambient temperature. A thin sapphire window can also hold a few thousand pounds per square inch of pressure.

With such credentials sapphire is the perfect window into aggressive process environments. The only disadvantage is its cost. We deal with cost by economies of scale, fabricating more windows and standardizing on sizes. This is a bit of a compromise between a totally custom design and a bit lower cost of a standard product that can be adapted into the customer’s higher level design. This is where some engineering between Encole and our customers can make sapphire laser windows possible in the final product. When it’s all said and done, our windows are installed in dairy and flour production plants, other food processing, plasma chambers, high pressure reactors, energy generation, oil & gas equipment and countless other applications.

Another factor reducing cost is how the window is mounted into the metal frame. We use high performance adhesives for low cost windows. When using O-rings, metal seals, and various gaskets, the cost goes up with increased complexity of the window assembly. Below is a picture of sapphire laser windows designed for food processing equipment. The window is only 1 mm thick. There are no mechanical seals, yet the assembly can hold some pressure and provides hermetically isolated space for the equipment laser sensors. The window is bonded to the frame using a special adhesive which needs to go through stages of mixing, application, post heating and baking. Where we saved money on simplicity of the assembly, we spent the time on fabrication. The time in this case was at a lower cost because of our almost automated assembly process.

Laser windows for food processing sensors.

One notable feature of this design, is how secure the window is mounted into the frame. It’s very secure, given it’s only 1mm thickness. We did not bond this window to its flat faces because with time the metal frame would expand and contract under changing temperature and would eventually break the bond between the sapphire and the metal. You see, sapphire expands and contracts at a different rate than the metal, when heated or cooled. So, we designed a way to mount the window accommodating the mismatch in thermal expansion. These windows have been working out there in the world somewhere for quite some time now. More are needed, shipping tomorrow.

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