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Toughened Windows: What they are, and When to use them

19th Dec 2018

Optical windows are designed to maximise transmission whilst minimising absorption and reflection. They are particularly useful for protecting optical systems and electronic sensors from harsh environmental elements.

In some situations, optical windows face excessive physical pressure and strain. In such cases, a robust solution is necessary, and this is where toughened windows play such a crucial role.

Toughened or tempered windows deliver a far higher degree of resistance to breakage than their un-toughened counterparts, making them suitable for safety use within industrial environments and for underwater camera applications, and for protective use in optical assemblies.

What makes an optical window toughened?

Optical windows are toughened by heating the glass beyond its annealing point, then quickly cooling the surface. The process causes the surface to contract which produces compressive stresses.

Whilst the surface is cooled quickly, the inner core is left to cool at a slower rate. It is this variation in cooling rate between the outside and inside of the glass results that leads to the creation of tensile stresses inside the window. The balance between tensile and compressive stress produces a greater level of mechanical resistance.

What materials are used for toughened windows?

Toughened windows are crafted from a range of glass types, the most popular of which are borosilicate and float glass.

Borosilicate offers excellent thermal and chemical shock resistance, making it ideal for use in high-temperature environments up to 500 degrees Celsius. This is a material that is typically used in high-powered light source applications and makes a good choice for cold and hot mirror substrates. The low expansion properties of borosilicate mean it maintains its flatness even when affected by a range of different environmental conditions.

Float glass windows are mostly used as a protective barrier in applications like CCTV cameras and flat panel displays.

Toughened Windows from Knight Optical

At Knight Optical we supply a range of stocked sized toughened windows in various diameters and thicknesses. Assembly windows can be supplied in sizes under 30mm diameter, and large protective windows greater than 250mm to suit a variety of applications. All toughened windows can be custom designed by our experts to work specifically with your individual application and operating environment requirements.

For tailored advice on your specific optical component needs, you are welcome to get in touch with our multilingual technical sales team on 01622 859444 or [email protected].