Ultra Low Expansion Materials for Precision Optics

Ultra low expansion materials live up to their name. Like all materials, optical glass expands and contracts in response to environmental changes in temperature. While these changes can be minuscule, even slight expansion can disrupt the performance of high-precision optical systems that rely on tight calibration. 

The coefficient of thermal expansion (CTE) quantifies how much a material changes in size with temperature. In aerospace applications, minimizing thermal expansion is critical. What performs reliably on Earth may behave very differently in the extreme cold of space—down to -455°F (2.7 Kelvin or -270°C). ULE materials are engineered to exhibit near-zero thermal expansion across a broad temperature range, making them ideal for these demanding conditions.

There are three main manufacturers of ultra low expansion glasses that we covered in a previous blog Corning® ULE®, Schott® Zerodur® and Ohara® Clearceram-z® .  

Beyond their thermal stability, ULE materials also offer superior thermal shock resistance.  

Corning's ULE glass, invented in 1943 as an amorphous titania-silicate glass with superior dimensional stability. Ohara’s Clearceram-z and Schott’s Zerodur have hybrid structures giving them a balance of properties from both ceramics and glasses. The material is made up of about 70% ceramic (usually a crystalline or partially crystalline structure), with the remaining 30% being a glassy or amorphous phase.   

Why It's Used:
Near-zero thermal expansion properties while maintaining enhanced mechanical strength and dimensional stability, which is especially useful in precision optics where even tiny deformations can affect performance. Regardless of brand, the material has excellent machinability, accuracy, and yield—making it easier to manufacture complex shapes without sacrificing performance.  

From a fabrication perspective, ultra low expansion glass exhibits machining characteristics similar to high-purity quartz, enabling exceptional flatness and high-precision polishing across a wide range of shapes and sizes. This makes it an ideal material for high-reflectivity first surface mirrors. Mirrors are often lightweighted—a CNC process that removes material in patterns like honeycombs to reduce mass while preserving structural integrity. In aerospace applications, ULE is used for components
such as mirrors, windows, filters, and lenses. Its excellent chemical durability also ensures stability during demanding cleaning cycles and thin-film coating processes.

If you're planning an upcoming low-expansion optics project, we maintain raw inventory on hand to support faster lead times. Reach out to start a conversation—we’re here to help.