Sapphire is one of the hardest optical materials in engineering applications. The transparent monocrystalline alumina (Al2O3) sapphire also offers superior thermal mechanical properties compared to almost all other window materials used in HV/UHV processing.
The compression strength of approximately 2000 MPa and the bending strength of up to 400 MPa are typical mechanical properties of sapphires. Sapphire viewpoints are known to be very hard and take advantage of the material’s excellent Yang’s modulus (-350 GPa), which helps ensure that the stress strain ratio of the glass plate is ideal for operating at pressures of one trillionth of an order of magnitude of atmospheric pressure.
For high temperature vacuum treatment applications, sapphire viewports are also suitable. Such applications may include physical vapor deposition (PVD). The pane has been proven to reliably withstand continuous operating temperatures in the range of 400 degrees C (752 degrees C), although this limit is limited to the chamber structure. Sapphire alone can withstand temperatures of up to 1800 degrees C (3272 degrees F).
Nevertheless, there are numerous alternative viewport materials that can be operated in applications like pressurized and heat treatment. The main advantage of sapphire over other window types is that the material has excellent light transmission.
For light wavelengths between 150 and 5500 nanometers (nm), the sapphire viewport is highly transparent, spans a large number of ultraviolet (UV) and visible spectra, and is excellently extended to near-infrared (IR) ranges. Ensure optimal observation of HV/UHV processing conditions without the need for additional surface coatings.
Sapphire’s unparalleled mechanical properties are key to achieving this excellent transmission quality, as poor surface finish can significantly affect wavelength transmission, especially for short-wave radiation.
Sapphire is the third hardest engineering material on our planet, ensuring incredible scratch resistance and wear resistance. Due to this hardness, the sapphire viewport maintains its post-installation transmission properties for long-term use in harsh processing environments.