<p>Vacuum coating, molecular beam epitaxy, and vacuum annealing processes all rely on highly reliable observation and feedthrough windows. Sapphire window plates, with their extremely low outgassing rate, excellent resistance to plasma etching, and broad transmission wavelength range (approximately 0.15 to 5.5 microns), have become the standard choice for high-vacuum and ultra-high-vacuum chambers.</p><p>The first step in selecting a window is to confirm the flange interface type: CF flanges paired with metal copper gaskets are suitable for ultra-high vacuum, while KF and ISO flanges with fluororubber seals are appropriate for high-vacuum applications. The second step involves calculating the window thickness based on chamber pressure; typically, a safety factor is applied according to the material's flexural strength and effective support diameter to prevent deformation or breakage during pumping. The third step focuses on surface quality—windows used for coating process observation should be double-sided polished with a low defect level to minimize scattered light interference with observation and optical monitoring.</p><p>During installation, follow the diagonal progressive tightening principle to avoid excessive localized stress on the sealing surface. If the process involves high-temperature baking, select a high-temperature-resistant sealing structure and ensure its maximum allowable baking temperature matches the process requirements, thereby maintaining vacuum integrity throughout the entire process cycle.</p>