The substrate material of LBTEK ultrafast mirrors is fused silica, with a high-reflectivity coating on the surface that consists of low group delay dispersion dielectric films, deposited using ion beam sputtering (IBS) technology. During the ion beam sputtering process, a high-energy electric field accelerates the ion beam toward the target, causing ions to be sputtered from the target and release more ions, which ultimately deposit as a coating on the rotating substrate. The use of ion beam sputtering enables high repeatability in batch coating and low coating thickness errors, ensuring the designed wavelength range and low group delay dispersion. Fused silica has a lower coefficient of thermal expansion and extremely high thermal shock stability, making it particularly suitable for high-power femtosecond pulse lasers and imaging applications. Note: The direction indicated by the side marking arrow points to the coated surface. LBTEK ultrafast mirrors are available in four working wavelength ranges: 460 nm–590 nm, 700 nm–930 nm, 970 nm–1150 nm, and 1400 nm–1700 nm. With a 45° angle of incidence, the reflectivity exceeds 99.5%.