ZnSe Windows are used to measure the flatness of optical surfaces or certain optical components to ensure accuracy for a wide range of quality assurance or inspection applications. Interferometry Windows are optical surfaces that have been polished to an extremely precise level of flatness which are used as reference plates. Interferometry Windows are laid atop inspected surfaces at a specific angle while a laser beam is directed between them so that interference bands may be measured to determine flatness levels. Dual or single surface Interferometry Windows are both available. Our dual surface optical flats are precision ground and polished to the stated accuracies on both surfaces so that either face may be used for test applications. Both surfaces are tested and certified by our Zygo Interferometer. Each flat ships in a durable storage case for permanent protection. 1/4 λflats also include a certificate of calibration