Abstract: A thin film thickness monitor using successive reflection of a polychromatic light beam off of reference thin film of variable optical thickness and a sample thin film whose thickness is to be determined, in which a monochromatic light source is used beforehand to first determine the actual optical thickness of the reference thin film at each relative position of the beam and reference thin film. In one embodiment, the ratio S/R of detected light intensity S from the sample thin film and detected light intensity R from the reference thin film is found for each relative position and the position at which the ratio is a maximum is determined. In another embodiment, this ratio is corrected by a corresponding ratio S.sub.1 /R.sub.1 derived from a bare wafer substrate. The sample can then be located behind additional optical surfaces, such as a vacuum port without causing substantial errors.

Abstract: A high security lock of the type having a base, a bolt which moves on the base and engages a strike, and a dead lock tripper which interacts with the strike to automatically lock the bolt is improved by including a lock prevent member in association with the bolt. The lock prevent member inhibits the bolt from moving from an unlocked to a locked position in spite of the dead lock tripper interacting with the strike. A secondary key can be used to inactivate the lock prevent member such that the lock returns to its normal mode of operation with the interaction of the dead lock tripper and the strike automatically locking the lock.