Nondestructive and Noncontact Measurement of Air Gap Thickness Between Stationary or Moving Opaque Films
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
A novel method for noncontact measurement of air gaps between opaque films like magnetic tape layers on a reel using lasers is disclosed. The measurement technique, illustrated in Fig. 1, relies on the use of a short duration light pulse to quickly heat a local area of the outermost layer of the magnetic tape (or other films in general). Using large solid-angle collection optics, like an elliptical reflector, the transient infrared thermal radiation from the outermost tape layer is efficiently refocused onto a suitable infrared detector, such as a mercury cadmium telleride element. The amplified detector output signal S(t) as a function of time t after the laser pulse is recorded on suitable electronic equipment like a signal digitizer and computer.