Apparatus and method for measuring the thickness of the layers of a multi-layer transparent film

摘要

Apparatus (10,100) and a method for measuring the thickness of a film (15) having top and bottom surfaces provides a low coherence light source (12) that generates a probe light signal. The film (15) is positioned between first and second reference reflectors, the first reference reflector being partially reflecting. The probe light signal is applied to the film (15) after passing through the first reference reflector. Part of the portion of the probe light signal leaving the film (15) is reflected back toward the first reference reflector by the second reference reflector. The light exiting through the first reference reflector is collected to form the input to a receiver (18) that determines the time delay between light reflected from the top and bottom surfaces of the film (15) as well as the change in optical path length between said first and second reflector (25,26) resulting from the introduction of said film (15) between said first and second reflector (25,26). In the preferred embodiment the receiver (18) is constructed from an optical autocorrelator or an optical spectrum analyzer that includes circuitry for providing the Fourier transform of the frequency domain spectrum measured from the combined light signal. Embodiments in which only one of the reference reflectors is utilized provide a means for simplifying the output spectrum from the receiver (18) when multi-layer films (15) are utilized. <IMAGE>