Wavelength scanning interferometry for measuring transparent films of the fusion targets

Wavelength scanning interferometry is an effective method for the measurement of both engineering surfaces and
structured surfaces. Currently its main applications in surface metrology are limited primarily to surfaces with reflections
occurring from the uppermost of the surfaces. When a transparent thin film is measured by wavelength scanning interferometer
the reflection signals from both top and bottom surfaces of the film will interfere with the reference signal. At the same time
the reflected signals from these two surfaces will also interfere with each other. Effective separation of the interference signals
from each other is the key to achieving a successive measurement of the film. By performing an frequency-domain analysis to
separate and reconstruct these interference signals, the measurement of the top and the bottom surface finishes of the film as
well as the film thickness map will be achieved. In this paper theoretical analysis of wavelength scanning interferometry for
transparent film measurement is discussed. Experiments with thin film layers of Parylene N coated on glass slide surface,
which are provided by the HiPER target fabrication group are studied and analysed.