An example of thin film deposition rate measurements is presented in the above figure. The plasma conditions are typical of microcrystalline silicon thin film growth i.e high pressure, high power high dilution of silane in hydrogen. The reflected intensity of the light wave is recorded as a function of the deposition time by applying the configuration that has been presented in the setup section. According to the interference concept that has been presented to the principles section the appearance of two successively maxima or minima will take place in specific thin film thickness and when the relative phase difference have a value β_1i-β_1(i+1)=π. When this condition is satisfied the variation of the film thickness will be equal to:

As a matter of fact, the record in time of the appearance of two successive maxima or minima corresponds to a specific thin film thickness and lead to the calculation of the deposition rate, according to the relation:

where ΔΤ is the time that required for the appearance of two successive maxima or minima.

Concerning the shape of the recorded intensity and according to the discussion in the principle section, one can say that the initial film growth (first two fringes) is better described from the three interface configuration and the continuous increase of the thin film refractive index and the absorption coefficient. On the other hand, as the film thickness increases the simpler scheme of the two interfaces and the constant refractive index describes better the recorded intensity. Thus, for the accuracy of the deposition rate measurement the first two fringes have to be ignored as the refractive index in this stage is also unknown. 

The usefulness of the method can be understood from the above figure. In cases where the synergetic effect of different combinations of plasma parameters on the deposition rate is searched, a quite large number of depositions are required. For example, the investigation of the combined effect of the total gas pressure and the interelectrode space on the microcrystalline silicon deposition rate and the determination of the optimal deposition rate conditions in terms of these two parameters requires about 100 measurements. If for the measurement of the film thickness an ex-situ method was applied this investigation would take about 200 working days (including dead times for reactor pumping to the base vacuum). On the other hand, the application of an in - situ method as Laser Reflectance Interferometry significantly reduces the investigation time to less than 50 working days as 3 to 5 conditions can be checked at each deposition.