On the multiple-wave superposition for interference with a crystal plate

When a beam of light was incident on a transparent crystal plate,there were multiple reflections at the plate surfaces,with the result that a series of beams of deferent amplitude emerged.Superposition of the different ways would have completely different results.The light intensity formulae were derived for coherent superposition and non-coherent superposition between ordinary wave and extraordinary wave.The experiment with lithium niobate crystals were completed and the results coincided with the theoretical results.The methods in this article are useful to analyse disturbing effects and improve measurement precision in polarizing interference measurement.