Signal intensity of the light diffracted from the superimposed dual transmission gratings is affected by the higher harmonic distortion (deviation from sinusoidal variation). In this study, the method using the modulated pitch grating that was proposed preciously was extended to more general conditions. The design method for modulating the grating was analyzed in detail and the distortions in the order up to the 13th were removed in the experiment using the proposed grating.
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