A pair of closely spaced slits is illuminated with 621.0-nm light in a Young's double-slit experiment. During the experiment, one of the two slits is covered by an ultrathin diamond plate with index of refraction n = 2.417.What is the minimum thickness of the diamond plate that produces a dark fringe at the center of the viewing screen?

A pair of closely spaced slits is illuminated with 621.0-nm light in a Young's double-slit experiment. During the experiment, one of the two slits is covered by an ultrathin diamond plate with index of refraction n = 2.417.What is the minimum thickness of the diamond plate that produces a dark fringe at the center of the viewing screen?