In laser beam propagation studies, wavefront aberrations introduced by the beam handling optics must be known to truly characterize the atmospheric effects on the laser beam. Hence, careful optical interferometry was performed on a laser beam expander and its associated relay optics, before it was used for propagation experiments. However, recent studies by Bennett, et al.', have shown that interferometric measurements of mirrors with enhanced reflection coatings must be performed at the designed wavelength. Bennett's studies show that measuring these enhanced reflecting coatings off-band produces erroneous wavefront errors. An experiment was performed to see if this interferometric measurement problem existed in our system which contained one enhanced reflecting mirror.