PARTIALLY COHERENT TRANSMITTANCE OF DIELECTRIC LAMELLAE

We derive an analytic formula for the transmittance of a dielectric la mella when the interference between successive internal reflections is only partially spatially coherent. This allows effects such as surfac e roughness and nonparallelism, which produce cumulative distortions i n the phase front with each reflection, and which result in a loss of fringe contrast at high frequencies, to be accounted for quantitativel y. The transmittance of a Si lamella, measured with a Fourier-transfor m interferometer over the range 20 to 1000 cm(-1), agrees with our for mula to within the accuracy of the data, which is dominated by systema tic instrumental effects.