ANALYSIS OF INTERFEROGRAMS WITH A SPATIAL RADIAL CARRIER OR CLOSED FRINGES AND ITS HOLOGRAPHIC ANALOGY

It is well known that an interferogram can be demodulated to find the wave-front shape ifa linear carrier is introduced. We show that it can also be demodulated if it has many closed fringes or a circular carri er appears. A basic assumption is that the carrier fringes are of a ba ndwidth adequate to contain the wave-front distortion. This phase dete rmination, called here demodulation, is made in the space domain, as o pposed to demodulation in Fourier space, but the low-pass filter chara cteristics must be properly chosen. For academic purposes a holographi c analogy of this demodulation process is also presented, which shows that the common technique of multiplying by a sine function and a cosi ne function is equivalent to holographically reconstructing with a til ted-flat wave front. Alternatively, a defocused (spherical) wave front can be used as a reference to perform the reconstruction or demodulat ion of some closed-fringe interferograms. (C) 1998 Optical Society of America.