Shearing Interferometers using diffraction gratings as elements wavefront division

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We developed two types of shearing interferometers using diffraction gratings. The one uses a double period diffraction grating. The grating has two periods which are very close to each other. The other interferometer uses four diffraction gratings with the same grating period.In the double period grating system, the difference in diffraction angles produces shearing images. Moreover, since a periodic fringe pattern appears on the shearing image due to the difference in diffraction angles, phase distribution of the interference fringes can be analyzed accurately with a help of Fourier analysis. We made an shearing system with the double period grating for optical CT to measure refractive-index distribution of a phase object. Moreover some discussions were made about errors in refractive-indices reconstructed from the shearing interferometer and the conventional two-beam interferometer. The discussion results an advantage of the sharing type used for the optical CT system.On the other h … More and, we proposed a white light-shearing interferometer using the four diffraction gratings. Sensitivity of a shearing interferometer is proportional to amount of the shear, and the shear amount depends on the diffraction angle which is in proportion to the wavelength of light approximately in case of a small diffraction angle. When the shear image is produced by using a couple of the gratings with a small separation, the phase difference between the interfering light beams does not depend on the wavelength of light. Then the shearing interferometer for a white light source is realized by setting the couple of gratings in front and back of the phase object. We made a simple sharing interferometer with 4 gratings and a halogen light source. The obtained interference fringes pattern did not allow coherent noise and the fringe contrast was close to 0.5 which corresponded to the ideal value. The phase shift technique for a sensitive phase analysis was realized by moving one of the gratings.Moreover, the idea of the four gratings system is applied to X-ray interferometer. We made a X-ray interferometer with four silicon thin-blade which are made from a single domain silicon crystal. Less