Research on carbon materials-based thin films with low light reflectance has received paramount importance in order to have high absorber coatings for stray light control applications. We report here a...

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Self-referencing collimation testing techniques are briefly reviewed. New self-referencing configurations using Talbot and doublewedge plate shear interferometric techniques are described. Setting sensitivities of various arrangements are compared. Subject terms: optical testing; collimation testing; Talbot interferometry; wedge plate shear interferometry. Optica/Engineering 32(1), 94-1 W (January 1993).where J.L iS the spatial frequency of the grating, X the wavelength of light, and m is an integer. A second identical grating G2 placed at one of the self-images produces straight and parallel moire fringes. These fringes are perpendicular to the bisector of the angle between the lines of gratings G1 and G2. If the grating lines are oriented at equal but opposite angles with respect to the Y axis, moire fringes parallel to the X axis are formed. Thus, fringes parallel to the X axis are a test for the collimation of the beam. When the grating is illuminated by a spherical wavefront of radius of curvature R, the change in the frequency of the self-image is given by i__i= .(2) R The frequency of the m'th self-image is p' = p depending on whether the illuminating beam is converging or diverging. This self-image with the second grating of frequency gives a moire fringe pattern oriented at an angle a with the X axis. The orientation angle a of the moire pattern is given bywhere 0/2 is the angle subtended by the lines of either grating with the Y axis. Noncollimation of the beam is thus detected by observing the orientation of the moire pattern with a reference direction.

A new and simple technique for the determination of the focal length of positive lenses and concave spherical surfaces by Talbot interferometry is described. Results of measurements are presented. We show that high measurement accuracy can be achieved with this technique.

A comparative study of the performance of linear dual-field, spiral, and evolute gratings for collimation testing with Talbot interferometry is reported.