When an optical surface has local deformations, it is not practical to measure the entire surface at one time, because an average of the entire surface is obtained, ignoring the local deformations. In a previous work we used the principle of the Chelmer’s test, for analyzing just local defects of an optical surface, the technique uses a reflective spatial light modulator (RSLM), which allows the screen to remain at a fixed position, and only two apertures are used at a time. Our proposed method measures only obtain the local or zonal defects in the wavefront. The use of an RSLM provides a very flexible way of selecting a particular zone to be tested. The advantage of the proposed dynamic Chelmer’s test is that using an RSLM it is possible to select a pair of holes in real time, for any zone, and with different sizes and orientation of the holes. In this work, we compare the results obtained previously, with three different techniques: the first one is the traditional analysis of fringes used in Chelmer’s experiment. The deviations of the interference fringes from a straight line were calculate, according to the equation of Guenther. The second is an analysis by computer, where we developed a computer program to analyze an interferogram produced by a commercial interferometer (ZYGO), with the computer program is possible to know the position of the dark fringes. The ideal separation the dark fringes are obtained by analyzing an area of the interferogram that has no deformations. Finally we analyze the profile of the interference fringes corresponding to the local areas using the commercial program “Durango Interferometry Software”.
In this research an interferometric system was developed that generates four simultaneous interferograms with independent phase shifts using modulated polarization. The proposed system consists of three coupled interferometers: the first system is a polarized Mach-Zehnder interferometer, which generates the pattern, the second and the third interferometer system, function as replicators of the first pattern, so the four patterns are generated. To show the novelty of the developed system, the calculation of optical path difference (OPD) for phase samples are shown.
This work shows the measurement of the refraction index of a glass plate using a Point Diffraction Interferometer (PDI). The plate of the PDI has a micro-hole and transmittance of less than 10%. The experimental setup consists in a He-Ne laser illuminating a spatial filter, a collimated beam is produced by an achromatic lens, and close to the focal point of a second lens (focusing lens), the plate of the Point Diffraction Interferometer is located. When the laser light pass through the plate of the PDI, it is generated an interference reference pattern, called Ir, which is recorded. As a second step, a glass plate with unknown index refraction is introduced between the focusing lens and the plate of the PDI, obtaining a new modified interference pattern, called It. We use the geometrical of figure of interference fringe for analysis of the interferograms. Value of the refraction index of the glass plate, nt, can be derived, with the previous knowledge of the glass plate thickness. Some experimental results will be shown.
Using the analogy of the double-slit experiment developed by Young and using interferometric technique
developed by Chalmers, we built an interferometric arrangement that can analyze local defects of an optical
surface. With a reflective spatial light modulator (RSLM) controlled by a PC, two apertures are open each
time, and the apertures became as secondary light sources, producing interference pattern for specific zones
for the surface under test. The interference pattern is observed, and storage into a computer by using a CCD
camera. Finally the results are compared with the results obtained using a Fizeau commercial interferometer.