In this work we develop an algorithm to determinate the accuracy of the Null-Screen Method, used for the testing of flat heliostats used as solar concentrators in a central tower configuration. We simulate the image obtained on a CCD camera when an orderly distribution of points are displayed on a Null-Screen perpendicular to the heliostat under test. The deformations present in the heliostat are represented as a cosine function of the position with different periods and amplitudes. As a resolution criterion, a deformation on the mirror can be detected when the differences in position between the spots on the image plane for the deformed surface as compared with those obtained for an ideally flat heliostat are equal to one pixel. For 6.4μm pixel size and 18mm focal length, the minimum deformation we can measure in the heliostat, correspond to amplitude equal a 122μm for a period equal to 1m; this is equivalent to 0.8mrad in slope. This result depends on the particular configuration used during the test and the size of the heliostat.
Some experimental qualitative results are presented with a setup that uses a knife edge for producing partial interferograms, in order to obtain the quality of a lens under test. However, the same method can be extended to test an optical surface. The knife edge is located near the focal point of the lens, covering almost half of the incident laser light beam. The different observed interferograms correspond to the orientation of the knife edge with respect to the optical axis, and its distance to the focus of the lens.
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.
In previous works Korneev, et al. and Cornejo, et. al. Shown the feasibility to produce an interference pattern, by
setting near by the focal point of a lens a razor knife edge. The interference phenomena is produced between the
wavefront coming from the lens, and the wavefront produced by the knife edge. In this work, such technique is applied
for testing a lens. Since partial interferograms are observed, due to the obstruction of the knife edge to the wavefront
coming from the lens; by rotation of the knife edge in several directions, interferograms with different information can
be registered by means of a CCD connected to a PC. Experimental measurements are given after several interferograms
with different number of fringes were analyzed.