Grazing Incidence Interferometer Research Articles

Phase retrieval of non-continuous fringe patterns by a genetic data reduction algorithm

In this work we focus on the possibilities of recovering the phase from a single fringe pattern that do not have a fringe order sequence or whose fringes are broken. The phase is obtained with a polynomial fitting method whose coefficients are calculated with a genetic algorithm technique that constrains the smoothness of the solutions of a merit function. It is explained how conjugate gradient methods fail in the solution of the proposed merit function. Experimental results are presented using discontinuous fringe patterns obtained from a grazing incidence interferometer while testing a polishing tool.

Simultaneous characterization of the quality and orientation of cylindrical lens surfaces

A diffractive grazing-incidence interferometer for the test of cylindrical lenses is described. Besides surface aberrations from the ideal shape, the interferometer allows for the simultaneous determination of the relative position and orientation of surfaces to another. The measurement principle as well as a classification of deviation types is given. Measurement results for planar concave lenses are presented.

Interferometric shape measurement of rough surfaces at grazing incidence

Interferometric shape measurements of technical objects are hampered by stochastic phase variations in the micro region caused by the surface roughness of the test object. Without special precautions, low-contrast interference patterns or even totally stochastic fringe patterns may be observed. However, illuminating the surface under test at grazing incidence reduces the phase variations because it increases the effective wavelength by a factor of 1/cos β, where β is the angle of incidence. Here, an interferometer for testing plane objects is described where the test wavefront is provided by means of diffractive optical elements (DOEs). A pair of identical DOEs is used to do the necessary beam splitting and beam shaping. The resulting fringes, showing the surface deviations of the test object from the ideal plane, are evaluated by means of phase-shifting interferometry. Serial measurements on different rough surfaces were made to find out the limits of grazing-incidence interferometry when technical objects are measured. To do this, different incidence angles have been realized by choosing a suitable set of diffractive elements. The contrast of the interference fringes has been taken as the evaluation criterion for the measurability of the shape of the rough surfaces within the grazing incidence interferometer.

Laboratory detection of X-ray fringes with a grazing-incidence interferometer

Starting with Galileo's observations of the Solar System, improvements of an order of magnitude in either the sensitivity or resolution of astronomical instruments have always brought revolutionary discoveries. The X-ray band of the spectrum, where exotic objects can have extremely high surface brightness, is ideally suited for significant improvements in imaging, but progress has been impeded by a lack of optics of sufficiently high sensitivity and quality. Here we present an X-ray interferometer design that is practical for adaptation to astronomical observatories. Our prototype interferometer, having just under one millimetre of baseline, creates fringes at 1.25 keV with an angular resolution of 100 milliarcseconds. With a larger version in orbit it will be possible to resolve X-ray sources at 10(-7) arcseconds, three orders of magnitude better than the finest-resolution images ever achieved on the sky (in the radio part of the spectrum) and over one million times better than the current best X-ray images. With such resolutions, we can study the environments of pulsars, resolve and then model relativistic blast waves, image material falling into a black hole, watch the physical formation of astrophysical jets, and study the dynamos of stellar coronae.

Testing of rod objects by grazing-incidence interferometry: experiment

A grazing-incidence interferometer for the testing of technical surfaces for macroscopic surface deviations is described. Computer-generated holograms serve as beam splitters and references for the workpieces tested. The sensitivity of the interferometer depends on the period of the computer-generated holograms. The method is demonstrated at a rod object of convex profile. Using phase-stepping techniques, the grazing-incidence interferometer provides fast measurements of the entire mantle surface of the test sample with submicrometer precision.

Automatic measurement of surface height with the interferoscope

Using a grazing incidence interferometer, the interferoscope, an automatic absolute measurement of a test object surface height can be made by counting the number of interference fringes when varying the surface incident angle. This is accomplished by combining the inter- feroscope with a computer-controlled stepping motor along with an im- age processing system. By transforming the equations describing the interferoscope, the sought depth can be regarded as a ''frequency,'' which can be attained using Fourier transforms or other frequency evalu- ation algorithms. © 1996 Society of Photo-Optical Instrumentation Engineers.