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Tagged with: Interferometers

A Model for Cavity Induced Errors with Wavefront Slope in High Accuracy Spherical Fizeau Metrology (ABSTRACT)

A paper by Sykora of Zygo showing that the Random Ball Test (RBT) works less and less precisely as the numerical aperture of the transmission sphere becomes smaller. In other words, the RBT works best for fast transmission spheres and another means of calibration should be used for slow test optics.

A Practical Implementation of the Random Ball Test (ABSTRACT)

ABSTRACT: The random ball test for calibrating interferometer transmission spheres was reported about 8 years ago but there did not appear to be an ideal ball. Now, nearly ideal balls are available. The paper describes commercially available hardware for performing the random ball test and example results from the test.

A Simple Ball Averager for Reference Sphere Calibrations (ABSTRACT)

ABSTRACT: A paper by authors at NIST about simulations and experiments done with the Random Ball Test (RBT) giving criteria for establishing the precision of transmission sphere calibration using the RBT.

Absolute Measurement of Surface Roughness (ABSTRACT)

ABSTRACT: A paper by Creath and Wyant explaining the method of calibration of surface roughness interferometers. This same method is used in the Random Ball Test (RBT) except that the random surface over which interferograms are averaged is not a plane but a sphere.

Calibration of Interferometer Transmission Spheres (ABSTRACT)

ABSTRACT: A readable copy of the original paper on the Random Ball Test (RBT) authored at NIST that was published in a non-archival meeting journal. Even here the figures are not legible. For better example figures see "A practical implementation of the random ball test".

Calibration of Spherical Reference Surfaces for Fizeau Interferometry (ABSTRACT)

ABSTRACT: A study by Burke and Wu of CSIRO comparing several methods of transmission sphere calibration that concludes the Random Ball Test (RBT) has the highest precision of all the methods tried though it is tedious to perform for highest precision if the RBT is not automated.

Fabrication and Testing of a High-Precision Concave Spherical Mirror (ABSTRACT)

ABSTRACT: Slides by Burke and Wu of CSIRO about Random Ball Test (RBT) calibration of a transmission sphere prior to its use in the test of a high precision hemisphere.

Interferometer Calibration using the Random Ball Test (ABSTRACT)

ABSTRACT: Paper by W. Cai, et. al., comparing experimental results in the Random Ball Test (RBT) between using a clean ball and systematic measurement versus a somewhat dirty ball and casual measurement.  The results gave identical precision within reasonable statistical limits.

Case Studies & Testimonials

  • How small can the PSM be used for centering on a cylindrical axis?

    The PSM is an ideal tool for finding the center of curvature of a ball or the axis of a cylinder. The question is for how small a ball or cylinder can the PSM do this?

    The smallest article that was readily available was a piece of monofilament 8 pound test fishing line that was 290 μm in diameter. There was no problem finding the axis of the fishline, and separating the Cat’s eye reflection from the surface from the confocal reflection of the axis. The experiment was done with a 5x objective, and the result would have been even more definitive using a 10x objective.

  • Why is proper alignment so important?

    Here is a case of a very happy customer due to better optics.

    A few days ago an astronomer friend of mine commented that he had gotten the optics of his telescope improved and the improvement reduced the time it took to get data by a factor of 3. For an astronomer this is a dramatic improvement since observing time on large telescopes can cost thousands of dollars an hour.

    My friend did not say how the optics had been improved, but the important point is that better optics, whether due to figure errors, mounting or alignment mean more productive optics. I generally think of better optics as a better product leaving the manufacturing facility without thinking about how much the better optics mean to the productivity of the customer.