Patent Application
20080043224
Further features and advantages of the invention will be seen from the following detailed description, taken in conjunction with the accompanying drawings, wherein like numerals depict like parts, and wherein
In the preferred embodiment, a polarization version of Twyman-Green interferometer shown in
After passing two times through the quarter-wave plates, both beams are linearly polarized with polarization direction rotated 900 with respect to the polarization direction of the illuminating beams and remain orthogonally polarized to each other. An imaging system 70 creates a sharp image of measured surface 60 on the set of linear detectors 100. Both test and reference beams are split equally into multiple channels 71 by a non-polarizing beam splitter 70 located between the imaging element and the set of linear detectors 100. A combination of polarization elements 80 and 90 in front of each linear detector 100 introduces predetermined phase shifts, which are different for each of those detectors, so that the phase of the interfering beams can be calculated using the principle of phase shifting. Data acquisition into a computer from the set of linear detectors 100 are synchronized together, so that multiple interferograms are collected at the same instance, which makes the measurement significantly insensitive to vibrations.
A measured object 60 is mounted on a linear scanner 110 that is capable of moving the object in a direction perpendicular to the long axis of the of the linear detector arrays. Alternatively, as shown in
Exposure time for collecting a single line of data can be very short—typically few tens of microseconds—and the data transfer rate ranges from 1 to 100 MPixels/s. This allows for scanning speeds from 2.5 to 250 mm/s assuming a typical size of a linear CCD detector of 4000 pixels and pixel size of 10×10 um. As a result an area of 200×200 mm. could be measured in between 4 and 400 s.
Various changes may be made in the invention without departing from the scope thereof. By way of example, the polarization version of the Twyman-Green interferometer can be replaced by any other interferometer in which reference and test beams are mutually orthogonally polarized. Also other devices capable of beam splitting for producing orthogonally polarized beams (such as polarization type cube or plate beam-splitters, Wollaston or Rochon prism, polarization beam displacer, combination of polarizers, etc) can be used instead of a typical polarization type beam splitter to obtain orthogonally polarized beams in any type of the interferometer.
And, the CCD imaging detector can be any device capable of producing a multitude of phase-shifted interferograms simultaneously. In particular the detector could be an arrangement of multiple linear detector arrays. The detector also could be a module composed of independent detector arrays, or a two-dimensional detector array where each row of the array is treated as a linear detector, or a two-dimensional detector array where each 2×2 set of pixels are composed of polarization optics for phase-shifting.
This application claims priority from U.S. Provisional Application Ser. No. 60/817,276, filed Jun. 29, 2006, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60817276 | Jun 2006 | US |
