Embedded interferometer for reference-mirror calibration of interferometric microscope
First Claim
1. An apparatus for calibrating the in-focus position of a reference mirror in an interference microscope objective, comprising:
- a light source adapted to provide a light beam directed to a reference mirror;
means for determining a shape of a return wavefront reflected from the reference mirror; and
focusing means for translating the reference mirror to an in-focus position.
3 Assignments
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Accused Products
Abstract
A laser interferometer is embedded into an interference microscope to precisely determine the in-focus position of the microscope objective'"'"'s reference mirror. A collimated laser beam is introduced into the microscope system and split into two beams directed toward a calibration reference surface and the interference objective. The light reflected from the calibration reference surface is returned to the camera. The light into the interference objective is focused onto the reference mirror and returned to the camera. For the purpose of calibration, the two beams are combined at the camera to produce interference fringes. When the reference mirror is in focus, the returned beam is collimated; if the mirror is on either side of focus, the beam is either converging or diverging. Accordingly, the interferogram produced at the camera reflects the in-focus or out-of-focus condition of the reference mirror. The curvature of the wavefront returned from the reference mirror is determined electronically by analyzing the interference fringes produced with the beam returned from the calibration reference surface. By minimizing the curvature of the reference-mirror wavefront as the mirror is translated along the optical path, the reference mirror can be focused with an accuracy greater than possible by visual observation. Furthermore, by automating the focusing system with a precise translation mechanism driven by closed-loop control, operator-to-operator variations are completely eliminated.
112 Citations
49 Claims
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1. An apparatus for calibrating the in-focus position of a reference mirror in an interference microscope objective, comprising:
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a light source adapted to provide a light beam directed to a reference mirror;
means for determining a shape of a return wavefront reflected from the reference mirror; and
focusing means for translating the reference mirror to an in-focus position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
a calibration reference surface adapted to reflect a calibration beam in optical alignment with an optical path of the interference microscope; and
a beam splitter dividing said light beam into said calibration beam and a reference beam directed to said reference mirror.
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22. The apparatus of claim 1, wherein said return wavefront is directed to a light-intensity sensor and said means for determining a shape of the return wavefront reflected from the reference mirror comprises a second light source adapted to provide a light beam directed to the light-intensity sensor.
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23. The apparatus of claim 22, wherein said second light source is produced by a fiber-optic splitter.
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24. The apparatus of claim 1, wherein said means for determining a shape of the return wavefront reflected from the reference mirror comprises a shearing interferometer placed in an optical path of the return wavefront to a light-intensity sensor.
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25. The apparatus of claim 1, wherein said light beam is collimated.
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26. The apparatus of claim 21, wherein said light beam is collimated.
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27. The apparatus of claim 22, wherein said light beam is collimated.
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28. The apparatus of claim 24, wherein said light beam is collimated.
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29. A method for calibrating the in-focus position of a reference mirror in an interference microscope objective, comprising the steps of:
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(a) providing a light beam;
(b) directing said light beam toward a reference mirror;
(c) determining a shape of a return wavefront reflected from the reference mirror;
(d) determining a position of the reference mirror relative to an in-focus position thereof as a function of said shape of the return wavefront reflected from the reference mirror; and
(e) translating the reference mirror toward said in-focus position. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49)
i.) splitting said collimated light beam into a calibration beam and a reference beam directed toward the reference mirror; and
ii.) producing an interferogram between said calibration beam and said return wavefront from the reference mirror.
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43. The method of claim 42, further including the steps of:
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iii.) providing a calibration reference surface; and
iv.) directing said calibration beam toward the calibration reference surface to produce a collimated calibration beam for interference with said return wavefront.
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44. The method of claim 29, wherein said step (c) includes the steps of:
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i.) passing said return wavefront through a shearing interferometer to produce two beams; and
ii.) producing an interferogram between said two beams.
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45. The method of claim 29, wherein said step (c) includes performing phase-shifting measurements.
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46. The method of claim 42, wherein said step (c) includes performing phase-shifting measurements.
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47. The method of claim 44, wherein said step (c) includes performing phase-shifting measurements.
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48. The method of claim 29, wherein said light beam is collimated.
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49. The method of claim 44, wherein said light beam is collimated.
Specification