Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2002-05-29
2004-07-06
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C359S871000
Reexamination Certificate
active
06760114
ABSTRACT:
RELATED APPLICATIONS
This application claims the priority of Japanese Patent Application No. 2001-168242 filed on Jun. 4, 2001, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a support apparatus for an optical wave interferometer reference plate, which is used for allowing an optical wave interferometer body to support a reference plate employed in an optical wave interferometer capable of measuring the surface form or internal distortion of optical components and the like with a high accuracy.
2. Description of the Prior Art
Various optical wave interferometers have been in use in order to measure very fine surface forms of samples and the like accurately, and so forth. In optical wave interferometers carrying out such highly accurate measurement, the reference plate is required to be prepared with a high precision as well.
Therefore, though depending on the accuracy required in measurement, the reference surface of a reference plate has been finished grinding with such a high precision that its amount of deviation from a perfect plane is {fraction (1/20)} of the optical wavelength in use or so in general. Though the rear side of the reference surface is not required to have accuracy as high as that of the reference surface, it has also been finished grinding with a precision of about ⅕ to {fraction (1/10)} of the optical wavelength in use.
The outer peripheral face of the reference plate has been ground or lapped with a roughness of about #400 to #800 in general. Also, the reference plate has been formed from a material having a low coefficient of thermal expansion, such as silica or ceramics in general. Therefore, in optical systems in which luminous fluxes are transmitted through a reference plate in particular, evenness is required in the refractive index distribution within the material.
It is important that a reference plate finished with a high precision as such be attached to an interferometer body and used while keeping its precision. Therefore, various methods for supporting a reference plate have been proposed and used conventionally.
Some of typical methods have been disclosed in commonly assigned Japanese Unexamined Patent Publication No. 2000-249512.
For example, there is a method in which a reference plate is supported from its optical axis direction end face (reference surface) side. This method is one in which a lens barrel for supporting a reference plate is formed with an annular abutment surface for supporting the reference surface of the reference plate, so that the reference plate is supported with the abutment surface from the reference surface side. However, since the machined abutment surface has a surface precision inferior to the reference surface finished grinding with a high precision in this method, the contact between the abutment surface and the reference surface may become uneven, so that the reference plate may flex unevenly, whereby the surface precision of reference surface may deteriorate.
Hence, a method in which a cushioning material is held between the reference surface and the annular abutment surface has been proposed in order to alleviate the uneven contact. However, though the uneven contact is alleviated by this method, the cushioning material may lose its elasticity with time due to the continuous pressure effected by the weight of the reference plate itself, so that the cushioning effect may be lost, whereby uneven contact may occur again.
Therefore, a method in which the reference plate is supported from its diametric end face (outer peripheral face) side has been proposed. This method bonds the outer peripheral face of the reference plate to the inner face of the lens barrel such that the reference plate is suspended with respect to the lens barrel, whereas an adhesive is mainly used for bonding. Since nothing comes into contact with the reference surface of the reference plate in this method, the problem of surface precision deterioration resulting from the contact between the reference surface and the abutment surface or cushioning material as in the method supporting the reference surface of the reference plate does not occur.
However, even in this supporting method, the material forming the lens barrel and the material forming the reference plate may have coefficients of thermal expansion different from each other, so that a force may act on the reference plate by way of the bonded part of the outer peripheral face of the reference plate when temperature changes, thereby deforming the reference surface having a high precision.
Also, using an adhesive for bonding may be problematic when curing the adhesive. Namely, if the thickness of an adhesive layer varies, a force may act on the reference plate due to volumetric changes upon curing, thereby altering the reference surface having a high precision.
Therefore, a method in which the reference plate is elastically supported from its diametric end face (outer peripheral face) side has been devised. In this method, an elastic member is disposed at the outer peripheral face of the reference plate, and the lens barrel and the outer peripheral face of the reference plate are secured to each other by way of the elastic member such that the reference plate is suspended with respect to the lens barrel. Since nothing comes into contact with the reference surface of the reference plate in this method, the problem of surface precision deterioration resulting from the contact between the reference surface and the abutment surface or cushioning material as in the method supporting the reference surface of the reference plate does not occur. Also, since the reference plate and the lens barrel are not in contact with each other directly but by way of the elastic member, no force acts on the reference plate by way of the bonded part of the outer peripheral face of the reference plate when temperature changes, and no force acts on the reference plate due to volumetric changes upon curing the adhesive, whereby the reference surface having a high precision does not deform.
However, since the elastic member is disposed at the outer peripheral face of the reference plate, whereby the lens barrel and the outer peripheral face of the reference plate are secured to each other by way of the elastic member such that the reference plate is suspended with respect to the lens barrel, the above-mentioned supporting method may also be problematic in that the reference surface position varies along with temporal changes in elastic force of the elastic member.
Also, when the reference plate is measured while repeatedly moving/stopping it in its optical axis direction at a high speed in order to obtain highly accurate numeric data by interference measurement, as in the case using fringe scanning, which is a highly accurate interference fringe analyzing technique, minute vibrations corresponding to the spring constant of the elastic member for holding the reference plate with respect to the lens barrel in a suspended state may occur at the time when the reference plate starts and stops moving, thus making it difficult to carry out highly accurate measurement.
Further, when the lens barrel having the reference plate suspended by way of the elastic member is attached to the interferometer body, the reference plate and the interferometer body are elastically secured to each other. Since the characteristic frequency of the interferometer body and that of the reference plate differ from each other, the reference surface and the surface of a sample to be inspected may not stand still relative to each other depending on the vibrating environment in which an interferometer apparatus having the reference plate attached thereto is placed.
SUMMARY OF THE INVENTION
In view of the circumstances mentioned above, it is an object of the present invention to provide a support apparatus for an optical wave interferometer reference plate which, when supporting the outer peripheral face of the reference plate, can prevent forces gene
Akaogi Toshikazu
Shibamoto Hiroshi
Connolly Patrick
Fuji Photo Optical Co., Ltd.
Snider Ronald R.
Snider & Associates
Turner Samuel A.
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