GB2184866A

GB2184866A - A contactless interferometric sensor for incremental scanning of variable interference structures

Info

Publication number: GB2184866A
Application number: GB8630195A
Authority: GB
Inventors: Gerd Jager; Hans Buchner
Original assignee: SUHL FEINMESSZEUGFAB VEB
Current assignee: SUHL FEINMESSZEUGFAB VEB
Priority date: 1985-12-23
Filing date: 1986-12-17
Publication date: 1987-07-01
Anticipated expiration: 2006-12-17
Also published as: FR2592152A1; GB8630195D0; GB2184866B; DE3623244A1; FR2592152B1

Abstract

An interferometer has a diaphragm (11) between an interferometer divider (1) and a beam divider (2), and allows greater angular mobility of a measuring reflector (7) by means of a lens (15, 16) which images the diaphragm, one lens being located in each of the two outlets of the beam divider. A radiation-sensitive face of a photodetector (19,20) is used to detect each of the two diaphragm images (17,18). It can be preferably used for measurement tasks in which changes in the interference structure to be scanned occur during measurement. it allows optically contactless scanning of plane and any type of curved surfaces (7) as well as, for example, use in pressure measuring chambers in which the gas flowing into and out of the chamber causes turbulence in the interference structure. <IMAGE>

Description

SPECIFICATION A contactless interferometric sensor for incremental scanning of variable interference structures The present invention relates to contactless interferometer sensors, and in particular to such sensors for incremental scanning of variable interference structures.

Interferometers can be used to measure all the physical and technical dimensions whose influence causes a change in the optical path difference.

An interferometer, in particular for the incremental scanning of variable interference structures, has already been proposed, in which a diaphragm is located between an interferometer divider and a beam divider. The beam is divided through the diaphragm in the beam divider into partial beams, and one photoelectric detector is disposed in each beam path.

It has the disadvantage that, in the case of changes in the angle of the plane measuring reflector or the plane measuring surface, the beam portion originating from the measuring arm of the interferometer and passing through the diaphragm is angularly displaced relative to the beam portion originating from the reference arm of the interferometer and passing through the diaphragm, by twice the amount of the angular change of the measurement surface. It is possible that, at an interval beyond the diaphragm, which interval is dependent on said angle and on the diaphragm diameter, the portions originating from the measuring and reference beams have moved away from one another to such an extent that interference of said portions no longer occurs.

This is particularly the case when the inteferometer has been designed for a relatively large tilting of the measuring surface and hence a small diaphragm diameter.

It is an object of the present invention to broaden the technically limited scope of application of a contactless interferometric sensor for incremental scanning of variable interference structures.

It is a further object of the present invention to provide a contactless interferometric sensor for incremental scanning of variable interference structures, in which the admissible angle of tilt of the measuring surface is increased.

N accordance with a first aspect of the present invention, there is provided a contacless interferometric sensor for incremental scanning of variable interference structures, comprising a monochromatic radiation source, reflecting, polarization-optical and optically birefringent elements, an interferometer divider, a beam divider, a diaphragm disposed between the interferometer divider and the beam divider, a first beam splitter disposed between the interferometer divider and the beam divider, and a second beam splitter disposed downstream of the first beam splitter, and two arrays of integrated photoelectric scanning elements, each of which is disposed in a partial beam produced by the second beam splitter, wherein one optical imaging element is disposed in each of the beam paths of the beam divider and component for scanning the interference structure are located in a respective image of the diaphragm.

Thus, in the present invention, one optically imaging element is disposed in each of the two beam paths of the beam divider, and a photoelectric detector is located in each image of the diaphragm.

If a lens is disposed at each of the two outlets of the beam divider in an interfero meter, in particular for the incremental scann ing of variable interference structures, then a real image of the diaphragm located between the interferometer divider and the beam divider will be formed through the two lenses in the corresponding image planes. If the plane measuring reflector in such an arrangement is tilted with respect to the incident measuring beam, the beam bundles which are allowed to pass through the diaphragm and which diverge from one another beyond the diaphragm as a result of the angular displacement between the reflected measuring beam and the reference beam are recombined by the lenses at the location of the image of the lenses and are once again brought to interference.

In particular, the present invention can be used for measurement tasks in which the object of measurement causes changes in the interference structure during measurement.

This particular characteristic of the invention enables contactless interferometric-incremental measurement of the flatness of plane surfaces, for example reflectors, silicon wafers and disc stores. Furthermore, it allows the use of flat reflectors in the measurement and reference arms of the interferometer without the reflec tors having to be guided in strict parallel, and the optically contactless scanning of spherical and aspherical surfaces is also possible as well as use in pressure measuring chambers in which the gas flowing into and out of the chamber causes turbulence in the interference structure.

In accordance with a second aspect of the present invention, there is provided a contact less interferometric device for incremental scanning of variable interference structures, the device comprising an interferometer divider having a first beam splitter, a beam divider having a second beam splitter, a diaphragm between the interferometer divider and the beam divider, an optical imaging element dis posed in each of the partial beams from the second beam splitter, and two arrays of pho todetectors, each of which is disposed in a respective partial beam from the second beam splitter, at the image of the diaphragm formed by the optical imaging element.

By way of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawing, which is a diagrammatic illustration of one embodiment of interferometric sensor in accordance with the present invention.

The accompanying figure shows an interferometer comprising an interferometer divider 1 and a beam divider 2. A monochromatic laser beam 3 enters the interferometer divider 1, where it is divided at the divided layer 4 into a measuring beam 5 and a reference beam 6.

The measuring beam 5 impinges on a measuring reflector 7 and is reflected back therefrom to the divider layer 4. The reference beam 6 impinges on a reference reflector 8 and is also reflected back to the divider layer 4, where interfernce occurs between the measuring beam 5 and reference beam 6, the result being a beam 9 modulated with the interference structure. A portion 10 of this beam 9 is allowed to pass through a diaphragm 11 positioned between the interference interferometer divider 1 and the beam divider 2, and is divided at a divider layer 12 in the beam divider 2 into partial beams 13 and 14. Optically imaging elements 15 and 16, for example lenses, through which the diaphragm 11 is imaged are located on the two exit faces of the beam divider 2. The optically imaging element 15 produced an image 17 of the diaphragm 11 and the optically imaging element 16 produces an image 18 of the diaphragm 11.

Photoelectrically active faces of the photodetectors 19 and 20, in the form of linear arrays of integrated photoelectric scanning elements, are disposed at the location of the diaphragm images 17 and 18.

Claims

1. A contactless interferometric sensor for incremental scanning of variable interference structures, comprising a monochromatic radiation source, reflecting, polarization-optical and optically birefringent elements, an interferometer divider, a beam divider, a diaphragm disposed between the interferometer divider and the beam divider, a first splitter disposed between the interferometer divider and the beam divider, and a second beam splitter disposed downstream of the first beam splitter, and two arrays of integrated photoelectric scanning elements, each of which is disposed in a partial beam produced by the second beam splitter, wherein one optical imaging element is disposed in each of the beam paths of the beam divider and components for scanning the interference structure are located in a respective image of the diaphragm.

2. A contactless interferometric device for incremental scanning of variable interference structures, the device comprising an interferometer divider having a first beam splitter, a beam divider having a second beam splitter, a diaphragm between the inerfereometer divider and the beam divider, an optical imaging element disposed in each of the partial beams from the second beam splitter, and two arrays of photodetectors, each of which is disposed in a respective partial beam from the second splitter, at the image of the diaphragm formed by the optical imaging element.

3. A contactless interferometric sensor for incremental scanning of variable interference structures, substantially as herein described, with reference to, and as illustrated in, the accompanying drawins.

4. A contactless interferometric device for incremental scanning of variable interference structures, substantially as herein described, with reference to, and as illustrated in, the accompanying drawing.