JPH0914911A - Interferometer - Google Patents

Abstract

PURPOSE: To enable proper adjustment of the length of an optical path without deviation of the optical path by providing an optical path length adjusting means which has a fluid inflow part to let a light beam pass and a fluid medium fillable a fluid injection part with a refractive index different from a medium on other optical paths. CONSTITUTION: An interfering light beam is separated into two light beams by a beam splitter, an optical path length adjusting means 50 is provided on an optical path of one light beam 16 and a fluid medium is arranged in a fluid injecting part 52 thereof with a refractive index different from a medium on other optical paths. A square holding body 54 is so arranged as not to be slidable and a square holding body 56 is so arranged to the slidable horizontally in an angular casing 68 of the adjusting means 50. The holding body 56 is energized by a pressing spring 70 to the left and the holding body 56 is formed so that size thereof is almost the same as the inner diameter of the casing 68 and thicker in the sliding direction. Thus, the holding body 56 moves within the casing 68 in proportion to the amount of the fluid medium injected into the fluid injection part 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer, and more particularly to an improvement in the optical path length adjusting means of an interferometer for recombining two split lights to generate an interference light.

[0002]

2. Description of the Related Art For example, interferometers are widely used for non-contact inspection of unevenness on the surface of a subject. As one of the basic aspects of these sample surface observing interferometers, there is a Michelson type interferometer or an improved interferometer thereof,
These separate the coherent light into a first light beam and a second light beam by a light beam separating means such as a beam splitter. Then, for example, the first light beam is reflected by the reference plane, the second light beam is reflected by the surface to be inspected, and both reflected beams are made incident on the beam splitter again, and their combination is performed. In this case, if the distance from the light beam separating means to the reference plane and the distance to the surface to be inspected are substantially the same, the unevenness of the surface to be inspected is grasped as a difference in optical path length from the reference plane, As a result, it is possible to observe the unevenness of the surface to be inspected by the interference fringes generated based on the optical path length difference between the first light beam and the second light beam.

[0003]

As described above, in order to express the unevenness of the surface of the object by the interferometer by the interference fringes, the interference between the first light beam and the second light beam must be properly generated. Of course, the optical path lengths of the first light beam and the second light beam need to be aligned. However, it is extremely difficult to exactly match the optical system through which the first light beam passes and the optical system through which the second light beam passes, and therefore either the first light beam or the second light beam is A wedge plate in which two wedge-shaped glass bodies are superposed is arranged on the optical path, and the optical path length is substantially adjusted by the degree of superposition of the two.

That is, since the glass body has a higher refractive index than air, if the glass body is arranged on the optical path traveling in the air, the optical optical path length changes according to the refractive index, and the wedge plates are superposed. By changing the geometrical optical path length while passing through the glass body by adjusting the degree, it becomes possible to adjust the optical optical path length without changing the arrangement itself of the optical element.

However, in the optical path length correcting mechanism using such a wedge plate, since the two glass bodies are arranged so as to face each other with a slight gap therebetween, the overlapping surfaces of the wedge-shaped glass bodies are arranged. However, there is a problem that the refraction of the light beam occurs and a slight deviation occurs in the optical path. The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide an interferometer capable of performing an appropriate optical path length adjustment without causing deviation of the optical path.

[0006]

In order to achieve the above object, an interferometer according to the present invention comprises a light beam emitting means for emitting a coherent light beam, the coherent light beam as a first light beam and a second light beam. An optical interferometer having a light beam separating means for separating the light beam, and recombining the first light beam and the second light beam to generate interference light, at least one of the first light beam and the second light beam. An optical optical path length adjusting means is arranged on one of the optical paths, and the optical optical path length adjusting means,
It is characterized in that it is provided with a fluid injecting section that allows the light beam to pass therethrough, and a fluid medium that can be filled in the fluid injecting section having a refractive index different from that of the medium on other optical paths.

In the interferometer, first and second reflecting means for returning the first light beam and the second light beam to substantially the same optical path as the respective incident beams, the light beam separating means, and First and second condensing means provided on the optical path between the reflecting means for condensing the first and second light beams on the first and second reflecting means, and the light beam separating means. Preferably, the first and second light beams are recombined to generate interference light, and the optical path length adjusting means is provided on the optical path between the light beam separating means and the reflecting means. Further, in the interferometer, it is preferable that the optical path length adjusting means is arranged on the optical path between the condensing means and the focus on the side of the light beam separating means.

[0008]

As described above, the interferometer according to the present invention has the optical optical path length adjusting means arranged on the optical path of at least one of the first light beam and the second light beam. Further, the optical optical path length adjusting means includes a fluid injecting portion that allows a light beam to pass therethrough, and a fluid medium that has a refractive index different from that of a medium on another optical path and that can be filled in the fluid injecting portion. There is.

Here, for example, when the optical path length of the first light beam is short, a fluid having a high refractive index is injected into the fluid injection portion.
In this way, by changing the amount of the medium in the fluid injection part arranged on the optical path, that is, the high refractive index medium passage distance or its refractive index, the optical optical path length can be adjusted without causing the optical path shift. It will be possible. In the case of a linique interferometer in which the first beam and the second beam are diffused and focused in the interferometer, the use of the wedge plate makes it easy to cause deviation in the optical path. Even in the interferometer, the deviation of the optical path does not occur, which is particularly preferable.

Further, in the case of a linique interferometer, a difference in lens characteristics, such as a difference in focal length, is a problem in the first and second condensing means that must compose different optical systems. In the interferometer, by inserting the optical path length adjusting means between any of the light collecting means and the focal point on the side of the light beam separating means, it becomes possible to compensate for the lens characteristic of each light collecting means, and enlarge The contrast of the observed image can be improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an interferometer according to an embodiment of the present invention. The interferometer illustrated in the figure is a linique type interferometer capable of observing the surface shape of a microscopic portion of the surface to be inspected.

In this embodiment, the interferometer 10 includes a light source (light beam emitting means) 14 for emitting a coherent light beam 12.
A beam splitter (light beam splitting means) 20 for splitting the coherent light beam 12 into a first light beam 16 and a second light beam 18, and a reference plane 22 for the first light beam 16.
And a second objective lens (second condensing means) 28 for condensing the second light beam 18 on the surface 26 to be inspected and a reference plane 22. The first reflected light thus reflected and the second reflected light reflected by the surface 26 to be inspected are returned to the beam splitter 20, and a combined beam 3 thereof is obtained.
The image forming lens 34 forms an image of 0 on the monitor camera 32. The coherent light beam 12 emitted from the light source 14 is condensed in the direction of the beam splitter 20 by the condenser lens 36, and the first light beam 16 transmitted through the beam splitter 20 is located at a position a distance a away from the beam splitter 20. Connect 14 statues. The second light beam 18 reflected by the beam splitter 20 also forms an image of the light source 14 at a position a distance a from the beam splitter 20.

Each of the first and second light beams 16,
Although 18 is in a diffused state when passing through the image forming point, the corresponding first objective lens 24 and second objective lens 28
Is adjusted to a substantially parallel light flux, and the reference plane 22 and the test surface 26 are irradiated with the light.

By the way, the distance a from the beam splitter 20 to each image forming point is the same because both the first light beam 16 side and the second light beam 18 side are caused by the condensing action of the same condenser lens 36. However, since the objective lenses 24 and 28 are different lens systems, it is inevitable that they have slightly different characteristics even if they are prepared to have the same optical characteristics. The difference in the lens characteristics of the objective lenses 24 and 28 affects the optical path difference between the emission of the first light beam 16 and the second light beam 18 from the beam splitter 20 to the return, that is, the wave number during this period.
This will affect the interference state of the synthetic beam 30.

This situation is shown in more detail in FIG. In the figure, the first objective lens 24 and the second objective lens 28 are prepared to have substantially the same standard, and are held by the lens holders 40 and 42. The objective lenses 24 and 28 in the lens holders 40 and 42 are prepared so that the distances l ₂ and l ₂ ′ from the respective lenses to the reference plane 22 and the test surface 26 have no individual difference. , The distance l from the screw abutting surfaces 44a, 44b to the image side focal point
It is extremely difficult to make ₁ and l ₁ 'exactly the same because of errors such as screw processing. As a result,
Since the distance from the image-side focus to the reference plane 22 or the surface to be inspected 26 is different, there is a possibility that interference will not occur with light having a short coherence length such as white light.

Therefore, in this embodiment, as shown in FIG. 3, the optical path length adjusting means 50 is inserted between the first objective lens 24 and its image side focal point. That is, the optical path length adjusting means 50 has a medium (refractive index n) having a refractive index different from that of other optical paths, and the first light beam 16 and the second light beam 18 are provided.
The optical path difference Δ is adjusted. As a result, as described above, in the linique interferometer, the condensing lens 24, which is inevitably a different optical system between the first light beam and the second light beam,
The focal length of 28 can also be adjusted, and a more accurate magnified image can be observed.

FIG. 4 shows the structure of the optical path length adjusting means 50 according to this embodiment. In the side sectional view shown in FIG. 9A and the front view shown in FIG. 7C, the optical path length adjusting means 50 is a bellows-shaped fluid injection section 52 that is expandable and contractible in the left-right direction in the figure, and the fluid injection section 52. Square shaped holding bodies 54 and 56 arranged at both ends of expansion and contraction, supporting holes 58a and 58b provided at lower ends of the holding bodies 54 and 56, and an elongated hole 60a formed at upper ends of the holding bodies 54 and 56. , 60b and the holes 58a,
Shape-retaining shafts 62 and 64 that are diagonally extended to 58b, 60a, and 60b, and support shafts that support the shafts at the intersections of the shape-retaining shafts 62 and 64 so as to be rotatable and movable in the vertical direction in the figure. 6
6 is provided.

In the rectangular casing 68, the holder 54 is arranged so that it cannot slide, and the holder 56 can slide in the left-right direction in the drawing. The square-shaped holder 5
6 is urged to the left in the figure by the pressing spring 70, and the square-shaped holder 56 is formed to be substantially the same as the inner shape of the casing 68 and thick in the sliding direction. The holder 56 moves in parallel in the casing 68 in proportion to the amount of the fluid medium injected into the fluid injection part 52 (FIG. 4 (B)). At least the light-entering surface 72 and the light-exiting surface of the fluid injection unit 52 are made of a light-transmitting material such as glass.

Optical optical path length adjusting means 5 according to the present embodiment.
0 is configured as described above, and its operation will be described below. First, as shown in FIG.
When an optical path difference Δ occurs between the optical path lengths 8, optical optical path length adjusting means 5
An optical path length adjusting medium having a refractive index different from the outside is injected into the hollow frame 52 of 0. Then, from the state shown in FIG. 4A, by sequentially injecting the fluid medium through the valve 72, the holding body 56 resists the pressing force of the pressing spring 70, and as shown in FIG. Move to the left and hold the holder 54,5
The separation distance between the six, that is, the distance of the medium through which the light beam 16 passes is extended. When the other part of the optical path of the light beam 16 travels in the air, for example, even if the fluid medium is water, since the refractive index is larger than that of the air, the optical path length of the light beam 18 increases, and It is possible to compensate for the difference Δ.

FIG. 5 shows an optical optical path length adjusting means 150 according to another embodiment of the present invention. The parts corresponding to those in FIG. The optical optical path length adjusting means 150 shown in FIG. 5 includes a storage tank 174 storing a low refractive index medium and a storage tank 176 storing a high refractive index medium, and both storage tanks 174, 17 are provided.
The valve 172 is used to adjust the mixing amount of both media from No. 6. Then, by using a combination having high compatibility with the high refractive index medium and the low refractive index medium, it is possible to obtain an arbitrary refractive index of the fluid medium by adjusting the valve 172, and change the amount of the medium as described above. It is possible to adjust the optical optical path length without doing so.

As the fluid medium used in each of the above-mentioned embodiments, it is usually preferable to use an aqueous solution, oil or the like. However, for example, a transparent resin which is cured after being injected into the injection part may be used. Further, in each of the above-mentioned embodiments, an example using a linique interferometer as the interferometer has been described.
The present invention is not limited to this, and can be applied to various interferometers such as the Twyman-Green interferometer and Michelson interferometer that require optical optical path length adjustment.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of the overall configuration of an interferometer according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a problem to be solved by the present invention.

FIG. 3 is an explanatory view of the operation of the present invention.

FIG. 4 is an explanatory view of an optical optical path length adjusting means according to an embodiment of the present invention.

FIG. 5 is an explanatory view of an optical optical path length adjusting means according to another embodiment of the present invention.

[Explanation of symbols]

 10 Interferometer 12 Coherent light beam 16 First light beam 18 Second light beam 20 Beam splitter (light beam separating means) 50,150 Optical optical path length adjusting means 52,152 Fluid injection part

Claims (3)

[Claims] 1. A first light beam comprising: a light beam emitting means for emitting a coherent light beam; and a light beam separating means for separating the coherent light beam into a first light beam and a second light beam. And an interferometer for recombining the second light beam to generate interference light, wherein an optical optical path length adjusting means is disposed on the optical path of at least one of the first light beam and the second light beam, The optical path length adjusting means includes a fluid injection part that allows a light beam to pass therethrough, and a fluid medium that can be filled in the fluid injection part having a refractive index different from that of a medium on another optical path. Total. 2. The first and second reflecting means for returning the first light beam and the second light beam on substantially the same optical path as the respective incident beams, and between the light beam separating means and the respective reflecting means. And first and second condensing means for condensing the first and second light beams on the first and second reflecting means, the first and second converging means being provided by the light beam separating means. The second light beam is recombined to generate interference light, and the optical path length adjusting means is provided on an optical path between the light beam separating means and the reflecting means.
The described interferometer. 3. The interferometer according to claim 2, wherein the optical path length adjusting means is arranged on the optical path between the condensing means and the focal position on the side of the light beam separating means.