JPH10132508A - Interferometer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a highly precise measurement by forming a measuring optical path and a reference optical path by an optical member in which the bonding surface of two right-angled prisms is formed of a polarizing separating plane. SOLUTION: A prescribed arithmetic expression is stored in an arithmetic processing part 10. Thus, the arithmetic processing part 10 executes the calculation of the prescribed expression by use of respective output signal XA, XB from first and second receivers 7a, 7b and the refractive index (n) of a gas in the initial stage of measurement start on the basis of the output of a refractive index detector, and outputs an arithmetic result in which the measurement error accompanying the refractive index change of the gas caused by the fluctuation of the gas is corrected. A first moving mirror and a second moving mirror 3 are then integrally moved so as to satisfy the related specified numerical expression, whereby the quantization error (e) added to the output of an interferometer can be suppressed to 4 times to 1 time or less. Since the measuring optical path and each reference optical path are constituted so as to be adjacent to each other by the interferometer according to this structure, the moving quantity or position of the moving mirror 3 can be precisely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer for measuring a displacement of an object to be measured.

[0002]

2. Description of the Related Art Conventionally, as an interferometer device for correcting a change in the refractive index of air as one of environmental changes, for example, Japanese Patent Application Laid-Open No. 60-263801 is known. This Japanese Patent Laid-Open No. 60-2
Device disclosed in JP 63801, as shown in FIG. 6, the light beam from the laser light source 31, the beam splitter 32 is divided into two parts, the beam L ₂ of one transmitted through the beam splitter 32, a measuring beam The light is reflected by the reflecting member 34 on the measurement side movably provided in the left-right direction in FIG. On the other hand, the other beam L reflected by the beam splitter 32
Reference numeral ₃ reflects, as a reference beam, the reflecting member 35 on the reference side fixed to the base via the reflecting mirror 33, and travels to the beam splitter 32 again via the reflecting mirror 33. Then, the measurement beam L ₂ is emitted by the beam splitter 32.
And the reference beam L ₃ is with, is received by the photoelectric detector 36 as beam L _4, the amount of movement of the reflective member 34 as the object to be measured is detected.

At this time, the reflection member 33 on the measurement side and the reflection member 34 on the reference side are positioned at substantially the same position so that the reference optical path length and the measurement optical path length in the portion affected by the fluctuation of air become equal. By arranging them, the influence of air fluctuation is corrected.

[0004]

[SUMMARY OF THE INVENTION However, in the conventional apparatus shown in FIG. 6, when the reflecting member 34 as the object to be measured has moved significantly, the measuring beam L ₂ and the reference beam L ₃ The optical path length difference increases. As a result, the measurement error becomes so large that it cannot be ignored, so that the influence of the change in the refractive index of air due to the fluctuation of air or the like cannot be fundamentally solved.

Therefore, the present invention solves the above-mentioned problem,
It is an object of the present invention to provide a high-performance interferometer capable of correcting a measurement error due to a change in the refractive index of air caused by air fluctuation or the like and always enabling high-precision measurement.

[0006]

In order to achieve the above object, a first aspect of the present invention is to provide an interferometer for measuring the displacement of a measurement object as shown in FIG. One of the inclined surfaces and the other bottom surface are joined to each other, and an optical member whose joint surface is formed by a polarization splitting surface is arranged, and the optical member forms a measurement optical path and a reference optical path. It is.

Further, in order to achieve the above object, a second
As shown in FIG. 1, for example, as shown in FIG. 1, first and second measuring reflecting means provided integrally movable along a measuring direction, and first and second reflecting means fixed at predetermined positions, respectively. (2) a reflection unit for reference, a light source unit for supplying a light beam, a first measurement optical path reciprocating via the first measurement reflection unit based on the light beam from the light source unit, and the first reference reflection unit. A first reference optical path reciprocating through the first
A first interferometer for generating a first measurement output by each light beam passing through the measurement light path and the first reference light path, and a second interferometer which reciprocates via the second measurement reflection means based on the light beam from the light source means. A second measurement light path and a second reference light path that reciprocates via the second reference reflection means, and a second measurement output that generates a second measurement output by each light beam passing through the second measurement light path and the second reference light path. Interferometer means, and arithmetic means for performing a predetermined operation based on the first and second measurement outputs, wherein the first reference optical path from the first interferometer means to the first reference reflection means is An optical path length shorter than the second reference light path from the second interferometer means to the second reference reflection means, and a reference position of the first measurement reflection means from the first interferometer means. the optical path length of the first measuring optical path up to the l _M1, Wherein from serial second interferometer means to l _M2, reflecting means for referring the first from the first interferometer means optically optical path length of the second measuring optical path until the reference position of the second measurement reflector means The optical path length of the first reference light path is l _R1 , the optical path length of the second reference light path from the second interferometer means to the second reference reflection means is l _R2 , and the optical path length of the second reference light path from the reference position is l _R2 . When the displacement of the first and second measuring reflecting means is x, the first and second measuring reflecting means are configured to be movable at least in the following range or at least movable in a part of the following range. It was to so.

L _R1 −l _M1 ≦ x ≦ l _R2 −l _M2

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-interferometer device for measuring the displacement of a measurement object, in which one inclined surface and the other bottom surface of two right-angle prisms are joined and this joint surface is polarized. An optical member formed by a separation surface is arranged, and the optical member forms a measurement optical path and a reference optical path, so that the influence of measurement errors due to environmental changes is reduced.

Further, the present invention provides that each reference optical path formed by two interferometers differs by a predetermined length, while each measurement optical path length and each reference optical path length formed by two interferometers are different from each other. Is focused on that the two reflecting means for measurement are moved integrally under at least a predetermined relationship. As a result, even when a refractive index change occurs in the reference optical path and the measurement optical path passing through a gas such as air, two different measurement outputs including information on a change in the refractive index of a gas such as air due to an environmental change are obtained. By performing a predetermined calculation based on these two measurement outputs, a measurement error due to a change in the refractive index in each optical path can be removed. In addition, by configuring the two measuring reflection means so that at least a predetermined moving range or a part of the predetermined moving range can be moved, the influence of the quantization error of the two interferometer means itself can be remarkably reduced. Thus, the measurement accuracy can be greatly improved.

If there is a possibility that a local change in the refractive index in a gas such as air may occur in each measurement optical path formed by each interferometer means and in the vicinity thereof, each interferometer means
It is desirable that the reference light path and the measurement light path formed by these elements be close to each other. The principle of the present invention will be described with reference to FIG. FIG.
(A) is a diagram showing a configuration of a first interferometer device of the present invention, and (b) is a diagram showing a configuration of a second interferometer device of the present invention.

First, as shown in FIG. 4A, a light beam supplied from a first light source 11 is split into two light beams by a beam splitter 12 serving as a light splitting member, and one of the two light beams passing through the beam splitter 12 is transmitted. beam L ₂₁ is a measuring beam, directed in FIG. 4 the beam splitter 12 again and is reflected by the reflection member 14 (measurement reflection means) for measurement which is movable in the lateral direction (a). On the other hand, the other beam L reflecting the beam splitter 12
_31, reflected by the reflection mirror 13 as a reference beam, which travels in a gas such as air in close proximity to the optical path of the measuring beam L ₂₁ so as to be parallel to the measuring beam L _21. Thereafter, the beam L ₃₁ is a measure in a gas such as air reflected by the reflection member 15 for reference which is fixed to the base (the first referential reflecting means), close again the optical path of the measuring beam L ₂₁ It proceeds so as to be parallel with the beam L _21, toward the beam splitter 12 via the reflecting mirror 13. Then, come together and the reference beam L ₃₁ and measuring beam L ₂₁ is the beam splitter 12, is received as a beam L ₄₁ in the first receiver 16 (first detector), a reflecting member of the object to be measured 14 is detected.

Here, the first interferometer shown in FIG.
A beam splitter 12, a reflecting mirror 13, and a first receiver 16 are provided.
As optical light path length of the reference optical path in the gas is l _R1, are fixed to the base spaced by a predetermined optical distance l _R1 with respect to the first interferometer. Further, the reflection member 14 for measurement is used.
The optical distance from the first interferometer to the reference position of the reflective member for measurement 14 is 1 _M1 such that the optical path length of the measurement optical path in the gas at the reference position is 1 _M1. It is set to be movable.

On the other hand, a second interferometer as shown in FIG. 4B is arranged in parallel in a direction perpendicular to the plane of FIG. 4A, and the second interferometer has a reflecting mirror. The optical path length l _R2 of the reference optical path in the gas of the second interferometer differs from the optical path length l _R1 of the reference optical path in the gas of the first interferometer. Each is fixed. In addition, the beam splitter 22 and the reflection member for measurement (reflection means for measurement) are arranged such that the optical path length l _M2 of the measurement optical path in the gas of the second interferometer has the second interference at the reference position of the reflection member 24. The optical path length l _M1 of the reference optical path in the gas of the meter is set to be different from each other, or the optical path length l _M2 of the measurement optical path in the gas of the second interferometer at the reference position of the reflecting member 24. Are set so as to be substantially equal to the optical path length l _M1 of the reference optical path in the gas of the second interferometer, and otherwise the first interferometer device shown in FIG. Basically the same.

As shown in FIG. 4B, the light beam supplied from the second light source 21 is split into two light beams by a beam splitter 22 as a light splitting member, and one of the beams L passing through the beam splitter 22 is transmitted. _Reference numeral ₂₂ indicates a measurement beam directed to a measurement reflection member 24 (measurement reflection unit). The reflection member 24 is joined so as to have the same displacement as the reflection member 14 shown in FIG. 4A, and is provided so as to be movable in the left-right direction in FIG. Then, the beam L ₂₂ toward the reflective member 24 for measurement is again reflected by the reflecting member 24 towards the beam splitter 22. Meanwhile, beam splitter 2
The other beam L ₃₂ which reflects the 2 reflected by the reflection mirror 23 as a reference beam, traveling in a gas such as air in close proximity to the optical path of the measuring beam L ₂₂ so as to be parallel to the measuring beam L ₂₂ I do. Thereafter, the beam L ₃₂ is reflected by the reflection member 25 (second referential reflecting means) for reference which is fixed to the base,
Proceeds in parallel with the measuring beam L ₂₂ a gaseous such as air in close proximity to the optical path of the measuring beam L ₂₂ again towards the beam splitter 22 via the reflecting mirror 23. Then, the measurement beam L ₂₂ is output by the beam splitter 22.
A reference beam L ₃₂ is turned together with, as beam L _42, is received by the second receiver 26 (second detector), the amount of movement of the reflective member 24 as an object to be measured is detected.

The second interferometer shown in FIG. 4B includes a beam splitter 22, a reflecting mirror 23, and a second receiver 26. With the above configuration, when the reflecting members 14 and 24 as the objects to be measured move integrally in the direction of the paper surface of FIG. 4, the first receiver 1 of the first interference device
6 and the second receiver 26 of the second interference device output two different detection signals.

Now, the first receiver 16 of the first interference device
The output from the X _A, a second receiver of the second interference device 2
The output from the 6 and X _B, the refractive index of the refractive index of the gas to be initial criteria such at the start of measurement (reset) n, the refractive index of the initial reference gas such as at the start of measurement (reset) The amount of change is Δn, and the length of the optical optical path of the portion affected by the change in the refractive index of the gas in the reference optical path of the first interferometer (the length of the optical path between the first interferometer and the first reference reflecting means). The optical path length of one reference light path is l _R1 , and the length of the optical path of the portion of the second interferometer affected by the change in the refractive index of the gas in the reference light path (the second interferometer and the second reference) The optical path length of the second reference light path between the light source and the reflection means for reflection is l _{R2 at} the start of measurement (at the time of reset).
The length of the optical path of the portion affected by the change in the refractive index of the gas in the measurement optical path of the first interferometer at the reference position of the initial measurement reflection means (reference of the first interferometer and measurement reflection means) The optical path length of the first measurement optical path between the measurement position and the position is l _M1 , and the gas in the measurement optical path of the second interferometer at the reference position of the initial measurement reflection means such as at the start of measurement (at the time of reset). The length of the optical path of the portion affected by the change in the refractive index (the optical path length of the second measurement optical path between the second interferometer and the reference position of the measuring reflecting means) is l _M2 , the first and the second. In each of the measurement optical paths, the object to be measured when the lengths of the optical paths at the portions affected by the change in the refractive index of the gas are l _M1 and l _M2 (first
And the displacement of the second measuring reflecting means) from the reference position (origin) is x. However, this displacement x is positive when the measured object moves rightward from the origin, and negative when the measured object moves leftward from the origin.

[0018] Here, the output X _A from the first receiver 16 of the first interference device, the influence of the change in the amount corresponding refractive index of the gas in the length of the reference light path which is exposed to the gas (l _R1) And the information affected by the change in the refractive index of the gas by the optical length (1 _M1 + x) of the measurement optical path exposed to the gas. Information on the other hand, the output X _B from the second receiver 26 of the second interference device, influenced by the change in the refractive index of the amount corresponding gas of the length of the reference light path which is exposed to the gas (l _R2) And information affected by a change in the refractive index of the gas by the optical length (1 _M2 + x) of the measurement optical path exposed to the gas.

Therefore, at this time, the following equations (1) and (2) are established.

[0020]

(Equation 1)

[0021]

(Equation 2)

The following equation (3) is derived from equations (1) and (2).

[0023]

(Equation 3)

Therefore, assuming that the error amount added to the measurement result due to the quantization error by each interferometer apparatus is Δx, the following equation (4) is obtained from the above equation (3).

[0025]

(Equation 4)

When the above equation (4) is modified, the following equation (5) is obtained.

[0027]

(Equation 5)

Here, the following expression (6) is derived from the relationship between the expressions (1), (2) and (5).

[0029]

(Equation 6)

Here, n + Δn ≒ 1, (l _M1 -l _R1 )-
If (l _M2 -l _R2 ) = α, the above equation (6) finally becomes the following equation (7).

[0031]

(Equation 7)

Then, based on the above equation (7), the quantization error
Maximum value Δx of quantity Δx_MAXTo consider. Now, α> 0
And the quantization error of the first and second interferometer devices
(Δ _A, Δ_B) Are the maximum and minimum values, respectively, e, -e,
The quantization error of each interferometer device is -e ≦ δ_A≦ e, −e ≦
δ_BWhen the range of ≦ e can be taken, the quantum by the above equation (7)
Maximum value of quantization error | Δx_MAX| Is the following (i) to (ii)
There are three cases i).(I) When l _R1 -l _M1 ≤x≤l _R2 -l _M2  In this case, l_M1−l_R1+ X ≧ 0, l_M2−l_R2+ X ≦
0, the maximum value of the quantization error amount | Δx_MAX|
From the equation (7), the following equation (8) is obtained.

[0033]

(Equation 8)

(Ii) In the case of x> l _R2 −l _{M2 In} this case, l _M1 −l _R1 + x> 0, l _M2 −l _R2 + x>
0, and the maximum value | Δx _MAX | of the quantization error amount becomes as the following expression (9) from the above expression (7).

[0035]

(Equation 9)

(Iii) When x <l _R1 -l _{M1 In} this case, l _M1 -l _R1 + x <0, l _M2 -l _R2 + x <
0, and the maximum value | Δx _MAX | of the quantization error amount is as shown in the following expression (10) from the above expression (7).

[0037]

(Equation 10)

Therefore, by using the above equations (8) to (10), the optimum movement of the reflection member (14, 24) for measurement for assuring high accuracy as the whole interferometer apparatus shown in FIG. Consider range x. To guarantee the high accuracy of the interferometer while compensating for the effects of changes in the refractive index of the gas due to fluctuations in the gas such as air, it is practically necessary to maximize the quantization error added to the measurement output of the interferometer. Value (| Δx
_MAX |) is preferably suppressed to 4e or less. Therefore,
Hereinafter, the optimum movement range x of the reflection member for measurement (14, 24) when the quantization error e added to the measurement output of the interferometer device is suppressed to 4 times to 1 time or less will be described. (I) Maximum quantization error | Δx _MAX | is suppressed to 4e or less.
In this case, the optimum moving range x (where x ≧ 0) of the reflective member for measurement (14, 24) in this case is expressed by Expressions (8) to (1).
From the expression (0), the following expression (11) is obtained.

[0039]

[Equation 11]

As an example, the quantization error e (or resolution) between the first interferometer device shown in FIG. 4A and the second interferometer device shown in FIG. l _R1 = 1.
0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 0.5 m and l _R1
= 1.0 m, l _R2 = 1.5 m, l _M1 = 0.3 m, l _M2 = 0.5 m, the maximum value of quantization error (| Δx _MAX |) added to the measurement output of the interferometer apparatus is set to 4e or less. The moving range x of the suppressed reflection member (14, 24) for measurement will be described.

L _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 0.
When the distance is 5 m, the movement range x of the reflective member for measurement (14, 24) is -0.25 to 1.75 m according to the above equation (11), and the accuracy of 2.0 nm (= 4e) is obtained for the entire interferometer apparatus. It can be understood that a wide measurement range can be secured while being guaranteed. Also, l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 0.3 m,
When l _M2 = 0.5 m, the moving range x of the reflective member for measurement (14, 24) is from 0.25 m to 1.45 according to the above equation (11).
m, and it can be understood that a relatively wide measurement range can be secured while the accuracy of 2.0 nm (= 4e) is guaranteed for the entire interferometer apparatus. (II) The maximum quantization error | Δx _MAX | is suppressed to 3e or less.
In this case, the optimum moving range x (where x ≧ 0) of the reflective member for measurement (14, 24) in this case is expressed by Expressions (8) to (1).
From the expression (0), the following expression (12) is obtained.

[0042]

(Equation 12)

As an example, the quantization error e (or resolution) between the first interferometer device shown in FIG. 4A and the second interferometer device shown in FIG. l _R1 = 1.
0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 1.25 m and l
_{R1 = 1.0m, l R2 = 1.5m} , l M1 = 2.0m, l M2 = the case of a 1.5 m, the maximum value of the quantization error applied to measure the output of the interferometer device (| Δx _MAX |) to 3e below The movement range x of the reflection member for measurement (14, 24) which is suppressed to the above will be described.

L _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 1.
When the distance is 25 m, the moving range x of the reflective member for measurement (14, 24) is -0.75 m to 0.75 m according to the above equation (12), and the accuracy of the entire interferometer apparatus is 1.5 nm (= 3e). It can be understood that a wide measurement range can be secured while guaranteeing. Also, l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 2.0 m,
When l _M2 = 1.5 m, the moving range x of the reflective member for measurement (14, 24) is -2.0 m to 1.0 m according to the above equation (12).
It can be understood that a relatively wide measurement range can be secured while the accuracy of 1.5 nm (= 3e) is guaranteed for the entire interferometer apparatus. (III) The maximum value of the quantization error | Δx _MAX |
In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) in this case is expressed by Expressions (8) to (1).
From the expression (0), the following expression (13) is obtained.

[0045]

(Equation 13)

As an example, the quantization error e (or resolution) between the first interferometer device shown in FIG. 4A and the second interferometer device shown in FIG. l _R1 = 1.
0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 2.0 m and l _R1
= 1.0 m, l _R2 = 1.5 m, l _M1 = 1.75 m, l _M2 = 2.0 m, the maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer apparatus is set to 2e or less. The moving range x of the suppressed reflection member (14, 24) for measurement will be described.

L _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 2.
When the distance is 0 m, the moving range x of the reflective member for measurement (14, 24) is -1.25 m to -0.25 m according to the above equation (13), and the interferometer apparatus as a whole is 1.0 nm (= 2e). It can be understood that a wide measurement range can be secured while the accuracy is guaranteed. Also, l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 1.75
When m, l _M2 = 2.0 m, the moving range x of the reflective member for measurement (14, 24) is -0.875 m from the above equation (13).
~ -0.375m, and the entire interferometer device is 1.0nm (=
It can be understood that a relatively wide measurement range can be secured while the accuracy of 2e) is guaranteed. (IV) When the maximum value Δx _MAX of the quantization error is suppressed to e or less
In this case, the optimal movement range x (where x ≧ 0) of the reflection member for measurement (14, 24) in this case is expressed by the following equations (8) to (1).
From the expression (0), the following expression (14) is obtained.

[0048]

[Equation 14]

As an example, the quantization error e (or resolution) between the first interferometer device shown in FIG. 4A and the second interferometer device shown in FIG. l _R1 = 0.
5 m, l _R2 = 1.5 m, l _M1 = l _M2 = 1.0 m and l _R1
= 1.0 m, l _R2 = 2.0 m, l _M1 = 2.0 m, l _M2 = 1.5 m, the maximum value of quantization error (| Δx _MAX |) added to the measurement output of the interferometer apparatus is set to e or less. The moving range x of the suppressed reflection member (14, 24) for measurement will be described.

L _R1 = 0.5 m, l _R2 = 1.5 m, l _M1 = l _M2 = 1.
When the distance is 0 m, the moving range x of the reflective member for measurement (14, 24) is -0.5 m to 0.5 m according to the above equation (14).
Also, l _R1 = 1.0 m, l _R2 = 2.0 m, l _M1 = 2.0 m, l _M2 = 1.
When the distance is 5 m, the moving range x of the reflective member for measurement (14, 24) is -1.0 m to 0.5 m from the above equation (14),
It can be understood that a wide measurement range can be secured while the accuracy of 0.5 nm (= e) is guaranteed for the entire interferometer device.

As described above, according to the present invention, it can be understood that stable measurement can be realized with high accuracy even when the refractive index of gas changes due to environmental changes. Moreover, in the present invention, the object to be measured (the first and second measuring reflecting means) is (1)
By moving within the range satisfying the expression 4), in principle, the quantization error e (or resolution) of the two interferometers can be suppressed to 1 or less, and extremely stable and accurate measurement can be performed. Can be achieved. If the accuracy is not required to be equal to or less than one time the quantization error e (or the resolution) of the two interferometers, the object to be measured (the first and second measurement reflecting means)
May be provided so as to be movable at least in a range satisfying the above-mentioned expression (14) or a part thereof.

Although the principle of the present invention has been described above, an analysis of the principle from another viewpoint will be described below with reference to FIG. 5 in order to further understand the present invention. However, this analysis is based on the assumption that the first and second interferometers have different reference optical path lengths and that the first and second interferometers have the same reference optical path length. First, l
_M1 = _1M2 = 0, _lR1 = a, _lR2 = b, and the optical path length from the first interferometer to the reflection member 14 for measurement (or the second interferometer to the reflection member 24 for measurement) ( Or the distance) is x.

In other words, the output from the first receiver 16 of the first interference device is X _A , and the output of the second
The output from the receiver 26 and X _B, the refractive index of the gas to be initial criteria such at the start of measurement (reset) n, affected by changes in the refractive index of the gas in the reference light path of the first interferometer The length of the optical path at the portion (the optical path length of the first reference path between the first interferometer and the first reference reflecting means) is a, and the refractive index of the gas in the reference path of the second interferometer B is the length of the optical path (the optical path length of the second reference path between the second interferometer and the second reference reflecting means) at the portion affected by the change of The length of the optical path at the portion affected by the change in the refractive index of the gas in the measurement optical path of the second interferometer (the optical path length of the first measurement optical path between the first interferometer and the measuring reflection means; Or, the optical path length of the second measurement optical path between the second interferometer and the measuring reflection means) is x
And

Here, the output X _A from the first receiver 16 of the first interference device was affected by the change in the refractive index of the gas by the length a of the reference optical path exposed to the gas. It contains information and information affected by a change in the refractive index of the gas by the optical length x of the measurement optical path exposed to the gas. On the other hand, the output X _B from the second receiver 26 of the second interference device, the length of the reference light path which is exposed to the gas b
And the information affected by the change in the refractive index of the gas by the optical length x of the measurement optical path exposed to the gas. I have.

Therefore, the outputs (X _A , X _B ) from the respective receivers (16, 26) are averaged at such a ratio that the influence of the change in the refractive index of the gas between the reference light and the measurement light becomes equal. Is desirable. At this time, the following equations (15) and (16) are established.

[0056]

(Equation 15)

[0057]

(Equation 16)

Then, the following expression (17) is obtained from the expressions (15) and (16).

[0059]

[Equation 17]

Therefore, the outputs (X _A , X _B ) from the respective receivers (16, 26) are calculated by the arithmetic means using the above equation (1).
By performing the calculation in 7), it is possible to remove the influence of the change in the refractive index of the gas. Next, the quantization error by the interferometer of the present invention will be discussed. Assuming now that the quantization error (or resolution) of the first interferometer device is δ _A and the quantization error (or resolution) of the second interferometer device is δ _B , the first interferometer device shown in FIG. The measurement output from is the original measurement signal X
_A is obtained by adding the quantization error δ _A to _A , and FIG.
The measurement output from the second interferometer device shown in (b) is obtained by adding the quantization error δ _B to the original measurement signal X _B. Therefore, if the error amount added to the measurement result due to the quantization error of each interferometer apparatus is Δx, the above equation (17) becomes the following equation (18).

[0061]

(Equation 18)

When the above equation (18) is modified, the following equation (19) is obtained.

[0063]

[Equation 19]

Now, each reference optical path and each measurement optical path of the first and second interferometers shown in FIG. 5 pass through the air, and the optical path of the difference between the reference optical path length and the measurement optical path length of each interferometer apparatus. Assuming that the refractive index of air changes by Δn due to air fluctuations or the like, the outputs of the first and second interferometers are X _A = (x−a) Δn, X _B = (x− b) Since Δn is obtained, from this relationship and the above equation (19), the following equation (20) is obtained.
Is derived.

[0065]

(Equation 20)

Here, assuming that n + Δn ≒ 1, the above equation (2)
0) finally becomes as shown in the following equation (21).

[0067]

(Equation 21)

Therefore, the maximum value Δx _MAX of the quantization error amount Δx will be examined based on the above equation (21). Now the first
And the maximum value and the minimum value of the quantization error (δ _A , δ _B ) of the second interferometer device are e and −e, respectively, and the quantization error of each interferometer device is −e ≦ δ _A ≦ e, − When the range of e ≦ δ _B ≦ e can be taken, the maximum value | Δx _MAX | of the quantization error amount according to the above equation (21) can be classified into the following three cases (i) to (iii). (I) When a ≦ x ≦ b (where a <b) When a ≦ x ≦ b, x−a ≧ 0 and x−b ≦ 0, and the maximum quantization error amount | Δx _MAX |
From the expression (1), the following expression (22) is obtained.

[0069]

(Equation 22)

(Ii) When x> b (where a <b) When x> b, xa> 0 and xb> 0, and the maximum quantization error amount | Δx _MAX | Is given by the following equation (23) from the above equation (21).

[0071]

(Equation 23)

(Iii) When x <a (where a <b) When x <a, x−a <0, x−b <0, and the maximum quantization error amount | Δx _MAX | Is given by the following equation (24) from the above equation (21).

[0073]

(Equation 24)

Therefore, using the above equations (22) to (24), the optimum movement of the reflection member for measurement (14, 24) for assuring high accuracy as the whole interferometer apparatus shown in FIG. Consider range x. To guarantee the high accuracy of the interferometer while compensating for the effects of changes in the refractive index of the gas due to fluctuations in the gas such as air, it is practically necessary to maximize the quantization error added to the measurement output of the interferometer. Value (| Δx _MAX
|) Is preferably suppressed to 4e or less. Therefore, in the following, the quantization error e added to the measurement output of the interferometer device
The optimal movement range x of the reflective member for measurement (14, 24) in the case where is suppressed to 4 times to 1 time or less will be described. (I) Maximum quantization error | Δx _MAX | is suppressed to 4e or less.
In this case, the optimum movement range x (where x ≧ 0) of the reflection member for measurement (14, 24) in this case is expressed by the following equations (22) to (2).
From the equation (4), the following equation (25) or (26) is obtained.

[0075]

(Equation 25)

[0076]

(Equation 26)

The relationship between the expressions (25) and (26) can be expressed as (1)
In the case where the measured optical path length l _M1 of the first interferometer and the measured optical path length l _{M2 of} the second interferometer in the equation (1) are equal to each other (l _M1 = l _M2).
= 1 _M ). As an example, FIG.
The quantization error e (or resolution) between the first interferometer device shown in FIG. 5A and the second interferometer device shown in FIG. 5B is 0.5 nm, and a = 0.5 m and b = 1.0. m and a =
When 0.7 m and b = 1.0 m, the maximum value (| Δx _MAX |) of the quantization error added to the measurement output of the interferometer apparatus is 4
The movement range x of the reflection member for measurement (14, 24) suppressed to e or less will be described.

When a = 0.5 m and b = 1.0 m, the moving range x of the reflecting member for measurement (14, 24) is 0 m to 1.75 m according to the above equation (25), and the interferometer apparatus as a whole is Is 2.
It can be understood that a wide measurement range can be secured while the accuracy of 0 nm (= 4e) is guaranteed. Also, a = 0.7m, b =
When the distance is 1.0 m, the moving range x of the reflective member for measurement (14, 24) is 0.25 m to 1.45 m according to the above equation (26), and the accuracy of the interferometer apparatus as a whole is 2.0 nm (= 4e). It can be understood that a relatively wide measurement range can be secured while ensuring the above. (II) The maximum quantization error | Δx _MAX | is suppressed to 3e or less.
In this case, the optimum movement range x (where x ≧ 0) of the reflection member for measurement (14, 24) in this case is expressed by the following equations (22) to (2).
From the expression (4), the following expression (27) or (28) is obtained.

[0079]

[Equation 27]

[0080]

[Equation 28]

The relationship between the expressions (27) and (28) can be expressed as follows according to the expression (12).
2) When the measured optical path length l _M1 of the first interferometer and the measured optical path length l _{M2 of} the second interferometer in the equation are equal to each other (l _M1 = l _M2)
= 1 _M ). As an example, FIG.
The quantization error e (or resolution) between the first interferometer device shown in FIG. 5A and the second interferometer device shown in FIG. 5B is 0.5 nm, and a = 0.4 m and b = 1.0. m and a =
When 0.6 m and b = 1.0 m, the maximum value (| Δx _MAX |) of the quantization error added to the measurement output of the interferometer apparatus is 3
The movement range x of the reflection member for measurement (14, 24) suppressed to e or less will be described.

When a = 0.4 m and b = 1.0 m, the moving range x of the reflective member for measurement (14, 24) is 0 m to 1.6 m according to the above equation (27), and the interferometer apparatus as a whole is Is 1.5n
It can be understood that a wide measurement range can be secured while the accuracy of m (= 3e) is guaranteed. Also, a = 0.6 m, b = 1.
When the distance is 0 m, the moving range x of the reflective member for measurement (14, 24) is 0.2 m to 1.4 m according to the above equation (28), and the accuracy of 1.5 nm (= 3 e) is obtained for the entire interferometer apparatus. It can be understood that a relatively wide measurement range can be secured while being guaranteed. (III) The maximum value of the quantization error | Δx _MAX |
In this case, the optimum movement range x (where x ≧ 0) of the reflection member for measurement (14, 24) in this case is expressed by Expressions (22) to (2).
From the equation (4), the following equation (29) or (30) is obtained.

[0083]

(Equation 29)

[0084]

[Equation 30]

The relationship between the expressions (29) and (30) can be expressed as (1)
3) When the measured optical path length l _M1 of the first interferometer and the measured optical path length l _{M2 of} the second interferometer in the equation are equal to each other (l _M1 = l _M2)
= 1 _M ). As an example, FIG.
The quantization error e (or resolution) between the first interferometer device shown in FIG. 5A and the second interferometer device shown in FIG. 5B is 0.5 nm, and a = 0.2 m and b = 1.0. m and a =
When 0.5 m and b = 1.0 m, the maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer apparatus is 2
The movement range x of the reflection member for measurement (14, 24) suppressed to e or less will be described.

When a = 0.2 m and b = 1.0 m, the moving range x of the reflecting member for measurement (14, 24) is 0 m to 1.4 m according to the above equation (29), and as a whole the interferometer apparatus is used. Is 1.0n
It can be understood that a wide measurement range can be secured while the accuracy of m (= 2e) is guaranteed. Also, a = 0.5m, b = 1.
When the distance is set to 0 m, the moving range x of the reflection member for measurement (14, 24) is 0.25 m to 1.25 m from the above equation (30), and the accuracy of 1.0 nm (= 2e) is obtained for the entire interferometer apparatus. It can be understood that a relatively wide measurement range can be secured while being guaranteed. (IV) When the maximum value Δx _MAX of the quantization error is suppressed to e or less
In this case, the optimum moving range x (where x ≧ 0) of the reflective member for measurement (14, 24) in this case is expressed by Expressions (22) to (2).
From the expression 4), the following expression (31) is obtained.

[0087]

(Equation 31)

It should be noted that the relationship of this equation (31) can be expressed in correspondence with the above equation (14).
The measurement optical path length l _M1 of the interferometer and the measurement optical path length l _{M2 of} the second interferometer
Are equal to each other (when l _M1 = l _M2 = l _M ). As an example, the quantization error e (or resolution) between the first interferometer device shown in FIG. 5A and the second interferometer device shown in FIG.
= 0.5 m and b = 1.0 m, the moving range x of the reflective member for measurement (14, 24) is from 0.5 m to 1.0 m according to the above equation (31).
It can be understood that a wide measurement range can be secured while the accuracy of 0.5 nm (= e) is guaranteed for the entire interferometer apparatus.

As described above, according to the present invention, it can be understood that stable measurement can be realized with high accuracy while securing a wide measurement range even if the refractive index of gas changes due to environmental changes. Moreover, in the present invention, in principle, FIG.
Since the quantization error e (or resolution) of the first interferometer device shown in FIG. 5 or the second interferometer device shown in FIG. High accuracy measurement can be achieved.

It is needless to say that the coordinate origin according to the present invention can be set anywhere in principle as long as the measuring reflecting member (14, 24) moves.

Hereinafter, the configuration of the interferometer according to the first embodiment of the present invention will be described with reference to FIG. In the present example, a configuration is used in which a combined interferometer shared by the measurement optical paths of the first interferometer and the second interferometer is used, and the shared measurement optical path is reciprocated via one measuring reflecting means (moving mirror 3). It is what it was.

In the first embodiment shown in FIG.
A reflecting means for measurement (moving mirror 3) movably provided;
First reference reflecting means fixed at predetermined positions, respectively
(Sealed tube 3, fixed mirror 6) and second reference reflecting means (fixed mirror)
6) and light source means 1 for supplying a coherent light beam;
Reflection means for measurement based on the light beam from the light source means 1
First (reciprocating along the measurement direction X via the (moving mirror 3))
Measurement optical path OP_MAnd the first reference reflecting means (sealed tube 3 and solid
First reference optical path OP reciprocating via the fixed mirror 6)_R1And form
And the first measurement optical path OP_MAnd the first reference optical path OP_R1Via
1st measurement output X_AProduces the first dried
Interferometer (prism member 2, 1/4 wavelength plate (8a ₁, 8a_Two, 8b₁, 8b
_Two), Half-wave plate 9, deflection prism 4, first detector 7
a) Based on the luminous flux from the means 1, the reflecting means for measurement (transfer)
First reciprocation along the measurement direction X via the moving mirror 3)
Optical path OP_MMeasurement optical path and second reference reflector shared with
Second reference optical path OP reciprocating through a step (fixed mirror 6)_R2When
And a second measurement optical path (first measurement optical path OP_M) And
2 Reference optical path OP_R2Measurement output by each light beam passing through
Force X_BInterferometer (prism member 2, 1/4
Wave plate (8a₁, 8_Two, 8b_Three, 8b_Four), 1/2 wavelength plate 9, deflection pre
Mechanism 4, the second detector 7b) and the second measurement output (X_A,
X_BAnd a calculation processing unit 10 that performs a predetermined calculation based on
Placed and its first reference reflecting means (closed tube 3, fixed mirror 6)
And the second reference reflecting means (fixed mirror 6) along the measuring direction.
Optically separated by a predetermined distance, and each optical path (OP
_M, OP_R1, OP_R2) Are parallel and close to each other
It is.

FIG. 1 shows a main part of the laser interferometer apparatus of this embodiment. In FIG. 1, reference numeral 2 denotes a first right-angle prism 2a.
And an optical member (hereinafter, referred to as a prism member 2) obtained by adhering the second right-angle prism 2b and the second right-angle prism 2b. As shown in FIG. 2A, the prism member 2 is a right-angle prism 2 having a hypotenuse inclined at 45 ° with the length of an orthogonal side being d1.
The oblique side of a is attached to one of two orthogonal sides of a right-angle prism 2b having an oblique side inclined at 45 ° with a length d2 (= 2 · d1). The bonding surface (the surface on one side of the two orthogonal sides of the right-angle prism 2b) is a polarization separation surface (polarization beam splitter surface) S _1.
In is formed, the surface of the other side of the orthogonal two sides of the rectangular prism 2b is formed on the reflective surface R _1. Incidentally, without providing a reflection film on the reflecting surface R _1, the surface R ₁
May be configured to totally reflect light.

Here, in principle, the prism member 2 only needs to have the polarization separation surface S ₁ and the reflection surface R ₁ arranged orthogonal to each other, and may be constituted only by the right-angle prism 2 b. Further, for example, as shown in FIG. 2 (d), by bonding three rectangular prisms 20a~20c constitutes a prism member 20, the bonding surface of the right-angle prism 20a and 20b by the polarization splitting surface S ₁ formed, if the external surface of the rectangular prism 20c and the reflective surface R _1, may use this prism body 20 in place of the prism body 2.

Returning to FIG. 1, first, assuming that the direction in which the light beam is emitted from the laser light source 1 as the light source means for supplying the coherent light beam is the X direction, the prism member 2 will The surface S ₁ is arranged so as to be inclined at 45 ° with respect to the X direction, and the moving mirror 3 as a reflecting means for measurement and the fixed mirror 6 as a reflecting means for reference are opposed to the prism member 2. Each is arranged. The movable mirror 3 is fixed to an object to be measured (not shown), and is configured as a plane mirror that is movable along the X direction. The fixed mirror 6 moves the prism member 2 by a predetermined distance b in the X direction. The movable mirror 3 and the fixed mirror 6 are displaced in a direction perpendicular to the X direction.

In the vicinity of the transmission surface T forming an oblique side which forms an equal angle with respect to two orthogonal sides (S ₁ , R ₁ ) of the right-angle prism 2 b in the prism member 2, six quarter-wave plates ( 8a ₁ , 8a ₂ , 8b _{1 to} 8b ₄ ) are respectively arranged in parallel, and between these two quarter-wave plates (8b ₃ , 8b ₄ ) and the fixed mirror 6, Although described in detail later, a sealed tube 60 to isolate the surrounding only two quarter-wave plate (8b _3, 8b ₄₎ each through a predetermined length of the two reciprocating optical path reflected back and forth at a fixed mirror 6 (Correction member).

The sealed tube 60 is a member composed of a hollow cylinder having at least both ends transparent and having a predetermined length L in the x direction, and the inside thereof is evacuated. Therefore, the optical path length D of the gas portion that is exposed to (air, etc.) of each reciprocating optical path reflected back and forth by two quarter-wave plates (8b _3, 8b ₄₎ each via by fixed mirror 6, When the length along the x direction from the prism member 2 to the fixed mirror is b, and the refractive index of the gas to which the interferometer device shown in FIG. 1 is exposed is n, D = (b−L) n. . Therefore, this sealed pipe 6
The arrangement of 0 substantially equals the arrangement of the fixed mirror 6 on the prism member 2 side along the x direction by the length L of the sealed tube 60. Note that a medium such as gas, liquid, or solid having a predetermined refractive index may be sealed in the sealed tube.

[0098] Now, in the direction in which the laser beam is reflected from the laser light source 1 by the polarization splitting surface S ₁ of the prism member 2, the deflecting prism as a deflecting member for 180 ° deflection of the light emitted from the polarization splitting surface S ₁ (Right angle prism) 4
Is arranged. In this case, assuming that the laser beam is returned to the polarization splitting surface S ₁ again by the two total reflections in the deflecting prism 4, the ridge line between the polarization splitting surface S ₁ and the reflecting surface R ₁ of the prism member 2 is determined. The deflecting prism 4 is positioned so that the plane including the optical path deflected by the prism member 2 is parallel.

A half-wave plate 9 is disposed in the lower optical path between the prism member 2 and the deflecting prism 4, and in the upper optical path between the prism member 2 and the deflecting prism 4. Is provided with an optical member having a shape similar to that of the prism member 2 (hereinafter, referred to as a prism member 5). The prism member 5 is formed by bonding two right-angle prisms (5a, 5b), and the bonding surface thereof (the surface on one side of two orthogonal sides of the right-angle prism 5b) is divided by light. Surface (beam splitter surface)
Formed by S _2, a surface of the other side of the orthogonal two sides of the rectangular prism 5b are formed on the reflecting surface R _2.

After the laser beam from the deflecting prism 4 is split and deflected by the prism member 5 (reflected by the light splitting surface S ₂ and then reflected by the reflecting surface R ₂ ), the polarization separating surface of the prism member 2 the direction in which it is reflected in P _1, a first receiver 7a of the first detector and is arranged, after the laser beam from the deflection prism 4 passes through the light splitting surface S ₂ of the prism member 5, a prism the direction in which it is reflected by the polarization splitting surface S ₁ of the member 2 a as a second detector 1
Receiver 7b is disposed.

As shown in FIG. 1, the first and second receivers (7a, 7b) are electrically connected to an operation unit 10 as operation means, and output signals from the respective receivers (7a, 7b). On the basis of this, for example, the calculation as in the above equation (3) is performed in the calculation processing unit 10, and the calculation result is output to a display unit (not shown). Instead of the half-wave plate 9, a single quarter-wave plate is arranged so as to cover the entirety of the entrance surface and the exit surface of the deflecting prism 4 or the entire surface of the prism member 2 on the deflecting prism 4 side. In this case, a 波長 wavelength plate may be directly bonded to the entrance surface and exit surface of the deflection prism 4 or the surface of the prism member 2 on the deflection prism 4 side. Further, a quarter-wave plate is disposed between the optical path between the prism member 2 and the deflecting prism 4 or between the optical path between the deflecting prism 4 and the prism member 5, and is formed between the prism member 5 and the prism member 2. A configuration in which a 波長 wavelength plate is disposed in the two optical paths may be adopted.

Next, the operation of this embodiment will be described. First,
The laser light source 1 serving as a light source unit that supplies a coherent light beam includes a beam having a first frequency f ₁ (hereinafter, referred to as a first beam) and a beam having a second frequency f ₂ (hereinafter, referred to as a second beam). supplied, the first and second beams, with respect to the polarization splitting surface S ₁ of the prism member 2 at an incident angle of 45 °.

Here, one of the two beams supplied from the laser light source 1 is a linearly polarized light (hereinafter, referred to as P-polarized light) vibrating in the plane of incidence of the polarization splitting surface S _1. .), and the other of the second beam is a linearly polarized light oscillating the polarization splitting surface S ₁ of the incident surface in a plane perpendicular (hereinafter, referred to as S-polarized light.). First, laser light source 1
Referring to the first beam of the P polarized light supplied from the first beam of the P polarized light, the polarization splitting surface S ₁ of the prism member 2 as it passes to the circularly polarized light through a quarter-wave plate 8a ₁ after being converted, is reflected by the movable mirror 3, it is converted into S-polarized light passes through the quarter-wave plate 8a ₁ again.
Then, the first beam of the S-polarized light is reflected by the polarization separation surface S ₁ of the prism member 2, and is reflected by the reflection surface R _{1 of the} prism member 2.
At 90 °. Thereafter, S first beam of polarized light is 1/4 is converted into circularly polarized light passes through the wave plate 8a _2, the moving mirror 3 is again quarter-wave plate 8a ₂ reflected by
Head to. The first beam having passed through the quarter-wave plate 8a ₂ again, after being converted into P-polarized light, passes through the polarization splitting surface S ₁ and reflected by the reflection surface R ₁ again. The first beam of P-polarized light that has passed through the polarization separation plane S ₁ passes through the half-wave plate 9, and the polarization plane is rotated by 90 ° to be converted from P-polarized light to S-polarized light. The first beam converted into S-polarized light by the half-wave plate 9 is reflected by
° is reflected and deflected, and is ₂ at the light dividing surface S ₂ of the prism member 5.
Divided.

First, the first beam of one S-polarized light reflected on the light splitting surface S ₂ of the prism member 5 is reflected and deflected by 90 ° on the reflecting surface R ₂ of the prism member 5, and the polarized light separating surface S After reflecting ₁ , the light is received by the first receiver 7a. On the other hand, the first beam of the other S-polarized light passing through the beam splitting surface S ₂ of the prism member 5 is reflected by the polarization splitting surface S ₁ of the prism member 2, and is received by the second receiver 7b.

Next, the second beam of S-polarized light supplied from the laser light source 1 will be described.
The beam is reflected by the polarization splitting surface S ₁ of the prism member 2 and travels to the half-wave plate 9. The second beam that has passed through the half-wave plate 9 has its polarization plane rotated by 90 ° and is converted from S-polarized light to P-polarized light.
° is reflected and deflected, and is ₂ at the light dividing surface S ₂ of the prism member 5.
Divided.

First, the second beam of one P-polarized light reflected by the light splitting surface S ₂ of the prism member 5 is reflected and deflected by 90 ° on the reflecting surface R ₂ of the prism member 5, and the polarized light separating surface S Pass through _{1 as} is. This polarization separation surface S ₁
Second beam which has passed through the after being reflected 90 ° deflected by the reflecting surface R _1, is converted into circularly polarized light passes through the 1/4-wave plate 8b _1. Then, the second beam converted to circularly polarized light is x
After passing through a sealed tube 60 having a predetermined length L in the direction (measurement direction) and being reflected by the fixed mirror 6, the light passes through the sealed tube 60 again, passes through the 波長 wavelength plate 8 b _1, and Converted to polarized light. The second beam converted into the S-polarized light is reflected by the reflection surface R ₁ of the prism member 2, reflected by the polarization separation surface S ₁ of the prism member 2, and travels to the _１ ／ wavelength plate 8 b ₂ . The second beam having passed through the １ ／ wavelength plate 8b ₂ is converted into circularly polarized light, passes through the closed tube 60, is reflected by the fixed mirror 6, and travels toward the closed tube 60 again. Second beam passing through the sealed tube 60 is converted through the 1/4-wave plate 8b ₂ to P-polarized light, is received by the first receiver 7a is transmitted through the polarization splitting surface S ₁ of the prism member 2 You.

On the other hand, the other P-polarized second beam passing through the light splitting surface S ₂ of the prism member 5 passes through the polarization separating surface S ₁ of the prism member 2 as it is, and is reflected by the reflecting surface R ₁ at 90 °.
It is reflected and deflected, toward the 1/4-wave plate 8b _3. This one
/ 4 second beam passing through the wave plate 8b ₃ is converted into circularly polarized light, is reflected through a quarter-wave plate 8b ₃ again by the fixed mirror 6, it is converted into S-polarized light. The second beam converted into the S-polarized light is reflected by the reflecting surface R ₁ of the prism member 2 and is reflected by the polarized light separating surface S ₁ to be a quarter-wave plate 8 b ₄
Head for. After the second beam passing through the quarter-wave plate 8b ₄ is converted into circularly polarized light, passes through the quarter-wave plate 8b ₄ again is reflected by the fixed mirror 6, is converted into P-polarized light. Second beam converted into P-polarized light passes through the quarter-wave plate 8b ₄ is received by the second receiver 7b and passes through the polarization splitting surface S _1.

Now, in the first receiver 7a, the
Via gas such as air between the rhythm member 2 and the moving mirror 3
Length x (from the surface T of the prism member 2 to the movable mirror 3)
Measurement optical path OP of distance along X direction)_MThe first to progress
Beam and this measurement optical path OP _MClose to the prism member
In the gas such as air between the fixed mirror 6 and the fixed mirror 6 and the sealed tube 60
Length b (from surface T of prism member 2 to fixed mirror 6)
(The distance along the X direction at the point) in the first reference optical path OP_R1Progress
The direction of polarization is changed by the internal analyzer
The light is aligned and enters the internal light receiving element.

Here, since the sealed tube 60 is disposed in the first reference optical path OP _R1 , assuming that the length of the sealed tube 60 in the X direction is L, as described above, the refractive index of gas such as air is as described above. The change is equivalent to disposing the fixed mirror 6 toward the prism member 2 by the length L of the sealed tube 60. Accordingly, the light-receiving element of the first receiver 10a has a length x (from the surface T of the prism member 2 to the moving mirror 3) substantially passing through a gas such as air between the prism member 2 and the moving mirror 3. a first beam propagating through the measurement optical path OP _M distance) in the X direction until, via a gas such as air between the fixed mirror 6 and the prism member 2 in close proximity to the measurement optical path OP _M The second beam traveling on the first reference optical path OP _R1 having the length a (= b−L) is incident.

Therefore, the light receiving element of the first receiver 7a
Are in a state where the movable mirror 3 is stopped with respect to the fixed mirror 6.
Outputs a beat signal having a frequency of (f1-f2),
When the movable mirror 3 moves in the X direction, the frequency-modulated beam
Signal is output. Therefore, this change in frequency is integrated
By doing so, the relative movement of the movable mirror 3 and the fixed mirror 6 in the X direction
It is possible to detect a typical moving amount. Therefore, such as air
Measurement optical path OP passing through gas_MLength (or interference
Measurement optical path OP from the prism member 2 of the meter to the movable mirror 6_M
X, the first optical path passing through a gas such as air.
Reference optical path OP_R1Length (or prism member of the interferometer)
First reference optical path OP from 2 to fixed mirror 6 _R1Optical path
A), initial air at the start of measurement (at reset), etc.
Is the refractive index of a gas such as n, and the change in the refractive index of a gas such as air is Δ
Assuming that n, in the first receiver 7a, nx + (x−a)
Signal X corresponding to Δn_AIs output to the arithmetic processing unit 10
You.

On the other hand, in the second receiver 7b, the length x (X from the surface T of the prism member 2 to the movable mirror 3) passing through a gas such as air between the prism member 2 and the movable mirror 3 is set.
A first beam propagating through the measurement optical path OP _M of along the direction distance), the prism member 2 in close proximity to the measurement optical path OP _M
Length b through a gas such as air between the mirror 6 and the fixed mirror 6
A second beam (a distance along the X direction from the surface T of the prism member 2 to the fixed mirror 6 in the X direction) traveling on the second reference optical path OP _R2 has its polarization direction aligned by the internal analyzer and is transmitted to the internal light receiving element. Incident.

Here, from the light receiving element of the second receiver 7b, as in the case of the first receiver 7a, when the movable mirror 3 is stopped with respect to the fixed mirror 6, the frequency is (f1-f2).
When the movable mirror 3 moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, by integrating the change of the frequency, the movable mirror 3
And the relative movement amount of the fixed mirror 6 in the X direction can be detected. Thus, the x (optical path length of the measurement optical path OP _M from the prism member 2 or the interferometer to the movable mirror 6) the length of the measurement optical path OP _M passing through a gas such as air, through the gas such as air The length of the second reference optical path OP _{R2 that} passes (or the second length from the prism member 2 of the interferometer to the fixed mirror 6)
Assuming that b is the optical path length of the reference optical path OP _R2 ), n is the initial refractive index of gas such as air at the start of measurement (at the time of resetting), and Δn is the change in the refractive index of gas such as air. in receiver 7b, signal X _B corresponding to nx + (x-b) Δn is outputted to the arithmetic processing unit 10.

A predetermined arithmetic expression is stored in the arithmetic processing unit 10, for example, an arithmetic expression as described in the above (3). Therefore, the arithmetic processing unit 10
Output signals (X _A , X _B ) from the first and second receivers (7a, 7b) and a refractive index detector (not shown) for detecting the initial refractive index n of the gas at the start of measurement. Is performed based on the output n of
The calculation result in which the measurement error caused by the change in the refractive index of the gas caused by the fluctuation of the gas or the like is output via a display unit (not shown).

Then, the first movable mirror and the second movable mirror (3) are integrally moved so as to satisfy the expressions (11) to (14) or the expressions (25) to (31). By doing so, the quantization error e added to the output of the interferometer device can be suppressed to 4 times to 1 time, respectively. As described above, according to this embodiment, since the measurement optical path and each reference optical path are configured to be close to each other by the interferometer, the measurement error due to the change in the refractive index of the gas generated in the measurement optical path is corrected, and the accuracy is improved. The moving amount and position of the movable mirror 3 can be detected well.

In addition, according to this embodiment, the movable mirror is moved along the space formed between the two fixed mirrors so that the movable mirror is internally divided with respect to the distance between the two fixed mirrors. Because they can be moved, very high precision measurements are guaranteed. By the way, in this example, the interferometer device is configured such that the measurement optical path length passing through the inside of the prism member 2 and each reference optical path length are both equal, and high-precision measurement is performed even when the prism member 2 changes in temperature. Can be done.

In explaining this in detail,
First, measurement is performed on each of the first receivers 7a.
A first beam for reference and a second beam for reference are prism members
2 (a) and FIG.
This will be described with reference to FIG. Under the prism member 2
The first beam for measurement passing through the section is a solid line in FIG.
As shown in the figure, the optical path A in the right-angle prism 2a₁₁And right angle
Light path B in rhythm 2b ₁₁And the prism member 2
The first beam for measurement passing through the upper part in FIG.
As shown by the solid line, the optical path A only in the right-angle prism 2a₁₂
Pass through.

On the other hand, the second beam for reference passing through the lower part in the prism member 2 is represented by a dotted line in FIG.
The second beam for measurement, which passes through the optical path A ₂₁ only in the right-angle prism 2a and passes through the upper part in the prism member 2, is shown in FIG.
As indicated by the dotted line in (b), passes through the optical path A ₂₂ within the rectangular prism 2a, passes through the optical path B ₂₂ is in the right-angle prism 2b.

Accordingly, the optical path lengths of the first beam for measurement and the second beam for reference passing through the prism member 2 are A ₁₁ + B ₁₁ + A ₁₂ , A ₂₁ + A ₂₂ + B ₂₂ , respectively, as shown in FIG. As is clear from a) and FIG. 2B, A ₁₁ = A ₁₂
= A ₂₁ = A ₂₂ = d ₁ and B ₁₁ = B ₂₂ = d ₂ , the first beam for measurement and the second beam for reference passing through the prism member 2 The optical path lengths are equal.

Next, the light enters the second receiver 7b.
The first beam for measurement and the second beam for reference
FIG. 2A shows an optical path passing through the inside of the vibration member 2.
This will be described with reference to FIG. Prism member 2
The first beam for measurement passing through the lower part in FIG.
As shown by the solid line in FIG.₁₁When
Optical path B in right angle prism 2b ₁₁And through the prism
The first beam for measurement passing through the upper part in the member 2 is shown in FIG.
As shown by the solid line in (c), light only in the right-angle prism 2a
Road A₁₂Pass through.

On the other hand, the second beam for reference passing through the lower part in the prism member 2 is represented by a dotted line in FIG.
The second beam for measurement, which passes through the optical path A ₂₁ only in the right-angle prism 2a and passes through the upper part in the prism member 2, is shown in FIG.
As indicated by the dotted line in (c), passes through the optical path A ₃₂ within the rectangular prism 2a, passes through the optical path B ₃₁ is in the right-angle prism 2b.

Therefore, the optical path lengths of the first beam for measurement and the second beam for reference passing through the prism member 2 are A ₁₁ + B ₁₁ + A ₁₂ , A ₂₁ + A ₃₂ + B _{32 respectively} , as shown in FIG. As is clear from a) and FIG. 2B, A ₁₁ = A ₁₂
= A ₂₁ = A ₃₂ = d ₁ and B ₁₁ = B ₃₂ = d ₂ , so that the first beam for measurement and the second beam for reference passing through the prism member 2 The optical path lengths are equal.

Therefore, even if a temperature difference occurs between the right-angle prism 2a and the right-angle prism 2b, the difference in the optical path length between the first beam and the second beam does not change.
The amount of movement in the direction can always be measured with high accuracy. In the first embodiment shown in FIG. 1, 1/4-wave plate _{(8a 1, 8a 2, 8b} 1 ~8b 4) The case has been described composed of six, one integrated these Or a single quarter-wave plate may be joined to the surface T of the prism member 2 to be integrally formed.

In the first embodiment shown in FIG. 1, a laser light source 1 and two receivers (7a, 7b) are arranged on a first surface side of a rectangular prism 2a having two surfaces orthogonal to each other. The half-wave plate 9, the prism member 5, and the right-angle prism 4 are arranged on the second surface side. However, the right angle prism 2 is not limited to this arrangement.
The laser light source 1 and two receivers (7
a, 7b) and a half-wave plate 9, a prism member 5, and a right-angle prism 4 on the first surface side of the right-angle prism 2a.
And may be arranged.

Next, an interferometer according to a second embodiment of the present invention will be described with reference to FIG. The second embodiment shown in FIG. 3 is a modification of the first embodiment shown in FIG.
In FIG. 3, members having the same functions as those in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 3, this embodiment is largely different from the first embodiment in that the prism member 5 disposed between the polarizing prism 4 and the prism member 2 shown in the first embodiment of FIG. The point is that the two fixed mirrors (6a, 6b) for reference are arranged between the laser light source 1 and the prism member 2 and at different positions along the X direction via the rod-shaped member 61. Furthermore, this embodiment is different from the first embodiment in that in the first embodiment, two quarter-wave plates (8a ₁ , 8a ₂ ) are arranged between the prism member 2 and the movable mirror 4. In contrast, one half-wave plate 9 is arranged between the prism member 2 and the deflecting prism 4, whereas in the second embodiment shown in FIG. one of the quarter wave plate (8a ₁ ~8a ₄₎ arranged, two quarter-wave plate between the prism member 2 and the deflection prism 4 (9a, 9
b) is arranged.

The rod-shaped member 61 is a member having a predetermined length and an extremely small coefficient of thermal expansion. The configuration of the second embodiment shown in FIG. 3 will be briefly described. In the present embodiment, a movable mirror 3 movably provided in a measurement direction X and a first fixed mirror 6a fixed at a predetermined position are provided. A second fixed mirror 6b, a light source means (laser light source 1, prism member 5) for supplying a coherent light beam, and a measuring direction through the movable mirror 3 based on the light beam from the light source means (1, 5). A first measurement optical path OP _M1 reciprocating along X and a first reference optical path OP _R1 reciprocating via the first fixed mirror 6a are formed, and the first measurement optical path OP _M1 and the first reference optical path OP _R1 pass through the first measurement optical path OP _M1 . first interferometer to generate a first measurement output X _a by each light beam (prism member 2,1 / 4-wave plate _{(8a 1, 8a 2, 8b} 1, 8b
₂ ), a 1/2 wavelength deflecting prism 4, a first detector 7a),
A second measurement optical path OP _M2 that reciprocates along the measurement direction X via the movable mirror 3 based on the light flux from the light source means (1, 5).
Reference optical path OP _R2 reciprocating via the second fixed mirror 6b and
And the second measurement optical path OP _M2 and the second reference optical path OP
By each beam via the _R2 second interferometer to generate a second measurement output X _B (prism members 2,1 / 4 wavelength plate (8a _3, 8a
_{4, 8b 3, 8b 4)} , 1 / 9b, deflecting prism 4, the second detector 7
b) and a processing unit 10 for performing a predetermined calculation based on the first and second measurement outputs (X _A , X _B ) are arranged, and the first fixed mirror 6a and the second fixed mirror 6b are measured. The optical paths (OP _M1 , OP _M2 ,
OP _R1 , OP _R2 ) in parallel.

Next, the routing optical path of this embodiment will be described with reference to FIG. First, the laser light source 1 supplies a beam having a first frequency f ₁ (hereinafter, referred to as a first beam) and a beam having a second frequency f ₂ (hereinafter, referred to as a second beam). 2 beam to the light splitting surface S ₂ of the prism member 5 at an incident angle of 45 °. here,
One of the first beam of the two beams supplied from the laser light source 1 is linearly polarized light that vibrates the light splitting surface S ₁ of the incident plane light is (hereinafter, referred to as P-polarized light.), While the second beam of linearly polarized light which oscillates the light splitting surface S ₁ of the incident surface in a plane perpendicular (hereinafter, referred to as S-polarized light.) it is.

The first and second beams are beams from a light source.
Member 5 functioning as a light splitting means for splitting the light into two
Light splitting surface (semi-transmissive surface) S_TwoDivided into two parts by
This light splitting surface S_TwoFirst and second beams reflecting light
Is the reflection surface R of the prism member 5 _TwoThrough the prism section
The light splitting surface S_TwoThe first and second passing through
The two beams enter the prism member 2 as they are.

First, the first and second beams traveling toward the prism member 2 via the light dividing surface S ₂ and the reflecting surface R ₂ of the prism member 5 will be described. First and second beam through the beam splitting surface S ₂ and the reflecting surface R ₂ of the prism member 5, with respect to the polarization splitting surface S ₁ of the prism member 2 at an incident angle of 45 °. Here, the first beam is a P-polarized light to linearly polarize the incident plane with respect to the polarization splitting surface S _1, the second beam is linearly polarized incident surface and a plane perpendicular with respect to the polarization splitting surface S ₁ since the light of S-polarized light, the first beam of the P polarized light is transmitted through the polarization splitting surface S _1, a second beam of S-polarized light is reflected by the polarization separation surface S _1.

First, the polarization separation surface S₁Of P-polarized light transmitted through
The first beam is a quarter-wave plate 8a₁Into circularly polarized light
After being changed, it is reflected by the moving mirror 3 and is again a quarter-wave plate.
8a ₁And is converted into S-polarized light. And this S
The first beam of polarized light is the polarized light separating surface S of the prism member 2.₁
And the reflection surface R of the prism member 2₁90 ° reflection polarization
Turned Thereafter, the first beam of S-polarized light is １ ／ wavelength
Board 8a_Two, And is converted into circularly polarized light.
反射 wavelength plate 8a_TwoHead to. Soshi
This quarter-wave plate 8a_TwoThe first beam that has passed through again
Is converted into P-polarized light, and then the reflecting surface R₁To reflect
Polarization separation surface S₁Pass through. This polarization separation surface S₁Go through
The first P-polarized beam passes through the half-wave plate 9a.
And the plane of polarization is rotated 90 ° to convert P-polarized light to S-polarized light.
Is done. Converted into S-polarized light by the half-wave plate 9a
The first beam is reflected and deflected by 180 ° by the deflecting prism 4.
After the polarization separation surface S₁Reflected by the first receiver
The light is received at 7a.

On the other hand, the second beam of S-polarized light reflected on the polarization splitting surface S ₁ of the prism member 2 via the light splitting surface S ₂ and the reflecting surface R ₂ of the prism member 5 transmits through the half-wave plate 9 a. Then, after the polarization plane is rotated by 90 ° to be converted from S-polarized light to P-polarized light, the light is reflected and deflected by 180 ° by the deflecting prism 4 and passes through the polarization separating surface S ₁ of the prism member 5.
Then, the second beam of the P-polarized light that has passed through the polarization separation surface S ₁ is reflected and deflected by 90 ° at the reflection surface R ₁ , passes through the 波長 wavelength plate 8 b _1, and is converted into circularly polarized light. Thereafter, the second beam converted into the circularly polarized light is reflected by the first fixed mirror 6a fixed at a predetermined distance a along the X direction with respect to the surface T of the prism member, and is again １ ／. passes through the wave plate 8b _1, is converted into S-polarized light. The second beam converted to the S-polarized light is reflected by the reflecting surface R ₁ of the prism member 2, and is reflected by the polarization separating surface S ₁ of the prism member 2 to be 1/1
4 towards the wave plate 8b _2. The second beam that has passed through the 波長 wavelength plate 8b ₂ is converted into circularly polarized light, reflected by the first fixed mirror 6a, passes through the 波長 wavelength plate 8b _2, and is converted into P-polarized light. . Then, the second beam converted into P-polarized light passes through the polarization splitting surface S ₁ of the prism member 2 and
Is received by the receiver 7a.

[0131] Next, a description will be given of the first and second beams from the laser light source 1 is transmitted through the beam splitting surface S ₂ of the prism member 5. The through beam splitting surface S ₂ of the prism member 5 1
And the second beam to the polarization splitting surface S ₁ of the prism member 2 at an incident angle of 45 °. Here, the first beam is linearly polarized in the plane of incidence with respect to the polarization separation plane S ₁ .
Since the second beam is S-polarized light that linearly polarizes a plane perpendicular to the plane of incidence with respect to the polarization separation surface S ₁ , the first beam of P polarization remains on the polarization separation surface S _{1 as it} is. The transmitted, S-polarized second beam reflects off the polarization splitting surface S ₁ .

First, the polarization separation surface S₁Of P-polarized light transmitted through
The first beam is a quarter-wave plate 8a_ThreeInto circularly polarized light
After being changed, it is reflected by the moving mirror 3 and is again a quarter-wave plate.
8a _ThreeAnd is converted into S-polarized light. And this S
The first beam of polarized light is the polarized light separating surface S of the prism member 2.₁
And the reflection surface R of the prism member 2₁90 ° reflection polarization
Turned Thereafter, the first beam of S-polarized light is １ ／ wavelength
Board 8a_Four, And is converted into circularly polarized light.
反射 wavelength plate 8a_FourHead to. Soshi
This quarter-wave plate 8a_FourThe first beam that has passed through again
Is converted into P-polarized light, and then the reflecting surface R₁To reflect
Polarization separation surface S₁Pass through. This polarization separation surface S₁Go through
The first P-polarized beam passes through the half-wave plate 9b.
And the plane of polarization is rotated 90 ° to convert P-polarized light to S-polarized light.
Is done. Converted into S-polarized light by the half-wave plate 9b
The first beam is reflected and deflected by 180 ° by the deflecting prism 4.
After the polarization separation surface S₁Reflected by the second receiver
The light is received at 7b.

On the other hand, the second beam of S-polarized light transmitted through the light splitting surface S ₂ of the prism member 5 and reflected by the polarization splitting surface S ₁ of the prism member 2 is transmitted through the half-wave plate 9 b and is polarized. After the surface is rotated by 90 ° and converted from S-polarized light to P-polarized light, the light is reflected and deflected by 180 ° by the deflecting prism 4 and passes through the polarization splitting surface S ₁ of the prism member 5. Then, the second beam of the P-polarized light that has passed through the polarization separation surface S ₁ is reflected and deflected by 90 ° at the reflection surface R ₁ , passes through the 波長 wavelength plate 8 b _3, and is converted into circularly polarized light. After that, the second beam converted into the circularly polarized light is reflected by the second fixed mirror 6b fixed at a predetermined distance b along the X direction with respect to the surface T of the prism member, and is again 1/4. It passes through the wavelength plate 8b _3,
It is converted to S-polarized light. The second beam converted to the S-polarized light is reflected by the reflection surface R ₁ of the prism member 2, reflected by the polarization separation surface S ₁ of the prism member 2, and
b toward _4. Second passing through the quarter-wave plate 8b ₄
The beam, after being converted into circularly polarized light, is reflected by the second fixed mirror 6b passes through the quarter-wave plate 8b _4, is converted into P-polarized light. The second beam converted into P-polarized light is received by the second receiver 7a is transmitted through the polarization splitting surface S ₁ of the prism member 2.

As described above, according to the second embodiment of the present invention,
In the first receiver 7a, the interferometer has a prism
The length passing through a gas such as air between the member 2 and the movable mirror 3
X (X direction from surface T of prism member 2 to movable mirror 3)
1st measurement optical path OP_M11st progressing
And the first measurement optical path OP_M1Close to the prism
It passes through a gas such as air between the material 2 and the first fixed mirror 6a.
Length a (from the surface T of the prism member 2 to the first fixed mirror 6a).
(The distance along the X direction at the point) in the first reference optical path OP _R1Progress
The direction of polarization is changed by the internal analyzer
The light is aligned and enters the internal light receiving element.

Therefore, a beat signal having a frequency of (f1-f2) is output from the light receiving element of the first receiver 7a while the movable mirror 3 is stopped with respect to the first fixed mirror 6, and When the mirror 3 moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, by integrating the change in the frequency, the relative movement amount of the movable mirror 3 and the fixed mirror 6 in the X direction can be detected. Therefore, the length of the first measurement optical path OP _M1 passing through a gas such as air (or the optical path length of the first measurement optical path OP _M1 from the prism member 2 of the first interferometer to the movable mirror 6) is x, The length of the first reference optical path OP _R1 passing through a gas such as air (or the first reference optical path O from the prism member 2 of the interferometer to the fixed mirror 6)
Optical path length) of a of P _R1, measured at the start (reset)
Assuming that the initial refractive index of a gas such as air such as n is n and the change in the refractive index of a gas such as air is Δn, the first receiver 7a
_A signal XA corresponding to nx + (x−a) Δn is output to the arithmetic processing unit 10.

On the other hand, in the second receiver 7b, the length x (X from the surface T of the prism member 2 to the movable mirror 3) passing through a gas such as air between the prism member 2 and the movable mirror 3 is used.
(A distance along the direction) along the second measurement optical path OP _M2 , and a gas such as air between the prism member 2 and the second fixed mirror 6 b adjacent to the second measurement optical path OP _M1. B (from the surface T of the prism member 2 to the second fixed mirror 6
The second beam traveling along the second reference optical path OP _{R2 (} a distance along the X direction to b) is incident on the internal light receiving element after the polarization direction is aligned by the internal analyzer.

Here, from the light receiving element of the second receiver 7b, as in the case of the first receiver 7a, when the movable mirror 3 is stopped with respect to the fixed mirror 6, the frequency is (f1-f2).
When the movable mirror 3 moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, by integrating the change of the frequency, the movable mirror 3
And the relative movement amount of the fixed mirror 6 in the X direction can be detected. Therefore, the length of the second measurement optical path OP _M2 passing through a gas such as air (or the optical path length of the second measurement optical path OP _M2 from the prism member 2 of the second interferometer to the movable mirror 6) is x, Second reference optical path OP passing through a gas such as air
The length of _R2 (or the optical path length of the second reference optical path OP _R2 from the prism member 2 of the interferometer to the fixed mirror 6) is b, and the refraction of gas such as air at the start of measurement (at the time of reset). Assuming that the refractive index is n and the change in the refractive index of a gas such as air is Δn,
In the second receiver 7b, signal X _B corresponding to nx + (x-b) Δn is outputted to the arithmetic processing unit 10.

As in the first embodiment, the arithmetic processing unit 10 stores, for example, an arithmetic expression as shown in the above equation (3). The arithmetic processing unit 10 stores the first and second arithmetic expressions. Output signals (X _A ,
X _B ) and the output n from a refractive index detector (not shown) for detecting the initial refractive index n of the gas at the start of the measurement, execute the calculation as shown in the above-mentioned equation (3). The calculation result in which the measurement error caused by the change in the refractive index of the gas caused by the fluctuation of the gas or the like is output via a display unit (not shown).

Then, the first movable mirror and the second movable mirror (3) are integrally moved so as to satisfy the expressions (11) to (14) or the expressions (25) to (31). By doing so, the quantization error e added to the output of the interferometer device can be suppressed to 4 times to 1 time, respectively. Moreover, in the second embodiment, similarly to the first embodiment, the movable mirror is internally divided with respect to the distance between the two fixed mirrors along the space formed between the two fixed mirrors. Since the movable mirror can be moved by means of this, extremely high-precision measurement is guaranteed.

Although not described in detail, also in the second embodiment, the interferometer device is configured such that the length of the measurement optical path passing through the inside of the prism member 2 and each of the reference optical paths are equal. Therefore, even if a temperature difference occurs inside the prism member 2, highly accurate measurement can be realized. In the second embodiment shown in FIG. 3, 1/4-wave plate (8a ₁ ~8a _4, 8b ₁
8b ₄ ) is constituted by eight sheets, but this may be constituted by a single quarter-wave plate, and the single quarter-wave plate may be formed on the surface of a prism member. It may be integrally formed by joining with T.

The two sheets of the second embodiment shown in FIG.
Instead of a half-wave plate (9a, 9b), a polarizing prism 4
One quarter-wave plate may be provided so as to cover four optical paths formed between the prism member 2 and.
A quarter-wave plate that covers the entire entrance and exit surfaces of the polarizing prism 4 may be integrally formed with the polarizing prism 4, and further covers the entire surface of the prism member 2 on the polarizing prism 4 side. Such a 波長 wavelength plate may be integrally formed with the prism member 2.

In the first embodiment shown in FIG. 3, a laser light source 1, a prism member 5, and two receivers (7a, 7b) are provided on a first surface side of a right-angle prism 2a having two surfaces orthogonal to each other. And 2 are arranged on the second surface side.
The two half-wave plates (9a, 9b) and the right-angle prism 4 are arranged respectively. However, the laser light source 1, the prism member 5, and the two receivers (7
a, 7b), and two half-wave plates (9a, 9b) and the right-angle prism 4 may be arranged on the first surface side of the right-angle prism 2a.

In the second embodiment shown in FIG. 3, the light source means for supplying a coherent light beam is composed of the laser light source 1 and the prism member 5 functioning as a light splitting means. Using as a light source means,
The light beam from one laser light source first interferometer (prism members 2,1 / 4-wave plate _{(8a 1, 8a 2, 8b} 1, 8b 2), elongated plate 9a,
The light is guided to the deflecting prism 4 and the first detector 7a, and the light beam from the other laser light source is transmitted to the second interferometer (the prism members 2, 1).
A configuration may also be adopted in which the light is guided to a 波長 wavelength plate (8a ₃ , 8a ₄ , 8b ₃ , 8b ₄ two-wave plate 9b, deflection prism 4, second detector 7b). In this case, when there is a change in the optical characteristics (wavelength fluctuation or the like) of the two light sources (laser light sources), it is desirable to provide a correction means for correcting the change in the optical characteristics.

In each of the above embodiments, the present invention is applied to a heterodyne type laser interferometer.
The present invention can be similarly applied to a homodyne type interferometer. Further, a corner cube or the like may be used instead of the right-angle prism 17. By the way, in each of the embodiments described above, an example is shown in which each measurement optical path and each reference optical path formed by the first and second interferometers are configured to be close to and parallel to each other, but the present invention is not limited to this. Not something.

Therefore, a third embodiment as another modification of the first embodiment shown in FIG. 1 will be described with reference to FIG. In FIG. 3, members having the same functions as those in FIG. 1 are denoted by the same reference numerals. In the present embodiment, the prism member 2 of the first embodiment shown in FIG. 1 is replaced with the prism member 62 on the lower side forming the measurement optical path OP _M and the upper side forming the two reference optical paths (OP _R1 , OP _R2 ). The prism member 63 of the upper portion is disposed in a state of being rotated by 90 degrees with respect to the prism member 62 of the lower portion, and two reference optical paths (with respect to the measurement optical path OP _M ). O
P _R1 , OP _R2 ) are non-parallel, that is, vertical.

Here, the lower prism member 62 is
Is composed of lamination of the rectangular prism 62a and the right-angle prism 62a, the lamination surface is formed on the polarization splitting surface (a polarization beam splitter surface) S _3. The prism member 63 of the upper portion is constituted by a lamination of a rectangular prism 63a and the rectangular prism 63 b, the lamination surface is formed on the polarization splitting surface (a polarization beam splitter surface) S _4.

Since the configuration is exactly the same as that of the first embodiment shown in FIG. 1 except for the configuration of the prism members 62 and 63, a detailed description including the operation of the apparatus will be omitted. As described above, according to the example shown in FIG. 7 as well, it is possible to correct the measurement error due to the change in the refractive index of the gas that occurs in the measurement optical path, and accurately detect the movement amount and position of the movable mirror 3. Moreover, also in this example, the movable mirror can be moved along the space formed between the two fixed mirrors so that the movable mirror is internally divided with respect to the distance between the two fixed mirrors. As a result, extremely high precision measurement is guaranteed.

In the second embodiment shown in FIG. 3, it is also possible to make the measurement optical path and the reference optical path orthogonal as shown in FIG. For example, instead of the polarizing prism 2 of FIG. 3, two polarizing prisms 6 shown in FIG.
The use of 2, 63 makes it possible to make the measurement optical path and the reference optical path orthogonal. Further, an optical path deflecting member for bending the optical path is appropriately arranged on at least one of the optical path of the measurement optical path and the reference optical path of each interferometer in each of the embodiments described above, and each optical path is formed so that the entire apparatus becomes compact. It is also possible to route.

In each of the above embodiments, the first and second
FIG. 4 shows an example in which the measurement optical path lengths of the interferometers are equal to each other.
It goes without saying that the measurement optical path lengths of the first and second interferometers may be made different from each other as described in the principle of the above.
As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0150]

As described above, according to the present invention, even if the fluctuation of gas such as air occurs, the measurement error is extremely small,
Moreover, a high-performance interferometer device that can realize high-precision measurement in principle can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of an interferometer apparatus of the present invention.

FIG. 2A is a plan view showing a measurement optical path and first and second reference optical paths passing below a prism member 2 of the first embodiment, and FIG. 2B is a plan view showing the prism member 2 of the first embodiment. FIG. 3C is a plan view showing a state of a measurement optical path and a first reference optical path passing through the upper part of FIG. 3, and FIG. 3C is a plan view showing a state of a measurement optical path and a second reference optical path passing above the prism member 2 of the first embodiment;
(D) is a plan view showing another example of the prism member 2 of the first embodiment.

FIG. 3 is a perspective view showing a second embodiment of the interferometer apparatus of the present invention.

FIG. 4 is a configuration diagram showing the principle of the interferometer device of the present invention.

FIG. 5 is a configuration diagram showing the principle of the interferometer apparatus of the present invention from a different viewpoint from FIG.

FIG. 6 is a configuration diagram showing a conventional interferometer device.

FIG. 7 is a perspective view showing a modification of the first embodiment of the interferometer apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Prism member 3 ... Moving mirror 4 ... Deflection prism (right angle prism) 5 ... Prism member ( light splitting member) 6,6a, 6b ······ fixed mirror 7a · · · · · · first receiver 7b · · · · · · second receiver _{8a 1 ~8a 4, 8b 1 ~8a} 4 ·· ... １ ／ wavelength plate 9, 9a, 9b ｂ １ ／ wavelength plate 10 演算 arithmetic processing unit 60 密閉 sealed tube 61 ・.Bar-shaped members

Claims (2)

[Claims] 1. An interferometer apparatus for measuring a displacement of an object to be measured, wherein one inclined surface of two right-angle prisms and the other bottom surface are joined to each other, and the joined surface is formed by a polarization splitting surface. An interferometer apparatus comprising: a member arranged; and a measurement optical path and a reference optical path formed by the optical member. 2. An interferometer apparatus for measuring a displacement of an object to be measured, comprising: first and second measuring reflecting means provided so as to be integrally movable along a measuring direction; First and second reference reflection means provided; light source means for supplying a light beam; a first measurement optical path reciprocating via the first measurement reflection means based on the light beam from the light source means; First interferometer means for forming a first reference light path reciprocating via the first reference reflection means, and generating a first measurement output by each light beam passing through the first measurement light path and the first reference light path; Based on a light beam from the light source means, a second measurement light path reciprocating via the second measurement reflection means and a second reference light path reciprocating via the second reference reflection means are formed. The second beam is passed through the second measurement optical path and the second reference optical path. A second interferometer for generating a constant output; and an operation unit for performing a predetermined operation based on the first and second measurement outputs; and the first interferometer and the first reference reflector. The first reference optical path from the second interferometer means to the second
The optical path of the first measurement optical path from the first interferometer means to a reference position of the first measurement reflection means, the optical path length being shorter than the second reference optical path to the reference reflection means. The length is l _M1 , the optical path length of the second measurement optical path from the second interferometer means to the reference position of the second measuring reflection means is l _M2 , and the first interferometer means refers to the first reference. The optical path length of the first reference light path up to the reflection means for use is l _R1 , the optical path length of the second reference light path from the second interferometer means to the reflection means for the second reference is l _R2 , When the displacement of the first and second measuring reflecting means from the reference position is x, the first and second measuring reflecting means can move at least in the following range, or move a part of the following range. An interferometer device configured to be movable at least. l _R1 -l _M1 ≤x≤l _R2 -l _M2