JPH0726706U - Interferometer device - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide an interferometer device capable of realizing measurement with higher accuracy than ever before. In an interferometer device for measuring the amount of displacement of an object to be measured, one of the two right-angle prisms (2a, 2b) is joined to the other bottom surface, and the joint surface is a polarization separation surface S ₁ The optical member 2 formed by
An interferometer device having a configuration in which a measurement optical path and a reference optical path are formed by.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to an interferometer device for measuring a displacement amount of an object to be measured.

[0002]

[Prior art]

Conventionally, as an interferometer device that corrects a change in the refractive index of air as one of environmental changes, for example, JP-A-60-263801 is known. In the apparatus disclosed in Japanese Patent Laid-Open No. 60-263801, as shown in FIG. 6, the light beam from the laser light source 31 is divided into two by a beam splitter 32, and one beam L transmitted through this beam splitter 32 is transmitted. Reference numeral ₂ is a measurement beam, which is reflected by a measurement-side reflecting member 34 movably provided in the left-right direction in FIG. 6 and travels toward the beam splitter 32 again. On the other hand, the other beam L ₃ reflected by the beam splitter 32 is reflected by the reference side reflecting member 35 fixed to the base via the reflecting mirror 33 as a reference beam, and again passes through the reflecting mirror 33. Towards the beam splitter 32. Then, the beam splitter 32 combines the measurement beam L ₂ and the reference beam L ₃ and the light beam is received by the photoelectric detector 36 as the beam L ₄ , and the movement amount of the reflection member 34 as the object to be measured is detected. It

At this time, the reflection member 33 on the measurement side and the reflection member 34 on the reference side are placed at substantially equal positions so that the reference optical path length and the measurement optical path length are equal in a portion affected by air fluctuations. The effect of air fluctuations is compensated for by arranging at.

[0004]

[Problems to be solved by the device]

However, in the conventional apparatus shown in FIG. 6, when the reflecting member 34 as the object to be measured moves largely, the optical path length difference between the measurement beam L ₂ and the reference beam L ₃ becomes large. As a result, the measurement error becomes so large that it cannot be ignored, so the effect of changes in the refractive index of air due to fluctuations in air, etc., could not be fundamentally resolved.

Therefore, the present invention solves the above problems and corrects a measurement error due to a change in the refractive index of air caused by fluctuations in the air, etc., and highly accurate interference that can always perform highly accurate measurement. The purpose is to provide a device.

[0006]

[Means for Solving the Problems]

 In order to achieve the above object, as a first device, for example, as shown in FIG. 1, in an interferometer device for measuring a displacement amount of a measurement object, one of the two right-angle prisms and the other of the inclined surface The optical member is joined to the bottom surface and the joined surface is a polarization splitting surface, and the optical member forms a measurement optical path and a reference optical path.

In order to achieve the above-mentioned object, as a second invention, as shown in FIG. 1, for example, as shown in FIG. 1, first and second reflections for measurement provided integrally movable along the measurement direction. Means, first and second reference reflecting means fixed respectively at predetermined positions, light source means for supplying a light flux, and based on the light flux from the light source means, through the first measuring reflection means. Forming a first measurement optical path that reciprocates and a first reference optical path that reciprocates via the first reference reflecting means, and a first measurement output is obtained by each light flux that has passed through the first measurement optical path and the first reference optical path. And a second measuring optical path that reciprocates via the second measuring reflecting means and a second measuring optical path that reciprocates based on the luminous flux from the light source means. Forming a second reference optical path, and forming a second reference optical path and a second reference optical path. A second interferometer means for generating a second measurement output by each light flux passing through the illumination path; and a computing means for performing a predetermined computation based on the first and second measurement outputs, the first interferometer The first reference optical path from the means to the first reference reflecting means has a shorter optical path length than the second reference optical path from the second interferometer means to the second reference reflecting means, The optical path length of the first photometry path from the first interferometer means to the reference position of the first measurement reflection means is set to l _M1, and the second interferometer means changes the optical path length from the second interferometer means to the second measurement reflection means. The optical optical path length of the second measurement optical path to the reference position is l _M2 , the optical optical path length of the first reference optical path from the first interferometer means to the first reference reflecting means is l _R1 , and the first optical path length is l _R1 . 2 of the second reference optical path from the interferometer means to the second reference reflecting means When the optical path length is l _R2 and the displacement of the first and second measuring reflecting means from the reference position is x, the first and second measuring reflecting means move at least in the following range. Possible, or at least part of the following range is configured to be movable.

L _R1 −l _M1 ≦ x ≦ l _R2 −l _M2

[0009]

[Work]

 According to the present invention, in two interferometer devices for measuring the amount of displacement of a measurement object, one of the two prisms is joined to the inclined surface and the other is the bottom surface, and the joint surface is formed by a polarization splitting surface. An optical member is arranged, and a measuring optical path and a reference optical path are formed by the optical member so as to reduce the influence of measurement error due to environmental changes.

Further, according to the present invention, the reference optical paths formed by the two interferometer means are different from each other by a predetermined length, and the measurement optical path length and the reference optical path length formed by the two interferometer means are different from each other. Attention is paid to the fact that the two measuring reflection means are integrally moved under at least a predetermined relationship. As a result, even if the refractive index changes in the reference optical path and the measurement optical path that pass through a gas such as air, two different measurement outputs containing information on the refractive index change of the gas such as air due to environmental changes Then, by performing a predetermined calculation based on these two measurement outputs, it is possible to remove the measurement error due to the change in the refractive index in each optical path. Moreover, by constructing the two measuring reflection means so that the predetermined movement range or at least a part of the range can be moved, the influence of the quantization error of the two interferometer means itself can be significantly reduced. Therefore, it is possible to significantly improve the measurement accuracy.

If there is a possibility that a local change in the refractive index of a gas such as air will occur in each measurement optical path formed by each interferometer means and in the vicinity thereof, each interferometer means uses these interferometer means. It is desirable that the reference optical path and the measurement optical path formed by the above are close to each other. The principle of the present invention will be described with reference to FIG. 4 below. FIG. 4A is a diagram showing the configuration of the first interferometer device of the present invention, and FIG. 4B is a diagram showing the configuration of the second interferometer device of the present invention.

First, as shown in FIG. 4A, the light beam supplied from the first light source 11 is split into two light beams by a beam splitter 12 as a light splitting member, and one of the light beams passing through the beam splitter 12 is divided into two light beams. The beam L ₂₁ is reflected as a measuring beam by a measuring reflecting member 14 (measuring reflecting means) movably provided in the left-right direction in FIG. 4A and travels toward the beam splitter 12 again. On the other hand, the other beam L ₃₁ reflected by the beam splitter 12 is reflected by the reflecting mirror 13 as a reference beam, and the gas such as air in the vicinity of the optical path of the measurement beam L ₂₁ becomes parallel to the measurement beam L _21. To proceed. After that, the beam L ₃₁ is reflected by the reference reflection member 15 (first reference reflection means) fixedly mounted on the base, and again in the gas such as air, which is close to the optical path of the measurement beam L ₂₁ , for measurement. It travels so as to be parallel to the beam L ₂₁ and goes toward the beam splitter 12 via the reflecting mirror 13. Then, the measurement beam L ₂₁ and the reference beam L ₃₁ are combined by the beam splitter 12, and are received by the first receiver 16 (first detector) as the beam L ₄₁ , which serves as an object to be measured. The amount of movement of the reflecting member 14 is detected.

Here, the first interferometer shown in FIG. 4A is composed of a beam splitter 12, a reflecting mirror 13 and a first receiver 16, and the reflecting member 15 for reference is in the gas. The reference optical path is fixed to the base with a predetermined optical distance l _R1 from the first interferometer so that the optical path length of the reference optical path is l _R1 . In addition, the measuring reflection member 14 is arranged so that the optical path length of the measuring optical path in the gas at the reference position is 1 _M1 from the first interferometer to the reference position of the measuring reflection member 14. It is set to be movable so that the optical distance is l _M1 .

On the other hand, a second interferometer device as shown in FIG. 4B is arranged in parallel in a direction perpendicular to the paper surface of FIG. 4A, and in the second interferometer device, a reflecting mirror is used. 23 and the reflecting member 25 for reference have an optical optical path length l _R2 of the reference optical path in the gas of the second interferometer with respect to an optical optical path length l _R1 of the reference optical path in the gas of the first interferometer. They are fixed in different ways. Further, the beam splitter 22 and the measuring reflection member 24 (measuring reflection means) are arranged such that, at the reference position of the reflecting member 24, the optical path length l _M2 of the measurement optical path in the gas of the second interferometer causes the second interference. The optical path length l _{M2 of} the second interferometer is different from the optical path length l _M1 of the reference optical path in the gas of the meter, or 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 other than that, the first interferometer shown in FIG. It is basically the same as the device.

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 transmitted through the beam splitter 22. Beam L _{22 of} is directed to the measurement reflection member 24 (measurement reflection means) as a measurement beam. The reflecting member 24 is joined so as to have the same displacement as that of the reflecting member 14 shown in FIG. 4A, and is provided so as to be movable together with the reflecting member 14 in the left-right direction of FIG. 4B. Then, the beam L ₂₂ traveling toward the reflecting member 24 for measurement is reflected by the reflecting member 24 and travels toward the beam splitter 22 again. On the other hand, the other beam L ₃₂ which reflects the beam splitter 22, reflected by the reflection mirror 23 as a reference beam, and parallel to a gas such as air in close proximity to the optical path of the measuring beam L ₂₂ and measuring beam L ₂₂ To proceed. After that, the beam L ₃₂ is reflected by the reference reflection member 25 (second reference reflection means) fixedly mounted on the base, and again measures in a gas such as air close to the optical path of the measurement beam L _22. It travels so as to be parallel to the beam L ₂₂ for use, and goes toward the beam splitter 22 via the reflecting mirror 23. Then, the measurement beam L ₂₂ and the reference beam L ₃₂ are combined by the beam splitter 22 and received by the second receiver 26 (second detector) as the beam L _{42 to} be measured. The amount of movement of the reflecting member 24 is detected.

The second interferometer shown in FIG. 4B is composed of 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 object to be measured move integrally in the direction of the paper surface of FIG. 4, the first receiver 16 of the first interfering device and the second receiver 26 of the second interfering device 26. Two different detection signals are output from and.

Now, let X _{A be} the output from the first receiver 16 of the first interfering device, and let X _B be the output from the second receiver 26 of the second interfering device. N is the refractive index of the gas used as the reference of the period, Δn is the amount of change in the refractive index from the refractive index of the initial reference gas at the start of measurement (at reset), and the gas in the reference optical path of the first interferometer The optical path length (optical path length of the first reference optical path between the first interferometer and the first reference reflecting means) of the portion affected by the change in the refractive index is l _R1 , and the second interferometer Of the optical path of the portion affected by the change in the refractive index of the gas in the reference optical path of (the optical path length of the second reference optical path between the second interferometer and the second reflecting means) L _R2 , the measurement optical path of the first interferometer at the reference position of the initial measuring reflection means at the start of measurement (at reset) The length of the optical path of the portion affected by the change of the refractive index of the gas (optical optical path length of the first measuring optical path between the first interferometer and the reference position of the measuring reflection means) is defined as l _M1 , 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 second interferometer at the reference position of the initial measuring reflection means at the start of measurement (at the time of resetting) (second The optical path length of the second measurement optical path between the interferometer and the reference position of the measuring reflection means is set to l _M2 , and the portion affected by the change in the refractive index of the gas in each of the first and second measurement optical paths. Let x be the displacement from the reference position (origin) of the object to be measured (first and second measuring reflection means) when the lengths of the optical paths are 1 _M1 and 1 _M2 , respectively. However, this displacement x is positive when the measured object moves to the right of the origin, and negative when the measured object moves to the left of the origin.

Here, the output X _A from the first receiver 16 of the first interference device is affected by the change in the refractive index of the gas by the length (l _R1 ) of the reference optical path exposed to the gas. The received information and the information affected by the change in the refractive index of the gas by the optical length (l _M1 + x) of the measurement optical path exposed to the gas are included. On the other hand, the output X _B from the second receiver 26 of the second interferometer is affected by the change in the refractive index of the gas by the length (l _R2 ) of the reference optical path exposed to the gas. And the information affected by the change in the refractive index of the gas by the optical length (l _M2 + x) of the measurement optical path exposed to the gas.

Therefore, at this time, the relationships of the following expressions (1) and (2) are established.

[0020]

[Equation 1]

[0021]

[Equation 2]

The following expression (3) is derived from the expressions (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 device is Δx, the following expression (4) is obtained from the above expression (3).

[0025]

[Equation 4]

Then, by modifying the above equation (4), the following equation (5) is obtained.

[0027]

[Equation 5]

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

[0029]

[Equation 6]

Here, assuming that n + Δn≈1 and (l _M1 −l _R1 ) − (l _M2 −l _R2 ) = α, the above equation (6) finally becomes the following equation (7).

[0031]

[Equation 7]

Therefore, the maximum value Δx of the quantization error amount Δx is calculated based on the above equation (7)._MAXExamine. Now, assuming that α> 0, the quantization error of the first and second interferometer devices (δ _A , Δ_B), The maximum value and the minimum value of e are respectively −e, and the quantization error of each interferometer device is −e ≦ δ_A≤e, -e≤δ_BWhen the range of ≦ e can be taken, the maximum value of the quantization error amount | Δx according to the above equation (7)_MAX| Can be classified into the following three cases (i) to (iii).(I) In the case of l _R1 −l _M1 ≦ x ≦ l _R2 −l _M2  In this case, l_M1-L_R1+ X ≧ 0, l_M2-L_R2+ X ≦ 0, and the maximum value of the quantization error amount | Δx_MAX| Is given by the following equation (8) from the above equation (7).

[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 of the quantization error amount | Δx _MAX | Is expressed by the following expression (9) from the above expression (7).

[0035]

[Equation 9]

(Iii) In the case of x <l _R1 −l _{M1 In} this case, l _M1 −l _R1 + x <0, l _M2 −l _R2 + x <0, and the maximum value of the quantization error amount | Δx _MAX | Is expressed by the following expression (10) from the above expression (7).

[0037]

[Equation 10]

Therefore, by using the above formulas (8) to (10), it is possible to optimize the reflection member (14, 24) for measurement in order to ensure high accuracy for the entire interferometer device shown in FIG. Examine the range of movement x. In order to guarantee high accuracy as an interferometer while compensating for the effect of changes in the refractive index of gas due to fluctuations of gas such as air, the quantization error added to the measurement output of the interferometer is realistic. It is preferable to suppress the maximum value (| Δx _MAX |) to 4e or less. Therefore, in the following, regarding the optimum movement range x of the reflection member (14, 24) for measurement when the quantization error e added to the measurement output of the interferometer device is suppressed to 4 times to 1 time or less, respectively. explain. (I) When the maximum value of the quantization error | Δx _MAX | is suppressed to 4e or less In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) is (8 From equations (10) to (10), the following equation (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. 4B is set to 0.5 nm. , 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 Regarding the case, the moving range x of the reflection member (14, 24) for measurement in which the maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer device can be suppressed to 4e or less will be examined.

When l _R1 = 1.0 m, l _R2 = 1.5 m, and l _M1 = l _M2 = 0.5 m, the moving range x of the reflecting member (14, 24) for measurement is calculated from the above formula (11). It becomes -0.25 to 1.75m, and it can be understood that a wide measuring range can be secured while the accuracy of 2.0nm (= 4e) is guaranteed for the whole interferometer. Further, when l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 0.3 m, and l _M2 = 0.5 m, the moving range of the reflecting member (14, 24) for measurement is calculated from the equation (11). Since x is 0.25 m to 1.45 m, it can be understood that a relatively wide measurement range can be secured while the accuracy of 2.0 nm (= 4 e) is guaranteed for the interferometer device as a whole. (II) When the maximum value of the quantization error | Δx _MAX | is suppressed to 3e or less In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) is (8 From formulas (10) to (10), the following formula (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. 4B is set to 0.5 nm. , L _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = l _M2 = 1.25 m, and l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 2.0 m, l _M2 = 1.5 m Regarding the case, the moving range x of the reflection member (14, 24) for measurement in which the maximum value (| Δx _MAX |) of the quantization error added to the measurement output of the interferometer device can be suppressed to 3e or less will be examined.

When l _R1 = 1.0 m, l _R2 = 1.5 m and l _M1 = l _M2 = 1.25 m, the moving range x of the reflecting member (14, 24) for measurement is calculated from the above formula (12). It becomes -0.75m to 0.75m, and it can be understood that a wide measurement range can be secured while the accuracy of 1.5nm (= 3e) is guaranteed for the interferometer device as a whole. When l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 2.0 m, and l _M2 = 1.5 m, the movement of the reflecting member (14, 24) for measurement is calculated from the above formula (12). The range x is -2.0 m to 1.0 m, and it can be understood that a relatively wide measurement range can be secured while the accuracy of the entire interferometer device is guaranteed to be 1.5 nm (= 3 e). (III) When the maximum value of the quantization error | Δx _MAX | is suppressed to 2e or less In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) is (8 From equations (10) to (10), the following equation (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. 4B is set to 0.5 nm. , 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 Regarding the case, the moving range x of the reflecting member (14, 24) for measurement in which the maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer device can be suppressed to 2e or less will be examined.

When l _R1 = 1.0 m, l _R2 = 1.5 m, and l _M1 = l _M2 = 2.0 m, the moving range x of the reflection member (14, 24) for measurement is calculated from the above equation (13). It becomes -1.25m to -0.25m, and it can be understood that a wide measuring range can be secured while the accuracy of 1.0nm (= 2e) is guaranteed for the whole interferometer. When l _R1 = 1.0 m, l _R2 = 1.5 m, l _M1 = 1.75 m, and l _M2 = 2.0 m, the movement of the reflecting member (14, 24) for measurement is calculated from the above equation (13). The range x is -0.875 m to -0.375 m, and it can be understood that a relatively wide measurement range can be secured while the accuracy of 1.0 nm (= 2e) is guaranteed for the interferometer device as a whole. (IV) When the maximum value Δx _MAX of the quantization error is suppressed to e or less, the optimum moving range x (where x ≧ 0) of the reflecting member (14, 24) for measurement in this case is expressed by the formula (8). From the equations (10) to (10), the following equation (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. 4B is set to 0.5 nm. , 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 Regarding the case, let us look at the moving range x of the reflection member (14, 24) for measurement in which the maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer device can be suppressed to e or less.

When l _R1 = 0.5 m, l _R2 = 1.5 m, and l _M1 = l _M2 = 1.0 m, the moving range x of the reflection member (14, 24) for measurement is calculated from the above equation (14). -0.5m to 0.5m, and when l _R1 = 1.0m, l _R2 = 2.0m, l _M1 = 2.0m, l _M2 = 1.5m, the reflection for measurement from the above formula (14) The movement range x of the members (14, 24) is -1.0 m to 0.5 m, and 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 if the refractive index of gas changes due to environmental changes. Moreover, in the present invention, if the object to be measured (the first and second measuring reflection means) is moved within the range satisfying the expression (14), the quantization error e ( (Or resolution) can be suppressed to 1 time or less, and extremely stable and highly accurate measurement can be achieved. In addition, when the accuracy of 1 times or less of the quantization error e (or resolution) of the two interferometers is not required, the object to be measured (the first and second measuring reflection means) has the above formula (14). It suffices if at least part of the range satisfying the above condition is provided so as to be movable.

Although the principle of the present invention has been described above, in order to further deepen the understanding of the present invention, an analysis of the principle from another viewpoint will be described below with reference to FIG. However, this analysis is performed when the reference optical path lengths of the first and second interferometers are different from each other and the reference optical path lengths of the first and second interferometers are equal to each other. First, with l _M1 = l _M2 = 0, l _R1 = a, l _R2 = b, and the optics from the first interferometer to the measurement reflection member 14 (or from the second interferometer to the measurement reflection member 24). Consider the case where the target optical path length (or distance) is x.

In other words, the output from the first receiver 16 of the first interfering apparatus is X _A , the output from the second receiver 26 of the second interfering apparatus is X _B, and at the start of measurement (reset N is the refractive index of the gas that serves as the initial reference, and the length of the optical optical path in the portion affected by the change in the refractive index of the gas in the reference optical path of the first interferometer (the first interferometer). The optical path length of the first reference light path between the first reference reflection means and the first reference reflection means), and the length of the optical light path in the reference light path of the second interferometer at the portion affected by the change in the refractive index of the gas. (The optical optical path length of the second reference optical path between the second interferometer and the second reference reflection means) is b, and the refractive index of the gas in the measurement optical path of the first interferometer (or the second interferometer) is The length of the optical path at the portion affected by the change (the first measuring optical path between the first interferometer and the measuring reflection means). Optical light path length, or optical histological optical path length of the second measuring optical path between the second interferometer and measurement reflection means) is defined as x.

Here, the output X _A from the first receiver 16 of the first interference device is affected by the change in the refractive index of the gas by the length a of the reference optical path exposed to the gas. The information 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 are included. On the other hand, in the output X _B from the second receiver 26 of the second interference device, information affected by the change in the refractive index of the gas by the length b of the reference optical path exposed to the gas, and the gas It includes the information affected by the change in the refractive index of the gas by the optical length x of the measurement optical path exposed at.

Therefore, the outputs (X _A , X _B ) from the respective receivers (16, 26) are averaged at such a ratio that the reference light and the measurement light have the same influence of the change in the refractive index of the gas. Is desirable. At this time, the relationships of the expressions (15) and (16) shown below 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 output (X _A , X _B ) from each receiver (16, 26) is calculated by the calculation means, and the calculation of the above formula (17) is performed to remove the influence of the change in the refractive index of the gas. can do. Next, the quantization error by the interferometer of the present invention will be examined. Assuming that the quantization error (or resolution) of the first interferometer device is δ _A and the quantization error (or resolution capability) of the second interferometer device is δ _B , the first interference shown in FIG. The measurement output from the measuring device is the original measurement signal X _A plus the quantization error δ _A, and the measurement output from the second interferometer device shown in FIG. 5B is the original measurement signal X _{A. The} quantization error δ _B is added to _B. Therefore, assuming that the error amount added to the measurement result due to the quantization error of each interferometer device 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]

[Formula 19]

Now, each reference optical path and each measurement optical path of the first and second interferometer devices 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 device. In the long term, assuming that the refractive index of air changes by Δn due to fluctuation of air, the outputs from the first and second interferometers are X _A = (x−a) Δn and X _B = (x Since −b) Δn, the following equation (20) is derived from this relationship and the above equation (19).

[0065]

[Equation 20]

Here, assuming that n + Δn≈1, the above equation (20) finally becomes like 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, let the maximum value and the minimum value of the quantization error (δ _A , δ _B ) of the first and second interferometer devices be respectively e and −e, and the quantization error of each interferometer device is −e ≦ δ _A When the range of ≦ e, −e ≦ δ _B ≦ e can be taken, the maximum value of the quantization error amount | Δx _MAX | by the above equation (21) is one of the following three cases (i) to (iii). Can be divided. (I) When a ≦ x ≦ b (however, a <b) When a ≦ x ≦ b, x−a ≧ 0 and x−b ≦ 0, and the maximum value of the quantization error amount | Δx _MAX | Is given by the following equation (22) from the above equation (21).

[0069]

[Equation 22]

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

[0071]

[Equation 23]

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

[0073]

[Equation 24]

Therefore, by using the above equations (22) to (24), the optimal movement of the reflecting member (14, 24) for measurement for ensuring high accuracy of the entire interferometer device shown in FIG. Consider range x. In order to guarantee high accuracy as an interferometer while compensating for the effect of changes in the refractive index of gas due to fluctuations of gas such as air, the quantization error added to the measurement output of the interferometer is realistic. It is preferable to suppress the maximum value (| Δx _MAX |) to 4e or less. Therefore, in the following, regarding the optimum movement range x of the reflection member (14, 24) for measurement when the quantization error e added to the measurement output of the interferometer device is suppressed to 4 times to 1 time or less, respectively. explain. (I) When the maximum value of the quantization error | Δx _MAX | is suppressed to 4e or less In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) is (22 From equations (4) to (24), the following equation (25) or (26) is obtained.

[0075]

[Equation 25]

[0076]

[Equation 26]

Regarding the relationship between the equations (25) and (26), if it is shown in correspondence with the equation (11), the measurement optical path length l _M1 of the first interferometer in the equation (11) and the second This is equivalent to the case where the measurement optical path length l _{M2 of the} interferometer is 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. 5 (a) and the second interferometer device shown in FIG. 5 (b) is 0.5 nm, and a = When 0.5m, b = 1.0m and a = 0.7m, b = 1.0m, the maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer device should be 4e or less. Look at the movement range x of the reflection member (14, 24) for measurement that can be suppressed.

When a = 0.5 m and b = 1.0 m, the moving range x of the reflecting member (14, 24) for measurement is 0 m to 1.75 m from the above formula (25), and the interferometer apparatus as a whole is It can be understood that can secure a wide measurement range while guaranteeing an accuracy of 2.0 nm (= 4e). When a = 0.7 m and b = 1.0 m, the moving range x of the reflecting member (14, 24) for measurement is 0.25 m to 1.45 m from the above formula (26), and the whole interferometer device is Therefore, it can be understood that a relatively wide measurement range can be secured while guaranteeing the accuracy of 2.0 nm (= 4e). (II) When the maximum value of the quantization error | Δx _MAX | is suppressed to 3e or less In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) is (22 From equations (4) to (24), the following equation (27) or equation (28) is obtained.

[0079]

[Equation 27]

[0080]

[Equation 28]

Regarding the relationship between the equations (27) and (28), the measurement optical path length l _M1 of the first interferometer in the equation (12) and the second equation This is equivalent to the case where the measurement optical path length l _{M2 of the} interferometer is 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. 5 (a) and the second interferometer device shown in FIG. 5 (b) is 0.5 nm, and a = 0.4 m, if the b = 1.0 m and a = 0.6 m, the case of the b = 1.0 m, the maximum value of the quantization error applied to the total measurement output of the interferometer device (| Δx _MAX |) to 3e below Look at the movement range x of the reflection member (14, 24) for measurement that can be suppressed.

When a = 0.4 m and b = 1.0 m, the moving range x of the reflecting member (14, 24) for measurement is 0 m to 1.6 m according to the above equation (27), and the interferometer apparatus as a whole. It can be understood that a wide measurement range can be secured while guaranteeing an accuracy of 1.5 nm (= 3e). Further, when a = 0.6 m and b = 1.0 m, the moving range x of the reflecting member (14, 24) for measurement is 0.2 m to 1.4 m from the above formula (28), and the interferometer device as a whole is It can be understood that a relatively wide measurement range can be secured while guaranteeing an accuracy of 1.5 nm (= 3e). (III) When the maximum value of the quantization error | Δx _MAX | is suppressed to 2e or less In this case, the optimum moving range x (where x ≧ 0) of the measuring reflection member (14, 24) is (22 From equations (24) to (24), the following equation (29) or equation (30) is obtained.

[0083]

[Equation 29]

[0084]

[Equation 30]

Regarding the relationship between the equations (29) and (30), if it is shown in correspondence with the equation (13), the measurement optical path length l _M1 of the first interferometer in the equation (13) and the second This is equivalent to the case where the measurement optical path length l _{M2 of the} interferometer is 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. 5 (a) and the second interferometer device shown in FIG. 5 (b) is 0.5 nm, and a = The maximum value of the quantization error (| Δx _MAX |) added to the measurement output of the interferometer device should be 2e or less when 0.2m, b = 1.0m and when a = 0.5m and b = 1.0m. Look at the movement range x of the reflection member (14, 24) for measurement that can be suppressed.

When a = 0.2 m and b = 1.0 m, the moving range x of the reflection member (14, 24) for measurement is 0 m to 1.4 m from the above formula (29), and the interferometer device as a whole is It can be understood that a wide measurement range can be secured while the accuracy of 1.0 nm (= 2e) is guaranteed. Further, when a = 0.5 m and b = 1.0 m, the moving range x of the reflecting members (14, 24) for measurement is 0.25 m to 1.25 m from the above formula (30), and the whole interferometer device is It can be understood that a relatively wide measurement range can be secured while ensuring an accuracy of 1.0 nm (= 2e). (IV) When the maximum value Δx _MAX of the quantization error is suppressed to e or less, the optimum moving range x (where x ≧ 0) of the reflecting member (14, 24) for measurement in this case is expressed by the formula (22). From the equations (24) to (24), the following equation (31) is obtained.

[0087]

[Equation 31]

Regarding the relationship of the equation (31), the measurement optical path length l _M1 of the first interferometer in the equation (14) and the measurement optical path of the second interferometer in the equation (14) can be shown. This is equivalent to the case where the lengths l _M2 and l _M2 are equal to each other (l _M1 = l _M2 = l _M ). As an example, the quantization error e (or resolution) between the first interferometer device shown in FIG. 5 (a) and the second interferometer device shown in FIG. 5 (b) is 0.5 nm, and a = When 0.5 m and b = 1.0 m, the moving range x of the reflecting member (14, 24) for measurement is 0.5 m to 1.0 m according to the above formula (31), and the interferometer apparatus as a whole has 0.5 nm (= e It can be understood that a wide measurement range can be secured while the accuracy of) is guaranteed.

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

It is needless to say that the coordinate origin according to the present invention can be set in principle anywhere in the range where the reflection member (14, 24) for measurement moves.

[0091]

【Example】

 The configuration of the interferometer of the first embodiment according to the present invention will be described below with reference to FIG. In this example, a compound interferometer in which the measurement optical paths of the first interferometer and the second interferometer are shared is used, and the shared measurement optical path is reciprocated via one measuring reflection means (moving mirror 3). It is what

In the first embodiment shown in FIG. 1, the measuring reflection means (movable mirror 3) provided so as to be movable in the measuring direction X, and the first reference reflecting means fixed at respective predetermined positions. (Sealed tube 3, fixed mirror 6), second reference reflection means (fixed mirror 6), light source means 1 for supplying a coherent light beam, and reflection means for measurement based on the light beam from this light source means 1 ( First measurement optical path OP reciprocating along the measurement direction X via the movable mirror 3)_MAnd the first reference optical path OP that reciprocates via the first referential reflecting means (the closed tube 3 and the fixed mirror 6)._R1And form the first measurement optical path OP_MAnd the first reference optical path OP_R11st measurement output X by each luminous flux which passed through_AFor generating the first interferometer (prism member 2, quarter wave plate (8a ₁ , 8a₂, 8b₁, 8b₂), The half-wave plate 9, the deflection prism 4, the first detector 7a), and the light beam from the light source means 1, and reciprocates along the measurement direction X 1 via the measurement reflection means (moving mirror 3). Then the first measurement optical path OP_MA second reference optical path OP that reciprocates via a second measurement optical path that is shared with the second reference reflection means (fixed mirror 6)._R2And the second measurement optical path (first measurement optical path OP_M) And the second reference optical path OP_R22nd measurement output X by each luminous flux passing through_BSecond interferometer (prism member 2, quarter wave plate (8a₁, 8a ₂ , 8b₃, 8b_Four), The half-wave plate 9, the deflection prism 4, the second detector 7b), and the first and second measurement outputs (X_A, X_B) Is arranged and the first reference reflection means (sealed tube 3, fixed mirror 6) and the second reference reflection means (fixed mirror 6) are arranged in the measurement direction. Optically separated by a specified distance along each optical path (OP_M, OP_R1, OP_R2) Are parallel and close to each other.

FIG. 1 shows a main part of a laser interferometer device of this example. In FIG. 1, 2 is an optical member (hereinafter, referred to as an optical member formed by bonding a first rectangular prism 2a and a second rectangular prism 2b). It is referred to as a prism member 2.). As shown in FIG. 2 (a), this prism member 2 has a diagonal side of a right-angled prism 2a having a diagonal side inclined by 45 ° at the length of the orthogonal side and a length d2 (= 2 · d1). One of two orthogonal sides of a right-angle prism 2b having a hypotenuse inclined at 45 ° is pasted together. The laminating surface (the surface on one side of the two orthogonal sides of the right-angle prism 2b) is formed by the polarization separation surface (polarization beam splitter surface) S ₁ and is orthogonal to the right-angle prism 2b. The surface on the other side of the two sides is formed by the reflecting surface R ₁ . Incidentally, without providing a reflection film on the reflecting surface R _1, the surface R ₁ may be configured so as to totally reflect the light.

Here, the prism member 2 may in principle have the polarization separation surface S ₁ and the reflection surface R ₁ arranged orthogonally to each other, and may be constituted by only the right-angle prism 2b. Further, for example, as shown in FIG. 2 (d), 3 pieces of constitute a prism member 20 Te bonded Align the right-angle prism 20 a to 20 c, the polarization splitting surface S ₁ of the bonding surface of the right-angle prism 20a and 20b The prism body 20 can be used in place of the prism body 2 if the outer surface of the rectangular prism 20c is formed as the reflecting surface R ₁ .

Now, returning to FIG. 1, first, assuming that the direction in which a light beam is emitted from the laser light source 1 as a light source means for supplying a coherent light beam is the X direction, the prism member 2 is The polarization splitting surface S ₁ is arranged so as to be inclined at 45 ° with respect to the X direction, and facing the prism member 2, a movable mirror 3 as a measuring reflection means and a fixed mirror as a reference reflection means. 6 and 6 are arranged respectively. The movable mirror 3 is fixed to an object to be measured (not shown), is movable along the X direction, and is composed of a plane mirror. The fixed mirror 6 has a predetermined distance b in the X direction with respect to the prism member 2. The movable mirror 3 and the fixed mirror 6 are arranged so as to be displaced in the direction perpendicular to the X direction.

Six quarter-wave plates (6) are respectively provided in the vicinity of the transmission surface T forming a hypotenuse forming an angle equal to two sides (S ₁ , R ₁ ) of the right-angle prism 2b in the prism member 2 which intersect at right angles. 8a ₁ , 8a ₂ , 8b _{1 to} 8b ₄ ) are arranged in parallel, and between the two quarter-wave plates (8b ₃ , 8b ₄ ) and the fixed mirror 6, As will be described later in detail, a sealed tube that separates from the surroundings by a predetermined length of two reciprocating optical paths that are reflected and reciprocated by the fixed mirror 6 via two quarter-wave plates (8b ₃ and 8b ₄ ), respectively. 60 (correction member) is arranged.

The closed tube 60 is a member formed of a hollow cylinder having at least both ends transparent and having a predetermined length L in the x direction, and the inside thereof has a vacuum. For this reason, the optical path length D of the part exposed to the gas (air, etc.) in each round-trip optical path that is reflected and reciprocated by the fixed mirror 6 through each of the two quarter-wave plates (8b ₃ and 8b ₄ ). Is D = (b−L), where b is the length from the prism part 2 to the fixed mirror along the x direction and n is the refractive index of the gas exposed to the interferometer device shown in FIG. n. Therefore, the arrangement of the closed tube 60 is substantially equivalent to the fixed mirror 6 being arranged on the prism member 2 side along the x direction by the length L of the closed tube 60. The sealed tube may be filled with a medium having a predetermined refractive index, such as gas, liquid, or solid.

Now, in the direction in which the laser beam from the laser light source 1 is reflected by the polarization splitting surface S ₁ of the prism member 2, the light emitted from the polarization splitting surface S _{1 is} deflected by 180 °. A prism (right angle prism) 4 is arranged. In this case, it is assumed that the laser beam is returned to the polarization splitting surface S ₁ by the two total reflections in the deflecting prism 4, and the ridgeline between the polarization splitting surface S ₁ and the reflecting surface R ₁ of the prism member 2 is assumed. The deflecting prism 4 is positioned so that the surface including the optical path deflected by the prism member 2 becomes parallel.

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

Further, 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 by the reflecting surface R ₂ ), the polarization separation of the prism member 2 is performed. A first receiver 7a as a first detector is arranged in the direction reflected by the surface P ₁ , and after the laser beam from the deflection prism 4 has passed through the light splitting surface S ₂ of the prism member 5, A first receiver 7b as a second detector is arranged in the direction reflected by the polarization splitting surface S ₁ of the prism member 2.

As shown in FIG. 1, the first and second receivers (7a, 7b) are electrically connected to an arithmetic unit 10 as an arithmetic means, and outputs from the respective receivers (7a, 7b). Based on the force, for example, a calculation such as the above formula (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 that covers the entire incident surface and exit surface of the deflection prism 4 or the surface of the prism member 2 on the deflection prism 4 side is used. It may be arranged, and in this case, a quarter wavelength plate may be directly bonded to the incident surface and the exit surface of the deflecting prism 4 or the surface of the prism member 2 on the deflecting prism 4 side. Further, a quarter wavelength plate is arranged between the optical paths of the prism member 2 and the deflecting prism 4 or between the optical paths of the deflecting prism 4 and the prism member 5, and between the prism member 5 and the prism member 2. It is also possible to adopt a configuration in which a quarter-wave plate is arranged in the two formed optical paths.

Next, the operation of this example will be described. First, a laser light source 1 as a light source means for supplying a coherent light beam has 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). .) Is supplied, and the first and second beams are incident on the polarization splitting surface S ₁ of the prism member 2 at an incident angle of 45 °.

Here, the first beam of one of the two beams supplied from the laser light source 1 is a linearly polarized light (hereinafter, P-polarized light) oscillating in the incident plane of the polarization separation surface S _1. The other second beam is linearly polarized light (hereinafter referred to as S-polarized light) that oscillates in a plane perpendicular to the incident surface of the polarization separation surface S ₁ . First, the P-polarized first beam supplied from the laser light source 1 will be described. The P-polarized first beam passes through the polarization splitting surface S ₁ of the prism member 2 as it is and passes through the quarter-wave plate 8a ₁ . After being converted into circularly polarized light via the same, it is reflected by the movable mirror 3 and again passes through the quarter-wave plate 8a ₁ to be converted into S-polarized light. Then, the first beam of S-polarized light is reflected by the polarization separation surface S ₁ of the prism member 2 and is reflected and deflected by 90 ° at the reflection surface R ₁ of the prism member 2. Thereafter, the first beam of S-polarized light passes through the quarter-wave plate 8a ₂ and is converted into circularly polarized light, reflected by the movable mirror 3 and headed again to the quarter-wave plate 8a ₂ . 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 splitting surface S ₁ passes through the ½ wavelength 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 to S-polarized light by the half-wave plate 9 is reflected and deflected by 180 ° by the deflecting prism 4, and is split into two by the light splitting surface S ₂ of the prism member 5.

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

Next, the S-polarized second beam supplied from the laser light source 1 will be described. The S-polarized second beam is reflected by the polarization splitting surface S ₁ of the prism member 2 to form a 1/2 wavelength plate. Go to 9. The second beam that has passed through the half-wave plate 9 has its polarization plane rotated by 90 ° and converted from S-polarized light to P-polarized light, and then is reflected and deflected by 180 ° by the deflecting prism 4 to be reflected by the prism member 5. It is divided into _two at the light dividing surface S ₂ .

First, one P-polarized second beam that reflects the light splitting surface S ₂ of the prism member 5 is reflected and deflected by 90 ° at the reflecting surface R ₂ of the prism member 5, and the polarization splitting surface of the prism member ₂ is reflected. Continue to pass S ₁ . The second beam that has passed through the polarization splitting surface S ₁ is reflected and deflected by 90 ° at the reflecting surface R ₁ , and then passes through the ¼ wavelength plate 8b ₁ to be converted into circularly polarized light. After that, the second beam converted into the circularly polarized light passes through the sealed tube 60 having a predetermined length L in the x direction (measurement direction), is reflected by the fixed mirror 6, and then again passes through the sealed tube 60. It passes through the quarter-wave plate 8b ₁ and is converted into S-polarized light. The second beam converted into the S-polarized light is reflected by the reflection surface R ₁ of the prism member 2 and is reflected by the polarization separation surface S ₁ of the prism member 2 and travels to the quarter-wave plate 8b ₂ . The second beam that has passed through the quarter-wave plate 8b ₂ is converted into circularly polarized light, then passes through the closed tube 60, is reflected by the fixed mirror 6, and heads for the closed tube 60 again. The second beam that has passed through the closed tube 60 passes through the quarter-wave plate 8b ₂ and is converted into P-polarized light, passes through the polarization splitting surface S ₁ of the prism member 2, and is transmitted by the first receiver 7a. Received light.

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 splitting surface S ₁ of the prism member 2 as it is, and is reflected and deflected by 90 ° at the reflecting surface R _1. Then, it goes to the quarter-wave plate 8b ₃ . The second beam that has passed through the quarter-wave plate 8b ₃ is converted into circularly polarized light, reflected by the fixed mirror 6, passes through the quarter-wave plate 8b ₃ again, and is converted into S-polarized light. The second beam converted into the S-polarized light is reflected by the reflection surface R ₁ of the prism member 2 and reflected by the polarization separation surface S ₁ and heads for the quarter-wave plate 8b ₄ . The second beam that has passed through the quarter-wave plate 8b ₄ is converted into circularly polarized light, reflected by the fixed mirror 6, passes through the quarter-wave plate 8b ₄ again, and is converted into P-polarized light. . The second beam, which has passed through the quarter-wave plate 8b ₄ and has been converted into P-polarized light, passes through the polarization separation surface S ₁ as it is and is received by the second receiver 7b.

In the first receiver 7a, 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. Measuring optical path OP along the direction)_MBeam that travels through the _M And a distance b between the prism member 2 and the fixed mirror 6 in a gas such as air and through the closed tube 60 (the distance from the surface T of the prism member 2 to the fixed mirror 6 in the X direction). ) First reference optical path OP_R1And the second beam propagating in the same direction are aligned in the polarization direction by the internal analyzer and are incident on the internal light receiving element.

Since the closed tube 60 is disposed in the first reference optical path OP _R1 , assuming that the length of the closed tube 60 in the X direction is L, as described above, the refractive index of gas such as air is The change is equivalent to arranging the fixed mirror 6 so as to be shifted to the prism member 2 side by the length L of the closed tube 60. Therefore, in the light receiving element of the first receiver 10a, the length x (from the surface T of the prism member 2 to the moving mirror 3 is substantially passed 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 O P _M of the distance) in the X direction up, via a gas such as air between the prism member 2 in close proximity to the measurement optical path OP _M and the fixed mirror 6 The second beam traveling along 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 outputs a beat signal having a frequency of (f1-f2) when the movable mirror 3 is stopped with respect to the fixed mirror 6, and the movable mirror 3 When moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, it is possible to detect the relative movement amount of the movable mirror 3 and the fixed mirror 6 in the X direction by integrating the change in the frequency. Therefore, the measurement optical path OP that passes through a gas such as air_M(Or the measurement optical path OP from the prism member 2 of the interferometer to the movable mirror 6)_MOptical path length of x), and the first reference optical path OP that passes through a gas such as air_R1 (Or the first reference optical path OP from the prism member 2 of the interferometer to the fixed mirror 6) _R1 Optical optical path length of a), a refractive index of gas such as air at the start of measurement (at the time of resetting) is n, and a change in refractive index of gas such as air is Δn, the first receiver 7a , Nx + (x−a) Δn corresponding to the signal X_AIs output to the arithmetic processing unit 10.

On the other hand, in the second receiver 7b, the length x (in the X direction 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. first beam and the length b (prism 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 traveling through the measurement optical path OP _M of along distance) The polarization direction of the second beam traveling along the second reference optical path OP _R2 at the distance from the surface T of the member 2 to the fixed mirror 6 along the X direction) is incident on the internal light receiving element with the polarization direction aligned by the internal analyzer. To do.

Here, from the light receiving element of the second receiver 7b, similarly to the first receiver 7a, when the moving mirror 3 is stopped with respect to the fixed mirror 6, the frequency is (f1-f2). A beat signal is output, and when the movable mirror 3 moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, by accumulating 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 measurement optical path OP _M that passes through a gas such as air (or the optical optical path length of the measurement optical path OP _M from the prism member 2 of the interferometer to the movable mirror 6) is x, and the inside of a gas such as air is The length of the second reference optical path OP _R2 that passes through (or the optical 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 denoted by b, and at the start of measurement (at reset), etc. Assuming that the initial refractive index of a gas such as air is n and the change in the refractive index of a gas such as air is Δn, a signal X _B corresponding to nx + (x−b) Δn is calculated in the second receiver 7b. It is output to the unit 10.

The arithmetic processing unit 10 stores a predetermined arithmetic expression, for example, the arithmetic expression as described in (3) above. Therefore, the arithmetic processing unit 10 detects the output signals (X _A , X _B ) from the first and second receivers (7a, 7b) and the initial refractive index n of the gas at the start of measurement. Based on the output n from the refractive index detector (not shown), the calculation as shown in the above equation (3) is executed, and the measurement error due to the change in the refractive index of the gas caused by the fluctuation of the gas is corrected. The calculated result is output via a display unit (not shown).

Then, the first movable mirror and the second movable mirror (3) are integrally formed so as to satisfy the expressions (11) to (14) or the expressions (25) to (31). If moved, the quantization error e added to the output of the interferometer device can be suppressed to 4 times to 1 times or less. As described above, according to the present embodiment, since the measurement optical path and each reference optical path are arranged close to each other by the interferometer, the measurement error due to the change in the refractive index of the gas occurring in the measurement optical path is corrected, It is possible to accurately detect the movement amount and position of the movable mirror 3.

Moreover, according to this example, the movable mirror is arranged 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. Since it can be moved, extremely accurate measurement is 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 equal, and even if the prism member 2 changes in temperature, it is highly accurate. It can be measured.

In specifically explaining this, first, the first beam for measurement and the second beam for reference, which are respectively incident on the first receiver 7a, pass through the inside of the prism member 2. The optical path will be described with reference to FIGS. 2 (a) and 2 (b). The first beam for measurement that passes through the lower portion of the prism member 2 has an optical path A within the rectangular prism 2a as shown by the solid line in FIG.₁₁And the optical path B in the right-angled prism 2b ₁₁ The first beam for measurement that passes through and the upper part of the prism member 2 has an optical path A only in the right-angle prism 2a as shown by the solid line in FIG.₁₂Pass through.

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

Therefore, the optical path lengths of the first beam for measurement and the second beam for reference that pass through the inside of the prism member 2 are A ₁₁ + B ₁₁ + A ₁₂ , A ₂₁ + A ₂₂ + B ₂₂ , respectively. As is clear from (a) and FIG. 2 (b), since the relationship of A ₁₁ = A ₁₂ = A ₂₁ = A ₂₂ = d ₁ and B ₁₁ = B ₂₂ = d ₂ is established, the prism member 2 The optical path lengths of the measurement first beam and the reference second beam passing through the inside are equal.

Next, regarding the optical paths through which the first beam for measurement and the second beam for reference, which respectively enter the second receiver 7b, pass through the inside of the prism member 2 are shown in FIGS. 2 (a) and 2 (c). ) Will be described. The first beam for measurement that passes through the lower portion of the prism member 2 has an optical path A within the rectangular prism 2a as shown by the solid line in FIG.₁₁And the optical path B in the right-angled prism 2b ₁₁ The first beam for measurement that passes through and the upper part of the prism member 2 has an optical path A only in the right-angle prism 2a as shown by the solid line in FIG.₁₂Pass through.

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

Therefore, the optical path lengths of the first beam for measurement and the second beam for reference that pass through the inside of the prism member 2 are A ₁₁ + B ₁₁ + A ₁₂ , A ₂₁ + A ₃₂ + B ₃₂ , respectively. As is clear from (a) and FIG. 2 (b), since the relationship of A ₁₁ = A ₁₂ = A ₂₁ = A ₃₂ = d ₁ and B ₁₁ = B ₃₂ = d ₂ is established, the prism member 2 The optical path lengths of the measurement first beam and the reference second beam passing through the inside are equal.

Therefore, even if a temperature difference occurs between the right-angled prism 2a and the right-angled prism 2b, the difference in optical path length between the first beam and the second beam does not change, so that the movable mirror 3 moves in the X direction. It is possible to always measure the amount of movement at 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 No. 1/4 wavelength plate, or the one quarter wavelength plate may be joined to the surface T of the prism member 2 to be integrally formed.

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

Next, an interferometer device 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. 1. In FIG. 3, members having the same functions as those in FIG. 1 are designated by the same reference numerals. As shown in FIG. 3, the main difference of this embodiment from the first embodiment is 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 it is arranged between the laser light source 1 and the prism member 2, and two fixed mirrors (6a, 6b) for reference are arranged at different positions along the X direction via the rod-shaped member 61. Further, the difference of this embodiment from the first embodiment is 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. However, while one half-wave plate 9 is arranged between the prism member 2 and the deflecting prism 4, in the second embodiment of FIG. 3, it is arranged between the prism member 2 and the movable mirror 4. four quarter-wave plate (8a ₁ ~8a ₄₎ arranged, in that are arranged two quarter wave plates (9a, 9b) between the prism member 2 and the deflection prism 4 .

The rod-shaped member 61 is made of a member having a predetermined length and an extremely small coefficient of thermal expansion. The structure of the second embodiment shown in FIG. 3 will be briefly described. In the present embodiment, the movable mirror 3 provided so as to be movable in the measurement direction X 1 and the first fixed mirror 6a fixed at predetermined positions. And a second fixed mirror 6b, a light source means (laser light source 1, prism member 5) for supplying a coherent light flux, and a light flux from the light source means (1, 5), through a moving mirror 3. First measurement optical path OP reciprocating along the measurement direction X_M1And the first reference optical path OP reciprocating via the first fixed mirror 6a._R1To form the first measurement optical path OP_M1And the first reference optical path OP_R1First measurement output X by each luminous flux passing through_AGenerating the first interferometer (prism member 2, quarter wave plate (8a₁, 8a₂, 8b₁, 8b₂), The half-wave plate 9a, the deflection prism 4, the first detector 7a), and the first and second light beams from the light source means (1, 5) which reciprocate along the measurement direction X via the movable mirror 3. 2 measurement optical path OP_M2And the second reference optical path OP reciprocating via the second fixed mirror 6b._R2To form the second measurement optical path OP_M2 And the second reference optical path OP_R22nd measurement output X by each luminous flux which passed through_BSecond interferometer (prism member 2, quarter wave plate (8a₃, 8a_Four, 8b₃, 8b_Four), A half-wave plate 9b, a deflection prism 4, a second detector 7b), and first and second measurement outputs (X_A, X _B ) Is arranged and the first fixed mirror 6a and the second fixed mirror 6b are arranged at a predetermined distance along the measurement direction, and each optical path ( OP_M1, OP_M2, OP_R1, OP_R2) Is a parallel configuration.

Next, the routing optical path of this example 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). The two beams are incident on the light splitting surface S ₂ of the prism member 5 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) that vibrates in the incident surface of the light splitting surface S _1. ), And the other second beam is linearly polarized light (hereinafter referred to as S-polarized light) that oscillates in a plane perpendicular to the incident surface of the light splitting surface S ₁ .

The first and second beams are the light splitting surface (semi-transmissive surface) S of the prism member 5 that functions as a light splitting unit that splits the beam from the light source into two.₂The light splitting surface S₂The first and second beams that reflect light are reflected by the reflecting surface R of the prism member 5. ₂ Is incident on the prism member 2 via the₂The first and second beams passing through the beam enter the prism member 2 as they are.

First, the first and second beams directed to the prism member 2 via the light splitting surface S ₂ and the reflecting surface R ₂ of the prism member 5 will be described. The first and second beams passing through the light splitting surface S ₂ and the reflecting surface R ₂ of the prism member 5 are incident on the polarization splitting surface S ₁ of the prism member 2 at an incident angle of 45 °. Here, the first beam, the light Der P-polarized light to linearly polarize the incident plane with respect to the polarization splitting surface S ₁ is, the second beam is linearly polarized light incident surface and a plane perpendicular with respect to the polarization splitting surface S ₁ Since it is S-polarized light, the P-polarized first beam passes through the polarization splitting surface S ₁ as it is, and the S-polarized second beam reflects off the polarization splitting surface S ₁ .

First, the polarization separation surface S₁The first beam of P-polarized light that has passed through the₁ After being converted into circularly polarized light via, the light is reflected by the movable mirror 3 and again the quarter wavelength plate 8a. ₁ And is converted into S-polarized light. Then, the S-polarized first beam is transmitted through the polarization splitting surface S of the prism member 2.₁To reflect the reflection surface R of the prism member 2.₁Is reflected and deflected by 90 °. Then, the first beam of S-polarized light is transmitted through the quarter-wave plate 8a.₂Is converted into circularly polarized light, is reflected by the movable mirror 3, and is again converted into quarter-wave plate 8a.₂Head to. And this quarter wave plate 8a₂After passing through the first beam again, it is converted into P-polarized light and then reflected again on the reflecting surface R₁To separate the polarized light separation surface S₁Pass through. This polarization separation surface S₁The first beam of P-polarized light that has passed through passes through the half-wave plate 9a, is rotated by 90 ° in the plane of polarization, and is converted from P-polarized light to S-polarized light. The first beam, which has been converted into S-polarized light by the half-wave plate 9a, is reflected and deflected by 180 ° by the deflecting prism 4, and then the polarization separation surface S₁And is received by the first receiver 7a.

On the other hand, the S-polarized second beam reflected by the polarization splitting surface S ₁ of the prism member 2 through the light splitting surface S ₂ and the reflecting surface R ₂ of the prism member 5 passes through the half-wave plate 9a. Then, after the polarization plane is rotated by 90 ° and converted from S polarization to P polarization, it is reflected and deflected by 180 ° by the deflection prism 4 and passes through the polarization separation surface S ₁ of the prism member 5. Then, the second beam of P-polarized light that has passed through the polarization splitting surface S ₁ is reflected and deflected by 90 ° at the reflecting surface R ₁ , and then passes through the ¼ wavelength plate 8b ₁ to be converted into circularly polarized light. After that, 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 reflected by the first fixed mirror 6a. / 4 Passes through the wavelength plate 8b ₁ and is converted into S-polarized light. The second beam converted into the S-polarized light is reflected by the reflection surface R ₁ of the prism member 2 and is reflected by the polarization separation surface S ₁ of the prism member 2 toward the quarter-wave plate 8b ₂ . The second beam that has passed through the quarter-wave plate 8b ₂ is converted into circularly polarized light, is then reflected by the first fixed mirror 6a, passes through the quarter-wave 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 first receiver 7a.

Next, the first and second beams from the laser light source 1 that pass through the light splitting surface S ₂ of the prism member 5 will be described. The first and second beams passing through the light splitting surface S ₂ of the prism member 5 are incident on the polarization splitting surface S ₁ of the prism member 2 at an incident angle of 45 °. Here, the first beam is P-polarized light that is linearly polarized in the plane of incidence with respect to the polarization separation plane S ₁ , and the second beam is linearly polarized in the plane perpendicular to the plane of incidence with respect to the polarization separation plane S ₁ . Since it is S-polarized light, the P-polarized first beam passes through the polarization splitting surface S ₁ as it is, and the S-polarized second beam reflects off the polarization splitting surface S ₁ .

First, the polarization separation surface S₁The first beam of P-polarized light that has passed through the₃ After being converted into circularly polarized light via, the light is reflected by the movable mirror 3 and again the quarter wavelength plate 8a. ₃ And is converted into S-polarized light. Then, the S-polarized first beam is transmitted through the polarization splitting surface S of the prism member 2.₁To reflect the reflection surface R of the prism member 2.₁Is reflected and deflected by 90 °. Then, the first beam of S-polarized light is transmitted through the quarter-wave plate 8a._FourIs converted into circularly polarized light, is reflected by the movable mirror 3, and is again converted into quarter-wave plate 8a._FourHead to. And this quarter wave plate 8a_FourAfter passing through the first beam again, it is converted into P-polarized light and then reflected again on the reflecting surface R₁To separate the polarized light separation surface S₁Pass through. This polarization separation surface S₁The first beam of P-polarized light that has passed through passes through the half-wave plate 9b, the polarization plane is rotated by 90 °, and converted from P-polarized light to S-polarized light. The first beam, which has been converted into S-polarized light by the half-wave plate 9b, is reflected and deflected by 180 ° by the deflecting prism 4, and then the polarization separation surface S₁And is received by the second receiver 7b.

On the other hand, the S-polarized second beam that transmits the light splitting surface S ₂ of the prism member 5 and reflects the polarization splitting surface S ₁ of the prism member 2 passes through the ½ wavelength plate 9b and After the surface is rotated by 90 ° and converted from S polarized light to P polarized light, it is reflected and deflected by 180 ° by the deflection prism 4 and passes through the polarization separation surface S ₁ of the prism member 5. The P-polarized second beam that has passed through the polarization separation surface S ₁ is reflected and deflected by 90 ° at the reflection surface R ₁ , and then passes through the ¼ wavelength plate 8b ₃ to be converted into circularly polarized light. . After that, the second beam converted into 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 again 1 / It passes through the four-wave plate 8b ₃ and 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, is reflected by the polarized light separating surface S ₁ of the prism member 2, and travels toward the quarter-wave plate 8b ₄ . The second beam that has passed through the quarter-wave plate 8b ₄ is converted into circularly polarized light, is then reflected by the second fixed mirror 6b, passes through the quarter-wave plate 8b _4, and is converted into P-polarized light. It 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 second receiver 7a.

As described above, in the interferometer device of the second embodiment according to the present invention, in the first receiver 7a, the long distance between the prism member 2 and the movable mirror 3 via gas such as air is used. The first measurement optical path OP having a length x (the distance from the surface T of the prism member 2 to the movable mirror 3 along the X direction)_M1Beam that travels through the first measurement optical path OP_M1And a length a passing through a gas such as air between the prism member 2 and the first fixed mirror 6a (a distance from the surface T of the prism member 2 to the first fixed mirror 6a in the X direction). ) First reference optical path OP _R1 And the second beam traveling in the direction of polarization are aligned in the polarization direction by the internal analyzer and are incident on the internal light receiving element.

Therefore, the light receiving element of the first receiver 7a outputs a beat signal having a frequency (f1-f2) when the movable mirror 3 is stopped with respect to the first fixed mirror 6. When the movable mirror 3 moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, by accumulating 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 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 optical optical path length of the first reference optical path OP _R1 from the prism member 2 of the interferometer to the fixed mirror 6) is a, at the start of measurement ( When the initial refractive index of a gas such as air is n and the change of the refractive index of a gas such as air is Δn (at the time of resetting), the first receiver 7a outputs a signal X _A 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 (in the X direction 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. The first beam traveling along the second measurement optical path OP _M2 along the distance) and the gas such as air between the prism member 2 and the second fixed mirror 6b in the vicinity of the second measurement optical path OP _M1. The second beam traveling along the second reference optical path OP _R2 having the length b (the distance along the X direction from the surface T of the prism member 2 to the second fixed mirror 6b) and the polarization direction by the internal analyzer. Are aligned and are incident on the internal light receiving element.

Here, from the light receiving element of the second receiver 7b, similarly to the first receiver 7a, when the moving mirror 3 is stopped with respect to the fixed mirror 6, the frequency is (f1-f2). A beat signal is output, and when the movable mirror 3 moves in the X direction, a beat signal whose frequency is modulated is output. Therefore, by accumulating 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 second measurement optical path OP _M2 passing through a gas such as air (or the optical 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 , B is the length of the second reference optical path OP _R2 passing through a gas such as air (or the optical optical path length of the second reference optical path OP _R2 from the prism member 2 of the interferometer to the fixed mirror 6), Assuming that the initial refractive index of gas such as air (at the time of reset) is n and the change of refractive index of gas such as air is Δn, the second receiver 7b has a signal corresponding to nx + (x−b) Δn. The signal X _B is output to the arithmetic processing unit 10.

Similar to the first embodiment, the arithmetic processing unit 10 stores, for example, an arithmetic expression represented by the above-mentioned expression (3), and the arithmetic processing unit 10 includes the first and second arithmetic expressions. The output signals (X _A , X _B ) from the receivers (7a, 7b) of the device and the output n from the refractive index detector (not shown) for detecting the initial refractive index n of the gas at the start of measurement. Based on the above, the calculation as shown in the above equation (3) is executed, and the calculation result in which the measurement error due to the change in the refractive index of the gas caused by the fluctuation of the gas is corrected is displayed on a display unit (not shown). Is output via.

Then, the first movable mirror and the second movable mirror (3) are integrally formed so as to satisfy the expressions (11) to (14) or the expressions (25) to (31). If moved, the quantization error e added to the output of the interferometer device can be suppressed to 4 times to 1 times or less. Moreover, in the second embodiment, as in 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 moving mirror can be moved by using this method, extremely accurate measurement is guaranteed.

Although detailed description is omitted, also in the second embodiment, the interferometer device is configured so that the measurement optical path length passing through the inside of the prism member 2 and each reference optical path length 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) While shows an example in which in the eight, which of one 1 / It may be configured with a four-wave plate, or this one quarter-wave plate may be bonded to the surface T of the prism member to be integrally configured.

Further, instead of the two half-wave plates (9a, 9b) of the second embodiment shown in FIG. 3, four optical paths formed between the polarization prism 4 and the prism member 2 are covered. It is also possible to provide a single quarter-wave plate as described above, and a quarter-wave plate that covers the entire entrance surface and exit surface of the polarization prism 4 is formed integrally with the polarization prism 4. Further, a quarter-wave plate that covers the entire surface of the prism member 2 on the side of the polarization prism 4 may be integrally formed with the prism member 2.

Further, in the first embodiment shown in FIG. 3, the laser light source 1, the prism member 5 and the two receivers (7 a, 7 a, 7b) and two half-wave plates (9a, 9b) and the right-angle prism 4 are respectively arranged on the second surface side. However, the arrangement is not limited to this arrangement, and the laser light source 1, the prism member 5 and the two receivers (7a, 7b) are arranged on the second surface side of the right-angle prism 2a, and the right-angle prism 2a has a second surface. Two half-wave plates (9a, 9b) and the right-angle prism 4 may be arranged on the surface 1 side, respectively.

Further, in the second embodiment shown in FIG. 3, the light source means for supplying the coherent light flux is composed of the laser light source 1 and the prism member 5 functioning as the light splitting means. Is used as a light source means, the light flux from one of the laser light sources is used as a first interferometer (prism member 2, quarter wave plate (8a ₁ , 8a ₂ , 8b ₁ , 8b ₂ ), 1/2 wave plate). 9a, the deflecting prism 4, the first detector 7a), and the light flux from the other laser light source is guided to the second interferometer (prism member 2, quarter wave plate (8a ₃ , 8a ₄ , 8b ₃ , 8b ₄ )). , 1/2 wavelength plate 9b, deflecting prism 4, second detector 7b). In this case, when there is a change in the optical characteristics (wavelength fluctuation, etc.) of the two light sources (laser light source), it is desirable to provide a correction means for correcting the change in the optical characteristics.

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

Therefore, a third embodiment, which is 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 designated 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 in the lower part forming the measurement optical path OP _M and the upper part forming the two reference optical paths (OP _R1 , OP _R2 ). 2 is divided into the prism member 63 portion, a prism member 63 of the upper portion is arranged in a state of being rotated 90 degrees with respect to the prism member 62 of the lower portion, two reference light paths relative to the measurement optical path OP _M ( OP _R1 and OP _R2 are non-parallel, that is, vertical.

Here, the lower prism member 62 is constituted by laminating the right-angle prism 62a and the right-angle prism 62a, and the pasting surface is formed by the polarization separation surface (polarization beam splitter surface) S _3. ing. The prism member 63 on the upper side is formed by bonding a right-angle prism 63a and a right-angle prism 63b, and the bonding surface is formed by a polarization splitting surface (polarization beam splitter surface) S ₄ .

Note that the configuration is the same as that of the first embodiment shown in FIG. 1 except for the configurations of the prism members 62 and 63, and therefore detailed description including the operation of the apparatus will be omitted. As described above, also in the example shown in FIG. 7, 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 to accurately detect the movement amount and position of the movable mirror 3. Moreover, also in this example, 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. Therefore, extremely high precision measurement is guaranteed.

In the second embodiment shown in FIG. 3 as well, it is possible to make the measurement optical path and the reference optical path as shown in FIG. 7 orthogonal to each other. For example, if the two polarizing prisms 62 and 63 shown in FIG. 7 are used instead of the polarizing prism 2 of FIG. 3, the measurement optical path and the reference optical path can be made orthogonal to each other. In addition, an optical path deflecting member for bending the optical path is appropriately arranged in at least one of the measurement optical path and the reference optical path of each interferometer in each of the above-described embodiments so that each optical path can be made compact in size. It is also possible to draw around.

Further, in each of the above embodiments, an example in which the measurement optical path lengths of the first and second interferometers are equal to each other has been shown. However, as described in the principle of FIG. It goes without saying that the measurement optical path length may be different. As described above, the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the scope of the present invention.

[0150]

【The invention's effect】

 As described above, according to the present invention, it is possible to realize a high-performance interferometer device which has a very small measurement error even when fluctuations of gas such as air occur and which can realize highly accurate measurement in principle.

[Brief description of drawings]

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

2A is a plan view showing the states of a measurement optical path and first and second reference optical paths that pass under the prism member 2 of the first embodiment, and FIG. 2B is a prism member 2 of the first embodiment. Is a plan view showing the states of the measurement optical path and the first reference optical path that pass through the upper part of FIG.
(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 device of the present invention.

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

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

[Explanation of symbols for main parts]

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 ·· .... Quarter wave plate 9, 9a, 9b ... 1/2 wave plate 10 ... Calculation processing unit 60 ... Sealed tube 61 ...・ Bar-shaped member

Claims (1)

[Scope of utility model registration request] 1. An interferometer device for measuring the amount of displacement of an object to be measured, wherein one slanted surface and the other bottom surface of two right-angle prisms are joined to each other, and the joined surface is a polarization splitting surface. An interferometer device characterized in that a member is arranged and a measuring optical path and a reference optical path are formed by the optical member.