JP2000055611A - Light wave interference measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of measuring precision to conduct precise measurement even when a space between a light transmitting window for measuring light arranged to oppose to a measuring object and the measuring object is fluctuated by vibration or the like. SOLUTION: In this measuring device, a moving mirror 120 is irradiated with measuring light from an inside of a vacuum container 201 through a window member 145 to measure a displacement amount ΔD1 of the mirror 120. A reflection mirror 162 provided in the vicinity of the window material 145 is irradiated with measuring light for measuring a correcting amount to measure a space fluctuation ΔD2 between the window material 145 and the mirror 120. An arithmetic unit 501 corrects the ΔD1 based on the ΔD2 to provide a true displacement amount ΔD of the moving mirror 120.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference measuring apparatus for measuring the length, displacement, etc. of an object with high accuracy.

[0002]

2. Description of the Related Art In an optical interference measuring apparatus, most of the optical paths through which measurement light passes are kept in a vacuum in order to avoid the influence of fluctuation of the refractive index of gas.

A heterodyne interferometer, which is a type of optical interference measuring apparatus, obtains a beat signal by causing light passing through a measurement optical path and a reference optical path reciprocating in a movable mirror to obtain a beat signal, and the beat signal is determined according to the amount of movement of the movable mirror. To obtain a signal. In such a conventional apparatus, the measuring optical path is covered with a bellows, and the open end of the bellows facing the movable mirror is covered with a window material. Then, the space formed by the bellows and the window material is evacuated. The measurement light emitted from the window material is reflected by the movable mirror, and then enters the window material again.
At this time, the bellows expands and contracts in accordance with the movement of the movable mirror, and the distance between the window material and the movable mirror is kept constant.

[0004]

In such a conventional apparatus, the distance between the window member and the movable mirror may fluctuate due to vibration or the like. For this reason, there is a problem in that the optical path length changes and a measurement error occurs, resulting in a decrease in measurement accuracy.

The situation described above is the same for various lightwave interference measuring devices other than the heterodyne interferometer.

The present invention has been made in view of such circumstances, and even if the distance between the transmission window of the measurement light disposed opposite to the measurement object and the measurement object fluctuates due to vibration or the like. It is an object of the present invention to provide a light wave interference measurement device capable of preventing a decrease in measurement accuracy and performing a precise measurement.

[0007]

According to a first aspect of the present invention, there is provided an optical interference measuring apparatus comprising: a container having a window; and an interferometer at least partially housed in the container. And an interferometer for irradiating measurement light from inside the container through the window and performing a predetermined measurement of a measurement object positioned at an interval from the window outside the container. In, based on the fluctuation amount or the displacement amount measured by the correction measuring means for measuring the fluctuation amount of the interval between the window and the measurement target or the displacement amount of the window, and measured by the correction measuring means And a correcting means for correcting the measurement result by the interferometer.
In addition, as the predetermined measurement of the measurement object, a length, a displacement, and the like can be given.

According to the first aspect, the amount of change in the distance between the window and the object to be measured or the amount of displacement of the window is measured by the measuring means for correction, and based on the measured amount of displacement or the amount of change. Thus, the measurement result by the interferometer is corrected. Therefore, even if the distance between the window of the container through which the measurement light passes and the object to be measured fluctuates due to vibration or the like, it is possible to prevent a decrease in measurement accuracy and to perform precise measurement of the object to be measured.

A light wave interference measuring apparatus according to a second aspect of the present invention is the light wave interference measuring apparatus according to the first aspect, wherein the correction measuring means includes a correction interferometer.

In the first aspect, the correction measuring means is not limited to the interferometer. However, if the interferometer is used as the correction measuring means as in the second aspect, the amount of change or displacement can be reduced. It is preferable because the amount can be measured with high accuracy, and the measurement accuracy of the measurement object is further improved.

The light wave interference measuring apparatus according to a third aspect of the present invention is the light wave interference measuring apparatus according to the second aspect, wherein the measuring optical path of the interferometer and the measuring optical path of the correcting interferometer are at least in the window. They are coaxial in the vicinity.

In the second aspect, the measurement optical paths of the interferometers do not necessarily have to be coaxial near the window, but if they are coaxial as in the third aspect, the window may be inclined. Even in such a case, the fluctuation amount or the displacement amount that causes the measurement error of the measurement target can be accurately measured, and the measurement accuracy of the measurement target is further improved, which is preferable.

A light wave interference measuring apparatus according to a fourth aspect of the present invention is the light wave interference measuring apparatus according to the second or third aspect, wherein a part of the interferometer and a part of the correcting interferometer are shared. It was done.

In the second and third aspects, the measuring means for correction can be provided completely independently of the interferometer for performing the original measurement. However, as in the fourth aspect, a part of both is provided. If a common configuration is used, the configuration is simple and inexpensive, and the size can be reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic block diagram showing an optical interference measuring apparatus according to a first embodiment of the present invention. The apparatus according to the present embodiment is configured as a heterodyne interferometer.

The vacuum vessel 201 is provided with window members 140, 141, 142 and 145 through which light passes, and an interferometer is built in the vacuum vessel 201.
The vacuum vessel 201 has a movable part 201a that can expand and contract in parallel with the measurement light (in the horizontal direction in FIG. 1) and a fixed part 200b. The movable mirror 120 is installed on a movable body that is displaced in parallel with the measurement light, and the movable mirror 120 is displaced in parallel with the measurement light. The movable part 201a of the vacuum vessel 201 is mechanically connected to the moving body, and the movable part 201a expands and contracts according to the driving of the moving body, and the window member 145 and the moving body 12
The gap G between 0 and 0 is kept almost constant. However, in the present invention, it is not always necessary to keep the interval G substantially constant. Regarding the expansion and contraction of the movable part 201a,
An external power source may be provided even if it is not mechanically connected to the driving of the moving body, and the moving body may be independently moved in synchronization with the movement of the moving body. A window member 145 through which the measuring light passes and a reflecting mirror 162 that reflects the measuring light for measuring the correction amount are attached to an end surface of the movable portion 201a facing the moving mirror 120.

The light source 300 coaxially emits light having a polarization direction parallel to the page of the frequency f0 and light perpendicular to the page of the frequency f1. These two lights pass through the window material 140 attached to the vacuum vessel 201 and are separated by the PBS 100 in accordance with the respective polarization directions. Light having a polarization direction parallel to the paper surface at the frequency f0 is transmitted through the PBS 100, and The light having the polarization direction perpendicular to the paper surface of f1 is reflected by the PBS 100 toward the quarter-wave plate 110.

A part of the light having the frequency f0 transmitted through the PBS 100 is a beam splitter (hereinafter referred to as "BS").
At 150, the light is reflected toward the wave plate 112, and the rest is B
The light passes through S150. Frequency f0 transmitted through BS150
Are transmitted through the PBS 102 and the window material 141 and are incident on the detector 400. On the other hand, PB
The light having the frequency f1 reflected by S100 is transmitted through the wave plate 110 and the window material 145, is substantially coaxially reflected by the moving mirror 120, is transmitted through the window material 145 and the wave plate 110, and is transmitted through the PBS1.
Come back to 00. Here, since the wave plate 110 is a 波長 wave plate, the light of the frequency f1 that has returned to the PBS 100 transmits through the wave plate 110 twice and has a polarization azimuth of nine.
The light is rotated by 0 degrees, and has a polarization direction parallel to the paper surface.
The light of the frequency f1 having the polarization direction parallel to the paper is PB
The light passes through S100, is reflected by the reflecting mirror 160 toward the BS 151, and is divided into transmitted light and reflected light at the BS 151. The light of the polarization direction parallel to the sheet of the frequency f1 reflected by the BS 151 is transmitted through the half-wave plate 113,
The light enters the PBS 102. Here, the wavelength plate 113 is 1 /
Since it is a two-wavelength plate, the light of frequency f1 is
Rotates the polarization direction by 90 degrees, and becomes light having a polarization direction perpendicular to the paper surface. The light of frequency f1 having a polarization direction perpendicular to the paper is reflected by the PBS 102 almost coaxially with the light of frequency f0, passes through the window material 141, and enters the detector 400.

Although not shown, a polarizer is attached to the detector 400, and the polarization direction of the polarizer is defined as that of light having a polarization direction parallel to the paper of frequency f0 and light having a polarization direction perpendicular to the paper of frequency f1. It is inclined by 45 degrees with respect to each polarization direction. For this reason, the two lights transmitted through the polarizer interfere with each other, the interference light is photoelectrically converted by the detector 400, and the difference between the frequency f0 and the frequency f1 (f0−f) is detected from the detector 400.
A beat signal having a frequency equal to 1) is output. This beat signal is input to the arithmetic unit 501 as a length measurement signal for measuring the displacement of the movable mirror 120. Further, the light source 300 has a difference (f0−f) between the frequency f0 and the frequency f1.
A beat signal having a frequency equal to 1) is output. This beat signal is input to the arithmetic unit 501 as a reference signal for measuring the displacement of the movable mirror 120.

The arithmetic unit 501 compares the phase of the reference signal from the light source 300 with the phase of the length measurement signal from the detector 400, and calculates the displacement ΔD1 along the optical axis of the movable mirror 120 from the phase change. Ask.

The frequency f reflected by the aforementioned BS 150
The light of the polarization direction parallel to the paper surface of
The movable part 2 of the vacuum vessel 201 is transmitted through the 波長 wavelength plate 112 and
The light is substantially coaxially reflected by the reflecting mirror 162 attached to the end surface of the light receiving surface 01a, passes through the wave plate 112, and enters the PBS 101. Here, since the wavelength plate 112 is a 波長 wavelength plate, the light of the frequency f0 that has returned to the PBS 101 is transmitted through the wavelength plate 112 twice, so that the polarization direction is rotated by 90 degrees, and the polarized light perpendicular to the paper surface is polarized. It is the light of the direction. The light of the frequency f0 having the polarization direction perpendicular to the paper is PBS101
And the light is sequentially reflected by the reflecting mirror 161 and enters the PBS 103. The light having a polarization direction perpendicular to the paper surface at the frequency f0 incident on the PBS 103 is reflected by the PBS 103, and is reflected by the window material 14.
After passing through No. 2, the light enters the detector 401. Meanwhile, BS
The light having a polarization direction parallel to the sheet of the frequency f1 that has passed through 151 passes through the PBS 103 almost coaxially with the light having the frequency of f0, passes through the window 142, and enters the detector 401.

Although not shown, a polarizer is attached to the detector 401, and the polarization direction of the polarizer is defined as a polarization direction of light having a polarization direction perpendicular to the paper of frequency f0 and a polarization direction of light having a polarization direction parallel to the paper of frequency f1. It is inclined by 45 degrees with respect to each polarization direction. Therefore, the two lights transmitted through the polarizer interfere with each other, the interference light is photoelectrically converted by the detector 401, and the difference between the frequency f0 and the frequency f1 (f0−f) is detected from the detector 401.
A beat signal having a frequency equal to 1) is output. This beat signal is used as a measurement signal for measuring a variation in the interval between the movable mirror 120 and the window member 145, and is used as a measurement signal by the arithmetic unit 501
Is input to

The arithmetic unit 501 compares the phase of the reference signal from the light source 300 with the phase of the measurement signal from the detector 401, and obtains the amount of variation ΔD2 between the moving mirror 120 and the window member 145 from the amount of phase change. .

The arithmetic unit 501 calculates the displacement ΔD1 of the movable mirror 120 obtained based on the length measurement signal from the detector 400.
Is corrected by an operation based on the interval variation ΔD2 obtained based on the length measurement signal from the detector 401, and the moving mirror 12
The true displacement ΔD of 0 is obtained.

Here, a correction formula for obtaining the true displacement ΔD of the movable mirror 120 will be described with reference to FIG. FIG.
Shows a model for calculating the true displacement ΔD of the movable mirror 120. In FIG. 2, O is a predetermined reference position, 12
0 is the position of the movable mirror 120 before the movement, 120 ′ is the movable mirror 1
20 is the position after the movement, 145 is the position of the window material 145 before the movement, 145 'is the actual position of the window material 145 after the movement, 14
5 "is the ideal position of the window material 145 after the movement, L0 is the geometric length between the reference position O and the position 120, and G is the position 145.
Length (geometric length between the window member 145 and the moving mirror 120 before movement) between G and the position 120, G + ΔG is the position 14
Geometry length between 5 'and position 120' (window material 1 after movement)
45 indicates the true displacement of the movable mirror 120 (geometric length between the position 120 and the position 120 '). Also, the window material 145 and the moving mirror 120
Is n0, and the refractive index in the vacuum vessel 201 is nv = 1.

The displacement amount ΔD1 of the movable mirror 120 obtained based on the length measurement signal from the detector 400 is represented by the position O and the position 12
Since this is equivalent to a value obtained by subtracting the optical path length between the position O and the position 120 from the optical path length between 0 ′, it is expressed by Expression 1 as can be seen from FIG.

[0027]

ΔD1 = [nv ｛L0 + ΔD− (G + ΔG)｝ + n0 (G + ΔG)] − [nv (L0−G) + n0 · G] = ΔD + (n0−1) ΔG

In the present embodiment, the interval variation ΔD2 obtained based on the length measurement signal from the detector 401 is represented by Δ
G, the displacement Δ
D1 is represented by Equation 2.

[0029]

ΔD = ΔD1− (n0−1) ΔD2

Therefore, the arithmetic unit 501 calculates the displacement Δ
From D1 and the interval variation ΔD2, the true displacement ΔD of the movable mirror 120 can be obtained by calculation according to Equation 2.

As described above, according to the present embodiment, the measured displacement ΔD1 is replaced by the interval variation ΔD measured for correction.
2, the true displacement amount ΔD is obtained, so that even if the interval G fluctuates, a decrease in measurement accuracy can be prevented, and accurate measurement of the displacement of the movable mirror 120 can be performed. it can.

The refractive index n0 of the gas may be a known constant value measured in advance. However, since the refractive index n0 always changes depending on the temperature, the atmospheric pressure, the partial pressure of water vapor, etc., the measurement accuracy is further improved. Therefore, it is preferable to use a value monitored during measurement of the displacement amount ΔD. As a method of obtaining the refractive index n0, for example, a method of optically obtaining using a wavelength compensator or the like, or measuring the values of the wavelength of the light to be measured, temperature, humidity, atmospheric pressure, partial pressure of water vapor, etc. A method of calculating from a refractive index formula such as the formula (B. Edlen: Metrologia 2. p. 71 (1966)) can be mentioned. The same is true for the second embodiment described later.

In this embodiment, as can be seen from the above description, the portion related to the two lights incident on the detector 400 via the window 141 is provided from the inside of the container 201 via the window 145. An interferometer configured to measure the displacement amount ΔD1 of the movable mirror 120 by irradiating the measurement light is configured. In addition, a portion related to the two lights incident on the detector 401 via the window member 142 constitutes an interferometer that measures a distance variation ΔD2 between the window member 145 and the movable mirror 120. These two interferometers share the light source 300 and the like.

(Second Embodiment) FIG. 3 is a schematic configuration diagram showing an optical interference measuring apparatus according to a second embodiment of the present invention. The device according to the present embodiment is also configured as a heterodyne interferometer that measures the displacement of the movable mirror 120 as a measurement target. 3, the same or corresponding elements as those in FIG. 1 are denoted by the same reference numerals.

While the first embodiment described above is an example in which the distance variation ΔD2 between the movable mirror 120 and the window member 145 is measured as a value used for correction, this embodiment is different from the first embodiment in that This is an example of measuring a displacement amount ΔD3 of the window material 146 as a value used for correction.

Window materials 140, 141, 142, and 146 through which light passes are attached to the vacuum vessel 202, and an interferometer is built in the vacuum vessel 202.
The vacuum container 202 has a movable part 202a that can expand and contract in parallel with the measurement light (in the horizontal direction in FIG. 3) and a fixed part 202b. The movable mirror 120 is installed on a movable body that is displaced in parallel with the measurement light, and the movable mirror 120 is displaced in parallel with the measurement light. The movable part 202a of the vacuum vessel 202 is mechanically connected to the moving body, and the movable part 202a expands and contracts according to the driving of the moving body, and the window member 145 and the moving body 12
The gap G between 0 and 0 is kept almost constant. Regarding the expansion and contraction of the movable part 202a, an external power source can be provided even if it is not mechanically connected to the driving of the moving body, and the moving body 202a can be moved independently of the movement of the moving body. A window member 145 through which measurement light passes is attached to an end surface of the movable unit 202a facing the movable mirror 120.

The light source 300 coaxially emits light having a polarization direction parallel to the paper of frequency f0 and light perpendicular to the paper of frequency f1. These two lights pass through the window member 140 attached to the vacuum container 202 and are separated by the PBS 100 in accordance with the respective polarization directions. Light having a polarization direction parallel to the paper surface of the frequency f0 is transmitted through the PBS 100 and the frequency f1 is transmitted. Is reflected by the PBS 100 toward the BS 152.

A part of the light having the frequency f0 transmitted through the PBS 100 is reflected by the BS 153 toward the half-wave plate 115, and the rest is transmitted through the BS 153. The light of the polarization direction parallel to the paper surface of the frequency f0 reflected by the BS153 is
The light passes through the wave plate 115 and enters the PBS 104. Here, since the wave plate 115 is a half-wave plate, the frequency f
The light of 0 has its polarization direction rotated by 90 degrees by the wavelength plate 115, and becomes light with a polarization direction perpendicular to the paper surface. The light of frequency f0 having the polarization direction perpendicular to the paper is reflected by the PBS 104,
The light passes through the window material 142 and enters the detector 402.

On the other hand, the frequency f1 reflected by the PBS 100
A part of the light having the polarization direction perpendicular to the paper of FIG. 6 passes through the BS 152 and enters the window material 146. A thin film that reflects part of light and transmits the rest is deposited on the window material 146. That is, the window material 146 forms a half mirror. The light of the frequency f1 transmitted through the window material 146 is transmitted through the 波長 wavelength plate 114, is reflected almost coaxially by the movable mirror 120, is transmitted through the wavelength plate 114 and the window material 146, and is transmitted through the BS 152.
Come back to. Here, since the wave plate 114 is a 波長 wave plate, the light of the frequency f1 returning to the BS 152 is
The light is transmitted through the wave plate 114 twice, so that the polarization direction is rotated by 90 degrees, so that the light has a polarization direction parallel to the paper surface. A part of the light of the frequency f1 having the polarization direction parallel to the paper is BS
Reflected at 152, the rest passes through BS 152.
The light of the frequency f1 having the polarization direction parallel to the paper surface reflected by the BS 152 is incident on the polarizer 170.
Is cut by the polarizer 170 because it is installed so as to transmit only light having a polarization direction perpendicular to the paper surface. BS1
The light having the polarization direction parallel to the sheet of the frequency f1 that has passed through the filter 52 passes through the PBS 100, is reflected by the reflecting mirror 160, and
It is incident on the BS 104. The light having a polarization direction parallel to the sheet of the frequency f1 incident on the PBS 104 is made substantially coaxial with the light of the frequency f0 by the PBS 104, passes through the window member 142, and enters the detector 402.

Although not shown, a polarizer is attached to the detector 402, and the polarization direction of the polarizer is determined by the detector 402.
Are tilted by 45 degrees with respect to the polarization directions of the two lights that have entered. For this reason, the two lights transmitted through the polarizer interfere with each other, and the interference light is photoelectrically converted by the detector 402, and the detector 402
As a result, a beat signal having a frequency equal to the difference (f0−f1) between the frequency f0 and the frequency f1 is output. This beat signal is input to the arithmetic unit 502 as a length measurement signal for measuring the displacement of the movable mirror 120. Also, the light source 300
Outputs a beat signal having a frequency equal to the difference (f0-f1) between the frequency f0 and the frequency f1. This beat signal is input to the arithmetic unit 502 as a reference signal for measuring the displacement of the movable mirror 120.

The arithmetic unit 502 compares the phase of the reference signal from the light source 300 with the phase of the length measurement signal from the detector 402, and calculates the amount of displacement ΔD1 along the optical axis of the movable mirror 120 from the amount of phase change. Ask.

Frequency f1 partially reflected by window material 146
Is reflected by the BS 152 and enters the polarizer 170. As described above, the polarizer 170 is installed so as to transmit only light having a polarization direction perpendicular to the paper surface. Therefore, the light passes through the polarizer 170, is reflected by the reflection mirror 161, and enters the PBS 105. PBS
The light having a polarization direction perpendicular to the paper surface of the frequency f1 incident on the light 105 is reflected by the PBS 105, passes through the window material 141, and then enters the detector 403. On the other hand, light having a polarization direction parallel to the sheet of the frequency f0 transmitted through the BS 153 is transmitted by the PBS.
105 is transmitted substantially coaxially with the light of the frequency f1, and
1 and enter the detector 403.

Although not shown, a polarizer is attached to the detector 403, and the polarization direction of the polarizer is determined by the detector 403.
Are tilted by 45 degrees with respect to the polarization directions of the two lights that have entered. Therefore, the two lights transmitted through the polarizer interfere with each other, and the interference light is photoelectrically converted by the detector 403, and
As a result, a beat signal having a frequency equal to the difference (f0−f1) between the frequency f0 and the frequency f1 is output. This beat signal is input to the arithmetic unit 502 as a measurement signal for measuring the displacement of the window material 146.

The arithmetic unit 502 compares the phase of the reference signal from the light source 300 with the phase of the measurement signal from the detector 403, and calculates the amount of displacement ΔD3 along the optical axis of the window member 146 from the amount of phase change. .

The arithmetic unit 502 includes a detector 402
The displacement amount ΔD1 of the movable mirror 120 obtained based on the length measurement signal from the detector 403 is corrected by calculation based on the displacement amount ΔD3 of the window member 146 obtained based on the length measurement signal from the detector 403, and the movable mirror 120 is corrected. Is calculated.

Here, the correction formula for calculating the true displacement ΔD of the movable mirror 120 will be described with reference to FIG. 2 again.
The meaning of each symbol in FIG. 2 is as already described in relation to the first embodiment. In the present embodiment, the displacement amount ΔD3 of the window material 146 obtained based on the length measurement signal from the detector 403 is the position 145 in FIG. 2 since the refractive index in the vacuum vessel is nv = 1. 145 'equals the geometric length. Therefore, as can be seen from FIG. 2, the interval variation ΔG is expressed by Expression 3 using the displacement ΔD3. Substituting Equation 3 into Equation 1 and rearranging yields Equation 4.

[0047]

## EQU3 ## ΔG = ΔD−ΔD3

[0048]

ΔD = (1 / n0) {ΔD1 + (n0-1) ΔD3}

Therefore, the arithmetic unit 502 calculates the displacement amount Δ
From D1 and the displacement amount ΔD3, the true displacement amount ΔD of the movable mirror 120 can be obtained by calculation according to Equation 4.

As described above, according to the present embodiment, the measured displacement amount ΔD1 is corrected based on the displacement amount ΔD3 measured for correction, and the true displacement amount ΔD is obtained. Even if it fluctuates, a decrease in measurement accuracy can be prevented, and accurate measurement of the displacement of the movable mirror 120 can be performed.

In this embodiment, as can be seen from the above description, the portion related to the two lights that enter the detector 402 through the window member 142 passes through the window member 146 from inside the container 201. An interferometer configured to measure the displacement amount ΔD1 of the movable mirror 120 by irradiating the measurement light is configured. In addition, a portion related to the two lights incident on the detector 403 through the window material 141 constitutes an interferometer that measures the displacement ΔD3 of the window material 146. These two interferometers share the light source 300 and the like. In the present embodiment, the measurement optical paths of these two interferometers are coaxial between BS 152 and window material 146. For this reason,
The measurement error of the displacement ΔD3 of the window material is reduced, and the true displacement ΔD of the movable mirror 120 can be measured with higher accuracy.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

For example, as in the first embodiment,
Even when the distance variation ΔD2 between the moving mirror 120 and the window material 145 is measured as a value used for the correction, the window material 145 is not used without using the reflecting mirror 162 as in the second embodiment. As a half mirror and 1
The measurement optical paths of the two interferometers can be made coaxial at least in the vicinity of the window member 145, for example, by using the 波長 wavelength plate 114. Conversely, even when the displacement ΔD3 of the window material 146 is measured as a value used for correction as in the second embodiment, the measurement optical paths of the two interferometers are changed by using the reflecting mirror 162 or the like. Separation can also be made in the vicinity of the window material 146.

In the case of the first embodiment, a reflecting mirror is added at a position symmetrical to the reflecting mirror 162 with respect to the window member 145 (a lower position in FIG. 1).
Irradiates the measuring light for the measurement for correction to the interval variation ΔD
Similarly to the measurement of No. 2, the additional reflecting mirror is irradiated with another measurement light to measure the interval variation ΔD2 ′,
The average value of ΔD2 and ΔD2 ′ may be used as ΔD2 in Equation 2. In this case, even when the window material 145 is inclined, the measurement error of the interval variation between the window material 145 and the variation 120 is reduced.

In each of the above-described embodiments, the amount of displacement ΔD1 of the movable mirror 20, the amount of variation ΔD2 between the movable mirror 120 and the window member 145, and the amount of displacement D3 of the window member 146 are measured by heterodyne. However, homodyne measurement can also be performed. Further, each measurement is performed by a single pass, but a double pass configuration is also possible.

Further, the present invention can be applied to various light wave interference measuring devices other than the length measuring machine.

In each of the embodiments described above, the container is evacuated. However, for example, an inert gas or the like may be sealed in the container.

[0058]

As described above, according to the present invention,
Even if the distance between the window of the container through which the measurement light passes and the object to be measured fluctuates due to vibration or the like, a decrease in measurement accuracy can be prevented, and accurate measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a lightwave modulation device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a model for calculating a true displacement amount of a movable mirror.

FIG. 3 is a schematic configuration diagram showing an optical interference measuring apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 100-105 Polarizing beam splitter (PBS) 110-112,114 1/4 wavelength plate 113,115 1/2 wavelength plate 120 Moving mirror 130 Fixed mirror 140-142,145,146 Window material 150-153 Beam splitter (BS) 160-162 Reflecting mirror 170 Polarizer 200-202 Vacuum container 300 Light source 400-403 Detector 500-502 Arithmetic unit

Claims (4)

[Claims] 1. A container having a window, and an interferometer at least partially housed in the container, wherein the measuring light is irradiated from inside the container through the window, and the window is provided outside the container. An interferometer for performing a predetermined measurement of a measurement object positioned at an interval from the light wave interferometer, wherein a variation amount of an interval between the window and the measurement object or a displacement amount of the window is measured. A light wave interference measurement device comprising: a correction measurement unit; and a correction unit that corrects a measurement result obtained by the interferometer based on the fluctuation amount or the displacement amount measured by the correction measurement unit. . 2. An optical interference measuring apparatus according to claim 1, wherein said correcting measuring means includes a correcting interferometer. 3. The optical interference measurement apparatus according to claim 2, wherein a measurement optical path of the interferometer and a measurement optical path of the correction interferometer are coaxial at least near the window. 4. An optical interference measuring apparatus according to claim 2, wherein a part of said interferometer and a part of said correcting interferometer are shared.