JP2004077194A - Optical measuring apparatus using variable length vacuum light path cell, and method for manufacturing variable length vacuum light path cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical measuring apparatus that can improve working efficiency and can avoid the influence to a measurement error due to the mixture of impurities to the minimum. <P>SOLUTION: One end face of a vacuum container 11 where length dimensions are variable in a longitudinal direction is sealed by a fixing window 17. Additionally, the other end face of the vacuum container 11 is sealed by an optical transparent body 12 having a reflection film 13. Before using a refractive index measuring apparatus 1, a vacuum pump is connected to exhaust piping 18 that is provided in the vacuum container 11 for evacuating the inside of the vacuum container 11 and the exhaust piping 18 is sealed by welding. Since it is not necessary to connect the vacuum pump repeatedly, working efficiency can be improved. Additionally, the influence to the measurement error can be avoided to the minimum by preventing dust or the like from being mixed into the vacuum container 11. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical measuring device using a variable-length vacuum optical path cell and a method for manufacturing a variable-length vacuum optical path cell. More specifically, the present invention relates to an optical measuring device such as a gas refractive index measuring device and an optical displacement detector utilizing interference of laser light, and a method of manufacturing a variable-length vacuum optical path cell used in the optical measuring device.
[0002]
[Background Art]
Conventionally, a refractometer has been used to measure the refractive index of the atmosphere. The refractometer has a container in which the optical path of the laser beam from the laser interferometer is formed, and the measurement value of the laser interferometer when the inside of the container is in a vacuum state, and the atmosphere is filled in the container. The refractive index of the atmosphere is obtained from the difference from the measured value of the laser interferometer at the time of the operation.
Some of such refractometers use two laser interferometers, for example, a laser interferometer using a laser beam traveling in vacuum and a laser interferometer using a laser beam traveling in the atmosphere.
[0003]
This refractometer uses two laser beams split from one laser beam. Among these laser beams, a variable-length vacuum optical path cell formed of a metal bellows is provided in the middle of one optical path, and the movable end surface of the variable-length vacuum optical path cell is provided with reflecting mirrors on both surfaces. . One laser beam travels in the variable-length vacuum optical path cell, is reflected by one surface of the reflecting mirror, and enters one laser interferometer. On the other hand, the other laser beam travels through the atmosphere, is reflected by the other surface of the reflecting mirror, that is, the surface opposite to the side on which the one laser beam is reflected, and enters the other laser interferometer.
In the refractometer having such a configuration, the movement amount of the vacuum light path caused by the movement of the movable end face of the variable-length vacuum light path cell is measured by one laser interferometer, and the movement amount of the atmospheric light path is measured by the other laser interferometer. Measurements are taken and the refractive index of the atmosphere is determined from these measurements.
[0004]
[Problems to be solved by the invention]
By the way, in the refractometer having such a structure, the variable length vacuum optical path cell is usually provided with an exhaust port, and a vacuum pump is connected to the exhaust port to evacuate the inside of the variable length vacuum optical path cell. However, in the path from the exhaust port to the vacuum pump, a vacuum valve, a pipe joint, a sealing member, and the like are provided, and since a small amount of air flows in from these members, vacuum cannot be maintained for a long time. . Therefore, it is necessary to perform an operation of evacuating the inside of the variable-length vacuum optical path cell every time the measurement is performed. For this reason, it takes time to connect the vacuum pump to the variable-length vacuum optical path cell and to evacuate the air with the vacuum pump, and the working efficiency is poor. In addition, since a vacuum pump is connected each time measurement is performed, dust and impurities such as pump oil may be mixed in from the exhaust port, which may greatly affect measurement accuracy.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical measuring device using a variable-length vacuum optical path cell and a variable-length vacuum optical path cell, which can improve the working efficiency and minimize the influence on the measurement error due to the contamination of impurities. It is to provide a method.
[0006]
[Means for Solving the Problems]
Therefore, the optical measuring device using the variable-length vacuum optical path cell according to claim 1 of the present invention splits one laser beam and converts one split beam into a beam having a variable longitudinal length. An optical measuring device that enters a variable-length vacuum optical path cell and measures displacement, refractive index, and the like using interference between a reflected light beam from the variable-length vacuum optical path cell and the other split light beam. The cell is hermetically provided at one end in the longitudinal direction, and a light outgoing and incident part through which laser light can pass, and a laser which is hermetically provided at the other end of the variable-length vacuum optical path cell and is incident from the light outgoing and incident part. It is characterized by comprising a reflecting mirror for reflecting light to the light entrance / exit portion, and an exhaust pipe communicating with the variable-length vacuum optical path cell, and having a vacuum-tight inside of the variable-length vacuum optical path cell and a sealed end. I do.
[0007]
In the present invention having this configuration, the exhaust pipe for evacuating the air in the variable-length vacuum optical path cell is provided, and the tip of the exhaust pipe is sealed in a state where the inside of the variable-length vacuum optical path cell is evacuated in advance. . Therefore, the inside of the variable-length vacuum optical path cell is sealed in a vacuum state, and the vacuum state is held semipermanently. For this reason, unlike the related art, it is not necessary to create a vacuum every time the measurement is performed, so that the measurement work efficiency is improved.
In addition, this allows a vacuum pump to be connected to the exhaust pipe only once before use to release air in the variable-length vacuum optical path cell, thereby preventing contamination of impurities such as dust into the variable-length vacuum optical path cell. In addition, the influence on the measurement error due to the contamination of impurities is minimized.
[0008]
Here, such an optical measuring device can be applied to, for example, an optical displacement detector that measures displacement, a gas refractive index measuring device that measures the refractive index of gas, and the like. When the optical measuring device is applied to an optical displacement detector, a tracing stylus or the like is attached to one end of the variable-length vacuum optical path cell whose variable length is variable. In this optical measuring device, interference between the reflected light beam from the variable-length vacuum optical path cell and the other demultiplexed light beam can be obtained. Change. The displacement can be measured from the change in the state of the interference.
Further, when the optical measuring device is applied to a gas refractive index measuring device, the interference between the reflected light beam from the variable length vacuum optical path cell and the other demultiplexed light beam obtained from the optical measuring device of the present invention. Separately, the configuration is such that interference by light flux before and after entering the gas is obtained. Then, the refractive index of the gas can be measured by comparing the interference of the light beam obtained by entering the gas with the interference of the light beam obtained by entering the variable length vacuum optical path cell.
[0009]
According to the method of manufacturing a variable length vacuum optical path cell according to claim 2 of the present invention, one laser beam is demultiplexed and one of the demultiplexed light beams is transmitted to a variable length vacuum optical path cell having a variable longitudinal length. A method of manufacturing a variable-length vacuum optical path cell used in an optical measuring device that measures the displacement, refractive index, and the like by utilizing the interference between the reflected light beam from the variable-length vacuum optical path cell and the other demultiplexed light beam. At one end in the longitudinal direction of the variable-length vacuum optical path cell, a light-emitting / light-entering portion through which laser light can pass is sealed, and at the other end of the variable-length vacuum optical path cell, laser light incident from the light-emitting / injecting portion is emitted. Along with sealing the reflecting mirror that reflects the light to the entrance, an exhaust pipe is provided with one end communicating with the variable-length vacuum optical path cell and the other end protruding outside the variable-length vacuum optical path cell. Air is sucked from the exhaust pipe communicating with the optical path cell, and the variable length vacuum light After the inside of the cell in a vacuum, characterized by sealing the tip of the exhaust pipe while holding the vacuum.
[0010]
In the present invention of this method, the air in the variable-length vacuum optical path cell is previously suctioned from the exhaust pipe before use, and the exhaust pipe is sealed in a vacuum state. Therefore, the variable-length vacuum optical path cell is sealed in a vacuum state, and the vacuum state is maintained semipermanently. Unlike the conventional method, it is not necessary to create a vacuum every time the measurement is performed, so that the measurement work efficiency is improved.
In addition, this allows a vacuum pump to be connected to the exhaust pipe only once before use to release air in the variable-length vacuum optical path cell, thereby preventing contamination of impurities such as dust into the variable-length vacuum optical path cell. In addition, the occurrence of measurement errors due to the contamination of impurities is minimized.
Here, “before use” refers to a state before the variable-length vacuum optical path cell is shipped as a product, a state before the variable-length vacuum optical path cell is incorporated into an optical measurement device, and before the product is shipped.
[0011]
According to a third aspect of the present invention, in the method for manufacturing a variable-length vacuum optical path cell according to the second aspect, the exhaust pipe is sealed by welding. .
In the present invention of this method, since the end of the exhaust pipe is sealed by welding, the opening is satisfactorily adhered and sealed, and the vacuum state of the variable-length vacuum optical path cell is reliably and satisfactorily maintained for a long period of time.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a gas refractive index measuring device 1 as an optical measuring device according to an embodiment of the present invention.
The gas refractive index measuring apparatus 1 has a vacuum laser beam Pa traveling in a vacuum vessel 11 as a variable-length vacuum optical path cell having a variable longitudinal length, and a vacuum laser interferometer using the vacuum laser beam Pa. 20 and a gas laser interferometer 30 having a gas laser beam Pb parallel to the vacuum laser beam Pa and traveling in the space of the test gas, and using the gas laser beam Pb. Among them, the vacuum laser beam Pa and the gas laser beam Pb are obtained by splitting one laser beam P emitted from the laser light source 41.
[0013]
The vacuum vessel 11 includes a metal bellows portion 14 and metal blocks 15 and 16 fixed to both ends of the bellows portion 14. The contact portions of the bellows portion 14 and the blocks 15, 16 are sealed by welding or the like. The inside of the vacuum vessel 11 is in a vacuum state, and the outside of the vacuum vessel 11 is a space for a test gas.
The block 15 fixed to one end of the vacuum vessel 11 is provided with a sealed window 17 as a light emitting / receiving part through which the laser beam Pa can pass. Further, the vacuum vessel 11 is fixed to a vacuum laser interferometer 20 at a block 15.
[0014]
The end face of the block 16 fixed to the other end of the vacuum vessel 11 is a movable end face that can move along the longitudinal direction of the vacuum vessel 11. An optical transparent body 12 is hermetically disposed in the block 16, and a reflective film 13 is formed on one side surface of the optical transparent body 12. The reflection film 13 has a reflection surface with high reflectance on both side surfaces. That is, the reflecting surface on the vacuum side of the reflecting film 13 is a vacuum-side reflecting mirror 13A as a reflecting mirror, and the reflecting surface on the test gas side is a gas-side reflecting mirror 13B. These reflecting mirrors 13A and 13B Each of them is disposed substantially perpendicular to the vacuum laser beam Pa and the gas laser beam Pb.
Further, the block 15 is integrally provided with an exhaust pipe 18 communicating with the vacuum vessel 11. The distal end of the exhaust pipe 18 is sealed, so that the inside of the vacuum vessel 11 is hermetically closed to be in a vacuum state. Is kept.
[0015]
Such a vacuum vessel 11 is manufactured as follows.
First, the blocks 15 and 16 are welded to both ends of the bellows portion 14. Then, the fixing window 17 is fixed to the block 15 by welding or the like, and the mounting surface is sealed over the entire circumference. Similarly, the optical transparent body 12 provided with the reflective film 13 is fixed to the block 16 by a method such as welding and is sealed over the entire circumference. At this stage, the exhaust pipe 18 provided integrally with the block 15 has an opening whose tip projects outside the vacuum vessel 11.
Here, it is desirable that both materials have close thermal expansion coefficients so that the welding between the block 15 and the fixed window 17 is good. Similarly, it is desirable that the block 16 and the optically transparent body 12 have similar thermal expansion coefficients so that the two are well welded.
[0016]
Next, as shown in FIG. 2A, a vacuum pump is connected to the exhaust pipe 18, and air in the vacuum vessel 11 is sucked by the vacuum pump to make a vacuum state. At this time, it is desirable that the degree of vacuum in the vacuum vessel 11 is adjusted to an extent not affected by the gas refractive index.
In this state, as shown in FIG. 2B, the exhaust pipe 18 is sealed off by welding or fusing. At this time, the tip protruding from the vacuum vessel 11 may remain in a protruding state, or the protruding portion from the vacuum vessel 11 may be removed by sealing off. Thereby, the inside of the vacuum vessel 11 is sealed in a vacuum state.
[0017]
Note that the vacuum laser beam Pa and the gas laser beam Pb are located on the movable end surface of the vacuum vessel 11, that is, on the coaxial line with the optical transparent body 12 interposed therebetween. Further, the vacuum laser interferometer 20 and the gas laser interferometer 30 are also arranged with the optically transparent body 12 interposed therebetween, and the vacuum laser beam Pa and the gas laser beam Pb are respectively provided by the laser interferometers 20, 30 and the reflecting mirrors 13A, 13B. An optical length measuring optical path is formed between them.
[0018]
The optical transparent body 12 can be moved along the laser beam by the driving mechanism 50, and the vacuum container 11 expands and contracts as the optical transparent body 12 moves.
The driving mechanism 50 includes a driving body 51 to which the optically transparent body 12 is fixed, and one driving roller that rotates in the driving direction of the driving body 51 while being in contact with the driving body 51 and moves the driving body 51 at a constant speed. 52, a driving means 53 for driving the driving roller, and a guide mechanism 55 for holding the driving body 51 in a predetermined posture via a fluid. The drive mechanism 50 is controlled at a constant speed by drive control means 54 described later.
[0019]
One laser beam P emitted from the laser light source 41 is split by the beam splitter 42 into two laser beams P1 and P2. These laser beams P1 and P2 are guided to the vacuum laser interferometer 20 and the gas laser interferometer 30 via the polarization maintaining fibers 43 and 44, respectively.
The laser beam P1 is guided into the vacuum laser interferometer 20 via the polarization preserving fiber 43, and then split into two laser beams P3 and Pa by the polarization beam splitter 21. The laser beam P3 reflected by the polarization beam splitter 21 passes through the quarter-wave plate 22 and is reflected by the fixed mirror 23, passes through the quarter-wave plate 22 again, and returns to the polarization beam splitter 21. On the other hand, the vacuum laser beam Pa transmitted through the polarization beam splitter 21 is transmitted through the quarter-wave plate 24 and the fixed window 17, travels inside the vacuum vessel 11, is reflected by the vacuum-side reflecting mirror 13 A, and is returned to the fixed window 17 and the fixed window 17. The light passes through the 波長 wavelength plate 24 and returns to the polarization beam splitter 21. Since an optical path difference occurs between the laser beam P3 and the vacuum laser beam Pa, interference fringes (not shown) are formed in the polarization beam splitter 21.
[0020]
The laser beam P4 combined by the polarization beam splitter 21 passes through the half-wave plate 25 and is split by the beam splitter 26 into two laser beams P5 and P6.
The laser beam P5 reflected by the beam splitter 26 is further split by the polarizing beam splitter 27 into two laser beams P7 and P8. The frequencies of the interference fringes of these two laser beams P7 and P8 are detected by detectors 20A and 20B, respectively.
On the other hand, the laser beam P6 transmitted through the beam splitter 26 is transmitted through the quarter-wave plate 28, and is further split by the polarization beam splitter 29 into two laser beams P9 and P10. The frequencies of the interference fringes of these two laser beams P9 and P10 are detected by detectors 20C and 20D, respectively.
[0021]
On the other hand, the laser beam P2 is guided into the gas laser interferometer 30 via the polarization preserving fiber 44, and then split by the polarization beam splitter 31 into two laser beams P11 and Pb. The laser beam P11 reflected by the polarization beam splitter 31 passes through the quarter-wave plate 32, is reflected by the fixed mirror 33, passes through the quarter-wave plate 32 again, and returns to the polarization beam splitter 31. On the other hand, the gas laser beam Pb that has passed through the polarizing beam splitter 31 passes through the quarter-wave plate 34, travels in the space of the test gas, is reflected by the gas-side reflecting mirror 13B, and is again returned to the quarter-wave plate 34. And returns to the polarization beam splitter 31. Since an optical path difference occurs between the laser beam P11 and the gas laser beam Pb, interference fringes (not shown) are formed in the polarization beam splitter 31.
The laser beam P12 united by the polarization beam splitter 31 passes through the polarizing plate 35, and the frequency of the interference fringe is detected by the detector 30A.
[0022]
The frequency of the interference fringes detected by the detectors 20A and 20B of the vacuum laser interferometer 20 is multiplied by 1000 by a multiplication circuit 60A as multiplication means and increased to 10 MHz, and counted as a reference clock of a frequency counter 70. I have. On the other hand, the frequency of the interference fringes detected by the detector 30A of the gas laser interferometer 30 is multiplied by 1000 by a multiplication circuit 60B as multiplication means and counted as a count clock of a frequency counter 70.
The ratio between the frequency of the interference fringes of the vacuum laser interferometer 20 and the frequency of the interference fringes of the gas laser interferometer 30 is represented by the ratio of the measured frequency fc to the reference clock 10 MHz, and the refractive index of the test gas with respect to vacuum. n becomes n = fc / 10 MHz.
[0023]
Here, the constant speed movement of the optical transparent body 12 (that is, the driving body 51) feeds back the measured value measured by the vacuum laser interferometer 20 to the driving control means 54, and the information fed back and the preset value It is controlled based on the comparison with the command value of the moving speed.
The drive control means 54 detects the position of the movable end surface (optically transparent body 12) of the vacuum vessel 11 and determines the moving direction by using the frequency of interference fringes detected by the detectors 20A to 20D of the vacuum laser interferometer 20. Is used. Specifically, a two-phase sine wave having a 90 ° phase is used, and four-phase sine waves having a phase difference of 90 ° are detected to obtain the two-phase sine wave as a stable signal. . A stable two-phase sine wave is created from the differential of these four-phase sine waves, and a movable end face (each of the reflecting mirrors 13A and 13B) is generated based on a comparison between this information and a preset moving speed command value. ) Is controlled.
[0024]
Next, the operation of the present embodiment will be described.
First, when measuring the refractive index of the test gas, the postures of the polarization-maintaining single-mode fibers 43 and 44 and the postures of the optically transparent bodies 12 (the respective reflecting mirrors 13A and 13B) are fixed.
The attitude of the polarization preserving fibers 43 and 44 is such that the laser beam P1 emitted from the polarization preserving fiber 43 is incident on the polarization preserving fiber 44 such that the laser beams P1 and P2 are optically substantially coaxial. So that the laser beam P2 emitted from the polarization maintaining fiber 44 enters the polarization maintaining fiber 43.
After fixing the attitudes of the polarization maintaining fibers 43 and 44, the attitude of the optically transparent body 12 is fixed. The attitude of the optical transparent body 12 is such that the laser beam Pa reflected by the vacuum-side reflecting mirror 13A is polarized so that the reflecting mirrors 13A and 13B are positioned substantially perpendicular to the laser beams Pa and Pb. Adjust to return to.
[0025]
By performing such adjustment, the optical measurement optical path formed by the vacuum laser beam Pa as the reference scale and the optical measurement optical path formed by the gas laser beam Pb having the measured size are connected to the vacuum vessel 11. It is located on the coaxial line across the movable end face. Therefore, Abbe's principle that the standard scale and the object to be measured must be arranged in a straight line in the measurement direction can be satisfied. Thereby, the measurement error in the gas refractive index measurement can be reduced, and the measurement accuracy can be improved.
[0026]
After fixing the attitudes of the polarization plane preserving fibers 43 and 44 and the optically transparent body 12 (each of the reflecting mirrors 13A and 13B), the refractive index of the test gas is measured.
[0027]
According to the above-described embodiment, the following effects can be obtained.
An exhaust pipe 18 is provided in the vacuum vessel 11, and the end of the exhaust pipe 18 is sealed in a state where the vacuum vessel 11 is evacuated. Therefore, the inside of the vacuum vessel 11 is completely sealed, and the vacuum state is maintained for a long period of time. it can. Therefore, it is not necessary to connect a vacuum pump every time the measurement is performed and to evacuate the air in the vacuum vessel 11, thereby improving the measurement operation efficiency. In addition, the running cost of the refractive index measuring device 1 can be improved.
[0028]
Since the work of sucking the air in the vacuum vessel 11 is performed only once at the first time before use, the possibility that dust and the like enter the vacuum vessel 11 through the exhaust pipe 18 can be minimized. Thus, even when an oil rotary pump is used as the vacuum pump, the possibility of oil being mixed can be minimized. Therefore, it is possible to prevent impurities from being mixed into the vacuum vessel 11, and it is possible to minimize the influence on the measurement error of the gas refractive index measuring device 1.
[0029]
When shipping the gas refractive index measuring device 1 as a product, the inside of the vacuum vessel 11 can be evacuated in advance and the exhaust pipe 18 can be sealed before shipping. That is, since it is not necessary to manufacture the vacuum pump as an accessory part of the refractive index measuring device 1, the price of the refractive index measuring device 1 can be reduced. Further, since a vacuum pump is not required, the installation space for the refractive index measuring device 1 can be reduced, and the miniaturization of the refractive index measuring device 1 can be promoted.
[0030]
Since the sealing of the exhaust pipe 18 is performed by welding, the opening of the exhaust pipe 18 can be securely adhered and sealed, and a good vacuum state can be maintained more reliably for a long time.
[0031]
Note that the present invention is not limited to the above-described embodiment, and modifications and improvements as long as the object of the present invention can be achieved are included in the present invention.
For example, the gas refraction index measuring device 1 measures the vacuum laser beam Pa and the gas laser beam Pb on a coaxial line using Abbe's principle, but is not limited thereto. For example, the vacuum laser beam Pa and the gas laser beam Pb may be arranged parallel to each other.
[0032]
Although the exhaust pipe 18 is provided integrally with the block 15, the invention is not limited thereto, and the exhaust pipe 18 may be provided in the bellows portion 14. Alternatively, it may be provided separately from the block 15 or the bellows portion 14 and fixed to the block 15 or the bellows portion 14 by welding or the like.
[0033]
The reflecting film 13 serves as both the vacuum-side reflecting mirror 13A and the gas-side reflecting mirror 13B. However, the present invention is not limited to this. For example, reflecting films may be attached to both sides of the optically transparent body 12. Alternatively, the test gas side reflecting mirror may be provided as a separate member.
[0034]
Although the optical measuring device is the gas refractive index measuring device 1, it is not limited to this, and may be, for example, an optical displacement detector that detects displacement by detecting the amount of movement of the movable end surface of the vacuum vessel. . In short, if it is an optical measuring device that splits one laser beam and makes one optical path that passes through the vacuum vessel, and measures the displacement, refractive index, etc. using the interference between this optical path and the other optical path Good.
[0035]
【The invention's effect】
According to the present invention, in the optical measurement device, the variable-length vacuum optical path cell is semi-permanently held in a vacuum state because the exhaust pipe is completely sealed while the variable-length vacuum optical path cell is previously evacuated. Therefore, the work of connecting a vacuum pump to the exhaust pipe and evacuating the variable-length vacuum optical path cell every time measurement is performed can be omitted, and work efficiency can be improved. In addition, since the variable-length vacuum optical path cell only needs to be evacuated once before use, it is possible to prevent impurities such as dust from being mixed into the variable-length vacuum optical path cell, and to minimize the influence of mixing of impurities on measurement errors. There is an effect that it can be suppressed to the minimum.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a gas refractive index measuring device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a method for manufacturing a vacuum vessel according to one embodiment of the present invention.
[Explanation of symbols]
1 gas refractive index measuring device (optical measuring device)
11 Vacuum container (variable-length vacuum optical path cell)
12 Optically transparent body 13 Reflective film 13A Vacuum side reflector (reflector)
13B Gas side reflector 17 Fixed window (light entrance / exit)
18 Exhaust pipe 20 Vacuum laser interferometer 30 Gas laser interferometer 43, 44 Polarization preserving fiber 50 Drive mechanism 51 Drive 52 Drive roller 54 Drive control means 55 Guide mechanisms 60A, 60B Multiplication circuit 70 Frequency counter Pa Vacuum laser beam Pb Gas laser beam

Claims (3)

One laser beam is demultiplexed, and one demultiplexed light beam is made incident on a variable-length vacuum optical path cell having a variable length in the longitudinal direction, and the reflected light beam from the variable-length vacuum optical path cell and the other demultiplexed light beam. In an optical measurement device using a variable-length vacuum optical path cell that measures displacement, refractive index, etc. using interference with a light beam,
The variable-length vacuum optical path cell is provided to be sealed at one end in the longitudinal direction, a light incident and incident part through which laser light can pass,
A reflecting mirror that is hermetically provided at the other end of the variable-length vacuum optical path cell and reflects the laser light incident from the light incident / incident section to the light incident / incident section,
An exhaust pipe communicating with the variable-length vacuum optical path cell and having an exhaust pipe whose tip is sealed in a state where the inside of the variable-length vacuum optical path cell is vacuum is provided. measuring device. One laser beam is demultiplexed, and one demultiplexed light beam is made incident on a variable-length vacuum optical path cell having a variable length in the longitudinal direction, and the reflected light beam from the variable-length vacuum optical path cell and the other demultiplexed light beam. A method for manufacturing the variable-length vacuum optical path cell used in an optical measurement device that measures displacement, refractive index, and the like using interference with a light beam,
Sealing a light emitting / receiving part through which laser light can pass at one longitudinal end of the variable-length vacuum optical path cell,
Along with sealing a reflecting mirror that reflects the laser light incident from the light entrance / exit portion to the other end of the variable length vacuum optical path cell to the light exit / incident portion,
One end communicates with the inside of the variable length vacuum optical path cell, and the other end is provided with an exhaust pipe protruding outside the variable length vacuum optical path cell,
Before using, after evacuating air from the exhaust pipe communicating with the variable length vacuum optical path cell in advance and evacuating the variable length vacuum optical path cell,
A method for manufacturing a variable-length vacuum optical path cell, wherein the end of the exhaust pipe is sealed while maintaining a vacuum. The method for manufacturing a variable-length vacuum optical path cell according to claim 2,
The method of manufacturing a variable-length vacuum optical path cell, wherein the sealing of the exhaust pipe is performed by welding.

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