JP7643274B2 - Airtight container and method of manufacturing same - Google Patents

Description

The present invention relates to an airtight container and a method for manufacturing the same.

Atomic clocks are equipped with atomic oscillators that oscillate based on energy transitions in alkali metal atoms such as cesium (Cs) and rubidium (Rb), and these atomic oscillators are known to provide highly accurate oscillation characteristics over the long term. The operating principles of atomic oscillators are divided into several types, but atomic oscillators that utilize the quantum interference effect (CPT: Coherent Population Trapping) are known to have frequency stability that is about three orders of magnitude higher than that of quartz oscillators.

In such an atomic oscillator, a gaseous alkali metal is sealed in the atomic cell, and in order to ensure the performance required for the atomic oscillator, a buffer gas such as nitrogen ( _N2 ), neon (Ne), or argon (Ar) is further sealed in the atomic cell.

An example of an atomic cell is disclosed in the following Patent Document 1. This atomic cell has a body portion with a through hole and a pair of window portions that cover the opening of the through hole. A gaseous alkali metal is sealed in the internal space surrounded by the body portion and the pair of window portions. One of the pair of windows is an entrance side window portion through which excitation light enters. The other is an exit side window portion through which excitation light exits.

JP 2015-185911 A

The body and window can be joined by optical contact, for example. However, because optical contact depends on the surface condition of the body and window, it is difficult to achieve a stable bond, and the buffer gas present inside the atomic cell may leak out of the cell, which is known as cell leakage. Joining using an adhesive is also possible, but it is difficult to maintain high shielding properties, and there is a risk of helium (He) in the atmosphere penetrating into the atomic cell. This creates a problem in that frequency fluctuations are likely to occur over time.

One possible solution is to make the body and window out of glass and then join them by heating and pressing, i.e., welding. However, welding must be performed in a temperature range from the yield point to the softening point of the glass, and pressure marks are likely to remain on the surface of the window. Even in joining methods other than welding, there is a risk that pressure applied to the window and body may leave traces of the joining on the surface of the window, which may result in different levels of joining marks remaining on both windows. This may impair the parallelism of the portions where the excitation light enters and exits, and may impair light transmittance.

The object of the present invention is to provide an airtight container and a manufacturing method thereof that can increase the parallelism of the light transmitting portion even when a method that can effectively increase airtightness, such as heat compression bonding, is adopted.

The airtight container according to the present invention comprises a cell body having a first main surface and a second main surface facing each other, a first through hole and a second through hole penetrating between the first main surface and the second main surface, and an inner side surface and an outer side surface connected to the first main surface and the second main surface; a first cover member provided on the first main surface of the cell body and closing one side of the first through hole and the second through hole; and a second cover member provided on the second main surface of the cell body and closing the other side of the first through hole and the second through hole. is a fire-polished surface, and includes a light-entering surface and a light-emitting surface, the first through hole is located between the light-entering surface and the light-emitting surface, the inner surface has first to fourth inner surfaces facing the first through hole, the first inner surface faces the light-entering surface, the second inner surface faces the light-emitting surface, the third inner surface and the fourth inner surface are connected to the first inner surface and the second inner surface, respectively, a plurality of second through holes are provided, and at least two second through holes face each other across the third inner surface and the fourth inner surface.

In a plan view, when the direction in which the light-entering surface and the light-exiting surface face each other is defined as a first direction and the direction perpendicular to the first direction is defined as a second direction, the cell body has a first region and a second region that face each other in the second direction, sandwiching a first through-hole, the positions of the centers of the first through-hole, the first region, and the second region in the first direction are the same, the dimensions of the first region and the second region along the first direction are 80% of the dimensions of the first through-hole along the first direction, at least one second through-hole is provided in each of the first region and the second region, and it is preferable that the total volume of the second through-holes in the first region is the same as the total volume of the second through-holes in the second region. In this case, when viewed in plan, an axis passing through the center of the first through hole and extending parallel to the first direction is defined as the first axis of symmetry, and an axis passing through the center of the first through hole and extending parallel to the second direction is defined as the second axis of symmetry. It is more preferable that the second through holes are arranged in line symmetry with respect to at least one of the first axis of symmetry and the second axis of symmetry. In this case, it is even more preferable that the second through holes are arranged in line symmetry with respect to both the first axis of symmetry and the second axis of symmetry.

It is preferable that the shape of each of the second through holes in a plan view is circular.

It is preferable that there are two second through holes.

In a plan view, the center of the first through hole coincides with the center of the cell body, and when the direction in which the light-entering surface and the light-exiting surface face each other in a plan view is defined as a first direction and the direction perpendicular to the first direction is defined as a second direction, it is preferable that the dimension of the first through hole along the first direction is larger than the dimension of the first through hole along the second direction.

The method for manufacturing an airtight container according to the present invention is a method for manufacturing the airtight container, and is characterized by comprising the steps of forming a cell body from a preform by redraw molding, joining a first lid member onto a first main surface of the cell body, and joining a second lid member onto a second main surface of the cell body.

After forming a plurality of holes in the preform to form the first through hole and a plurality of second through holes, it is preferable to carry out a process of forming the cell body by redraw molding.

The present invention provides an airtight container and a method for manufacturing the same that can increase the parallelism of the light-transmitting portion even when a method that can effectively increase airtightness, such as heat compression bonding, is adopted.

1 is a perspective view showing an atom cell according to a first embodiment of the present invention. 2 is a cross-sectional view taken along line II in FIG. 1. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 2 is a cross-sectional view of a cell body of a reference example. 11 is a front cross-sectional view for explaining an example of a method for sealing an alkali metal in a first through-hole of the atomic cell. FIG. FIG. 4 is a cross-sectional view showing a portion corresponding to the cross section shown in FIG. 3 for explaining a region of a cell body in the first embodiment of the present invention. 4 is a cross-sectional view showing a portion of a cell body according to a first modified example of the first embodiment of the present invention, which corresponds to the cross-section shown in FIG. 3 . FIG. 4 is a perspective view illustrating an example of a step of preparing a preform in a method for manufacturing an airtight container according to the present invention. FIG. 2 is a perspective view illustrating an example of a step of obtaining an intermediate in a method for producing an airtight container according to the present invention. FIG. 2 is a front cross-sectional view illustrating an example of a step of obtaining a cell body in a method for producing an airtight container of the present invention.

The following describes preferred embodiments. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in the drawings, components having substantially the same functions may be referred to by the same reference numerals.

(Atomic Cell)
(First embodiment)
Fig. 1 is a perspective view showing an atom cell according to a first embodiment of the present invention, Fig. 2 is a cross-sectional view taken along line II in Fig. 1, and Fig. 3 is a cross-sectional view taken along line II-II in Fig. 1.

As shown in FIG. 1, the atomic cell 1 includes a cell body 2, a first lid member 3, and a second lid member 4. The atomic cell 1 is an airtight container of the present invention. However, the airtight container of the present invention is not limited to atomic cells, and can be applied to components that require airtightness, such as wavelength conversion components.

As shown in FIG. 2, the cell body 2 has a first main surface 5, a second main surface 6, an outer surface 7, and an inner surface 8. The first main surface 5 and the second main surface 6 face each other. The outer surface 7 and the inner surface 8 are connected to the second main surface 6. Furthermore, the outer surface 7 is connected to the first main surface 5.

The cell body 2 is provided with a first through hole 13 and two second through holes 14. The first through hole 13 and the second through hole 14 penetrate between the first main surface 5 and the second main surface 6. The two second through holes 14 face each other with the first through hole 13 in between. Furthermore, the cell body 2 is provided with two communication parts 15. Each communication part 15 communicates the first through hole 13 and each second through hole 14. Note that at least one communication part 15 needs to be provided. It is sufficient that the first through hole 13 and at least one second through hole 14 are communicated.

In this embodiment, the communication portion 15 is a groove portion that connects the first through hole 13 and the second through hole 14. The communication portion 15 opens on the first main surface 5 side. However, the arrangement of the communication portion 15 is not limited to the above.

As shown in Figures 1 and 3, in a plan view, the first through hole 13 has a rectangular shape, and the second through hole 14 has a circular shape. Note that the shapes of the first through hole 13 and the second through hole 14 in a plan view are not limited to the above. The shape of the first through hole 13 in a plan view may be, for example, a substantially rectangular shape, or a polygonal shape other than a square. The shape of the second through hole 14 in a plan view may also be a polygonal shape, etc.

The volume of each second through hole 14 is smaller than the volume of the first through hole 13. Specifically, the area of the portion of each second through hole 14 that opens onto the first main surface 5 is smaller than the area of the portion of the first through hole 13 that opens onto the first main surface 5. Similarly, the area of the portion of each second through hole 14 that opens onto the second main surface 6 is smaller than the area of the portion of the first through hole 13 that opens onto the second main surface 6.

As shown in FIG. 1, the outer surface 7 of the cell body 2 includes a first outer surface 7a, a second outer surface 7b, a third outer surface 7c, and a fourth outer surface 7d. The first outer surface 7a and the second outer surface 7b face each other. The third outer surface 7c and the fourth outer surface 7d face each other and are connected to the first outer surface 7a and the second outer surface 7b. The first outer surface 7a and the second outer surface 7b have a planar shape. On the other hand, the third outer surface 7c and the fourth outer surface 7d have a curved shape. The outer shape of the cell body 2 in a planar view is approximately elliptical. However, the outer shape of the cell body 2 in a planar view is not limited to the above and may be, for example, rectangular. In this specification, a planar view refers to a direction viewed from above in FIG. 1.

As shown in FIG. 3, the inner surface 8 faces the first through hole 13. The portion of the first main surface 5 where the first through hole 13 opens is the portion where the first main surface 5 and the inner surface 8 are connected. The inner surface 8 includes a first inner surface 8a, a second inner surface 8b, a third inner surface 8c, and a fourth inner surface 8d. The first inner surface 8a and the second inner surface 8b face each other. The third inner surface 8c and the fourth inner surface 8d face each other and are connected to the first inner surface 8a and the second inner surface 8b. The first inner surface 8a, the second inner surface 8b, the third inner surface 8c, and the fourth inner surface 8d have a planar shape. The first inner surface 8a faces the first outer surface 7a. The second inner surface 8b faces the second outer surface 7b.

As shown in FIG. 1, one of the communication portions 15 opens in a portion of the third inner surface 8c. The other communication portion 15 opens in a portion of the fourth inner surface 8d.

The first lid member 3 is bonded onto the first main surface 5. The first lid member 3 blocks one side of the first through hole 13 and the two second through holes 14, and the two communication parts 15. The second lid member 4 is bonded onto the second main surface 6. The second lid member 4 blocks the other side of the first through hole 13 and the two second through holes 14. In this embodiment, the first lid member 3 and the second lid member 4 have the same shape as the cell body 2 in a plan view, and are substantially elliptical. However, the shape of the first lid member 3 and the second lid member 4 may be any shape that can block the first through hole 13, the second through hole 14, and the communication part 15. The shape of the first lid member 3 and the second lid member 4 may be, for example, a disk shape or a rectangular plate shape.

The atomic cell 1 is a container in which an alkali metal or a buffer gas is sealed, and the gaseous alkali metal or the buffer gas is sealed in the first through hole 13 of the atomic cell 1 for use. The atomic cell 1 is used in an atomic oscillator. As shown in FIG. 1, light A emitted from a light source enters the atomic cell 1 and passes through the first through hole 13. Then, light B is emitted from the atomic cell 1. Specifically, in this embodiment, the first outer surface 7a is a light-entering surface, and the second outer surface 7b is a light-emitting surface. The light A incident from the first outer surface 7a is irradiated onto the alkali metal in the first through hole 13. Then, the light B is emitted from the second outer surface 7b. The light B emitted from the atomic cell 1 enters a photodetector. As a result, a signal is acquired. Note that cesium (Cs) or rubidium (Rb) can be used as the alkali metal. Nitrogen (N ₂ ), neon (Ne), or argon (Ar) can be used as the buffer gas.

The feature of this embodiment is that the outer surface 7 of the cell body 2 is a fire-polished surface and includes a light-entering surface and a light-exiting surface, and the two second through holes 14 face each other across the third inner surface 8c and the fourth inner surface 8d. This makes it possible to increase the parallelism of the light-transmitting portion even when a method that can effectively increase airtightness, such as heat-pressing, is adopted. The details of this will be explained below.

In this specification, the fire-polished surface refers to a smooth surface formed by heat molding such as redraw molding. Specifically, in this specification, the arithmetic mean roughness (Ra) of the fire-polished surface is 1 nm or less. In the atomic cell 1, the light entrance surface and the light exit surface are fire-polished surfaces and are smooth, so that light scattering is unlikely to occur on the light entrance surface and the light exit surface, and light transmittance can be increased. In addition, since the light entrance surface and the light exit surface are included in the outer surface 7 of the cell body 2, even if traces of bonding remain on the surfaces of the first cover member 3 and the second cover member 4 due to pressure applied by heat bonding or the like, the light transmittance of the atomic cell 1 is unlikely to be affected. The arithmetic mean roughness (Ra) in this specification is based on JIS B 0601:2013.

However, if the portions where the outer and inner surfaces face each other are not approximately parallel, the thickness of the portion of the cell body where the light enters or exits will be non-uniform. In this case, the distance the light passes through the atomic cell 1 will differ depending on the position where the light passes through the atomic cell 1. For example, if there is variation in the positional relationship between the light source and the atomic cell 1 due to manufacturing variations in atomic oscillator products, there will also be variation in the position where the light passes through the atomic cell 1. This will result in variation in the signal state of the passed light.

For example, if only one second through hole 14 is provided, there is a risk that distortion will occur in the inner surface 8 during hot forming such as redraw forming. Therefore, as described above, there is a risk that the portions where the outer surface 7 and the inner surface 8 face each other will no longer be approximately parallel. More specifically, there is a risk that the first outer surface 7a and the first inner surface 8a, and the second outer surface 7b and the second inner surface 8b will no longer be approximately parallel. This is thought to be because the configuration around the first through hole 13 is asymmetric.

In contrast, in this embodiment, as shown in FIG. 3, the two second through holes 14 face each other across the third inner side 8c and the fourth inner side 8d. This can increase the symmetry of the configuration around the first through hole 13. This makes it difficult for the inner side 8 to be distorted during hot molding such as redraw molding. Therefore, the parallelism of the light transmitting portion in the cell body 2 can be increased. For example, when a plane parallel to the first outer side 7a is taken as a reference plane, the first inner side 8a, the second inner side 8b, and the second outer side 7b are all close to parallel to the reference plane. In the cell body 2 of the atomic cell 1, the first outer side 7a, the first inner side 8a, the second inner side 8b, and the second outer side 7b are approximately parallel to the reference plane. In addition, approximately parallel in the present invention means that the angle between the planes is 0.5° or less. When the planes are approximately parallel, the angle is preferably 0.2° or less.

In this embodiment, since the light entrance surface and the light exit surface are included in the outer surface 7 of the cell body 2, even if traces of bonding remain on the surfaces of the first cover member 3 and the second cover member 4 due to pressure applied by thermocompression or the like, the parallelism of the light transmission part in the atomic cell 1 is unlikely to be affected. Therefore, even if a mode that can effectively increase airtightness, such as thermocompression, is adopted, the parallelism of the light transmission part can be increased. And, because the parallelism is high, the thickness of the part where light enters the cell body 2 can be made uniform, and the thickness of the part where light exits can be made uniform. Therefore, even if there is variation in the positional relationship between the light source and the atomic cell 1 due to manufacturing variations in atomic oscillator products, the distance that light passes through the atomic cell 1 can be made uniform for each product. Therefore, the signal of light passing through the atomic cell 1 can be stably acquired by the photodetector.

The glass used for the cell body 2 is not particularly limited, and examples that can be used include lead-free glass, leaded glass, and bismuth-based glass.

The lead-free glass may be, for example, an aluminosilicate glass having a glass composition, in mass %, of 50% to 70% SiO ₂ , 10% to 20% Al ₂ O ₃ , 0% to 10% B ₂ O ₃ , 0% to 5% MgO, 15% to 30% CaO, 0% to 5% R ₂ O (R represents at least one selected from Li, Na, and K), and 0% to 3% P ₂ O ₅ .

As the leaded glass, for example, a lead-based glass containing, in mass %, 10% to 45% SiO ₂ , 40% to 75% PbO, and 0.5% to 10% K ₂ O as a glass composition can be used.

As the bismuth-based glass, for example, glass containing, in mass %, 5% to 80% Bi ₂ O ₃ , 5% to 35% B ₂ O ₃ , 0% to 20% ZnO, 0% to 20% SiO ₂ , and 0% to 30% SrO can be used.

It is more preferable that the cell body 2, the first cover member 3, and the second cover member 4 have the same glass composition. It is even more preferable that the cell body 2, the first cover member 3, and the second cover member 4 have the same glass composition. This allows the thermal expansion coefficients of the cell body 2, the first cover member 3, and the second cover member 4 to be matched, and the stability of the joint can be improved, such as by avoiding peeling. Therefore, the airtightness of the atomic cell 1 can be effectively improved. In this specification, glasses with "same glass composition" refer to glasses in which the top three components contained as the glass composition are the same. In addition, in the present invention, glasses with "the same glass composition" include glasses in which the components contained as the glass composition are the same, and the difference in the content of each component of one glass relative to the composition of the other glass is within the range of +5% to -5%.

The effect of increasing the parallelism of the light transmitting portion in this embodiment will be shown in detail by comparing the cell bodies of this embodiment and the comparative example. As shown in FIG. 4, the cell body 102 of the comparative example differs from this embodiment in that only one second through hole 14 is provided. The dashed line in FIG. 4 indicates a reference plane parallel to the first outer surface 7a.

The cell bodies of the present embodiment and the comparative example were produced by redraw molding using an aluminosilicate glass having a glass composition, expressed in mass %, _of 55% _SiO2 , ₁₂ % _Al2O3 , 5% _B2O3 , 2% MgO, 25% CaO, and ₁ % Na2O.

The angle between the first outer surface 7a and the first inner surface 8a is θ1, the angle between the first outer surface 7a and the second inner surface 8b is θ2, and the angle between the first outer surface 7a and the second outer surface 7b is θ3. In this embodiment, θ1, θ2, and θ3 are all 0.1°. In contrast, in the comparative example, θ1 is 0.5°, and θ2 and θ3 are 1°. Thus, in this embodiment, it can be confirmed that the parallelism in the light-transmitting portion is increased, and light transmittance can be more reliably increased.

In this embodiment, it is possible to achieve both optical transparency and airtightness. By increasing the airtightness, He in the atmosphere is less likely to enter the inside of the atomic cell 1. Furthermore, the buffer gas sealed inside the atomic cell 1 is less likely to escape from the cell. This makes it possible to make it less likely that the oscillation frequency of the atomic oscillator will change over time.

In the atomic cell 1, not only the outer surface 7 but also the inner surface 8 is a fire-polished surface. Therefore, when light enters the first through hole 13 and when light exits from the first through hole 13, light scattering is unlikely to occur. This can further increase the light transmittance.

In this embodiment, the cell body 2, the first lid member 3, and the second lid member 4 are made of the same glass. The material of the cell body 2 is not limited to the above, and any material that can make the outer surface 7 a fire-polished surface and has optical transparency may be used. The material of the first lid member 3 and the second lid member 4 is not limited to the above, and may be made of, for example, metal, quartz, silicon, etc. However, it is preferable that the cell body 2, the first lid member 3, and the second lid member 4 are made of glass. This allows the thermal expansion coefficients of the cell body 2, the first lid member 3, and the second lid member 4 to be matched, and the stability of the joint can be improved, such as by avoiding peeling.

Figure 5 is a front cross-sectional view for explaining an example of a method for sealing an alkali metal in the first through hole of the atomic cell. One of the second through holes 14 in the cell body 2 is provided for placing an ampoule 19 or the like in which an alkali metal M is sealed. This is not limited to this, and an ampoule 19 or the like may be placed in both second through holes 14. By irradiating the ampoule 19 placed in the second through hole 14 with laser light L from the outside of the atomic cell 1, the ampoule 19 is broken and the gaseous alkali metal is released into the second through hole 14. In addition, when a solid alkali metal M is sealed in the ampoule 19, the alkali metal M may be gasified by heating. The gaseous alkali metal passes through the communication part 15 and diffuses into the first through hole 13. However, the method for sealing the alkali metal in the atomic cell 1 is not limited to the above. For example, the alkali metal may be directly placed in the atomic cell 1 and then gasified by heating. Alternatively, the alkali metal may be directly sealed in the atomic cell 1 in a gaseous state.

The following shows a preferred configuration of the present invention.

Figure 6 is a cross-sectional view showing a portion corresponding to the cross section shown in Figure 3 to explain the regions of the cell body in the first embodiment. The cell body 2 has a first region C1 and a second region C2. Specifically, in a plan view, when the direction in which the light-entering surface and the light-emitting surface face each other is defined as the first direction y and the direction perpendicular to the first direction y is defined as the second direction x, the first region C1 and the second region C2 face each other in the second direction x with the first through hole 13 therebetween. The positions of the centers of the first through hole 13, the first region C1, and the second region C2 in the first direction y are the same. The dimensions of the first region C1 and the second region C2 along the first direction y are 80% of the dimensions of the first through hole 13 along the first direction y.

At least one second through hole 14 is provided in each of the first region C1 and the second region C2, and it is preferable that the total volume of the second through holes 14 in the first region C1 is the same as the total volume of the second through holes 14 in the second region C2. This makes it possible to more reliably increase the symmetry of the configuration around the first through hole 13, and more reliably prevent distortion of the inner surface 8 during hot molding such as redraw molding, thereby making it possible to make the portions where the outer surface 7 and the inner surface 8 face each other approximately parallel. Therefore, it is possible to more reliably increase the parallelism of the light transmitting portion.

As shown in FIG. 6, in a plan view, an axis passing through the center of the first through hole 13 and extending parallel to the first direction y is defined as a first axis of symmetry Oy, and an axis passing through the center of the first through hole 13 and extending parallel to the second direction x is defined as a second axis of symmetry Ox. It is preferable that the multiple second through holes 14 are arranged linearly symmetrically with respect to at least one of the first axis of symmetry Oy and the second axis of symmetry Ox. This effectively increases the symmetry in the configuration around the first through hole 13, and more reliably prevents distortion of the inner surface 8 during hot molding such as redraw molding, thereby making it possible to make the portions where the outer surface 7 and the inner surface 8 face each other approximately parallel. Therefore, the parallelism of the light transmitting portion can be more reliably increased.

As in this embodiment, it is more preferable that the multiple second through holes 14 are arranged line-symmetrically with respect to both the first symmetry axis Oy and the second symmetry axis Ox. This can further increase the symmetry in the configuration around the first through hole 13, and can more reliably prevent distortion of the inner surface 8 during hot molding such as redraw molding, thereby making the portions where the outer surface 7 and the inner surface 8 face each other approximately parallel. Therefore, the parallelism of the light transmitting portion can be more reliably increased. Note that the second through holes 14 being arranged line-symmetrically with respect to the second symmetry axis Ox also includes the case where the second through holes 14 are arranged on the second symmetry axis Ox and the shape of the second through holes 14 is line-symmetric with respect to the second symmetry axis Ox, as in this embodiment.

It is preferable that the shapes of the multiple second through holes 14 are the same in a plan view. This makes it possible to more reliably increase the symmetry of the configuration around the first through holes 13, and more reliably prevent distortion of the inner surface 8 during hot forming such as redraw forming, thereby making it possible to make the portions where the outer surface 7 and the inner surface 8 face each other approximately parallel. Therefore, it is possible to more reliably increase the parallelism of the light transmitting portion.

It is more preferable that the shape of the multiple second through holes 14 in a plan view is circular. In this case, the symmetry of the configuration around the first through holes 13 can be easily and more reliably increased, and distortion of the inner surface 8 during hot forming such as redraw forming can be more reliably prevented, so that the portions where the outer surface 7 and the inner surface 8 face each other can be made approximately parallel. Therefore, the parallelism of the light transmitting portion can be more reliably increased.

It is further preferable that one second through hole 14 is provided in each of the first region C1 and the second region C2. In this case, the total volume of the second through holes 14 in the first region C1 and the total volume of the second through holes 14 in the second region C2 can be easily made the same. When the two total volumes are made the same, as described above, it is possible to more reliably prevent distortion of the inner surface 8 during hot molding such as redraw molding, and this makes it possible to make the portions where the outer surface 7 and the inner surface 8 face each other approximately parallel. Therefore, the parallelism of the light transmitting portion can be more reliably increased.

In plan view, it is preferable that the center of the first through hole 13 coincides with the center of the cell body 2, and that the dimension of the first through hole 13 along the first direction y is equal to the dimension of the first through hole 13 along the second direction x in plan view. In this case, the effect of the second through hole 14 on the distortion of the inner surface 8 is small.

The first region C1 and the second region C2 may each have a plurality of second through holes 14. An example of this is shown below.

(Modification)
FIG. 7 is a cross-sectional view showing a part of the cell body in the first modified example of the first embodiment, which corresponds to the cross section shown in FIG. 3. In this modified example, two second through holes are provided in each of the first region C1 and the second region C2. The two second through holes 14 in the first region C1 are arranged line-symmetrically with respect to the second symmetric axis Ox. Similarly, the two second through holes 14 in the second region C2 are also arranged line-symmetrically with respect to the second symmetric axis Ox. Furthermore, the two second through holes 14 in the first region C1 and the two second through holes in the second region C2 are arranged line-symmetrically with respect to the first symmetric axis Oy. In this modified example, the volume of all the second through holes 14 is the same. In this modified example, as in the first embodiment, the parallelism of the light transmitting portion can be increased even if a mode that can effectively increase the airtightness, such as heat compression bonding, is adopted.

(Production method)
Fig. 8 is a perspective view for explaining an example of a step of preparing a preform in the method for manufacturing an airtight container. Fig. 9 is a perspective view for explaining an example of a step of obtaining an intermediate body in the method for manufacturing an airtight container. Fig. 10 is a front cross-sectional view for explaining an example of a step of obtaining a cell body in the method for manufacturing an airtight container.

In the manufacturing method of the atomic cell 1 as an airtight container, the cell body 2 is formed by redraw molding. Specifically, as shown in FIG. 8, a preform 22 to be used in the redraw molding is prepared by cutting or the like. In a plan view, the external shape of at least a part of the preform 22 and the external shape of the cell body 2 to be obtained have a similar relationship.

Next, a first hole 23 and a plurality of second holes 24 are provided in the preform 22. In the example shown in FIG. 8, two second holes 24 are provided in the preform 22. More specifically, one second hole 24 is provided in each of a portion corresponding to the first region C1 and a portion corresponding to the second region C2 of the cell body 2 to be obtained.

In plan view, the shape of the first hole 23 and the shape of the first through hole 13 of the cell body 2 to be obtained have a similar relationship. Similarly, in plan view, the shape of the second hole 24 and the shape of the second through hole 14 of the cell body 2 to be obtained have a similar relationship. The first hole 23 and the second hole 24 can be formed, for example, by cutting with a drill or ultrasonic processing. The first hole 23 and the second hole 24 may be through holes, or may not be through holes. Note that the first hole 23 and the second hole 24 do not necessarily have to be provided in the preform 22.

Next, as shown in FIG. 9, the preform 22 is heated and stretched. Next, the stretched portion of the preform 22 is cut to obtain an intermediate body 25. The line D-D in FIG. 9 indicates that the preform 22 is cut. The above cutting can be performed, for example, by a dicing saw or a glass cutter. The intermediate body 25 has a first through hole 13 and a plurality of second through holes 14. The first through hole 13 of the intermediate body 25 is formed from the first hole portion 23 in the preform 22. The second through hole 14 of the intermediate body 25 is formed from the second hole portion 24 in the preform 22.

Furthermore, the intermediate body 25 has an outer surface 7 and an inner surface 8. The intermediate body 25 is formed by redraw molding as described above. Therefore, the outer surface 7 is a fire-polished surface. Furthermore, by performing redraw molding when the first hole portion 23 is formed in the preform 22, the inner surface 8 can also be made into a fire-polished surface. By repeating the process shown in Figure 9, multiple intermediate bodies 25 are obtained from one preform 22.

When the preform 22 does not have the first hole 23 and the second hole 24, the first through hole 13 and the second through hole 14 may be provided in each intermediate body 25. However, it is preferable to provide the preform 22 with the first hole 23 and the second hole 24. This allows the inner surface 8 to be a fire-polished surface, as described above. In addition, the process of providing the first through hole 13 and the second through hole 14 in each intermediate body 25 can be eliminated. This improves productivity.

Next, as shown in FIG. 10, a plurality of communication parts 15 are provided to communicate the first through hole 13 and each of the second through holes 14. The plurality of communication parts 15 can be formed, for example, by cutting using a drill or ultrasonic processing. In this embodiment, the communication parts 15 are formed by providing a groove in the portion between the first through hole 13 and the second through hole 14 on the first main surface 5. In this way, the cell body 2 is obtained. However, it is sufficient to provide at least one communication part 15.

On the other hand, the first lid member 3 and the second lid member 4 shown in FIG. 1 are prepared. Next, the first main surface 5 of the cell body 2 is joined to the first lid member 3. At this time, the first through hole 13 and one side of the multiple second through holes 14, as well as the multiple communication portions 15, are blocked by the first lid member 3. Furthermore, the second main surface 6 of the cell body 2 is joined to the second lid member 4. At this time, the other side of the first through hole 13 and the multiple second through holes 14 are blocked by the second lid member 4. In this way, the atomic cell 1 shown in FIG. 1 is obtained.

When the alkali metal is sealed in the atomic cell 1, an ampoule or the like in which the alkali metal is sealed may be placed in the cell body 2 before the cell body 2 and both lid members are joined. Specifically, for example, the second main surface 6 of the cell body 2 is joined to the second lid member 4. Next, an ampoule or the like is placed in at least one second through hole 14 of the cell body 2. Then, the first main surface 5 of the cell body 2 is joined to the first lid member 3. When the first main surface 5 of the cell body 2 is joined to the first lid member 3, a buffer gas is introduced into the first through hole 13 and the second through hole 14, and the joining is performed in this buffer gas atmosphere. In the present invention, the alkali metal in the atomic cell 1 may be in a state such as a solid before gasification, may be in a gaseous state, or may be sealed in an ampoule. When the atomic cell 1 is used, it is sufficient that the gaseous alkali metal is sealed in the first through hole 13.

The cell body 2 is preferably joined to the first and second lid members 3 and 4 by thermocompression bonding. In this case, traces of pressure may remain on the surfaces of the first and second lid members 3 and 4. In contrast, in this embodiment, the light entrance surface and the light exit surface are included in the outer surface 7 of the cell body 2, so the parallelism of the light transmitting portion is unlikely to be impaired. Therefore, the present invention is suitable when thermocompression bonding is used for the above-mentioned bonding. Moreover, the airtightness of the atomic cell 1 can be effectively increased.

In the thermocompression bonding, it is preferable to heat the first cover member 3, the second cover member 4, and the cell body 2 to a temperature range above the yield point and below the softening point of the glass material constituting the first cover member 3 and the second cover member 4, and apply a load. When applying the load, the cell body 2 and the first cover member 3 and the second cover member 4 are sandwiched. The pressure in the thermocompression bonding is preferably 1 kPa or more, and more preferably 10 kPa or more. This effectively increases the airtightness of the atomic cell 1. Moreover, in this embodiment, the parallelism of the light transmitting portion in the atomic cell 1 is unlikely to be impaired. The pressure in the thermocompression bonding is preferably 0.5 MPa or less, and more preferably 0.1 MPa or less.

When the above bonding is performed by thermocompression, there is no need to polish the first and second main surfaces 5 and 6 of the cell body 2 and the bonding surfaces of the first and second lid members 3 and 4. This can improve productivity. However, the above bonding surfaces may be polished before bonding. In this case, the arithmetic mean roughness (Ra) of the bonding surfaces is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. The above bonding may be performed by a method other than thermocompression.

The cell body 2 may be joined to the first and second lid members 3 and 4 by optical contact. In this case, the first and second main surfaces 5 and 6 of the cell body 2 and the joining surfaces of the first and second lid members 3 and 4 are polished before joining. The arithmetic mean roughness (Ra) of the joining surfaces of the first and second lid members 3 and 2 is preferably 1 nm or less, more preferably 0.6 nm or less, and even more preferably 0.4 nm or less. The heating temperature is preferably equal to or less than the glass transition temperature of the glass constituting the first and second lid members 3 and 2, more preferably 400°C or less, and even more preferably 300°C or less. The pressure of the pressurization in the optical contact is preferably 10 MPa or more, and more preferably 100 MPa or more. This effectively increases the airtightness of the atomic cell 1. Moreover, as described above, the parallelism of the light transmitting portion of the atomic cell 1 is unlikely to be impaired. The pressure at the optical contact is preferably 300 MPa or less, and more preferably 200 MPa or less.

The cell body 2 may be bonded to the first and second lid members 3 and 4 by anodic bonding. Anodic bonding may be performed at a temperature of, for example, 300°C or higher and 350°C or lower. Anodic bonding may be performed, for example, under atmospheric pressure. Anodic bonding may be performed at a voltage of, for example, 250V or higher and 300V or lower. In this case, the voltage may be increased depending on the alkali content in the glass composition. Anodic bonding may be performed under a pressure of, for example, 0.1MPa or higher and 0.3MPa or lower. In this case, the pressure may be increased depending on the thickness of the cell body 2, the first lid member 3, and the second lid member 4.

The cell body 2 may be joined to the first and second lid members 3 and 4 by laser sealing. The laser sealing is preferably performed using glass frit. For example, bismuth-based glass may be used as the glass frit. The glass composition of the bismuth-based glass may be, for example, in mol %, Bi ₂ O ₃ 39%, B ₂ O ₃ 23.7%, ZnO 14.1%, Al ₂ O ₃ 2.7%, CuO 20%, and Fe ₂ O ₃ 0.6%.

In one example of bonding by laser sealing, first, a paste containing glass frit, resin, and solvent is prepared. Next, this paste is applied and glazed (heat-treated) on the first main surface 5 and the second main surface 6 of the cell body 2 to form a frame-shaped sealing material layer. Next, the first lid member 3 and the second lid member 4 are placed on the first main surface 5 and the second main surface 6 of the cell body 2 on which the sealing material layer has been formed, respectively. This allows the sealing material layer to be disposed between the first main surface 5 and the second main surface 6 of the cell body 2 and the first lid member 3 and the second lid member 4. The frame-shaped sealing material layer may be formed on the first lid member 3 and the second lid member 4 side. Alternatively, the sealing material may be applied to both the first main surface 5 and the second main surface 6 of the cell body 2 and the first lid member 3 and the second lid member 4. Next, laser light is irradiated through the first lid member 3 to heat and melt one of the sealing material layers. Similarly, the laser light is irradiated through the second lid member 4 to heat and melt the other sealing material layer. This softens and deforms the sealing material layer, thereby airtightly bonding the first main surface 5 and the second main surface 6 of the cell body 2 to the first lid member 3 and the second lid member 4. Note that as the laser light, for example, a semiconductor laser with a wavelength of 808 nm and an output of 3 W to 20 W can be used.

The cell body 2 may be joined to the first and second lid members 3 and 4 using an adhesive such as a resin adhesive or an inorganic adhesive.

When the airtight container of the present invention is used as an atomic cell, it can be used, for example, in an atomic oscillator that uses the quantum interference effect of two types of light with different wavelengths to cause an alkali metal to undergo a resonant transition. However, it may also be used in an atomic oscillator that uses the double resonance phenomenon of light and microwaves to cause an alkali metal to undergo a resonant transition, and is not particularly limited. It should be noted that the airtight container of the present invention is not limited to atomic cells, and can also be applied to components that require airtightness, such as wavelength conversion components.

REFERENCE SIGNS LIST 1...atom cell 2...cell body 3...first cover member 4...second cover member 5...first main surface 6...second main surface 7...outer surfaces 7a to 7d...first to fourth outer surfaces 8...inner surfaces 8a to 8d...first to fourth inner surfaces 13...first through hole 14...second through hole 15...communicating portion 19...ampule 22...preform 23...first hole portion 24...second hole portion 25...intermediate body 102...cell body

Claims (9)

a cell body having a first main surface and a second main surface facing each other, a first through hole and a second through hole penetrating between the first main surface and the second main surface, and an inner side surface and an outer side surface connected to the first main surface and the second main surface;
a first cover member provided on the first main surface of the cell body and closing one side of the first through hole and the second through hole;
a second cover member provided on the second main surface of the cell body and closing the other side of the first through hole and the second through hole;
Equipped with
The outer surface is a fire polished surface and includes a light entrance surface and a light exit surface;
the first through hole is located between the light entrance surface and the light exit surface, the inner surface has first to fourth inner surfaces facing the first through hole, the first inner surface faces the light entrance surface, the second inner surface faces the light exit surface, the third inner surface and the fourth inner surface are connected to the first inner surface and the second inner surface, respectively;
An airtight container comprising a plurality of the second through holes, at least two of the second through holes facing each other across the third inner side surface and the fourth inner side surface. In a plan view, when a direction in which the light entrance surface and the light exit surface face each other is defined as a first direction and a direction perpendicular to the first direction is defined as a second direction, the cell body has a first region and a second region that face each other across the first through hole in the second direction,
the first through hole, the first region, and the second region have centers located at the same position in the first direction, and the dimensions of the first region and the second region in the first direction are 80% of the dimension of the first through hole in the first direction;
2. The airtight container according to claim 1, wherein at least one second through hole is provided in each of the first region and the second region, and a total volume of the second through holes in the first region is the same as a total volume of the second through holes in the second region. The airtight container according to claim 2, wherein, in a plan view, when an axis passing through the center of the first through hole and extending parallel to the first direction is defined as a first axis of symmetry, and an axis passing through the center of the first through hole and extending parallel to the second direction is defined as a second axis of symmetry, the second through holes are arranged in line symmetry with respect to at least one of the first axis of symmetry and the second axis of symmetry. The airtight container according to claim 3, wherein the second through holes are arranged symmetrically with respect to both the first axis of symmetry and the second axis of symmetry. The airtight container according to any one of claims 1 to 4, wherein the shape of the second through holes in plan view is all circular. The airtight container according to any one of claims 1 to 5, wherein two second through holes are provided. In a plan view, a center of the first through hole coincides with a center of the cell body,
7. The airtight container according to claim 1, wherein, in a plan view, when a direction in which the light entering surface and the light exiting surface face each other is defined as a first direction and a direction perpendicular to the first direction is defined as a second direction, a dimension of the first through hole along the first direction is larger than a dimension of the first through hole along the second direction. A method for producing the airtight container according to any one of claims 1 to 7, comprising the steps of:
forming the cell body from a preform by redraw molding;
joining the first cover member onto the first main surface of the cell body;
joining the second cover member onto the second main surface of the cell body;
A method for manufacturing an airtight container comprising the steps of: The method for manufacturing an airtight container according to claim 8, further comprising forming a plurality of holes in the preform for forming the first through hole and the plurality of second through holes, and then forming the cell body by redraw molding.

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