Gas cell and quantum sensor

Abstract

The present invention addresses the problem of providing: a gas cell having high airtightness; and a quantum sensor provided with the gas cell.　A gas cell according to the present invention has alkali metal atoms sealed therein, and has a body having at least one opening, and a transparent substrate provided to the opening. The body is provided with a fitting part to which the transparent substrate is fitted.

Description

Gas cell and quantum sensor 【0001】 The present invention relates to a gas cell and a quantum sensor including the gas cell. 【0002】 When light acts on an alkali metal vapor, phenomena such as spin polarization or a quantum interference effect (CPT: Coherent Population Trapping) occur. In recent years, quantum sensors such as atomic oscillators and optical pumping magnetic sensors that utilize these phenomena have attracted attention. For example, an optical pumping magnetic sensor is used as a brain function imaging device to measure and image the physiological activities and functions of each part in the brain. Therefore, improving the optical pumping magnetic sensor can lead to early detection and treatment of lesions and improvement of the quality of life (QOL), and it is expected to contribute to the achievement of Goal 3, "Ensure healthy lives and promote well-being for all", of the Sustainable Development Goals (SDGs) proposed by the United Nations. 【0003】 Quantum sensors such as atomic oscillators and optical pumping magnetic sensors include, for example, a gas cell filled with an alkali metal vapor and buffer gases such as nitrogen, helium, and argon, a light source that emits excitation light for exciting electrons of alkali metal atoms in the gas cell, and a photodetector that detects light transmitted through the gas cell. The alkali metal vapor is obtained by heating and vaporizing an alkali metal or an alkali metal compound enclosed in the gas cell. Therefore, the gas cell needs to operate in a high-temperature environment, and it is important to uniformly fill the inside of the gas cell with alkali vapor. 【0004】 Patent Document 1 describes an airtight container including a cell body having opposed first and second main surfaces and provided with a through-hole penetrating between the first and second main surfaces, a first lid member provided on the first main surface of the cell body, and a second lid member provided on the second main surface of the cell body. 【0005】 Japanese Patent No. 7491112 【0006】 The inventor of the present invention intensively studied the gas cell used in quantum sensors and the like while referring to Patent Document 1, and found that there is room for further improvement in the airtightness of the gas cell. 【0007】 The present invention aims to provide a gas cell with high airtightness. Furthermore, the present invention aims to provide a quantum sensor equipped with the above-mentioned gas cell. 【0008】 As a result of diligent study on the above problems, the inventors of this invention have found that the above problems can be solved by the following configuration. 【0009】In other words, the inventors have found that the above problems can be solved by the following configurations: [1] A gas cell in which alkali metal atoms are sealed inside, comprising a main body having at least one opening and a transparent substrate provided in the opening, wherein the main body comprises a fitting portion into which the transparent substrate is fitted. [2] The gas cell according to [1], wherein the transparent substrate has a first main surface that together with the main body constitutes a closed space for sealing the alkali metal atoms, a second main surface opposite to the first main surface, and a side surface incorporated into the outer edges of the first and second main surfaces, and the fitting portion of the main body is joined to at least two of the first main surface, the second main surface, and the side surface of the transparent substrate. [3] The gas cell according to [2], in which the fitting portion of the main body is joined to the two surfaces of the second main surface and the side surface, and the thickness of the transparent substrate in the thickness direction from the first main surface to the second main surface is t, and the length of the fitting portion that joins the side surface in the thickness direction is a, such that t > a. [4] The gas cell according to [2], in which the fitting portion of the main body is joined to the three surfaces of the first main surface, the second main surface and the side surface, and the thickness of the transparent substrate in the thickness direction from the first main surface to the second main surface is t, and the length of the fitting portion that joins the first main surface, the second main surface and the side surface in the thickness direction is c, such that t ≤ c. [5] The gas cell according to [3], wherein when the fitting portion of the main body is joined to the first main surface and the side surface, the length of the fitting portion that contacts the first main surface in a direction perpendicular to the thickness direction is 0.5 mm or more and less than 5.0 mm. [6] The gas cell according to [4], wherein when the fitting portion of the main body is joined to the first main surface, the second main surface and the side surface, the length of the fitting portion that contacts the first main surface in a direction perpendicular to the thickness direction is 0.5 mm or more and less than 5.0 mm. [7] The gas cell according to any one of [2], [4], and [6], wherein when the fitting portion of the main body is joined to the first main surface, the second main surface and the side surface, the fitting portion of the main body has a frame-shaped lid portion arranged along the outer edge of the second main surface.[8] The gas cell according to any one of [2], [4], and [6], wherein when the fitting portion of the main body is joined to the three surfaces of the first main surface, the second main surface, and the side surface, the main body has a sealing portion that is in contact with the side surface of the transparent substrate and in contact with the outside of the gas cell. [9] The gas cell according to any one of [1] to [8], wherein the main body has one opening and a reflective member provided inside the main body at a position facing the opening.

[10] The gas cell according to any one of [1] to [8], wherein the main body has two or more openings.

[11] A quantum sensor characterized by comprising the gas cell according to any one of [1] to

[10] , a light source that emits excitation light to excite electrons of alkali metal atoms contained in the gas cell, and a photodetector that detects light transmitted through the gas cell.

[12] The quantum sensor according to

[11] , which is an optical pumping magnetic sensor.

[13] A quantum sensor as described in

[11] , which is an atomic oscillator. 【0010】 According to the present invention, a gas cell with high airtightness can be provided. Furthermore, according to the present invention, a quantum sensor equipped with the above-mentioned gas cell can be provided. 【0011】 This is a perspective view showing an example of a gas cell according to the first embodiment of the present invention. This is a cross-sectional view showing an example of a gas cell according to the first embodiment of the present invention. This is a cross-sectional view showing a modified version of the gas cell according to the first embodiment of the present invention. This is a perspective view showing a modified version of the gas cell according to the first embodiment of the present invention. This is a cross-sectional view showing a modified version of the gas cell according to the first embodiment of the present invention. This is a cross-sectional view showing an example of a gas cell according to the second embodiment of the present invention. This is a cross-sectional view showing an example of a gas cell according to the second embodiment of the present invention. This is a cross-sectional view showing a modified version of the gas cell according to the second embodiment of the present invention. This is a perspective view showing an example of a gas cell according to the third embodiment of the present invention. This is a cross-sectional view showing an example of a gas cell according to the third embodiment of the present invention. This is a perspective view showing a modified version of the gas cell according to the third embodiment of the present invention. This is a cross-sectional view showing a modified version of the gas cell according to the third embodiment of the present invention. 【0012】Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The following descriptions of constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In the drawings and their descriptions, common elements are denoted by the same reference numerals, and redundant descriptions are omitted. In each drawing, the scale of the constituent elements may differ from the actual scale as appropriate to facilitate viewing and explanation. 【0013】 In this specification, a numerical range indicated by "~" means a range that includes the numbers indicated before and after "~" as the lower and upper limits. In numerical ranges described stepwise in this specification, the upper or lower limit indicated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. 【0014】 Figures 1 to 14 are conceptual diagrams showing a gas cell according to the present invention. The gas cell according to the present invention is a gas cell in which alkali metal atoms are sealed inside, and comprises a main body having at least one opening and a transparent substrate provided in the opening, the main body having a fitting portion into which the transparent substrate is fitted. 【0015】 [First Embodiment] An example of a gas cell according to the first embodiment of the present invention is shown in Figures 1 and 2. Figure 1 is a perspective view showing the gas cell 1 according to this embodiment. Figure 2 is a cross-sectional view of the gas cell 1 along the line I-I in Figure 1. Hereinafter, components common to the gas cell according to the first embodiment will be denoted by the same reference numerals, and their detailed descriptions will be omitted. The gas cell 1 of this embodiment has a main body 10, a transparent substrate 20, and a reflective member 30 (see Figure 2). In the gas cell 1, the main body 10 has one opening 11. The transparent substrate 20 is provided in the opening 11 of the main body 10, and light that excites electrons of alkali metal atoms, as will be described later, is transmitted through the transparent substrate 20. Inside the gas cell 1, a closed space 40 (see Figure 2) is formed, surrounded on all sides by the main body 10 and the transparent substrate 20, and alkali metal atoms and a sealed gas (buffer gas) are sealed in this closed space 40. 【0016】The transparent substrate 20 has, for example, a first main surface 21 that, together with the main body 10, constitutes a closed space 40 for encapsulating alkali metal atoms, a second main surface 22 opposite to the first main surface 21, and a side surface 23 incorporated into the outer edges of the first main surface 21 and the second main surface 22. For example, the first main surface 21 and the second main surface 22 are parallel, and the side surface 23 is perpendicular to the first main surface 21 and the second main surface 22. However, the side surface 23 is not particularly limited to being perpendicular to the first main surface 21 and the second main surface 22. 【0017】 In the gas cell 1 of this embodiment, the main body 10 is provided with a fitting portion 14 into which a transparent substrate 20 is fitted at the opening 11. By providing the fitting portion 14 into which the transparent substrate 20 is fitted in the main body 10, a gas cell 1 with excellent airtightness between alkali metal atoms and sealed gas can be obtained. This is thought to be because the area in which the main body 10 (side wall portion 13) and the transparent substrate 20 are joined has increased, thereby increasing the length of the fitting portion between the main body 10 and the transparent substrate 20, that is, the distance from the closed space 40 to the outside of the gas cell 1. Furthermore, if the transparent substrate is not fitted into the main body, displacement of the transparent substrate may occur during manufacturing or use, shortening the distance from the closed space 40 to the outside in the fitting portion, which may make it easier for the sealed gas to leak. In contrast, in the gas cell 1 of this embodiment, since the transparent substrate 20 is fitted by the fitting portion 14 of the main body 10, the above displacement does not occur, and the airtightness of the gas cell 1 is further improved. The gas cell of this embodiment will be described in more detail below. 【0018】The main body 10 has, for example, a plate-shaped base 12 with a rectangular outer shape in plan view, and a rectangular tubular side wall portion 13 having four side walls. The side wall portion 13 is provided so as to surround the entire circumference of the peripheral edge of the base portion 12. The main body 10 shown in Figures 1 and 2 has a configuration in which the base portion 12 and the side wall portion 13 are integrally molded. In the main body 10, the protruding end of the side wall portion 13 opposite to the base portion 12 is an opening 11, and a fitting portion 14 is provided on the inside (opening 11 side) of the protruding end of the side wall portion 13. As shown in Figure 2, the fitting portion 14 has, for example, two orthogonal first fitting surfaces 141 and a second fitting surface 142. The first main surface 21 of the transparent substrate 20 is joined to the first fitting surface 141, and the side surface 23 of the transparent substrate 20 is joined to the second fitting surface 142. 【0019】 In this embodiment, the main body 10 has one opening 11. When the gas cell having one opening in this embodiment is used as a quantum sensor or the like, the light source that emits excitation light to excite electrons of alkali metal atoms and the photodetector that detects light transmitted through the inside of the gas cell are arranged on the same side (transparent substrate 20 side) as the gas cell. This makes it possible to miniaturize the quantum sensor equipped with the gas cell 1. 【0020】 In this embodiment, a reflective member 30 is provided on the surface of the base portion 12 of the main body portion 10 facing the transparent substrate 20, which has the function of reflecting light that excites electrons of alkali metal atoms. In this way, in a gas cell in which the main body portion has one opening, by providing a reflective member at a position facing the opening inside the main body portion, light that passes through the transparent substrate provided in the opening and enters the closed space can excite electrons of alkali metal atoms, and then pass through the transparent substrate again to be detected by an external photodetector. 【0021】 The thickness of the base portion 12 and side wall portion 13 of the main body portion 10 is preferably 0.3 mm or more and less than 10 mm, and more preferably 0.5 mm or more and less than 5.0 mm. By having the thickness of the base portion 12 and side wall portion 13 within the above range, it is possible to improve shape stability and uniform heat distribution while maintaining mechanical properties, and further improve airtightness by securing the bonding area with the transparent substrate. Mechanical properties refer to bending strength and impact resistance. 【0022】 The constituent material of the main body 10 is not particularly limited, but examples include inorganic crystals such as glass, quartz, ceramics, and silicon, as well as resin materials, with glass, ceramics, or silicon being preferred. 【0023】 The transparent substrate 20 is provided in the opening 11 of the main body 10 and fitted in place by the fitting portion 14. The constituent material of the transparent substrate 20 is not particularly limited as long as it is a material that transmits light at the wavelength used in the quantum sensor, but examples include glass material, inorganic crystals such as quartz and sapphire, and translucent ceramics, with glass material being preferred. Examples of glass include alkali-free borosilicate glass, borosilicate glass, soda-lime glass, high-silica glass, and other oxide-based glasses mainly composed of silicon dioxide. In addition, an alkali barrier film may be formed on the first main surface 21 of the transparent substrate 20 as needed. In addition, an anti-reflective film may be formed on at least one of the first main surface 21 and the second main surface 22 of the transparent substrate 20. 【0024】 The thickness t of the transparent substrate 20 in the thickness direction from the first main surface 21 to the second main surface 22 is preferably 0.2 to 4.0 mm, and more preferably 0.5 to 2.0 mm. When the thickness t of the transparent substrate 20 is greater than or equal to the lower limit, the rigidity of the transparent substrate 20 is increased, which suppresses warping of the substrate due to heating, etc., when the gas cell is used in a quantum sensor, and improves signal stability. Furthermore, when the thickness t of the transparent substrate 20 is less than or equal to the upper limit, the size of the gas cell 1 is suppressed, making it easier to miniaturize and lighten the quantum sensor equipped with the gas cell 1. 【0025】 The external shape of the transparent substrate 20 is, for example, a rectangle in plan view. However, the shape of the transparent substrate in the gas cell of this embodiment is not limited to the shape into which the transparent substrate is fitted by the fitting portion of the main body, and may or may not be the same as the shape of the closed space inside the main body. It is preferable that the shape of the transparent substrate in plan view and the shape of the closed space in plan view are the same or similar in that a sufficient contact area with the main body is secured and the airtightness of the gas cell is improved. 【0026】The fitting portion into which the transparent substrate is fitted will be explained in more detail. In the gas cell 1 shown in Figure 2, the fitting portion 14 is joined to two of the transparent substrate 20's surfaces: the first main surface 21 and the side surface 23, out of the first main surface 21, the second main surface 22, and the side surface 23. In this specification, "joining" includes not only cases where two members are joined directly, but also cases where they are joined via other layers such as a bonding layer. 【0027】 In the fitting portion 14, if the length in the thickness direction of the fitting portion that joins with the side surface 23 of the transparent substrate 20 is a, it is preferable that the length a of the fitting portion 14 and the thickness t of the transparent substrate are t > a. This allows for more uniform stress to be applied to the transparent substrate by pressing when joining it to the main body, and allows the transparent substrate to be properly fitted into the fitting portion. This further improves the airtightness of the gas cell 1. In terms of further improving the airtightness of the gas cell 1, it is preferable that the difference between the thickness t of the transparent substrate and the length a is 0.1 mm or more and less than 1.0 mm. 【0028】 The length a of the fitting portion 14 is preferably 0.1 mm or more, and more preferably 0.5 mm or more. When the length a is greater than or equal to the lower limit, the contact area between the transparent substrate 20 and the main body portion 10 increases, and the airtightness of the gas cell 1 is further improved. The length a of the fitting portion 14 may also be 3.9 mm or less, or 2.0 mm or less. 【0029】 In the mating portion 14, if b is the length of the mating portion that joins the first main surface 21 of the transparent substrate 20 in a direction perpendicular to the thickness direction of the transparent substrate 20 (in Figure 2, the direction toward the central axis of the side wall portion 13 of the main body portion 10), then b is preferably 0.5 mm or more and less than 5.0 mm, and more preferably 0.7 to 3.0 mm. When b is greater than or equal to the lower limit, the joining area between the transparent substrate 20 and the main body portion 10 becomes larger, and the airtightness of the gas cell 1 is further improved. When b is less than the upper limit, the size of the main body portion is suppressed, making it easier to miniaturize and lighten the quantum sensor equipped with the gas cell, or the volume of the closed space becomes larger, and the signal sensitivity is further improved. 【0030】A bonding layer may be present between the main body and the transparent substrate of the gas cell in this embodiment. Examples of materials constituting the bonding layer include the bonding agent used to bond the main body and the transparent substrate, and components derived from the bonding agent. Examples of known bonding agents include glass frit, resin adhesives, and inorganic adhesives. 【0031】 In this embodiment, alkali metal atoms are sealed in a closed space inside the gas cell. Examples of alkali metal atoms include lithium, potassium, cesium, rubidium, and sodium. The alkali metal atoms sealed in the closed space may be in the form of a combination of the above alkali metal atoms with compounds such as zirconium, silicon, titanium, and aluminum, or they may be compounds of alkali metal atoms such as azides, halides, and nitrates. A buffer gas may be sealed in the closed space together with the alkali metal atoms. Examples of buffer gases include nitrogen gas, helium gas, xenon gas, neon gas, and argon gas. The alkali metal atoms and buffer gas sealed in the closed space are appropriately selected according to the application of the gas cell. 【0032】 It is preferable to provide a heater to gasify the alkali metals in the internal space of the main body. The heater is not particularly limited, but it is preferable to use a ceramic heater with high power density when it is necessary to shorten the warm-up time of the atomic oscillator or quantum sensor such as an optical pumping magnetic sensor, or when high-temperature operation is required. On the other hand, it is preferable to use a polyimide heater with low power density when it is necessary to make the temperature distribution of the main body uniform, to miniaturize and lower the position of the atomic oscillator or optical pumping magnetic sensor, or to reduce the cost of the atomic oscillator or optical pumping magnetic sensor. 【0033】 <Method for Manufacturing a Gas Cell of the First Embodiment> The method for manufacturing the gas cell 1 of this embodiment will be described below. The method for manufacturing the gas cell 1 of this embodiment includes, for example, a preparation step of preparing a main body 10 and a transparent substrate 20, and a fitting step of fitting the transparent substrate 20 into the fitting portion 14 to join the main body 10 and the transparent substrate 20, and fitting the transparent substrate 20 into the fitting portion 14. 【0034】 In the preparation process, the main body 10 and the transparent substrate 20 are prepared. The main body 10, which consists of a base portion 12 and side wall portions 13, can be manufactured using known techniques such as etching, photolithography, casting, and 3D printing. In addition, a reflective member 30 is provided on the inner surface of the base portion 12 of the main body 10. 【0035】 In the fitting process, the main body 10 and the transparent substrate 20 can be joined by known methods such as bonding with an adhesive, anodic bonding, heat bonding, and laser bonding, and the method is appropriately selected according to the respective constituent materials of the main body 10 and the transparent substrate 20. In the fitting process, it is preferable to join the main body 10 and the transparent substrate 20 using an adhesive, and then heat-treat the joint, in order to further improve airtightness. 【0036】 When manufacturing a gas cell in which alkali metal atoms are sealed in a closed space 40, the sealing material containing alkali metal atoms should be placed inside the main body 10 before the fitting process. Examples of sealing materials containing alkali metal atoms include liquid or solid alkali metals, ampoules containing alkali metals, wax, etc. When liquid or solid alkali metals are placed, heating the gas cell during use creates a closed space 40 containing alkali metal atoms. When ampoules containing alkali metals are placed, after joining the main body 10 and the transparent substrate 20, the ampoules are destroyed by irradiation with an external laser beam, or the wax is melted, creating a closed space 40 containing alkali metal atoms. Alternatively, a stable alkali metal compound and an azide may be placed, and then heated to generate alkali metal vapor through a chemical reaction. 【0037】 Another method for manufacturing a gas cell in which alkali metal atoms are sealed in a closed space 40 is to first provide open holes in either the base portion 12 or the side wall portion 13 of the main body portion 10, then join the main body portion 10 and the transparent substrate 20, introduce a sealing material containing alkali metal atoms, and then seal the open holes. The method for forming the closed space 40 in which alkali metal atoms are sealed by the sealing material is as described above. As a method for sealing the open holes, one method is to fill the open holes with the above-mentioned bonding agent and then perform heat treatment. 【0038】 The gas cell of this embodiment has been described above based on the gas cell 1 shown in Figures 1 and 2, but other forms of gas cell besides the gas cell 1 are also included in this embodiment. The external shape of the gas cell 1 is a hexahedron with one face shaped like a square, but the external shape of the gas cell of this embodiment can be selected to suit the design of the quantum sensor. The external shape of the gas cell of this embodiment may be, for example, a polygonal prism, cylinder, elliptical prism, or polygon other than a rectangular parallelepiped (cube). The closed space 40 inside the main body 10 is a rectangular parallelepiped (cube), but the shape of the closed space may be a polygonal prism, cylinder, elliptical prism, or polygon other than a rectangular parallelepiped. The external shape of the gas cell and the shape of the closed space may be the same or different. 【0039】 The following modifications are also possible for the gas cell of this embodiment. In each modification, elements common to the gas cell 1 shown in Figure 1 are denoted by the same reference numerals, and their descriptions are omitted. 【0040】 <Modification 1 of the First Embodiment> A modification 1 of the gas cell according to this embodiment is shown in Figure 3. The main body 10 of the gas cell 2 shown in Figure 3 is not a member in which the base 12 and the side wall 13 are integrally molded, but a member formed by joining a rectangular plate-shaped member corresponding to the base 12 and a rectangular tubular member corresponding to the side wall 13. The joining method is not particularly limited, but examples include joining using a bonding agent, anodic joining, heat compression bonding, and laser joining. In this modification, a reflective member 30 can be easily formed on the base 12. In this modification, the material constituting the base 12 and the material constituting the side wall 13 may be the same or different, but it is preferable that they be the same material in that the design regarding thermal expansion is easier. 【0041】<Modification 2 of the First Embodiment> A modification 2 of the gas cell according to this embodiment is shown in Figures 4 and 5. Figure 4 is a perspective view showing the gas cell 3 according to this modification. Figure 5 is a cross-sectional view of the gas cell 3 along the line I-I in Figure 4. As shown, the main body 10 of the gas cell 3 has, for example, a plate-shaped base 12 with a rectangular outer shape in plan view, and a rectangular tubular side wall portion 13 having four side walls. The side wall portion 13 is provided so as to surround the entire circumference of the peripheral edge of the base portion 12. On the inside of the protruding end of the side wall portion 13 opposite to the base portion 12 (on the opening 11 side), a fitting portion 14 having a frame-shaped lid portion 15 in plan view is provided. As shown, the fitting portion 14 has, for example, three orthogonal first fitting surfaces 141, a second fitting surface 142, and a third fitting surface 143. The first main surface 21 of the transparent substrate 20 is joined to the first mating surface 141, the side surface 23 of the transparent substrate 20 is joined to the second mating surface 142, and the second main surface 22 of the transparent substrate 20 is joined to the third mating surface 143. In this modified gas cell 3, the mating portion 14 of the main body 10 is joined to three surfaces of the transparent substrate 20: the first main surface 21, the second main surface 22, and the side surface 23. This configuration increases the bonding area between the main body 10 and the transparent substrate 20, further improving airtightness and resulting in a gas cell with superior robustness for use in harsher environments. 【0042】 In this modified example, if c is the length in the thickness direction of the transparent substrate 20 of the fitting portion 14 that joins the first main surface 21, the second main surface 22, and the side surface 23 of the transparent substrate 20, then it is preferable that the length c and the thickness t of the transparent substrate are t ≤ c. This is because the airtightness of the gas cell 3 can be further improved, and a gas cell with superior robustness when used in more severe environments can be obtained. In terms of further improving the airtightness of the gas cell 3, the difference obtained by subtracting the thickness t of the transparent substrate from the length c of the fitting portion 14 is preferably 0 to 0.5 mm. It should be noted that the above length c can also be said to be the distance between the surface of the transparent substrate 20 facing the first main surface 21 at the fitting portion 14 and the surface of the transparent substrate 20 facing the second main surface 22 at the lid portion 15 of the fitting portion 14. 【0043】In this modification example, the length c of the fitting portion 14 is preferably 0.6 mm or more, and more preferably 1.0 mm or more. When the length c is equal to or greater than the above lower limit value, the bonding area between the transparent substrate 20 and the main body portion 10 becomes wider, and the airtightness of the gas cell 1 is further improved. Also, the length c of the fitting portion 14 may be 4.5 mm or less, and may be 2.1 mm or less. 【0044】 In the lid portion 15 of the fitting portion 14, when the length in the direction orthogonal to the thickness direction of the transparent substrate 20 of the fitting portion 14 that joins with the first main surface 22 of the transparent substrate 20 (the direction toward the central axis of the side wall portion 13 of the main body portion 10 in FIG. 5) is d, the length d is preferably 0.5 to 6.0 mm, and more preferably 0.7 to 4.0 mm. When the length d is equal to or greater than the above lower limit value, the bonding area between the transparent substrate 20 and the lid portion 15 becomes wider, and the airtightness of the gas cell 3 is further improved. When the length d is equal to or less than the above upper limit value, since the area where the light that excites the electrons of the alkali metal atoms enters the closed space 40 and the area where it exits from the closed space 40 can be sufficiently ensured, the optical axis adjustment becomes easier. 【0045】 The main body portion 10 of this modification example is a member formed by joining a member corresponding to the base portion 12 and the side wall portion 13 and a frame-shaped member corresponding to the lid portion 15. The joining method is not particularly limited, and examples include the joining method described in Modification Example 1. In this modification example, the material constituting the base portion 12 and the side wall portion 13 and the material constituting the lid portion 15 may be the same or different, but the same material is preferred in terms of easier design regarding thermal expansion. 【0046】 The base portion 12 and the side wall portion 13 of the main body portion 10 may be a member formed by joining a rectangular plate-shaped member corresponding to the base portion 12 and a square tube-shaped member corresponding to the side wall portion 13, similar to Modification Example 1. 【0047】 The manufacturing method of the gas cell 3 of this modification example includes, for example, a preparation step of preparing a member A that becomes the base portion 12 and the side wall portion 13, a member B that becomes the lid portion 15, and the transparent substrate 20, a first joining step of joining the member A and the transparent substrate 20, and a second joining step of joining the member B to the member A and the transparent substrate 20. 【0048】Regarding the preparation of member A and the transparent substrate 20 in the preparation process, it is the same as described in the above manufacturing method of the gas cell 1. The member B that becomes the frame-shaped lid portion 15 can be manufactured using known techniques such as etching, photolithography, casting molding, and 3D printing. The first bonding process, including preferred forms, is the same as the fitting process in the above manufacturing method of the gas cell 1. 【0049】 In the second bonding process, the member B is bonded to the member A and the transparent substrate 20 manufactured in the first bonding process. The bonding method in the second bonding process may be the bonding method described in the fitting process in the above manufacturing method of the gas cell 1, and it is preferably the same as the bonding method in the first bonding process. Among them, in terms of being able to further improve airtightness, it is preferable to bond using an adhesive and then heat-treat the bonded portion for the bonding methods in the first bonding process and the second bonding process. 【0050】 Regarding the method of manufacturing a gas cell in which alkali metal atoms are enclosed in the closed space 40 of the gas cell 3 (the method of enclosing alkali metal atoms in the closed space 40), it is the same as described in the above manufacturing method of the gas cell 1. 【0051】<Modification 3 of the First Embodiment> A modification 3 of the gas cell according to this embodiment is shown in Figure 6. Figure 6 is a cross-sectional view showing the gas cell 4 according to this modification. The main body 10 of the gas cell 4 shown in Figure 6 has, for example, a plate-shaped base 12 with a rectangular outer shape in plan view, and a rectangular tubular side wall portion 13 having four side walls. The side wall portion 13 is provided so as to surround the entire circumference of the peripheral edge of the base portion 12. On the inner side (opening 11 side) of the protruding end side of one of the four side walls of the side wall portion 13, a fitting portion 14 into which a transparent substrate 20 is fitted is provided. As shown in Figure 6, the fitting portion 14 has, for example, three orthogonal first fitting surfaces 141, a second fitting surface 142, and a third fitting surface 143. The first main surface 21 of the transparent substrate 20 is joined to the first mating surface 141, the side surface 23 of the transparent substrate 20 is joined to the second mating surface 142, and the second main surface 22 of the transparent substrate 20 is joined to the third mating surface 143. In addition, on one side of the side wall portion 13 facing the mating portion 14, a through hole 16 is provided at the position where the mating portion 14 is located, with a shape corresponding to one of the side surfaces 23 of the transparent substrate 20. The main body portion 10 of the gas cell 4 has a structure in which the transparent substrate 20 is slid into the through hole 16 and fitted at the mating portion 14. The space outside the transparent substrate 20 within the internal space of the through hole 16 is sealed by the sealing portion 17. Thus, in this modified gas cell 4, the mating portion 14 of the main body portion 10 is joined to three surfaces of the transparent substrate 20: the first main surface 21, the second main surface 22, and the side surface 23. This configuration increases the contact area between the main body 10 and the transparent substrate 20, further improving airtightness and resulting in a gas cell with superior robustness for use in harsher environments. 【0052】 In this modified example, if c is the length in the thickness direction of the transparent substrate 20 of the fitting portion 14 that joins the first main surface 21, the second main surface 22, and the side surface 23 of the transparent substrate 20, then the difference obtained by subtracting the thickness t of the transparent substrate 20 from the length c of the fitting portion 14 is preferably 0.1 to 0.5 mm. This is because it is possible to further improve the airtightness of the gas cell 4 and obtain a gas cell with superior robustness when used in more severe environments. Furthermore, if the above difference is 0.1 mm or more, the manufacturing of the gas cell 4, including insertion into the through hole 16 of the transparent substrate 20, becomes easier. 【0053】 In the through-hole 16 of the main body 10, if e is the length of the fitting portion that joins the first main surface 21 (or second main surface 22) of the transparent substrate 20, in a direction perpendicular to the thickness direction of the transparent substrate 20 (in Figure 6, the direction toward the central axis of the side wall portion 13 of the main body 10), then e is preferably 0.7 to 10 mm, and more preferably 2 to 7 mm. When e is greater than or equal to the lower limit, the joining area between the transparent substrate 20 and the side wall portion 13 is increased, and the airtightness of the gas cell 4 is further improved. When e is less than or equal to the upper limit, the size of the main body is suppressed, making it easier to miniaturize and lighten the quantum sensor equipped with the gas cell. 【0054】 In this modified example, the space outside the transparent substrate 20 within the through-hole 16 is sealed by the sealing portion 17. As the material constituting the sealing portion 17, the adhesive used to join the main body and the transparent substrate, or components derived from the adhesive, is preferred, as it further improves the airtightness of the gas cell 4. 【0055】 In this modified example, the main body portion 10 is a member formed by integrally molding a base portion 12 and a side wall portion 13. In the gas cell 1 of this modified example, even though the main body portion 10 is integrally molded, the first main surface 21, second main surface 22, and side surface 23 of the transparent substrate 20 are joined to the main body portion 10, and the transparent substrate 20 can be fitted into the fitting portion 14 of the main body portion 10. The main body portion 10 may be a member formed by joining a rectangular plate-shaped member corresponding to the base portion 12 and a rectangular tubular member corresponding to the side wall portion 13, similar to the first modified example. 【0056】 The manufacturing method for the gas cell 4 of this modified example includes, for example, a main body 10 having a base portion 12 and a side wall portion 13, with a through hole 16 provided in one of the four side walls of the side wall portion 13; a fitting step of inserting a transparent substrate 20 into the through hole 16 of the main body portion 10, joining the main body portion 10 and the transparent substrate 20, and fitting the transparent substrate 20 into the fitting portion 14; and a sealing step of sealing the through hole 16 with a sealing portion 17. 【0057】The preparation process is as described in the manufacturing method of the gas cell 1 above. The main body 10 having a through hole 16 on one surface of the side wall 13 may be manufactured by 3D printing, or a member consisting of a base 12 and a side wall 13 without a through hole 16 may be manufactured, and then a through hole may be formed on one surface of the side wall 13 using a technique such as etching. 【0058】 In the fitting process, the transparent substrate 20 is inserted into the through hole 16 and slid to fit it into the fitting portion 14. The joining method for the main body 10 and the transparent substrate 20 can be the joining method described in the manufacturing method of the gas cell 1 above. In particular, in order to further improve the airtightness of the gas cell 4, it is preferable to apply an adhesive to the joining area of ​​the transparent substrate 20 in advance, insert it into the through hole 16 and fit it into the fitting portion 14, and then heat treat it. 【0059】 The sealing process involves sealing the space outside the transparent substrate 20 within the through-hole 16 with a sealing agent to form a sealed portion 17. The sealing agent can be the bonding agent used to join the main body and the transparent substrate. It is preferable to further improve the airtightness of the gas cell 4 by heat-treating the sealing agent (preferably a bonding agent) after sealing. 【0060】 The method for manufacturing a gas cell in which alkali metal atoms are sealed in the closed space 40 of the gas cell 4 (the method for sealing alkali metal atoms in the closed space 40) is as described in the manufacturing method of the gas cell 1 above. 【0061】 The gas cells of the second and third embodiments are described below. As shown in the second and third embodiments, the gas cell of the present invention may have two or more openings in its main body. The gas cells of the second and third embodiments differ from those of the first embodiment in the number of transparent substrates and fitting parts, depending on the number of openings. The constituent materials, shape and size of the main body and transparent substrate, as well as the enclosed gas containing alkali metal atoms, are the same as those of the gas cell of the first embodiment in the gas cells of the second and third embodiments, unless otherwise specified. 【0062】[Second Embodiment] An example of a gas cell according to the second embodiment of the present invention is shown in Figures 7 and 8. Figure 7 is a perspective view showing a gas cell 5 according to this embodiment. Figure 8 is a cross-sectional view of the gas cell 5 along the line I-I in Figure 7. In the following description of the gas cell according to the second embodiment, components common to the gas cell of the first embodiment are denoted by the same reference numerals, and their detailed explanation is omitted. As shown in Figure 8, in the gas cell 5 according to this embodiment, the main body portion 10 consists of a rectangular tubular side wall portion 13, and the side wall portion 13 has two openings 11a and 11b on both ends of the central axis, facing each other with a closed space 40 in between. Also, fitting portions 14a and 14b are provided on the inside of the side wall portion 13 of the main body portion 10 (on the side of the opening 11a or 11b). The gas cell 5 has transparent substrates 20a and 20b, which are fitted into the fitting portions 14a and 14b, respectively. In this embodiment of the gas cell 5, as in the first embodiment, the transparent substrates 20a and 20b are fitted into the fitting portions 14a and 14b of the main body portion 10, respectively, thereby providing a gas cell 5 with excellent airtightness for the enclosed gas containing alkali metal atoms. 【0063】 The transparent substrates 20a and 20b of the gas cell 5 according to this embodiment may differ in their constituent material, shape, and size, but it is preferable that they all be the same in terms of superior gas cell manufacturing and signal stability. The fitting portions 14a and 14b of the main body 10 are the same as the fitting portion 14 of the gas cell 1 of the first embodiment, including preferred forms. The gas cell 5 according to this embodiment can be manufactured in accordance with the manufacturing method of the gas cell 1 of the first embodiment. 【0064】 In this embodiment, the main body 10 has two openings 11a and 11b that face each other across a closed space 40. When the gas cell 5 of this embodiment is used as a quantum sensor or the like, a light source that emits excitation light to excite electrons of alkali metal atoms is placed on one opening side (for example, opening 11a), and a photodetector that detects light transmitted through the closed space 40 is placed on the other opening side (for example, opening 11b). 【0065】The following modifications are also possible for the gas cell of this embodiment. In each modification, elements common to the gas cell 5 shown in Figure 8 are denoted by the same reference numerals, and their descriptions are omitted. 【0066】 <Modification 1 of the Second Embodiment> A modification 1 of the gas cell according to this embodiment is shown in Figure 9. Figure 9 is a cross-sectional view showing the gas cell 6 according to this modification. In the gas cell 6 shown in Figure 9, the main body portion 10 has two openings 11a and 11b at positions facing each other across a closed space 40. The gas cell 6 has two transparent substrates 20a and 20b corresponding to these two openings 11a and 11b. The main body portion 10 also has a rectangular tubular side wall portion 13, and fitting portions 14a and 14b having frame-shaped lid portions 15a and 15b in a plan view are provided on the inside of both ends of the central axis of the side wall portion 13 (on the side of the opening 11a or 11b). The lid portions 15a and 15b are joined to the second main surface 22a of the transparent substrate 20a and the second main surface 22b of the transparent substrate 20b, respectively. As shown in the figure, the mating portion 14a has, for example, three orthogonal first mating surfaces 141a, a second mating surface 142a, and a third mating surface 143a. The first main surface 21a of the transparent substrate 20a is joined to the first mating surface 141a, the side surface 23a of the transparent substrate 20a is joined to the second mating surface 142a, and the second main surface 22a of the transparent substrate 20a is joined to the third mating surface 143a. Similarly, the mating portion 14b has, for example, three orthogonal first mating surfaces 141b, a second mating surface 142b, and a third mating surface 143b. The first main surface 21b of the transparent substrate 20b is joined to the first mating surface 141b, the side surface 23b of the transparent substrate 20b is joined to the second mating surface 142b, and the second main surface 22b of the transparent substrate 20b is joined to the third mating surface 143b. In this modified gas cell 6, the mating portion 14a is joined to the three surfaces of the transparent substrate 20a: the first main surface 21a, the second main surface 22a, and the side surface 23a, and the mating portion 14b is joined to the three surfaces of the transparent substrate 20b: the first main surface 21b, the second main surface 22b, and the side surface 23b. With this configuration, the bonding area between the main body 10 and the transparent substrates 20a and 20b is increased, which further improves airtightness and provides a gas cell with superior robustness when used in more severe environments. 【0067】The fitting portions 14a and 14b of the main body 10 in this modified example are the same as the fitting portion 14 of the main body 10 in Modification Example 2 of the first embodiment, including the preferred form. The gas cell 6 according to this modified example can be manufactured in accordance with the manufacturing method of the gas cell 3 according to Modification Example 2 of the first embodiment. 【0068】 <Modification 2 of the Second Embodiment> A modification 2 of the gas cell according to this embodiment is shown in Figure 10. Figure 10 is a cross-sectional view showing the gas cell 7 according to this modification. In the gas cell 7 shown in Figure 10, the main body portion 10 has two openings 11a and 11b at positions facing each other across a closed space 40. The gas cell 7 has two transparent substrates 20a and 20b corresponding to these two openings 11a and 11b. The main body portion 10 has a rectangular tubular side wall portion 13, and fitting portions 14a and 14b are provided on the inside of both ends of the central axis of the side wall portion 13 (on the side of the opening 11a or 11b), into which the transparent substrates 20a and 20b are fitted, respectively. Furthermore, on one side of one of the four side walls of the side wall portion 13, a through hole 16a is provided at the position where the fitting portions 14a and 14b are provided, corresponding to one of the side surfaces 23a of the transparent substrate 20a and one of the side surfaces 23b of the transparent substrate 20b. The main body portion 10 of the gas cell 7 has a structure in which the transparent substrates 20a and 20b are slid into the through holes 16a and 16b and fitted together at the fitting portions 14a and 14b, respectively. In addition, the space outside the transparent substrate 20a within the through hole 16a is sealed by the sealing portion 17a, and the space outside the transparent substrate 20b within the through hole 16b is sealed by the sealing portion 17b. In this modified gas cell 7, the fitting portion 14a is joined to three surfaces of the transparent substrate 20a: the first main surface 21a, the second main surface 22a, and the side surface 23a, and the fitting portion 14b is joined to three surfaces of the transparent substrate 20b: the first main surface 21b, the second main surface 22b, and the side surface 23b. This configuration increases the bonding area between the main body 10 and the transparent substrates 20a and 20b, thereby further improving airtightness and providing a gas cell with superior robustness for use in harsher environments. 【0069】The fitting portions 14a and 14b of the main body portion 10 in this modified example are the same as the fitting portion 14 of the main body portion 10 in Modification 3 of the first embodiment, including preferred forms. The sealing portions 17a and 17b of this modified example are the same as the sealing portion 17 of the main body portion 10 in Modification 3 of the first embodiment, including preferred forms. In the gas cell 7 shown in Figure 10, the through holes 16a and 16b are provided on the same side wall of the side wall portion 13, but in this modified example, the two through holes may be provided on different side walls of the side wall portion. Whether or not to provide the two through holes on the same side wall portion is selected as appropriate depending on the structural design and manufacturing method. The gas cell 7 according to this modified example can be manufactured in accordance with the manufacturing method of the gas cell 4 according to Modification 3 of the first embodiment. 【0070】[Third Embodiment] An example of a gas cell according to the third embodiment of the present invention is shown in Figures 11 and 12. Figure 11 is a perspective view showing a gas cell 8 according to this embodiment. Figure 12 is a cross-sectional view of the gas cell 8 along the line I-I in Figure 11. In the following description of the gas cell according to the third embodiment, components common to the gas cells of the first and second embodiments are denoted by the same reference numerals, and their detailed descriptions are omitted. As shown in the figure, in the gas cell 8 according to this embodiment, the main body 10 has two base portions 12 and side wall portions 13. The two base portions 12 are plate-shaped with a rectangular outer shape in plan view and face each other across a closed space 40. The side wall portions 13 have four side walls provided so as to surround the entire circumference of each peripheral edge of the base portion 12. The main body 10 has openings 11a to 11d provided in each of the four side walls of the side wall portions 13. The gas cell 8 has four transparent substrates 20a to 20d corresponding to these four openings 11a to 11d. Each of the transparent substrates 20a to 20d has a first main surface 21a to 21d that, together with the main body 10, constitutes a closed space 40 for encapsulating alkali metal atoms, a second main surface 22a to 22d opposite to the first main surface 21a to 21d, and a side surface 23a to 23d incorporated into the outer edges of the first main surface 21a to 21d and the second main surface 22a to 22d. The base 12 and side wall 13 of the main body 10 are provided with fitting portions 14a to 14d into which the transparent substrates 20a to 20d are fitted. As shown in the figure, each of the fitting portions 14a to 14d has, for example, two orthogonal first fitting surfaces 141a to 141d and second fitting surfaces 142a to 142d. The first main surfaces 21a to 21d of the transparent substrates 20a to 20d are joined to the first mating surfaces 141a to 141d, respectively, and the side surfaces 23a to 23d of the transparent substrates 20a to 20d are joined to the second mating surfaces 142a to 142d, respectively. In the gas cell 8 according to this embodiment, as in the first embodiment, the transparent substrates 20a to 20d are fitted to the mating portions 14a to 14d of the main body 10, respectively, thereby obtaining a gas cell 8 with excellent airtightness for the enclosed gas containing alkali metal atoms. 【0071】In the gas cell 8 of this embodiment, the four openings 11a to 11d consist of two sets: a set of openings 11a and 11b facing each other across the closed space 40, and a set of openings 11c and 11d facing each other across the closed space 40. When the gas cell 8 of this embodiment is used in a quantum sensor or the like, two different alkali metal atoms are sealed in the closed space 40, and two sets of light sources and photodetectors suitable for each alkali metal are prepared, and the same sets of light sources and photodetectors are arranged to face each other across the gas cell 8. For example, a light source corresponding to alkali metal A is placed on the opening 11a side, a photodetector corresponding to alkali metal A is placed on the opening 11b side, a light source corresponding to alkali metal B is placed on the opening 11c side, and a photodetector corresponding to alkali metal B is placed on the opening 11d side. The positions of the same sets of light sources and photodetectors may be reversed from the above embodiment depending on the design of the quantum sensor. 【0072】 The transparent substrates 20a to 20d of the gas cell 8 may differ in their constituent material, shape, and size, but it is preferable that they all be the same in terms of superior gas cell manufacturing and signal stability. The fitting portions 14a to 14d of the main body 10 are the same as the fitting portion 14 of the gas cell 1 of the first embodiment, including preferred forms. The external shape of the gas cell 8 shown in Figure 12 is a rectangular parallelepiped (cube), but the external shape of the gas cell in this embodiment can be selected to suit the design of the quantum sensor. The external shape of the gas cell in this embodiment may be, for example, a polygonal prism or polygonal shape other than a rectangular parallelepiped. The gas cell 8 according to this embodiment can be manufactured in accordance with the manufacturing method of the gas cell 1 of the first embodiment. 【0073】 The following modifications are also possible for the gas cell of this embodiment. In these modifications, elements common to the gas cell 8 shown in Figure 12 are given the same reference numerals, and their descriptions are omitted. 【0074】<Modification of the Third Embodiment> Modifications of the gas cell according to this embodiment are shown in Figures 13 and 14. Figure 13 is a perspective view showing the gas cell 9 according to this embodiment. Figure 14 is a cross-sectional view of the gas cell 9 along the line I-I in Figure 13. In the gas cell 9 according to this embodiment, the main body portion 10 has two base portions 12 and side wall portions 13 provided so as to surround the entire circumference of each peripheral edge of the base portion 12. The main body portion 10 also has openings 11a to 11d provided in each of the four side walls of the side wall portion 13. The gas cell 9 has four transparent substrates 20a to 20d corresponding to these four openings 11a to 11d. The base portions 12 and side wall portions 13 of the main body portion 10 are provided with fitting portions 14a to 14d into which the transparent substrates 20a to 20d are fitted. Each of the fitting portions 14a to 14d has a frame-shaped lid portion 15a to 15d in plan view, and the lid portions 15a to 15d are joined to the second main surfaces 22a to 22d of the transparent substrates 20a to 20d, respectively. In this modified gas cell 9, each of the fitting portions 14a to 14d is joined to the first main surface, the second main surface, and the side surface of the transparent substrates 20a to 20d. This configuration increases the bonding area between the main body portion 10 and each of the transparent substrates 20a to 20d, thereby further improving airtightness and providing a gas cell with superior robustness for use in harsher environments. 【0075】 The fitting portions 14a to 14d of the main body 10 in this modified example are the same as the fitting portion 14 of the main body 10 in Modification Example 2 of the First Embodiment, including the preferred form. The gas cell 9 according to this modified example can be manufactured in accordance with the manufacturing method of the gas cell 3 according to Modification Example 2 of the First Embodiment. 【0076】The gas cell according to the present invention, as described above, is suitably used in quantum sensors such as atomic oscillators and optical pumping magnetic sensors. An example of a quantum sensor is an embodiment comprising the gas cell according to the present invention, a light source that emits excitation light to excite electrons of alkali metal atoms sealed in the gas cell, and a photodetector that detects light transmitted through the gas cell. A known laser light source can be used as the light source that emits the excitation light. The excitation light may be linearly polarized or circularly polarized. The photodetector that detects light transmitted through the gas cell may detect the excitation light transmitted through the gas cell, or it may detect probe light different from the excitation light transmitted through the gas cell. The quantum sensor may also include a coil for adjusting the magnetic field within the gas cell, a power supply for the coil, and a magnetic shield that covers the gas cell and blocks or attenuates external magnetic fields. Furthermore, the gas cell according to the present invention can also be applied to airtight containers in devices such as wavelength conversion members. Furthermore, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-217580, filed on December 12, 2024, are incorporated herein by reference as disclosure of the present invention. 【0077】 1, 2, 3, 4, 5, 6, 7, 8, 9: Gas cell 10: Main body 11, 11a, 11b, 11c, 11d: Opening 12, 12a, 12b: Base 13: Side wall 14, 14a, 14b, 14c, 14d: Fitting portion 15, 15a, 15b, 15c, 15d: Lid portion 16, 16a, 16b: Through hole 17, 17a, 17b: Sealing portion 20, 20a, 20b, 20c, 20d: Transparent substrate 21, 21a, 21b, 21c, 21d: First main surface 22, 22a, 22b, 22c, 22d: Second main surface 23, 23a, 23b, 23c, 23d: Side surface 30: Reflective member 40: Closed space 141, 141a, 141b, 141c, 141d: First fitting surface 142, 142a, 142b, 142c, 142d: Second fitting surface 143, 143a, 143b: Third fitting surface

Claims

1. A gas cell in which alkali metal atoms are sealed inside, comprising a main body having at least one opening, and a transparent substrate provided in the opening, wherein the main body has a fitting portion into which the transparent substrate is fitted.

2. The gas cell according to claim 1, wherein the transparent substrate has a first main surface that together with the main body constitutes a closed space for encapsulating the alkali metal atoms, a second main surface opposite to the first main surface, and a side surface that is incorporated into the outer edges of the first and second main surfaces, and the fitting portion of the main body is joined to at least two of the first main surface, the second main surface, and the side surface of the transparent substrate.

3. When the fitting portion of the main body is joined to the two surfaces, the second main surface and the side surface, let t be the thickness of the transparent substrate in the thickness direction from the first main surface to the second main surface, and let a be the length of the fitting portion in the thickness direction that joins the side surface, then t > a, as described in claim 2.

4. The gas cell according to claim 2, wherein when the fitting portion of the main body is joined to the three surfaces of the first main surface, the second main surface, and the side surface, t is the thickness of the transparent substrate in the thickness direction from the first main surface to the second main surface, and c is the length of the fitting portion in the thickness direction that joins the first main surface, the second main surface, and the side surface, t ≤ c.

5. The gas cell according to claim 3, wherein when the fitting portion of the main body is joined to the two surfaces of the first main surface and the side surface, the length of the fitting portion that contacts the first main surface in a direction perpendicular to the thickness direction is 0.5 mm or more and less than 5.0 mm.

6. The gas cell according to claim 4, wherein when the fitting portion of the main body is joined to the three surfaces of the first main surface, the second main surface, and the side surface, the length of the fitting portion that contacts the first main surface in a direction perpendicular to the thickness direction is 0.5 mm or more and less than 5.0 mm.

7. The gas cell according to claim 2, wherein when the fitting portion of the main body is joined to the three surfaces of the first main surface, the second main surface, and the side surface, the fitting portion of the main body has a frame-shaped lid portion arranged along the outer edge of the second main surface.

8. The gas cell according to claim 2, wherein when the fitting portion of the main body is joined to the three surfaces of the first main surface, the second main surface, and the side surface, the main body has a sealing portion that is in contact with the side surface of the transparent substrate and in contact with the outside of the gas cell.

9. The gas cell according to claim 1, wherein the main body portion has one opening, and a reflective member is provided inside the main body portion at a position facing the opening.

10. The gas cell according to claim 1, wherein the main body portion has two or more openings.

11. A quantum sensor comprising: a gas cell according to any one of claims 1 to 10; a light source that emits excitation light to excite electrons of alkali metal atoms contained in the gas cell; and a photodetector that detects light transmitted through the gas cell.

12. The quantum sensor according to claim 11, which is an optical pumping magnetic sensor.

13. The quantum sensor according to claim 11, which is an atomic oscillator.

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