Gas cell, method for manufacturing gas cell, and quantum sensor

Abstract

Provided are a gas cell having excellent shape stability, a method for manufacturing the gas cell, and a quantum sensor.　The gas cell has alkali metal atoms sealed therein. The gas cell is provided with a main body having at least one opening and a transparent substrate provided in the opening, the main body being an integrally molded product and having a fitting portion into which the transparent substrate is fitted.

Description

Gas cell, method for manufacturing a gas cell, and quantum sensor 【0001】 The present invention relates to a gas cell used in a quantum sensor such as an atomic oscillator or an optical pumping magnetic sensor, a method for manufacturing a gas cell, and a quantum sensor. 【0002】 When light interacts with alkali metal vapors, phenomena such as spin polarization and quantum interference effects (CPT; Coherent Population Trapping) occur. Recently, atomic oscillators and optical pumping magnetic sensors have attracted attention due to their application in these phenomena. For example, optical pumping magnetic sensors are used as brain function imaging devices to measure and image the physiological activity and function of various parts of the brain. Therefore, improvements to optical pumping magnetic sensors are expected to contribute to the early detection and treatment of diseases, as well as to improving quality of life (QOL), thus contributing to the achievement of Sustainable Development Goal 3, "Ensure healthy lives and promote well-being for all," advocated by the United Nations. 【0003】 Quantum sensors, such as atomic oscillators or optically pumped magnetic sensors, generally consist of a gas cell containing alkali metal vapor or buffer gases such as nitrogen, helium, or argon; a light source that emits excitation light to excite the alkali metals in the gas cell; and a photodetector that detects the light that has passed through the gas cell. 【0004】 Alkali metal vapor is obtained by heating and vaporizing alkali metals or alkali metal compounds sealed inside a gas cell. Therefore, the gas cell must operate in a high-temperature environment, and it is crucial to uniformly fill the inside of the gas cell with alkali vapor. Furthermore, quantum sensors require miniaturization, and with this miniaturization, there is a demand for gas cells with stable signals and the ability to be mass-produced at low cost. 【0005】 Japanese Patent Publication No. 2009-10547 【0006】Patent Document 1 proposes an optical pumping magnetometer equipped with a glass cell, a thermometer for measuring the cell's temperature, and a control unit that energizes a laser irradiation light-transmitting section to control the temperature. However, flame processing is generally used to form glass cells, which presents challenges such as difficulty in miniaturizing gas cells and large variations in shape, resulting in poor shape stability. The present invention aims to provide a gas cell with excellent shape stability, a method for manufacturing a gas cell, and a quantum sensor. 【0007】 As a result of diligent research, the present inventors have found that the above-mentioned problems can be solved by the following configuration: (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 is a single molded product and has a fitting portion into which the transparent substrate is fitted. 【0008】 (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 encapsulating 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) The gas cell according to (2), wherein when the fitting portion of the main body is joined to the two surfaces of 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. (4) 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, 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 c be the length in the thickness direction of the fitting portion that joins the first main surface, the second main surface and the side surface, then t ≤ c, as described in (2). (5) The gas cell according to any one of (1) to (4), wherein the main body has a sealing portion for enclosing an alkali metal inside. (6) The gas cell according to any one of (1) to (5), wherein the main body has a transmittance of 15% or less with respect to the wavelength of excitation light that excites the electrons of the enclosed alkali metal atoms. 【0009】(7) A method for manufacturing a gas cell in which alkali metal atoms are sealed inside, comprising the steps of forming a main body having at least one opening and a fitting portion into which a transparent substrate is fitted as an integrally molded product using a three-dimensional printer, and fitting the transparent substrate into the fitting portion of the main body. (8) The method for manufacturing a gas cell according to (7), wherein the main body is provided with an open hole that connects the internal space of the main body to the outside, and further comprising the steps of introducing alkali metal and sealed gas into the internal space of the main body through the open hole and sealing the open hole. (9) A quantum sensor characterized by comprising a gas cell according to any one of (1) to (6), a light source that emits excitation light that excites electrons of alkali metal atoms contained in the gas cell, and a photodetector that detects light that has passed through the gas cell. (10) The quantum sensor according to (9), which is an optical pumping magnetic sensor. (11) The quantum sensor according to (9), which is an atomic oscillator. 【0010】 According to the present invention, it is possible to provide a gas cell with excellent shape stability, a method for manufacturing a gas cell, and a quantum sensor. 【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 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 perspective view showing an example of a gas cell according to the second embodiment of the present invention. This is a cross-sectional 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 flowchart showing an example of a method for manufacturing the main body of a gas cell according to an embodiment of the present invention. This is a schematic perspective view showing the shape of the main body samples of Example 1 and Example 2. 【0012】Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments and figures described below are illustrative for illustrating the present invention, and the present invention is not limited to the embodiments and figures shown below. Various modifications and substitutions can be made to the embodiments below without departing from the scope of the present invention. In the following, numerical ranges expressed using "~" mean a range that includes the numerical values ​​written before and after "~" as the lower and upper limits. 【0013】 A key feature of the gas cell of the present invention is that it contains alkali metal atoms, and comprises a main body having at least one opening, and a transparent substrate provided in the opening. The main body is a single-piece molded product and has a fitting portion into which the transparent substrate is fitted. Because the main body is a single-piece molded product, the gas cell has excellent shape stability. A key feature of the manufacturing method of the gas cell of the present invention is that it is a method for manufacturing a gas cell containing alkali metal atoms, comprising the steps of forming a main body having at least one opening and a fitting portion into which a transparent substrate is fitted as a single-piece molded product using a 3D printer, and fitting the transparent substrate into the fitting portion of the main body. Because the main body is formed as a single-piece molded product, the gas cell has excellent shape stability. The single-piece molded product has no joints. Therefore, in a single-piece molded product, deterioration of joints over time does not occur, and leakage of gas from the gasified alkali metal to the outside is suppressed, resulting in excellent durability of the gas cell. 【0014】 Figures 1 to 9 are conceptual diagrams showing a gas cell according to an embodiment of the present invention. The gas cell according to an embodiment of 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 being an integrally molded product and 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. The closed space 40 is the internal space of the main body 10. 【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 in 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 that has passed through the inside of the gas cell, for example, the excitation light, 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 20 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 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. 【0023】 The fitting portion 14 into which the transparent substrate 20 is fitted will be described 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. 【0024】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. 【0025】 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. 【0026】 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 is increased, 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 10 is suppressed, making it easier to miniaturize and lighten the quantum sensor equipped with the gas cell, or the volume of the closed space 40 is increased, and the signal sensitivity is further improved. The central axis of the side wall portion 13 is the axis that passes through the center in the direction in which the side wall portion 13 faces each other (the center of the closed space 40) and extends in the direction from the base portion 12 toward the opening 11. 【0027】 A bonding layer may exist between the main body 10 and the transparent substrate 20 of the gas cell 1 in this embodiment. Examples of materials constituting the bonding layer include the bonding agent used to bond the main body 10 and the transparent substrate 20 and components derived from the bonding agent. Examples of known bonding agents include glass frit, resin adhesives, and inorganic adhesives. 【0028】In this embodiment, alkali metal atoms are sealed in the closed space 40 inside the gas cell 1. A buffer gas (filling gas) may also be sealed in the closed space 40 along with the alkali metal atoms. The alkali metal atoms and the filling gas (buffer gas) will be described later. 【0029】 <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 the steps of forming a main body 10, which has at least one opening 11 and a fitting portion 14 into which a transparent substrate 20 is fitted, as an integrally molded product using a three-dimensional printer, and fitting the transparent substrate 20 into the fitting portion 14 of the main body 10 (hereinafter referred to as the fitting step). In the fitting step described above, for example, the transparent substrate 20 is fitted into the fitting portion 14, the transparent substrate 20 is joined to the fitting portion 14, and the transparent substrate 20 is fitted to the fitting portion 14. The joining of the transparent substrate 20 to the fitting portion 14 can be done by known methods such as joining using a bonding agent such as glass frit, anodic joining, heat compression bonding, and laser joining, and can be appropriately selected according to the respective constituent materials of the main body 10 and the transparent substrate 20. As for the fitting process, it is preferable to use a bonding agent to join the main body 10 and the transparent substrate 20, and then heat-treat the joint, in order to further improve airtightness. The process of forming the main body as a single molded product using a 3D printer will be described later. 【0030】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, and ampoules or waxes containing alkali metals. 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 or waxes containing alkali metals are placed, after joining the main body 10 and the transparent substrate 20, the ampoules are destroyed or the wax is melted by irradiation with an external laser beam to create 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. 【0031】 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 for the method of sealing the open holes, one example is to fill the open holes with the above-mentioned bonding agent and then perform heat treatment. 【0032】 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. 【0033】The following modifications of the gas cell of this embodiment are also possible. In the modifications of the gas cell, elements common to gas cell 1 shown in Figure 1 are denoted by the same reference numerals, and their descriptions are omitted. 【0034】 <Modified Version of the First Embodiment> Modified versions of the gas cell according to this embodiment are shown in Figures 3 and 4. Figure 3 is a perspective view showing the gas cell 3 according to this modified version. Figure 4 is a cross-sectional view of the gas cell 3 along the line I-I in Figure 3. The main body 10 of the gas cell 3 shown in Figure 4 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 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. The main body 10 is an integrally molded product in which the base portion 12 and the side wall portion 13 are integrally molded. As shown in Figure 4, 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 the side surface 23 of the transparent substrate 20. The main body portion 10 of the gas cell 3 has a structure in which the transparent substrate 20 is slid into the through hole 16 and fitted at the mating portion 14. The gap 24 of the through hole 16a created by the transparent substrate 20 is sealed by the sealing portion 17. Thus, in this modified gas cell 3, the mating portion 14 of the main body portion 10 is joined to the 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. 【0035】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 3 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 3, including insertion into the through hole 16 of the transparent substrate 20, becomes easier. 【0036】 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 4, 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 3 is further improved. When e is less than or equal to the upper limit, the size of the main body is suppressed, and it becomes easier to miniaturize and lighten the quantum sensor equipped with the gas cell. 【0037】 In this modified example, when the transparent substrate 20 is fitted into the fitting portion 14, the side surface 23 of the transparent substrate 20 opposite to the fitting portion 14 is located partway through the through hole 16. The through hole 16 is not filled by the transparent substrate 20. A gap 24 is created in the through hole 16 on the side surface 23 of the transparent substrate 20 opposite to the fitting portion 14. This gap 24 in the through hole 16 caused by the transparent substrate 20 is sealed by the sealing portion 17. As for the material constituting the sealing portion 17, the adhesive used to join the main body portion 10 and the transparent substrate 20, or components derived from the adhesive, is preferred, as it further improves the airtightness of the gas cell 3. 【0038】The manufacturing method of the gas cell 3 of this modification example is to form, using a 3D printer, a main body part 10 having a fitting part 14 on one of the four side walls of the side wall part 13 shown in FIG. 4 and having a through hole 16 on the side wall part 13 facing the fitting part 14 as an integrally molded product. It has a fitting process of inserting a transparent substrate 20 into the through hole 16 of the main body part 10, joining the main body part 10 and the transparent substrate 20, and fitting the transparent substrate 20 into the fitting part 14, and a sealing process of sealing the through hole 16 with a sealing part 17. 【0039】 In the fitting process, the transparent substrate 20 is inserted into the through hole 16 and slid to fit the transparent substrate 20 into the fitting part 14. As the joining method of the main body part 10 and the transparent substrate 20, the joining method described in the manufacturing method of the above gas cell 1 can be applied. Among them, in terms of further improving the airtightness of the gas cell 3, it is preferable to apply an adhesive to the joining portion of the transparent substrate 20 in advance, insert it into the through hole 16, fit it into the fitting part 14, and then perform heat treatment. 【0040】 The sealing process is a process of sealing the gap 24 of the through hole 16 with a sealing agent to form a sealing part 17. Examples of the sealing agent include the adhesive used for joining the above main body part and the transparent substrate. In terms of further improving the airtightness of the gas cell 3, it is preferable to heat-treat the sealing agent after sealing with the sealing agent (preferably an adhesive) to form the sealing part 17. 【0041】 The method of manufacturing a gas cell in which an alkali metal atom is enclosed in the closed space 40 of the gas cell 3 (the method of enclosing an alkali metal atom in the closed space 40) is as described in the manufacturing method of the above gas cell 1, so a detailed description thereof will be omitted. 【0042】Hereinafter, the gas cells of the second and third embodiments will be described. As shown in the second and third embodiments, the gas cell of the present invention may have two or more openings in the main body. The gas cells of the second and third embodiments differ from the gas cell of the first embodiment in the number of transparent substrates and fitting portions according to the number of openings. Regarding the constituent materials, shapes, and sizes of the main body and the transparent substrate, and the enclosed gas containing alkali metal atoms, etc., the gas cells of the second and third embodiments are the same as those of the first embodiment unless otherwise specified. 【0043】 [Second Embodiment] An example of the gas cell according to the second embodiment of the present invention is shown in FIGS. 5 and 6. FIG. 5 is a perspective view showing the gas cell 5 according to the present embodiment. FIG. 6 is a cross-sectional view of the gas cell 5 along the line I-I in FIG. 5. Hereinafter, regarding the gas cell according to the second embodiment, the same reference numerals are given to the configurations common to the gas cell of the first embodiment, and the detailed description thereof is omitted. As shown in FIG. 6, in the gas cell 5 according to the present embodiment, the main body 10 is composed of a rectangular tubular side wall portion 13, and has two openings 11a and 11b facing each other across the closed space 40 on both ends of the central axis of the side wall portion 13. Further, fitting portions 14a and 14b are provided inside the side wall portion 13 of the main body 10 (on the side of the opening 11a or 11b). The main body 10 of the gas cell 5 is an integrally molded product. The gas cell 5 has transparent substrates 20a and 20b that are respectively fitted into the fitting portions 14a and 14b. Also in the gas cell 5 according to the present embodiment, as in the first embodiment, the transparent substrates 20a and 20b are respectively fitted into the fitting portions 14a and 14b of the main body 10, whereby a gas cell 5 having excellent airtightness of the enclosed gas containing alkali metal atoms can be obtained. 【0044】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 shown in Figure 2, 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. 【0045】 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 that has passed through the closed space 40, for example, excitation light, is placed on the other opening side (for example, opening 11b). 【0046】 The fitting portions 14a and 14b of the main body portion 10 in this embodiment are the same as the fitting portion 14 of the main body portion 10 of the gas cell 1 in the first embodiment shown in Figure 2, including the preferred form. 【0047】<Modification of the Second Embodiment> A modification of the gas cell according to this embodiment is shown in Figure 7. Figure 7 is a cross-sectional view showing the gas cell 7 according to this modification. In the gas cell 7 shown in Figure 7, the main body portion 10 has two openings 11a and 11b at positions opposite 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 corresponding to one of the side surfaces 23a of the transparent substrate 20a and a through hole 16b corresponding to one of the side surfaces 23b of the transparent substrate 20b are provided at the positions where the fitting portions 14a and 14b are provided. 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. Also, similar to the gas cell 3 shown in Figure 4, the gap 24 of the through hole 16a created by the transparent substrate 20a is sealed by the sealing portion 17a. Also, similar to the gas cell 3 shown in Figure 4, the gap 24 of the through hole 16b created by the transparent substrate 20b 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. 【0048】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 of the modified gas cell 3 of the first embodiment shown in Figure 4, 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 of the modified gas cell 3 of the first embodiment shown in Figure 4, including preferred forms. In the gas cell 7 shown in Figure 7, the through holes 16a and 16b are provided on the same side wall among the four side walls of the side wall portion 13, but in this modified example, the two through holes may be provided on different side walls among the four side walls of the side wall portion. Whether or not to provide the two through holes on the same side wall among the four side walls of the 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 3 according to the modified gas cell 3 of the first embodiment shown in Figure 4. 【0049】[Third Embodiment] An example of a gas cell according to the third embodiment of the present invention is shown in Figures 8 and 9. Figure 8 is a perspective view showing a gas cell 8 according to this embodiment. Figure 9 is a cross-sectional view of the gas cell 8 along the line I-I in Figure 8. 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. In the gas cell 8 according to this embodiment shown in Figure 8, 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 (see Figure 9) provided in each of the four side walls of the side wall portions 13. In accordance with these four openings 11a to 11d, the gas cell 8 has four transparent substrates 20a to 20d (see Figure 9). 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 and second main surfaces 21a to 21d and 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 Figure 9, 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. 【0050】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. 【0051】 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 shown in Figure 2, including preferred forms. The external shape of the gas cell 8 shown in Figure 9 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. 【0052】(Transparent Substrate) The transparent substrate, together with the main body, constitutes a gas cell (airtight container). The transparent substrate allows excitation light, which excites electrons of alkali metal atoms, to be incident on the internal space of the main body. It also allows the light that has passed through the internal space of the main body to be emitted to the outside of the main body. The transparent substrate is not particularly limited as long as it is made of a material that is transparent to wavelengths of light used in quantum sensors, but examples include glass materials, inorganic crystals such as quartz and sapphire, and translucent ceramic materials, with glass materials 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. Furthermore, if necessary, an alkali barrier film may be formed on the first main surface 21 of the transparent substrate 20. Also, 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. 【0053】 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 a gas cell is used in a quantum sensor, and improves signal stability. Also, when the thickness t of the transparent substrate 20 is less than or equal to the upper limit, the size of the gas cell is suppressed, making it easier to miniaturize and lighten the quantum sensor equipped with the gas cell. 【0054】(Main body) The main body, together with the transparent substrate as described above, constitutes a gas cell (airtight container). The internal space of the main body is the inside of the gas cell, and alkali metal atoms are sealed in the internal space of the main body. In addition to alkali metal atoms, a sealing gas (buffer gas) is sealed in the internal space of the main body. Examples of alkali metals used include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs). The alkali metal may also be in the form of a combination of the above alkali metals with compounds such as zirconium, silicon, titanium, and aluminum, or compounds such as azides, halides, and nitrates. Examples of sealing gases (buffer gases) used include nitrogen gas, helium gas, xenon gas, argon gas, or neon gas. The alkali metal atoms and sealing gas (buffer gas) sealed in the closed space are appropriately selected according to the application of the gas cell. The main body preferably has a transmittance of 15% or less, more preferably 5% or less, and even more preferably 0% with respect to the wavelength of excitation light that excites the electrons of the enclosed alkali metal atoms. This allows the excitation light to be emitted from the transparent substrate only to the outside of the main body, making it easy to detect the light that has passed through the internal space (inside the gas cell) of the main body. The main body also has a sealing portion for enclosing the alkali metal atoms inside. The sealing portion is provided in the main body and has an open hole that connects the internal space of the main body to the outside, and a sealing agent that seals the open hole. The sealing portion seals the alkali metal atoms and the enclosed gas into the internal space (inside the gas cell) of the main body. Examples of sealing agents include low-melting-point solder, low-melting-point glass molded body, or glass frit. The position of the formation of the open hole is not particularly limited as long as it is other than the opening of the main body. As described later, after introducing the alkali metal and the sealed gas into the internal space of the main body, the open vents are sealed with a sealing agent. 【0055】The main body preferably has a heater to gasify the alkali metals in the closed space (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. 【0056】 The main body is a single-piece molded product and has a fitting portion into which a transparent substrate is fitted. The shape of the main body is not particularly limited to the illustrated example. The shape of the main body may be, for example, a cube, a rectangular prism, a polygon, or a cylinder, and a shape suitable for the design of a quantum sensor can be selected. In addition to being able to be formed as a single-piece molded product, the main body is preferably made of SiC-Si because it has high specific strength, a low coefficient of thermal expansion, and high thermal conductivity. The main body is made of SiC-Si. ３ N ４ or Al ２ O ３ It can also be composed of ceramic materials such as SiC-Si, for example, SiSiC (reaction-sintered SiC). 【0057】 (Reflective Member) The reflective member reflects light such as excitation light from the closed space 40 (internal space) of the main body and emits it to the outside of the main body. As long as the reflective member can reflect light such as excitation light from the internal space of the main body and emit it to the outside of the main body as described above, its configuration is not particularly limited. 【0058】(Manufacturing Method for the Main Body) The manufacturing method for the main body, which is an integrally molded product, will be described below. As described later, in the manufacturing method for the main body 10, an integrally molded product is formed using a three-dimensional printing method with a three-dimensional printer, so even if the shape of the main body 10 is complex, the main body 10 can be formed as an integrally molded product. For this reason, although the main body 10 has various configurations as shown in Figures 2, 4, 6, 7, and 9 above, any configuration can be manufactured by the manufacturing method shown below. Figure 10 is a flowchart showing an example of a manufacturing method for the main body of a gas cell according to an embodiment of the present invention. The manufacturing method for the main body shown in Figure 10 includes: (1) a step of preparing a first molded body containing SiC particles by a three-dimensional printing method (step S10); (2) a step of impregnating the pores of the first molded body with carbon particles to form a second molded body (step S11); (3) a step of drying the second molded body (step S12); and (4) a step of impregnating the second molded body with Si and reaction sintering the second molded body to obtain a SiC-Si composite member (step S13). The SiC-Si composite member is the main body, and the main body is manufactured in this way. However, step S12 is a step that is performed as needed and is not an essential step in the manufacturing method of the main body. Each step will be described in detail below. A three-dimensional printer is used for the three-dimensional printing method. 【0059】[Step S10] In step S10, a first molded body containing SiC particles is formed using a three-dimensional printing method. In step S10, the shape of the first molded body is made to be the same as the shape of the main body that is formed. If CAD (Computer Aided Design) data for the main body that is formed is available, the shape of the first molded body can be made to be the same as the shape of the main body that is formed using the CAD data. The data for the three-dimensional printer of the first molded body can also be obtained from the CAD data. <<Three-Dimensional Printing Method>> First, a three-dimensional printing method that may be used in the manufacturing method of the main body will be described. The three-dimensional printing method used in this step S10 is not particularly limited. In step S10, for example, a three-dimensional printing method such as "laser irradiation molding" and "binder jet molding" may be used. Of these, in the laser irradiation molding method, a laser is irradiated onto the powder layer containing SiC particles and binder. Due to the heat of this laser, the binder present in the irradiated area melts and solidifies, and the SiC particles are bonded together. By performing this process on each of the sequentially stacked powder layers, a first three-dimensional molded body is formed. 【0060】 In binder jet molding, a binder is ejected from an inkjet nozzle onto a powder layer. In the areas where the binder is ejected, SiC particles are bonded together. By repeating this operation each time a powder layer is added, a first three-dimensional molded body is formed. 【0061】 In binder jet 3D printing, a curing agent may be pre-mixed into the powder layer, allowing the binder to react and harden only in the area where it comes into contact with the sprayed binder. A curing agent content of approximately 0.1% to 1% by mass relative to the powder layer is sufficient. In either printing method, thermosetting resins such as phenolic resins and self-curing resins such as furan resins can be used as binders. The thickness of a single powder layer used in 3D printing is typically in the range of 200 μm to 300 μm. 【0062】[SiC Particles] The average particle size of the SiC particles contained in the powder layer is, for example, in the range of 30 μm to 200 μm. Preferably, the average particle size of the SiC particles is in the range of 50 μm to 180 μm. Preferably, the SiC particles are α-SiC. 【0063】 As a general trend, the larger the average particle size of the SiC particles, the larger the average pore diameter M1 of the pores contained in the formed first molded body. Therefore, if a relatively small average pore diameter M1 is desired, SiC particles with a relatively small average particle size are selected, and if a relatively large average pore diameter M1 is desired, SiC particles with a large average particle size are selected. However, if the average particle size of the SiC particles becomes too small, it may not be possible to sufficiently impregnate the pores of the first molded body with carbon particles in the subsequent step S11. Therefore, it is preferable that the average particle size of the SiC particles be 30 μm or larger. Any powder, such as granulated powder or spherical powder, can be used for the SiC particles. The average particle size of the SiC particles can be measured using a laser diffraction / scattering particle size distribution analyzer (MT3300EXII manufactured by Microtrac-Bell Co., Ltd.). 【0064】 [First Molded Body] The first molded body, manufactured by the three-dimensional printing method, is typically porous and has numerous pores. The volume occupied by SiC particles in the first molded body is, for example, in the range of 30 vol% to 50 vol%. In other words, the volume of pores in the first molded body, i.e., porosity, may be in the range of 50 vol% to 70 vol%. The bulk density of the first molded body is, for example, 0.97 g / cm³. ３ ~1.61 g / cm ３ It is within the range of [the specified range]. 【0065】 Furthermore, the average pore diameter M1 of the first molded body may be in the range of 20 μm to 100 μm, particularly 30 μm to 100 μm. However, the average pore diameter M1 of the first molded body also changes depending on the particle size of the SiC particles used and the degree of compression of the powder layer. The porosity and average pore diameter M1 of the first molded body can be measured using a mercury porosimeter as described above. 【0066】[Step S11] Next, in step S11, carbon particles are impregnated into the pores of the first molded body, forming a second molded body with the same shape as the main body. Note that this step S11 and the following step S12 may be omitted if high mechanical properties are not required or if it is desired to keep manufacturing costs low. In step S11, a dispersion liquid containing dispersed carbon particles is used. That is, the carbon particles contained in the dispersion liquid can be impregnated into the pores by immersing the first molded body in the dispersion liquid or by flowing the dispersion liquid into the first molded body. In the former case, it is preferable to carry out the impregnation treatment under reduced pressure. By creating a reduced pressure environment, the dispersion liquid can be impregnated into the pores more effectively. Furthermore, after the dispersion liquid has been impregnated into the pores, it is preferable to keep the first molded body in a pressurized environment. This allows the dispersion liquid to be introduced into the pores of the first molded body even more effectively. The concentration of carbon particles contained in the dispersion liquid is, for example, in the range of 20% to 60% by mass. A higher concentration of carbon particles is preferable, as long as the carbon particles do not settle. Therefore, the concentration of carbon particles is preferably in the range of, for example, 30% to 55% by mass. 【0067】 The carbon particles are preferably nanoparticles or aggregates of nanoparticles. For example, the average particle size M2 of the aggregated carbon particles (secondary particles) is in the range of 100 nm to 200 nm, and preferably in the range of 110 nm to 150 nm. Making the average particle size M2 of the aggregated carbon particles smaller than 100 nm is not practical, as it would require a significant increase in the amount of dispersant, and it also tends to increase the viscosity of the dispersion, which is undesirable. If the average particle size M2 of the aggregated carbon particles is larger than 200 nm, the dispersibility deteriorates and sedimentation becomes more likely, which is also undesirable. 【0068】 The dispersion medium contained in the dispersion is not particularly limited. The dispersion medium may include, for example, water and / or alcohol. 【0069】Here, the carbon particles are selected such that their average particle size M2 is 1 / 10 or less of the average pore diameter M1 of the pores contained in the first molded body. That is, M2 ≤ M1 / 10. This is to ensure that the carbon particles are reliably introduced into the pores of the first molded body. For example, if the average particle size M2 of the carbon particles is approximately the same as the average pore diameter M1 of the pores contained in the first molded body, it becomes difficult to impregnate the pores with a sufficient amount of carbon. For example, it is preferable that the average particle size M2 of the carbon particles be selected such that M2 ≤ M1 / 30, M2 ≤ M1 / 50, M2 ≤ M1 / 100, or M2 ≤ M1 / 200 with respect to the average pore diameter M1 of the pores of the first molded body. 【0070】 Incidentally, instead of using the dispersion liquid mentioned above, it is conceivable to impregnate the first molded body with a carbon source such as phenolic resin or epoxy resin, and then heat-treat it to generate (precipitate) carbon from the carbon source. However, such a method requires an additional reaction step to generate (precipitate) carbon from the carbon source. Furthermore, in order to generate (precipitate) a sufficient amount of carbon, it is necessary to repeat the process of impregnation with the carbon source and carbon precipitation multiple times. As a result, there is a problem that the manufacturing method becomes complicated. Moreover, especially when the carbon source is solid, there is a problem that it is difficult to introduce carbon into each pore of the first molded body as intended through the carbon precipitation reaction. 【0071】 Thus, methods that use a carbon source to precipitate carbon are problematic and not practical. However, in the manufacturing method of the main body, a dispersion containing carbon particles is used to impregnate the pores of the first molded body with carbon particles. Therefore, in the manufacturing method of the main body, steps such as carbon precipitation reactions can be omitted, and the manufacturing method can be simplified. 【0072】Furthermore, the concentration of carbon particles in the dispersion can be adjusted as appropriate. This allows for a reduction in the number of impregnation steps using the dispersion, thereby simplifying the manufacturing process. For example, if a dispersion with a carbon particle concentration of 30% by mass or more is used, one impregnation step is sufficient. Moreover, in the manufacturing method of the main body, a dispersion containing carbon particles such that the relationship M2 ≤ M1 / 10 holds between the average pore diameter M1 and the average particle size M2 is used, allowing for the relatively easy introduction of many carbon particles into each pore of the first molded body. 【0073】 Furthermore, in the manufacturing method of the main body, carbon particles with a relatively small average particle size are introduced into the pores of the molded body. With such small carbon particles, the reaction surface area is significantly increased, which has the advantage of enhancing the reactivity in the reaction step between the carbon particles and Si in the subsequent step S13. By the method described above, a molded body in which carbon particles have been introduced into the pores, i.e., a second molded body, can be formed. 【0074】 [Step S12] Next, if necessary, the second molded body is dried. Step S12 is performed to ensure that the dispersion medium contained in the second molded body is removed. There are two main types of drying methods: "heat drying method" and "vacuum freeze-drying method". The heat drying method is a drying method in which the second molded body is heated to remove the dispersion medium by volatilization. The heating temperature varies depending on the type of dispersion medium, etc. If the dispersion medium is water, the heating temperature may be in the range of 100°C to 120°C. 【0075】 On the other hand, in the vacuum freeze-drying method, first, the second molded body placed in the drying chamber is cooled and frozen. This also freezes the dispersion liquid contained in the second molded body. The cooling temperature is set to a temperature below the freezing temperature of the dispersion medium. For example, if the dispersion medium contains water, the cooling temperature may be in the range of -5°C to -50°C. After that, the dispersion medium is removed by sublimation by evacuating the drying chamber, and the second molded body is dried. 【0076】In the heat drying method, as the vaporization of the dispersion medium within the pore gradually progresses, the remaining dispersion medium moves to the pore walls that form the pore, adheres to the pore walls, and then completely vaporizes. Since carbon particles also follow this liquid flow, after the drying process, the carbon particles tend to be segregated on the pore walls in an aggregated state. 【0077】 In contrast, in the vacuum freeze-drying method, the dispersion medium is sublimated and removed within the pore with minimal movement. Therefore, in the vacuum freeze-drying method, the dispersion medium can be removed while maintaining the distribution of carbon particles within the pore before the drying process. Consequently, aggregation of carbon particles is less likely to occur. As described above, step S12 is a step that is performed as needed and does not necessarily need to be actively performed. For example, the second molded body may be air-dried. 【0078】 [Step S13] Next, in step S13, a SiC-Si composite member is manufactured from the dried second molded body to form the main body of the integrally molded product. The SiC-Si composite is called SiSiC. As described above, the main body of the integrally molded product is formed of SiSiC using a 3D printer. 【0079】 Prior to step S13, a process of sintering the second molded body (hereinafter referred to as "pre-sintering treatment") may be performed. By performing pre-sintering treatment, at least some of the SiC particles in the second molded body are sintered and bonded together, thereby further stabilizing the shape. Furthermore, it is believed that the mechanical strength of the SiC-Si composite member (main body) obtained finally (i.e., after step S13) can be further increased. The conditions for pre-sintering treatment, i.e., the treatment temperature, treatment time, and treatment environment, are not particularly limited as long as at least some of the SiC particles are sintered and bonded together. Note that pre-sintering treatment is not necessarily a required step and may be omitted. 【0080】In step S13, metallic silicon (Si) is impregnated into the second molded body. If pre-sintering treatment has been performed, the pre-sintered second molded body is impregnated with metallic silicon (Si). In addition, some of the metallic Si impregnated into the second molded body reacts with carbon particles contained in the pores of the second molded body to produce silicon carbide (SiC). Furthermore, the SiC particles contained in the second molded body and the SiC newly generated in step S13 are sintered together to form a sintered body. Hereinafter, these processes are collectively referred to as the "reaction sintering process". If steps S11 and S12 are omitted, this "reaction sintering process" hardly proceeds. 【0081】 Furthermore, any of the introduced metallic Si that does not react with the carbon particles remains. Therefore, after the reaction sintering process, it becomes a SiC-Si composite member, forming the main body of the integrally molded product. In other words, the main body of the integrally molded product formed from the SiSiC described above is obtained. 【0082】 Here, as described above, the pores of the second molded body are impregnated with carbon particles with a relatively small average particle size. Therefore, it is important to note that in the reaction sintering process, the reaction between the carbon particles and Si, i.e., the SiC formation reaction, proceeds relatively quickly. As a result, the sintering reaction between some SiC particles is also accelerated. 【0083】 In step S13, the method for impregnating the second molded body with metallic Si is not particularly limited. For example, the second molded body and the metallic Si may be heated in contact with each other to melt the metallic Si. In this case, the molten metallic Si will be impregnated into the pores in the second molded body by capillary action. Furthermore, if the metallic Si is melted with the metallic Si placed on top of the second molded body, the effect of gravity can be used to impregnate the molten metallic Si into the pores of the second molded body. 【0084】When employing such a method, the heating temperature of the second molded body and metallic Si (hereinafter collectively referred to as the "heated body") should be above the melting point of metallic Si, and preferably in the range of the melting point of metallic Si to 1650°C. The melting point of metallic Si varies slightly depending on the measurement method, but is generally around 1410°C to 1414°C. 【0085】 When the heating temperature of the object to be heated is in the range of the melting point of metallic Si to 1650°C, the reaction sintering process can be carried out along with the impregnation of the second molded body with molten metallic Si. In the above method, it is preferable that the processing environment of the object to be heated be a reduced-pressure environment. In addition, metallic Si may be impregnated into the second molded body by other methods. 【0086】 The amount of metallic Si introduced into the second molded body is determined based on the amount of carbon particles contained in the second molded body and the Si concentration contained in the final SiC-Si composite member. 【0087】 For example, if R1 is the amount of Si required for the SiC reaction sintering, calculated from the amount of carbon particles contained in the second molded body, and R2 is the required amount of Si, calculated from the concentration of metallic Si in the SiC-Si composite member, then the amount of metallic Si R introduced into the second molded body is determined by R = R1 + R2. Through the above process, a SiC-Si composite (SiSiC) member can be manufactured, and the main body of the integrally molded product is formed. 【0088】 The Si content in the resulting SiC-Si composite member is preferably in the range of 5% to 60% by mass, and more preferably in the range of 8% to 55% by mass, relative to the total weight. In other words, the SiC content in the SiC-Si composite member is preferably in the range of 40% to 95% by mass, and more preferably in the range of 45% to 92% by mass, relative to the total weight. If the Si content in the SiC-Si composite member is less than 5% by mass, the process becomes complicated and undesirable because it requires multiple impregnation operations of the carbon particle dispersion into the first molded body. If the Si content in the SiC-Si composite member exceeds 60% by mass, the mechanical strength of the SiC-Si composite member decreases significantly, which is undesirable. 【0089】 The manufacturing method for the main body allows for the production of SiC-Si composite members with low porosity and high bulk density. For example, the porosity of the SiC-Si composite member is in the range of 0 vol% to 3 vol%. Furthermore, the bulk density of the SiC-Si composite member is 2.62 g / cm³. ３ ~3.16 g / cm ３ This is within the range. Therefore, the manufacturing method of the main body can produce a SiC-Si composite member with good mechanical strength. The four-point bending strength of the SiC-Si composite member may be 100 MPa or more, for example, 190 MPa or more. Note that the four-point bending strength is a value measured by the method specified in JIS (Japanese Industrial Standards) 1601 (Test method for room temperature bending strength of fine ceramics). 【0090】 <Method for Manufacturing a Gas Cell> A gas cell can be manufactured as described above. First, a main body 10 having at least one opening 11 and a fitting portion 14 into which a transparent substrate 20 is fitted is formed as a single molded product using a 3D printer, as described in the manufacturing method of the main body 10 above. Next, the transparent substrate 20 is fitted into the fitting portion 14 of the main body 10. When fitting the transparent substrate 20 into the fitting portion 14 of the main body 10, if the transparent substrate 20 is a glass substrate, the transparent substrate 20 is joined to the fitting portion 14 using glass frit. Next, if an open hole (not shown) is provided that connects the closed space 40 (internal space) of the main body 10 to the outside, alkali metal and sealed gas are introduced into the closed space 40 of the main body 10 through the open hole, and the open hole is sealed with a sealing agent such as glass frit. This manufactures a gas cell in which alkali metal atoms are sealed inside. A heater is also attached to the main body 10. The heaters mentioned above are available. 【0091】Alkali metals are introduced into the closed space 40 of the main body 10 in the form of alkali metal powder or alkali metal compound powder. After sealing, the main body 10 is heated with a heater to vaporize the alkali metal or alkali metal compound, thereby obtaining a gas cell containing alkali metal atoms. As the main body 10 is a single molded product formed using a 3D printer as described above, open holes can be formed during the formation of the main body 10 without subsequent processing. Therefore, if open holes are provided in the main body 10, the process of forming open holes is unnecessary. However, if open holes are not provided in the main body 10, the process of forming open holes in the main body 10 is carried out. The method of forming open holes is not particularly limited and can be done using a drill or a laser. Also, if a reflective member 30 is provided in the closed space 40 of the main body 10 as part of the gas cell configuration, the reflective member 30 is provided before the transparent substrate 20 is fitted into the main body 10. 【0092】 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 that has passed 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 attenuates or blocks 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. 【0093】 The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 shown below is an example, and Example 2 is a comparative example. 【0094】 <Example 1> In Example 1, 10 samples 100 of the main body part with the shape shown in FIG. 11 were fabricated as follows. The design values of each location D1 - D5 of the sample 100 of the main body part shown in FIG. 11 are shown in Table 1 below. Note that it is a schematic perspective view showing the shape of the sample of the main body part in Example 1 and Example 2. Since the sample 100 shown in FIG. 11 is the same as the configuration of the main body part shown in FIG. 1, its detailed description is omitted. In Example 1, for the 10 fabricated samples of the main body part, three-dimensional shape measurement was performed using a VR-3200 (model) manufactured by Keyence Corporation for each. Then, for the 10 fabricated samples of the main body part, the average value of the dimensions of each location and 3σ of the dimensions of each location were obtained. The results are shown in Table 1 below. Note that 3σ is an index of shape stability. The smaller the value of 3σ, the better the shape stability. In Example 1, according to the above-described manufacturing method of the main body part, a sample of the main body part of an integrally molded product formed of SiSiC was manufactured. Hereinafter, the manufacturing method of the sample of the main body part will be described. 【0095】 First, a first molded body having the same shape as the sample of the main body part was prepared by a three-dimensional printing method. The data for the three-dimensional printer of the first molded body was obtained from the CAD data of the sample 100 shown in FIG. 11. As the three-dimensional printing method, the "binder jetting method" was adopted, and a binder was jetted from an inkjet nozzle toward the powder layer. Phenolic resin was used as the binder. The powder layer was made a mixture of SiC particles and a curing agent. The content of the curing agent was about 0.1% by mass. As the SiC particles, α-SiC powder (manufactured by Shinano Electric Refining Co., Ltd.) with an average particle diameter of 80 μm was used. Also, the thickness of one layer of the powder layer was about 200 μm, and binder jetting was repeated every time each powder layer was laminated. Thereby, a first molded body having the same shape as the sample of the main body part was prepared. The bulk density of the first molded body was 1.14 g / cm ３ It was. The porosity of the first molded body was 64.6%. Also, the average pore diameter M1 of the pores of the first molded body was 46.9 μm. 【0096】Next, a second molded body was formed from a first molded body having the same shape as the main body sample. First, the first molded body was immersed in a dispersion containing carbon particles. The concentration of carbon particles in the dispersion was 40% by mass, and the carbon particles were nanoparticles. The average particle size M2 of the secondary carbon particles was approximately 120 nm. Therefore, M2 / M1 was approximately 0.00256. The dispersion medium was water. 【0097】 The first molded body was immersed in a dispersion under reduced pressure. This impregnated the pores of the first molded body with carbon particles, forming a second molded body with the same shape as the main sample. Subsequently, the second molded body was dried. Vacuum freeze-drying was used for drying. Specifically, the second molded body was frozen by passing through a temperature range of 0°C to -10°C in less than 20 minutes, and then the moisture was sublimated from the second molded body by evacuating it under vacuum. The bulk density of the second molded body was 1.37 g / cm³. ３ The porosity was 53.2%. Furthermore, when the concentration of carbon particles contained in the second molded body was measured using thermal analysis, the carbon particle content relative to SiC in the molded body was 20% by mass. 【0098】 Next, metallic Si was impregnated into the second molded body. For the metallic Si impregnation process, a heated body, constructed by placing metallic Si on top of the second molded body, was placed in the reaction furnace. The amount of metallic Si was 12.7 g. Next, the heated body was heated to 1550°C under reduced pressure in the reaction furnace. This process caused the metallic Si to melt, and the molten material impregnated into the second molded body. Simultaneously, a reaction sintering process proceeded. That is, SiC was formed by the reaction between the carbon in the pores and the impregnated Si, and a sintering reaction occurred between the SiC contained in the second molded body, including these newly formed SiC, resulting in a sintered body (SiC-Si composite member), and a sample of the main body of an integrally molded product made of SiSiC was obtained. 【0099】<Example 2> In Example 2, ten samples 100 of the main body part, which have the shape shown in Figure 11, were prepared as follows. The design values ​​for each part D1 to D5 of the main body part sample 100 shown in Figure 11 are shown in Table 2 below. For the main body part sample, first a quartz substrate with dimensions of 20 mm × 20 mm × 1.5 mm (thickness) was prepared. Next, the quartz substrate was assembled into a cube and temporarily fixed using the inorganic adhesive Aron Ceramic E (product name) manufactured by Toagosei Co., Ltd., and then heated with an oxyhydrogen burner to produce ten samples of the quartz main body part. In Example 2, three-dimensional shape measurement was performed on each of the ten main body part samples prepared, in the same manner as in Example 1, and the average value of the dimensions of each part and the 3σ of the dimensions of each part were determined. The results are shown in Table 2 below. 【0100】 【0101】 【0102】 As shown in Table 1 above, in Example 1, the dimensions of all parts were within the range of 0.5 mm for 3σ, an indicator of shape stability, and showed better shape stability compared to Example 2. As shown in Table 2 above, in Example 2, the dimensions of all parts were above 0.5 mm for 3σ, an indicator of shape stability, and showed worse shape stability compared to Example 1. Therefore, the density of alkali metal atoms in the optical path length differs for each gas cell, and tuning of the quantum sensor is required for each gas cell. The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-217619, filed on December 12, 2024, are incorporated herein by reference as disclosure of the present invention. 【0103】1, 3, 5, 7, 8 Gascell 10 Body 11, 11a, 11b, 11c, 11d Opening 12 Base 13 Sidewall 14, 14a, 14b, 14c, 14d Fitting 16, 16a, 16b Through Hole 17, 17a, 17b Sealing 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 24 Gap 30 Reflective Material 40 Closed Space 100 Substitute 141, 141a, 141b, 141c, 141d 1st fitting surface 142, 142a, 142b, 142c, 142d 2nd fitting surface 143 3rd fitting surface t thick み

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 is a single molded product and 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 any one of claims 1 to 4, wherein the main body portion has a sealing portion for sealing alkali metals inside.

6. The gas cell according to any one of claims 1 to 4, wherein the main body has a transmittance of 15% or less with respect to the wavelength of excitation light that excites the electrons of the enclosed alkali metal atoms.

7. A method for manufacturing a gas cell in which alkali metal atoms are sealed inside, comprising the steps of: forming a main body having at least one opening and a fitting portion into which a transparent substrate is fitted as an integrally molded product using a three-dimensional printer; and fitting the transparent substrate into the fitting portion of the main body.

8. The method for manufacturing a gas cell according to claim 7, wherein the main body is provided with an open hole that connects the internal space of the main body to the outside, and further comprising the steps of introducing an alkali metal and a sealed gas into the internal space of the main body through the open hole and sealing the open hole.

9. A quantum sensor comprising: a gas cell according to any one of claims 1 to 4; 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 that has passed through the gas cell.

10. The quantum sensor according to claim 9, which is an optical pumping magnetic sensor.

11. The quantum sensor according to claim 9, which is an atomic oscillator.

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