JP2018133644A - Gas cell, magnetism measurement device, and atom oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas cell, a magnetism measurement device, and an atom oscillator which can measure a magnetic field with high sensitivity and with high accuracy by effectively suppressing reflection of light.SOLUTION: A gas cell 10 comprises: a cell 12 constituted of a wall 11; a first grid structure 50a provided on the inner surfaces 112 and 113 of the wall 11; a coating layer 32 covering the surface of the first grid structure 50a; and an alkali metal gas 13 enclosed in the cell 12.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a gas cell, a magnetic measurement device, and an atomic oscillator.

  There is known an optical pumping type magnetic measuring device that irradiates a gas cell filled with an alkali metal gas with linearly polarized light and measures a magnetic field in accordance with a rotation angle of a polarization plane (see, for example, Patent Document 1). Patent Document 1 discloses a configuration of a gas cell in which the inner surface of the wall of a closed container (cell) is coated with chain saturated hydrocarbon (paraffin or the like) and the inside is filled with an alkali metal gas. The layer of coating material (hereinafter referred to as the coating layer) has a function of suppressing or reducing a change in behavior (for example, spin) when an alkali metal atom directly collides with the cell wall.

JP 2013-7720 A

  However, there is a problem that when the irradiated linearly polarized light passes through the gas cell, light is reflected on the surface of the wall of the gas cell. When a loss occurs in the light transmitted through the gas cell due to the reflection of light, the signal component in the measurement of the magnetic field decreases. Further, the reflected light becomes stray light and becomes a noise component in the measurement of the magnetic field. As a result, the sensitivity in the magnetic field measurement is lowered and the measurement accuracy is lowered. Therefore, there is a need for a gas cell that can effectively suppress reflection on the surface of the cell wall and perform measurement with high sensitivity and high accuracy.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  [Application Example 1] A gas cell according to this application example includes a closed container constituted by a wall, an antireflection structure provided on an inner surface of the wall, and a chain saturated hydrocarbon covering the surface of the antireflection structure. And an alkali metal gas sealed in the closed container.

  According to the configuration of this application example, since the antireflection structure is provided on the inner surface of the wall constituting the closed container, when light passes through the gas cell, the inner surface of the incident side wall and the emission side Reflection of light on the inner surface of the wall is suppressed. In addition, since the surface of the antireflection structure is covered with a coating layer made of chain saturated hydrocarbons, the change in behavior when alkali metal atoms enclosed in the closed container collide with the wall of the closed container is suppressed or reduced. it can. Thereby, in the gas cell which has a coating layer in the inner surface of a closed container, the fall of the sensitivity resulting from reflection of light and the fall of a measurement precision can be suppressed.

  Application Example 2 In the gas cell according to the application example described above, it is preferable that the antireflection structure includes a first grid structure in which a plurality of first protrusions are one-dimensionally arranged.

  According to the configuration of this application example, the first grid structure in which the first ridges are one-dimensionally arranged can suppress light reflection on the inner surface of the closed container.

  Application Example 3 In the gas cell according to the application example described above, it is preferable that an occupation ratio, which is a ratio of a width to a cycle of the first ridge portion, is 0.3 or more and 0.7 or less.

  According to the configuration of this application example, the first grid structure can be easily and surely formed by setting the occupation ratio of the first protrusions to 0.3 or more and 0.7 or less, and the first grid A coating layer covering the structure can be formed with a uniform film thickness.

  Application Example 4 In the gas cell according to the application example described above, it is more preferable that the occupation ratio of the first protrusion is 0.4 or more and 0.6 or less.

  According to the configuration of this application example, the first grid structure can be easily and surely formed more stably by setting the occupation ratio of the first protrusions to 0.4 or more and 0.6 or less. The coating layer covering the first grid structure can be formed with a uniform film thickness.

  Application Example 5 In the gas cell according to the application example described above, it is preferable that a second grid structure in which a plurality of second protrusions are one-dimensionally arranged is provided on the outer surface of the wall. .

  According to the configuration of this application example, since the second grid structure is provided as an antireflection structure on the outer surface of the wall constituting the closed container, when the light passes through the gas cell, the incident-side wall In addition to the inner surface and the inner surface of the exit side wall, reflection of light on the outer surface of the incident side wall and the outer surface of the exit side wall is also suppressed. Thereby, in a gas cell, the fall of the sensitivity resulting from reflection of light and the fall of measurement accuracy can be suppressed more effectively.

  Application Example 6 In the gas cell according to the application example described above, the occupancy ratio of the first ridge portion in the first grid structure and the occupancy of the second ridge portion in the second grid structure. When the rate is the same, it is preferable that the height of the first ridge is smaller than the height of the second ridge.

  According to the configuration of this application example, when the occupation ratio of the first ridges in the first grid structure is the same as the occupation ratio of the second ridges in the second grid structure, the coating layer is covered. Thus, the reflectance of light on the inner surface of the wall and the reflectance of light on the outer surface of the wall not covered with the coating layer can be suppressed to the same extent.

  Application Example 7 A gas cell according to the application example, wherein the height of the first ridge portion in the first grid structure and the height of the second ridge portion in the second grid structure Are the same, the occupancy of the first ridge is preferably smaller than the occupancy of the second ridge.

  According to the configuration of this application example, when the height of the first ridge portion in the first grid structure is the same as the height of the second ridge portion in the second grid structure, the wall covered with the coating layer The reflectance of light on the inner surface of the film and the reflectance of light on the outer surface of the wall not covered with the coating layer can be suppressed to the same level.

  Application Example 8 In the gas cell according to the application example described above, a moth-eye structure may be provided as the antireflection structure.

  According to the configuration of this application example, by providing the moth-eye structure as the antireflection structure, reflection of light can be suppressed similarly to the grid structure.

  Application Example 9 A magnetic measuring device according to this application example includes the gas cell described above.

  According to the configuration of this application example, it is possible to provide a magnetic measurement device capable of measuring magnetism with high sensitivity and high accuracy.

  Application Example 10 An atomic oscillator according to this application example includes the gas cell described above.

  According to the configuration of this application example, a highly accurate atomic oscillator can be provided.

The block diagram which shows the structure of the magnetic measuring device which concerns on 1st Embodiment. The sectional side view along the longitudinal direction of the gas cell concerning a 1st embodiment. FIG. 3 is a plan sectional view taken along line A-A ′ of FIG. 2. Sectional drawing along the longitudinal direction of the ampoule which concerns on 1st Embodiment. FIG. 5 is a cross-sectional view taken along line B-B ′ of FIG. 4. The perspective view which shows schematic structure of the reflection preventing structure which concerns on 1st Embodiment. Sectional drawing of the 1st grid structure along the C-C 'line of FIG. Sectional drawing of the 2nd grid structure along the C-C 'line of FIG. The figure explaining the formation method of the antireflection structure concerning a 1st embodiment. The figure explaining the formation method of the antireflection structure concerning a 1st embodiment. The figure explaining the formation method of the antireflection structure concerning a 1st embodiment. The figure explaining the formation method of the antireflection structure concerning a 1st embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The figure explaining the manufacturing method of the gas cell which concerns on 1st Embodiment. The plane sectional view showing the composition of the gas cell concerning a 2nd embodiment. Sectional drawing which shows schematic structure of the reflection preventing structure which concerns on 2nd Embodiment. The figure explaining the formation method of the reflection preventing structure concerning a 2nd embodiment. The figure explaining the formation method of the reflection preventing structure concerning a 2nd embodiment. The figure explaining the formation method of the reflection preventing structure concerning a 2nd embodiment. Schematic which shows the structure of the atomic oscillator which concerns on 3rd Embodiment. The figure explaining operation | movement of the atomic oscillator which concerns on 3rd Embodiment. The figure explaining operation | movement of the atomic oscillator which concerns on 3rd Embodiment. The plane sectional view showing an example of the gas cell which is not provided with the conventional antireflection structure.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. The drawings to be used are appropriately enlarged, reduced or exaggerated so that the part to be described can be recognized. In addition, illustrations of components other than those necessary for the description may be omitted.

(First embodiment)
<Magnetic measuring device>
The configuration of the magnetic measurement apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the magnetic measurement apparatus according to the first embodiment. The magnetic measurement device 100 according to the first embodiment is a magnetic measurement device using non-linear optical rotation (NMOR). The magnetic measurement device 100 is, for example, a biological state measurement device (such as a magnetocardiograph or a magnetoencephalograph) that measures a minute magnetic field generated from a living body such as a magnetic field from the heart (magnetomagnetic field) or a magnetic field from the brain (magnetomagnetic field). Used for. The magnetic measuring device 100 can also be used for a metal detector or the like.

  As shown in FIG. 1, the magnetic measurement device 100 includes a light source 1, an optical fiber 2, a connector 3, a polarizing plate 4, a gas cell 10, a polarization separator 5, and a photodetector (Photo Detector: PD) 6. And a light detector 7, a signal processing circuit 8, and a display device 9. In the gas cell 10, an alkali metal gas (a gas-state alkali metal atom) is sealed. As the alkali metal, for example, cesium (Cs), rubidium (Rb), potassium (K), sodium (Na), or the like can be used. Hereinafter, a case where cesium is used as the alkali metal will be described as an example.

  The light source 1 is a device that outputs a laser beam having a wavelength corresponding to the absorption line of cesium (for example, 894 nm corresponding to the D1 line), for example, a tunable laser. The laser beam output from the light source 1 is so-called CW (Continuous Wave) light having a constant light amount continuously.

  The polarizing plate 4 is an element that polarizes the laser beam in a specific direction to make it linearly polarized light. The optical fiber 2 is a member that guides the laser beam output from the light source 1 to the gas cell 10 side. For the optical fiber 2, for example, a single mode optical fiber that propagates only the fundamental mode is used. The connector 3 is a member for connecting the optical fiber 2 to the polarizing plate 4. The connector 3 is a screw type and connects the optical fiber 2 to the polarizing plate 4.

  The gas cell 10 is a box (cell) having a gap inside, and an alkali metal vapor (alkali metal gas 13 shown in FIG. 2) is sealed in the gap (main chamber 14 shown in FIG. 2). The configuration of the gas cell 10 will be described later.

  The polarization separator 5 is an element that separates an incident laser beam into beams of two polarization components orthogonal to each other. The polarization separator 5 is, for example, a Wollaston prism or a polarization beam splitter. The photodetector 6 and the photodetector 7 are detectors sensitive to the wavelength of the laser beam, and output a current corresponding to the amount of incident light to the signal processing circuit 8. It is desirable that the photodetector 6 and the photodetector 7 are made of a non-magnetic material because they themselves may affect the measurement when a magnetic field is generated. The photodetector 6 and the photodetector 7 are disposed on the same side (downstream side) as the polarization separator 5 as viewed from the gas cell 10.

  The arrangement of each part in the magnetic measuring device 100 will be described along the laser beam path. The light source 1 is located at the uppermost stream of the laser beam path. Hereinafter, the optical fiber 2, the connector 3, and the polarizing plate 4 from the upstream side. The gas cell 10, the polarization separator 5, and the photodetectors 6 and 7 are arranged in this order.

  The laser beam output from the light source 1 is guided to the optical fiber 2 and reaches the polarizing plate 4. The laser beam that has passed through the polarizing plate 4 becomes linearly polarized light having a higher degree of polarization. The laser beam passing through the gas cell 10 excites (optically pumps) the alkali metal atoms sealed in the gas cell 10. At this time, the polarization plane of the laser beam is rotated by receiving the polarization plane rotation action corresponding to the strength of the magnetic field. The laser beam transmitted through the gas cell 10 is separated into two polarized component beams by the polarization separator 5. The light amounts of the two polarized component beams are measured (probing) by the photodetector 6 and the photodetector 7.

  The signal processing circuit 8 receives from each of the signals indicating the light amounts of the beams measured by the photodetector 6 and the photodetector 7. The signal processing circuit 8 measures the rotation angle of the polarization plane of the laser beam based on each received signal. The rotation angle of the polarization plane is expressed as a function based on the strength of the magnetic field in the propagation direction of the laser beam (for example, D. Budker, et al., “Resonant nonlinear magneto-optical rotation effect of atoms”, Review of See Equation (2) in Modern Physics, USA, American Physical Society, October 2002, Vol. 74, No. 4, p.1153-11201, although Equation (2) relates to linear optical rotation. In the case of NMOR, almost the same formula can be used). The signal processing circuit 8 measures the strength of the magnetic field in the propagation direction of the laser beam from the rotation angle of the polarization plane. The display device 9 displays the strength of the magnetic field measured by the signal processing circuit 8.

  Then, the structure of the ampule used for the gas cell which concerns on 1st Embodiment, and a gas cell is demonstrated with reference to FIGS.

<Gas cell>
FIG. 2 is a side sectional view along the longitudinal direction of the gas cell according to the first embodiment. 3 is a cross-sectional plan view taken along the line AA ′ of FIG. 2 and 3, the height direction of the gas cell 10 is taken as the Z axis, and the upper side is taken as the + Z direction. A direction intersecting the Z axis and the longitudinal direction of the gas cell 10 (a direction in which a main chamber 14 and a reservoir 16 to be described later are arranged) is taken as an X axis, and the right side in FIG. And it is a direction which cross | intersects a Z-axis and a X-axis, Comprising: Let the width direction of the gas cell 10 be a Y-axis, and let the right side in FIG. 3 be a + Y direction.

  As shown in FIG. 2, the gas cell 10 according to the first embodiment includes a cell 12 and a lid 19 as a closed container. The cell 12 is a box (cell) having a void inside the wall 11. The wall 11 is a glass plate member made of, for example, quartz glass. The wall 11 (plate-like member) has a thickness of 1 mm to 5 mm, for example, about 1.5 mm.

  The cell 12 has a main chamber 14 and a reservoir 16 whose longitudinal direction is the X-axis direction as an internal space. The main chamber 14 and the reservoir 16 are arranged along the X-axis direction, and communicate with each other through the communication hole 15. The communication hole 15 is provided on the upper side (+ Z direction side) of the main chamber 14 and the reservoir 16. Although not shown, the shape of the communication hole 15 viewed along the X-axis direction is, for example, a circular shape. The inner diameter of the communication hole 15 is, for example, about 0.4 mm to 1 mm.

  The cell 12 (the main chamber 14 and the reservoir 16) is filled with a gas 13 in which alkali metal has evaporated (hereinafter referred to as alkali metal gas). In addition to the alkali metal gas 13, an inert gas such as a rare gas may be present in the main chamber 14 and the reservoir 16.

  An ampoule 20 is accommodated in the reservoir 16. A through hole (opening) 21 is formed in the glass tube 22 of the ampoule 20. The alkali metal gas 13 is obtained by evaporating (gasifying) the alkali metal solid 24 (see FIG. 4) filled in the ampule 20. The configuration of the ampule 20 will be described later.

A film-like coating layer 32 is disposed inside the wall 11 of the cell 12. The coating layer 32 has a function of suppressing or reducing a change in behavior (for example, spin) when an alkali metal atom directly collides with the wall 11 of the cell 12 (main chamber 14). The coating layer 32 is composed of chain saturated hydrocarbon such as paraffin. As an example of paraffin, for example, pentacontane represented by a chemical formula (CH ₃ (CH ₂ ) ₄₈ CH ₃ ) can be used.

  An opening 18 is provided on the opposite side (−X direction side) of the main chamber 14 and the communication hole 15 in the longitudinal direction of the reservoir 16. The shape of the opening 18 viewed along the X-axis direction is, for example, a circular shape. The inner diameter of the opening 18 is, for example, about 0.4 mm to 1.5 mm. The opening 18 is sealed with a lid 19 joined to the cell 12 via a sealing member 30. Thereby, the cell 12 (the main chamber 14 and the reservoir 16) is sealed.

  In FIG. 3, the longitudinal direction of the cell 12 is illustrated along the vertical direction in FIG. 3. As shown in FIG. 3, a first grid structure 50 a is provided as an antireflection structure on the inner surface 112 and the surface 113 of the wall 11 of the side portion (part along the XZ plane) of the main chamber 14. ing. The surface of the first grid structure 50 a is covered with the coating layer 32. Further, a second grid structure 50b is provided on the outer surface 111 and the surface 114 of the side wall 11 of the main chamber 14 as an antireflection structure.

  In the magnetic measurement apparatus 100 (see FIG. 1), the laser beam Lb is irradiated from the −Y direction side to the + Y direction side along the Y axis direction in FIG. When viewed from the irradiation direction of the laser beam Lb, the laser beam Lb is applied to the substantially central portion of the side wall 11 of the main chamber 14 (see FIG. 2) and passes through the main chamber 14. The laser beam Lb is incident on the outer surface 111 of the wall 11 on the −Y direction side substantially perpendicularly, passes through the inner surface 112 from the surface 111, enters the main chamber 14, and passes through the main chamber 14. , The inner surface 113 of the wall 11 on the + Y direction side passes through the outer surface 114 and is injected out of the main chamber 14.

  At this time, the laser beam Lb passes through the second grid structure 50b provided on the outer surface 111 in the wall 11 on the −Y direction side, and passes through the first grid structure 50a provided on the inner surface 112. To Penetrate. The laser beam Lb passes through the first grid structure 50a provided on the inner surface 113 and passes through the second grid structure 50b provided on the outer surface 114 in the wall 11 on the + Y direction side. .

  Here, the effect of the antireflection structure (the first grid structure 50a and the second grid structure 50b) provided in the gas cell 10 will be described in comparison with a gas cell not provided with a conventional antireflection structure. FIG. 29 is a plan sectional view showing an example of a gas cell not provided with a conventional antireflection structure. The gas cell 90 shown in FIG. 29 has the same configuration as the gas cell 10 according to the first embodiment, except that the antireflection structure (the first grid structure 50a and the second grid structure 50b) is not provided. Yes.

  When the gas cell 90 is irradiated with the laser beam Lb, reflection occurs on the outer surface 111 of the wall 11 on the −Y direction side. Similar reflection occurs on the inner surface 112 of the wall 11 on the −Y direction side, the inner surface 113 and the outer surface 114 of the wall 11 on the + Y direction side. The light loss of the laser beam Lb due to reflection on each surface of the wall 11 is about 4%. Accordingly, when the laser beam Lb passes through the four surfaces of the main chamber, the optical loss of the laser beam Lb is about 15%. As a result, the light amount of the laser beam Lb emitted from the gas cell 90 is reduced to about 85% of the light amount of the laser beam Lb incident on the gas cell 90.

  When a loss occurs in the laser beam Lb that passes through the gas cell 90 due to such reflection, a signal component in the measurement of the magnetic field in the magnetic measurement device 100 is reduced. The reflected light from which the laser beam Lb is reflected becomes stray light and becomes a noise component in the measurement of the magnetic field. As a result, the conventional gas cell 90 causes a decrease in sensitivity and a decrease in measurement accuracy in the measurement of the magnetic field.

  On the other hand, since the gas cell 10 according to the first embodiment includes the antireflection structure (the first grid structure 50a and the second grid structure 50b) on the wall 11 of the main chamber 14, the laser beam Lb. When light passes through the gas cell 10, reflection of light on the outer surface 111 and the inner surface 112 of the incident-side wall 11 and the inner surface 113 and the outer surface 114 of the emission-side wall 11 is suppressed. Thereby, the fall of the sensitivity resulting from reflection of the laser beam Lb and the fall of a measurement precision can be suppressed. The structure of the antireflection structure (the first grid structure 50a and the second grid structure 50b) and the effect thereof will be described in detail later.

  The gas cell 10 according to the first embodiment includes the first grid structure 50a on the inner surface 112 and the surface 113 of the wall 11 of the main chamber 14, and the second grid structure on the outer surface 111 and the surface 114. 50 b is provided, but the gas cell may be configured not to include the second grid structure 50 b on the outer surface 111 and the surface 114. In such a configuration, although the antireflection effect is lower than that of the gas cell 10 according to the first embodiment, it is possible to suppress a decrease in sensitivity and a decrease in measurement accuracy as compared with the gas cell 90 not provided with the antireflection structure. Can do.

<Ample>
FIG. 4 is a cross-sectional view along the longitudinal direction of the ampoule according to the first embodiment. FIG. 5 is a cross-sectional view taken along the line BB ′ of FIG. As shown in FIG. 4, the ampoule 20 as a solid substance containing an alkali metal according to the present embodiment has a longitudinal direction. FIG. 4 shows an XZ cross section when the ampoule 20 is arranged so that the longitudinal direction thereof is along the X-axis direction. The ampoule 20 is composed of a hollow glass tube 22. The glass tube 22 is made of, for example, borosilicate glass.

  The glass tube 22 extends along one direction (X-axis direction in FIG. 4), and both ends thereof are welded. Thereby, the hollow glass tube 22 is sealed. In addition, the shape of the both ends of the glass tube 22 is not limited to a round shape as shown in FIG. 4, The shape close | similar to a plane, the shape where one part sharpened, etc. may be sufficient. The hollow interior of the glass tube 22 is filled with an alkali metal solid (granular or powdery alkali metal atoms) 24. As the alkali metal solid 24, as described above, rubidium, potassium, and sodium can be used in addition to cesium.

  FIG. 4 shows a state where the ampoule 20 (glass tube 22) is sealed. At the stage where the ampule 20 is manufactured, the glass tube 22 is in a sealed state. However, when the gas cell 10 is completed, a through hole 21 (see FIG. 2) is formed in the glass tube 22 and the sealing is broken. Thereby, the alkali metal solid 24 in the ampoule 20 evaporates and flows into the gas cell 10, and the gap of the cell 12 is filled with the alkali metal gas 13 (see FIG. 2). In addition, a gap of about 1.5 mm is provided in the + Z direction, for example, between the upper surface of the ampoule 20 and the inner surface of the cell 12 so that the alkali metal solid 24 can easily evaporate and flow out from the ampoule 20. (See FIG. 2).

  FIG. 5 shows a YZ cross section in a direction intersecting the longitudinal direction of the ampoule 20. As shown in FIG. 5, the shape of the glass tube 22 in the YZ cross section is, for example, substantially circular, but may be other shapes. The outer diameter φ of the glass tube 22 is 0.3 mm ≦ φ ≦ 1.2 mm. The thickness t of the glass tube 22 is 0.1 mm ≦ t ≦ 0.5 mm, and is preferably about 20% of the outer diameter φ. When the thickness t of the glass tube 22 is less than 0.1 mm, the glass tube 22 is likely to be damaged, and when the thickness t of the glass tube 22 exceeds 0.5 mm, the through hole 21 is formed in the glass tube 22. (Details will be described later).

<Antireflection structure>
Next, the antireflection structure for a gas cell according to the first embodiment will be described with reference to FIGS. 6, 7, and 8. FIG. 6 is a perspective view illustrating a schematic configuration of the antireflection structure according to the first embodiment. FIG. 7 is a cross-sectional view of the first grid structure taken along the line CC ′ of FIG. FIG. 8 is a cross-sectional view of the second grid structure taken along the line CC ′ of FIG. 6, 7, and 8 are enlarged views of a portion of the side wall 11 of the main chamber 14 provided with the antireflection structure (the first grid structure 50 a or the second grid structure 50 b). FIG.

  As shown in FIG. 6, the schematic configuration of the first grid structure 50a and the schematic configuration of the second grid structure 50b are the same. As described above, the first grid structure 50 a is provided on the inner surface 112 and the surface 113 of the side wall 11 of the main chamber 14. The first grid structure 50a has a configuration in which a plurality of first protrusions 52a are one-dimensionally arranged in a stripe shape.

  The first ridges 52 a are portions that remain by forming a plurality of concave ridges 53 a on the surface 112 and the surface 113 of the wall 11. Therefore, the 1st protruding item | line part 52a is a part of wall 11, and the upper surface of the 1st protruding item | line part 52a is the surface (surface 112 and surface 113) of the wall 11. FIG.

  The second grid structure 50 b is provided on the outer surface 111 and the surface 114 of the side wall 11 of the main chamber 14. The second grid structure 50b has a configuration in which a plurality of second ridges 52b are arranged one-dimensionally in a stripe shape. The second ridges 52 b are portions that are left by forming a plurality of concave ridges 53 b on the surface 111 and the surface 114 of the wall 11. Therefore, the 2nd protruding item | line part 52b is also a part of the wall 11, and the upper surface of the 2nd protruding item | line part 52b is the surface (surface 111 and surface 114) of the wall 11. FIG.

  The extending direction of the first ridges 52a in the first grid structure 50a is parallel to the extending direction of the second ridges 52b in the second grid structure 50b. As described above, the wavelength of the laser beam Lb (see FIG. 3) incident on the main chamber 14 of the gas cell 10 is 894 nm. The laser beam Lb is perpendicularly incident on the side wall 11 of the main chamber 14. The laser beam Lb is linearly polarized TE polarized light. That is, the direction of vibration of the linearly polarized electric field is a direction parallel to the extending direction of the first ridges 52a and the second ridges 52b.

  FIG. 7 is a schematic cross-sectional view of the inner surface 112 and the surface 113 of the wall 11 provided with the first grid structure 50a. The first ridges 52a are arranged at a predetermined pitch (period). FIG. 7 shows a coating layer 32 not shown in FIG. The coating layer 32 is arrange | positioned so that the upper surface and side surface of the 1st protruding item | line part 52a in the 1st grid structure 50a, and between the adjacent 1st protruding item | line parts 52a may be covered. The film thickness of the coating layer 32 is, for example, about 60 nm.

  FIG. 8 is a schematic cross-sectional view of the outer surface 111 and the surface 114 of the wall 11 provided with the second grid structure 50b. The second ridges 52b are also arranged at the same pitch (cycle) as the first ridges 52a. The coating layer 32 is not disposed on the second grid structure 50b.

  With reference to FIG. 7 and FIG. 8, the detailed structure of the 1st grid structure 50a and the 2nd grid structure 50b is demonstrated. Let p be a period that is the arrangement pitch of the first ridges 52a and the second ridges 52b (that is, the arrangement pitch of the dents 53a and 53b). The width of the first ridges 52a and the second ridges 52b is w. The heights of the first ridges 52a and the second ridges 52b (that is, the depths of the recesses 53a and 53b) are h. Here, it is assumed that the period p, the width w, and the height h of the first ridge 52a and the second ridge 52b are once the same.

The wavelength of the laser beam Lb is λ, and the refractive index of the glass plate member constituting the wall 11 is n ₁ . The relationship between the period p of the first ridges 52a and the second ridges 52b, the wavelength λ of the laser beam Lb, and the refractive index n ₁ of the glass plate member constituting the wall 11 is expressed by the following formula 1. Represented by

In Equation 1, and the refractive index n ₁ of the glass sheet member (for example, quartz glass) and 1.45, lambda is because it is 894 nm, the period p <617 nm. Therefore, the period p is set to 600 nm.

The first grid structure 50a and the second grid structure 50b can be regarded as thin films having an effective refractive index (n _eff ). The effective refractive index n _eff required for the first grid structure 50a and the second grid structure 50b corresponding to the wavelength satisfying the condition of Expression 1 can be calculated by the following Expression 2.

In Equation 2, n _eff (TE) is an effective refractive index for TE polarized light. n ₂ is the refractive index around the wall 11 and is assumed to be 1. f is the occupancy rate of the one-dimensional grid in the first grid structure 50a and the second grid structure 50b, and is expressed by Equation 3 below.

As shown in Formula 3, the occupation ratio f is a ratio of the width w to the period p of the first ridges 52a and the second ridges 52b. Regarding the first grid structure 50a, the surface of the first ridge portion 52a is covered with the coating layer 32. However, in order to prevent the ridge portion 53a from being filled with the coating layer 32, the occupation ratio f is 0. .5 (that is, the width w is about ½ of the period p). Here, considering that the coating layer 32 is isotropically formed (formed with a uniform film thickness), the occupation ratio f is set to 0.4. Then, the effective refractive index n _eff required for the first grid structure 50a and the second grid structure 50b is 1.2 according to Equation 2.

  Moreover, the height h of the 1st protruding item | line part 52a and the 2nd protruding item | line part 52b can be calculated by the following Numerical formula 4.

According to Equation 4, the height h of the first ridges 52a and the second ridges 52b is 186 nm. Using these results, the reflectance in the first grid structure 50a and the second grid structure 50b is estimated. The Fresnel coefficient is calculated from the effective refractive index n _eff obtained by Equation 2 and the height h of the first and second ridges 52a and 52b obtained by Equation 4, and the first grid structure is obtained. When the approximate reflectance in the 50a and the second grid structure 50b is obtained, the reflectance is almost zero.

  The above reflectance can be applied to the second grid structure 50b in which the coating layer 32 is not formed. Regarding the first grid structure 50a, the above-described reflectance is a reflectance in a state where the coating layer 32 is not formed, and therefore the conditions differ depending on the formation of the coating layer 32. Therefore, hereinafter, the reflectance of the first grid structure 50a in the state covered with the coating layer 32 is estimated.

The refractive index of the material of the coating layer 32 (for example, pentacontane) is almost the same as the refractive index n ₁ of the wall 11. A coating material having a film thickness of about 60 nm is isotropically deposited on the first grid structure 50a, and between the upper surface and the side surface of the first ridge 52a and between the adjacent first ridges 52a. It is assumed that the coating layer 32 is formed with the same film thickness.

When the coating layer 32 is included in the first ridge 52a, as shown in FIG. 7, the period p and the height h of the first ridge 52a are not changed, but the coating layer 32 is formed in the width w1. It becomes larger than the width w of the state where it is not. As a result, the occupation ratio f changes from 0.4 to about 0.6. Since the refractive index of the coating layer 32 is substantially the same as the refractive index n _{1 of the} wall 11, the first grid structure 50 a covered with the coating layer 32 is a one-dimensional grid structure with an occupation ratio f of 0.6. Can be considered.

The occupancy f as 0.6, when determining the effective refractive index n _eff according to Equation 2, the effective refractive index n _eff of the first grid structure 50a which is covered with a coating layer 32 becomes 1.29. And when the height h of the 1st convex-line part 52a is calculated | required by Numerical formula 4, height h will be 173 nm. Therefore, it is desirable that the height h of the first grid structure 50a covered with the coating layer 32 is set to 173 nm in advance when the first protrusion 52a is formed.

About the 1st grid structure 50a in the state covered with the coating layer 32, a Fresnel coefficient is calculated from the effective refractive index _neff calculated _| required by Numerical formula 2, and the height h of the 1st protruding item | line part 52a calculated _| required by _Numerical formula 4. FIG. When the approximate reflectance is obtained by calculation, the reflectance is about 0.5%. Although the reflectance is slightly increased by being covered with the coating layer 32, the reflectance can be significantly reduced for the gas cell 90 which is not provided with the antireflection structure.

  From the above calculation results, the first grid structure 50a and the second grid structure 50b are preliminarily determined based on the fact that the occupancy f is changed by being covered with the coating layer 32 on the first grid structure 50a. It is desirable that the height h of the first ridge 52a is different from the height h of the second ridge 52b. Based on the above estimation results, the occupation rate f is 0.4 for the first ridges 52a and the second ridges 52b, the height h of the first ridges 52a is 173 nm, The height h of the second protrusion 52b may be 186 nm.

  In other words, when the occupancy rate f of the first ridges 52a in the first grid structure 50a and the occupancy rate f of the second ridges 52b in the second grid structure 50b are the same, The height h of the first ridge 52a may be made smaller than the height h of the second ridge 52b.

  The occupancy rate f of the first ridges 52a and the occupancy rate f of the second ridges 52b are not particularly limited, but the first ridges 52a and the second ridges 52b are easy and reliable. In view of the fact that the coating layer 32 can be formed with a uniform film thickness on the first ridge 52a, a range of 0.3 or more and 0.7 or less is preferable with 0.5 as the center value, The range of 0.4 or more and 0.6 or less is more preferable.

  Also, the height h of the first ridge 52a and the height h of the second ridge 52b may be the same. When the height h of the first ridges 52a and the height h of the second ridges 52b are the same, the occupancy rate f of the first ridges 52a is set to be equal to that of the second ridges 52b. What is necessary is just to make it smaller than the occupation rate f. For example, when the height h of the first ridge 52a and the height h of the second ridge 52b are 173 nm, the occupancy f of the first ridge 52a is 0.4, What is necessary is just to make the occupation rate f of the 2 protruding item | line part 52b into 0.6.

  In the above calculation, the thickness of the coating layer 32 is set to 60 nm. Even when the thickness of the coating layer 32 is different, the occupation ratio f of the first ridges 52a and the second ridges 52b, and the first It is possible to cope with this by appropriately setting the height h of the first ridge 52a and the second ridge 52b.

In the above description, the laser beam Lb is linearly polarized TE polarized light. However, the laser beam Lb is linearly polarized TM polarized light (the vibration direction of the electric field is the first ridge 52a and the second ridge 52b. Linearly polarized light in a direction perpendicular to the extending direction of The effective refractive index n _eff in the case where the laser beam Lb is linearly polarized TM polarized light can be similarly calculated by Equation 5.

  Next, a method for manufacturing a gas cell including the method for forming an antireflection structure according to the first embodiment will be described with reference to FIGS. 9 to 12 are views for explaining a method of forming the antireflection structure according to the first embodiment. FIG. 13 to FIG. 20 are views for explaining a method for manufacturing a gas cell according to the first embodiment.

<Method for forming antireflection structure>
First, a method for forming a grid structure as an antireflection structure according to the first embodiment will be described with reference to FIGS. Although FIGS. 9 to 12 show a method for forming the first grid structure 50a, the method for forming the second grid structure 50b is the same. The 1st grid structure 50a and the 2nd grid structure 50b are formed in the state of the glass plate member used as the wall 11 before assembling the cell 12. FIG. Here, the glass plate member is referred to as a wall 11.

  As shown in FIG. 9, a positive resist 60 is formed on the inner surfaces 112 and 113 of the wall 11 by using, for example, a spin coating method. Then, the resist 60 is patterned using laser interference exposure. As a light source used for laser interference exposure, for example, a continuous wave DUV (Deep Ultra Violet) laser having a wavelength of 266 nm can be used.

  As shown in FIG. 9, the continuous wave DUV laser beam is appropriately branched into two laser beams DL1 and DL2, and the two laser beams DL1 and DL2 are crossed at a predetermined angle θ. Thereby, light (interference light) including interference fringes composed of periodic light and dark is generated. The pitch of the interference fringes (brightness / darkness cycle) is determined by a predetermined angle θ. For example, the pitch of the interference fringes can be set to 600 nm by setting the angle θ to 13 degrees. By irradiating the resist 60 with such interference light, a latent image pattern corresponding to the pitch of the interference fringes is formed on the resist 60.

  Subsequently, the resist 60 on which the latent image pattern corresponding to the pitch of the interference fringes is formed is developed. Thereby, as shown in FIG. 10, a resist pattern 62 having a period corresponding to the pitch of the interference fringes is formed on the surfaces 112 and 113 of the wall 11. For example, if the pitch of the interference fringes is 600 nm, the period of the resist pattern 62 is also approximately 600 nm.

  Subsequently, as shown in FIG. 11, the surfaces 112 and 113 of the wall 11 are dry-etched using the resist pattern 62 as a mask. As a result, portions of the surfaces 112 and 113 of the wall 11 that are not covered with the resist pattern 62 are selectively removed, and the shape of the resist pattern 62 is transferred to the surfaces 112 and 113 of the wall 11. Specifically, the removed portions of the surfaces 112 and 113 of the wall 11 become the concave portions 53a, and the portions covered with the resist pattern 62 and remaining therein become the first convex portions 52a.

  Subsequently, as shown in FIG. 12, by removing the resist pattern 62, a first grid structure 50 a having a plurality of first ridges 52 a is formed on the surfaces 112 and 113 of the wall 11.

<Gas cell manufacturing method>
Next, a gas cell manufacturing method according to the first embodiment will be described with reference to FIGS. 13 to 20, FIG. 14 and FIG. 16 are plan sectional views corresponding to FIG. 3, and the other portions are side sectional views corresponding to FIG. 2.

  In the steps shown in FIGS. 13 and 14, the cell 12 is assembled. The cell 12 is configured by combining, for example, a glass plate member made of quartz glass as the wall 11. Although not shown, a glass plate made of quartz glass is cut to prepare glass plate members corresponding to the walls 11 constituting the cell 12. Then, these glass plate members (walls) 11 are assembled, and the glass plate members (walls) 11 are joined to each other by an adhesive or welding to form the main chamber 14 and the reservoir 16 as shown in FIGS. 13 and 14. A cell 12 is obtained.

  As shown in FIG. 14, a first grid structure 50 a is provided in advance on the inner surface 112 and the surface 113 of the glass plate member that becomes the side wall 11 of the main chamber 14. Further, a second grid structure 50b is provided in advance on the outer surface 111 and the surface 114 of the glass plate member to be the side wall 11 of the main chamber 14. In the stage shown in FIGS. 13 and 14, the coating layer 32 is not formed. At this stage, the opening 18 of the cell 12 is opened.

  15 and 16, the coating layer 32 is formed on the inner side of the wall 11 of the cell 12. Although illustration is omitted, the assembled cell 12 is sufficiently degassed, and the material of the coating layer 32 is arranged from the opening 18 of the cell 12 into the reservoir 16 using a needle or the like in a reduced pressure environment. . And the opening part 18 is temporarily sealed with a temporary stopper etc., and the whole cell 12 is heated to about 200 degreeC, for example.

  Thereby, as shown in FIG. 15 and FIG. 16, the coating layer 32 which covers the inner side of the wall 11 of the cell 12 (the main chamber 14 and the reservoir | reserver 16) is formed. As a result, as shown in FIG. 16, the first grid structure 50 a is covered with the coating layer 32 on the inner surface 112 and the surface 113 of the side wall 11 of the main chamber 14. In addition, the inside of the cell 12 may be in a state close to a vacuum, and the material of the coating layer 32 may be heated and introduced into the cell 12 through the opening 18 in a gas phase or liquid phase state.

  Subsequently, in the step shown in FIG. 17, the ampoule 20 is stored in the reservoir 16 of the cell 12 having the coating layer 32 formed on the inner surface. The ampule 20 is inserted from an opening 18 provided on the reservoir 16 side of the cell 12 and is disposed in the reservoir 16. At this stage, as shown in FIG. 4, the ampoule 20 is in a state where the hollow glass tube 22 is filled with an alkali metal solid 24 and sealed.

  The ampoule 20 is filled with an alkali metal solid 24 in the hollow portion of the tubular glass tube 22 in a low-pressure environment close to vacuum (ideally in a vacuum), and both ends of the glass tube 22 are welded and sealed. To form. Alkali metals such as cesium used as the alkali metal solid 24 are highly reactive and cannot be handled in the atmosphere, and thus are stored in the cell 12 in a sealed state in the ampoule 20 under a low pressure environment.

  Subsequently, in the step shown in FIG. 18, the cell 12 is sufficiently evacuated, and the cell 12 is sealed in a state where impurities are extremely small in the main chamber 14 and the reservoir 16. For example, the opening 18 of the cell 12 is sealed with the lid 19 using the sealing member 30 (low melting point glass frit) in a low-pressure environment close to vacuum (ideally in vacuum) or in an inert gas. . Thereby, the cell 12 is sealed in a state where the ampoule 20 is housed inside.

  Subsequently, in the step shown in FIG. 19, a through hole 21 is formed in the ampoule 20 (glass tube 22). In this step, the pulsed laser light 40 is condensed by the condenser lens 42 and irradiated onto the glass tube 22 of the ampule 20 from above (+ Z direction) via the cell 12. Since the laser beam is excellent in directivity and convergence, the glass tube 22 can be easily processed. By irradiating the pulse laser beam 40, the processing proceeds from the upper surface (surface) of the glass tube 22 in the depth direction (−Z direction). And when the through-hole 21 is formed in the glass tube 22, the hollow part of the ampoule 20 will connect with the reservoir | reserver 16, and the sealing of the ampoule 20 will be broken.

  As shown in FIG. 20, by forming the through hole 21 in the glass tube 22, the alkali metal solid 24 (see FIG. 4) in the ampoule 20 evaporates and flows into the reservoir 16 as the alkali metal gas 13. . The alkali metal gas 13 flowing out into the reservoir 16 flows into the main chamber 14 of the cell 12 through the communication hole 15 and diffuses. As a result, the main chamber 14 of the cell 12 is filled with the alkali metal gas 13. The gas cell 10 can be manufactured by the above process.

  In the process shown in FIG. 20, it is necessary to form the through hole 21 in the glass tube 22 of the ampoule 20 without damaging the wall 11 of the cell 12. Therefore, when the wall 11 is made of quartz glass and the glass tube 22 is made of borosilicate glass, for example, pulse laser light 40 having a wavelength in the ultraviolet region is used. Light having a wavelength in the ultraviolet region passes through the quartz glass, but is slightly absorbed by the borosilicate glass. Accordingly, the through hole 21 can be formed by selectively processing the glass tube 22 of the ampoule 20 without damaging the wall 11 of the cell 12.

  In this step, the alkali metal solid 24 only needs to evaporate and flow out from the ampoule 20, so that the invention is not limited to the formation of the through hole 21. For example, the ampule 20 is divided by causing a crack in the glass tube 22. Alternatively, the glass tube 22 may be broken.

(Second Embodiment)
The second embodiment has the same configuration as the first embodiment except that the configuration of the antireflection structure is different. Here, the gas cell and the antireflection structure according to the second embodiment will be described.

<Gas cell>
The configuration of the gas cell according to the second embodiment will be described with reference to FIG. FIG. 21 is a plan sectional view showing the configuration of the gas cell according to the second embodiment. FIG. 21 is a diagram corresponding to FIG. 3 in the first embodiment. Here, differences from the first embodiment will be described.

  As shown in FIG. 21, the gas cell 10 </ b> A according to the second embodiment includes a third antireflection structure on the outer surface 111 of the incident-side wall 11 and the outer surface 114 of the emission-side wall 11. The grid structure 54 is provided. In the gas cell 10A according to the second embodiment, the third grid structure 54 transmits the laser beam Lb at the center of the outer surface 111 of the incident-side wall 11 and the outer surface 114 of the emission-side wall 11. It is provided in the area (see FIG. 2).

<Antireflection structure>
FIG. 22 is a cross-sectional view illustrating a schematic configuration of the antireflection structure according to the second embodiment. FIG. 22 is a diagram corresponding to FIG. 8 in the first embodiment. As shown in FIG. 22, the third grid structure 54 as the antireflection structure according to the second embodiment has a configuration in which a plurality of third ridges 56 are arranged one-dimensionally in a stripe shape. Yes. The third ridge 56 is disposed on the outer surfaces 111 and 114 of the wall 11. The 3rd protruding item | line part 56 is comprised with resin.

  In addition, although illustration is abbreviate | omitted also about the 3rd grid structure 54, the period p of the 3rd protruding item | line part 56, the width | variety w, and the height h are 1st grids based on 1st Embodiment. It is set similarly to the structure 50a and the second grid structure 50b.

<Method for forming antireflection structure>
With reference to FIG. 23, FIG. 24, and FIG. 25, the formation method of the reflection preventing structure which concerns on 2nd Embodiment is demonstrated. 23, 24, and 25 are views for explaining a method of forming an antireflection structure according to the second embodiment.

  In the method of forming the third grid structure 54 as the antireflection structure according to the second embodiment, the third grid structure 54 is formed using a stamper 64 as shown in FIG. The stamper 64 is made of, for example, metal, and has a die shape having a concavo-convex pattern in which ridges 66 and dents 68 are alternately arranged. The concavo-convex pattern of the ridges 66 and the recesses 68 can be formed by, for example, a photolithography method.

  As shown in FIG. 23, the stamper 64 is pressed against the surfaces 111 and 114 of the wall 11 forming the third ridge 56. Next, as shown in FIG. 24, a photocurable resin 55 is applied to one end of the stamper 64 and penetrates into the gap between the surfaces 111 and 114 of the wall 11 and the uneven pattern of the stamper 64 by capillary action. The resin 55 may be a thermosetting resin or the like.

The applied resin 55 is evacuated from the opposite side of the stamper 64 to the side where the resin 55 is applied, so that the entire uneven pattern of the stamper 64 is spread. The supplied resin 55 is pressurized with, for example, an inert gas such as nitrogen gas (N ₂ ), and evacuation is performed on the surfaces 111 and 114 of the wall 11 by evacuation from the side opposite to pressing from the coating side. Can be spread along.

  When the resin 55 filled in the concavo-convex pattern of the stamper 64 is exposed and cured by a method such as ultraviolet irradiation, the resin 55 filled in the concavo-convex pattern becomes the third ridge 56. After the resin 55 is cured, the stamper 64 is peeled (or separated) from the surfaces 111 and 114 of the wall 11. Thereby, as shown in FIG. 25, the third ridge 56 is arranged on the surfaces 111 and 114 of the wall 11. Thus, the third grid structure 54 is formed. Since the third grid structure 54 according to the second embodiment is formed using the stamper 64, the third grid structure 54 can be formed on the outer surfaces 111 and 114 of the wall 11 of the main chamber 14 even after the cell 12 is assembled. it can.

  In FIG. 21, the third grid structure 54 is formed in the region of the outer surfaces 111 and 114 of the wall 11 where the central laser beam Lb passes, but the outer surfaces 111 and 114 of the wall 11 The third grid structure 54 may be formed on the entire surface. Further, the third grid structure 54 is formed not only on the outer surfaces 111 and 114 of the wall 11 but also on the inner surfaces 112 and 113 of the wall 11 in the state of the glass plate member before the cell 12 is assembled. Also good.

(Third embodiment)
<Atomic oscillator>
In the first embodiment, the magnetic measurement apparatus 100 has been described as an apparatus to which the gas cells 10 and 10A can be applied. In the third embodiment, an apparatus to which the gas cell 10 (or the gas cell 10A) according to the above embodiment is applied. An atomic oscillator such as an atomic clock will be described. FIG. 26 is a schematic diagram illustrating a configuration of an atomic oscillator according to the third embodiment. FIGS. 27 and 28 are diagrams for explaining the operation of the atomic oscillator according to the third embodiment.

  An atomic oscillator (quantum interference device) 101 according to the third embodiment shown in FIG. 26 is an atomic oscillator using a quantum interference effect. As shown in FIG. 26, the atomic oscillator 101 includes a gas cell 10 (or a gas cell 10A) according to the above embodiment, a light source 71, optical components 72, 73, 74, and 75, a light detection unit 76, a heater 77, and the like. , A temperature sensor 78, a magnetic field generator 79, and a controller 80.

  The light source 71 emits two kinds of light (resonance light L1 and resonance light L2 shown in FIG. 27) having different frequencies, which will be described later, as excitation light LL for exciting alkali metal atoms in the gas cell 10. The light source 71 is composed of, for example, a semiconductor laser such as a vertical cavity surface emitting laser (VCSEL). The optical components 72, 73, 74, and 75 are provided on the optical path of the excitation light LL between the light source 71 and the gas cell 10, respectively, and the optical component 72 (lens) and the optical component from the light source 71 side to the gas cell 10 side. 73 (polarizing plate), optical component 74 (darkening filter), and optical component 75 (λ / 4 wavelength plate) are arranged in this order.

  The light detection unit 76 detects the intensity of the excitation light LL (resonance light L1, L2) that has passed through the gas cell 10. The light detection part 76 is comprised, for example with the solar cell, the photodiode, etc., and is connected to the excitation light control part 82 of the control part 80 mentioned later. The heater 77 (heating unit) heats the gas cell 10 in order to maintain the alkali metal in the gas cell 10 in a gaseous state (as the alkali metal gas 13). The heater 77 (heating unit) is composed of, for example, a heating resistor.

  The temperature sensor 78 detects the temperature of the heater 77 or the gas cell 10 in order to control the amount of heat generated by the heater 77. The temperature sensor 78 includes various known temperature sensors such as a thermistor and a thermocouple. The magnetic field generator 79 generates a magnetic field that causes Zeeman splitting of a plurality of energy levels of the alkali metal in the gas cell 10 that are degenerated. Zeeman splitting can increase the resolution by widening the gap between different energy levels of alkali metal degeneration. As a result, the accuracy of the oscillation frequency of the atomic oscillator 101 can be increased. The magnetic field generator 79 is composed of, for example, a Helmholtz coil or a solenoid coil.

  The control unit 80 controls the excitation light control unit 82 that controls the frequency of the excitation light LL (resonant light L 1, L 2) emitted by the light source 71, and the temperature that controls the energization of the heater 77 based on the detection result of the temperature sensor 78. The controller 81 and the magnetic field controller 83 that controls the magnetic field generated from the magnetic field generator 79 to be constant. The control unit 80 is provided, for example, on an IC chip mounted on a substrate.

  The principle of the atomic oscillator 101 will be briefly described. FIG. 27 is a diagram for explaining the energy state of alkali metal in the gas cell 10 of the atomic oscillator 101, and FIG. It is a graph which shows the relationship. As shown in FIG. 27, the alkali metal (alkali metal gas 13) enclosed in the gas cell 10 has a three-level energy level and two ground states (bases) having different energy levels. There can be three states: a state S1, a ground state S2) and an excited state. Here, the ground state S1 is a lower energy state than the ground state S2.

  When such an alkali metal gas 13 is irradiated with two types of resonant lights L1 and L2 having different frequencies, according to the difference (ω1−ω2) between the frequency ω1 of the resonant light L1 and the frequency ω2 of the resonant light L2. The optical absorptance (light transmittance) of the resonance lights L1 and L2 in the alkali metal gas 13 changes. When the difference (ω1−ω2) between the frequency ω1 of the resonant light L1 and the frequency ω2 of the resonant light L2 matches the frequency corresponding to the energy difference between the ground state S1 and the ground state S2, the ground states S1 and S2 Each excitation to the excited state stops.

  At this time, the resonance lights L1 and L2 are transmitted without being absorbed by the alkali metal gas 13. Such a phenomenon is called a CPT phenomenon or an electromagnetically induced transparency (EIT) phenomenon. The EIT signal, which is a steep signal generated in accordance with the EIT phenomenon, is detected by the light detection unit 76, and the EIT signal is used as a reference signal. From the viewpoint of improving short-term frequency stability, the EIT signal preferably has a small line width (half-value width) and high strength.

  The light source 71 emits two types of light (resonant light L1 and resonant light L2) having different frequencies as described above toward the gas cell 10. Here, for example, when the frequency ω1 of the resonant light L1 is fixed and the frequency ω2 of the resonant light L2 is changed, the difference (ω1−ω2) between the frequency ω1 of the resonant light L1 and the frequency ω2 of the resonant light L2 is obtained. When the frequency coincides with the frequency ω0 corresponding to the energy difference between the ground state S1 and the ground state S2, the detection intensity of the light detection unit 76 increases sharply as shown in FIG.

  Such a steep signal is called an EIT signal. The EIT signal has an eigenvalue determined by the type of alkali metal. In this embodiment, a high-quality and large EIT signal is obtained with a small line width. Therefore, by using such an EIT signal as a reference, a highly accurate atomic oscillator 101 can be realized.

  The gas cell 10 used in the atomic oscillator 101 is required to be small and have a long life and high accuracy. However, according to the configuration of the gas cell of the above embodiment, the gas cell 10 is small and has a long life and high accuracy. Therefore, the atomic oscillator 101 with a small size, high accuracy, and long life can be provided.

  The above-described embodiments merely show one aspect of the present invention, and can be arbitrarily modified and applied within the scope of the present invention. As modifications, for example, the following can be considered.

(Modification 1)
The gas cells 10 and 10A according to the above embodiment have a grid structure in which the first ridges 52a, the second ridges 52b, and the third ridges 56 are one-dimensionally arranged in stripes as an antireflection structure. However, the present invention is not limited to such a form. For example, the gas cells 10 and 10A may have a moth-eye structure as an antireflection structure. By providing a moth-eye structure as an antireflection structure, a laser beam that passes through the gas cells 10 and 10A in the same manner as the first grid structure 50a, the second grid structure 50b, and the third grid structure 54 included in the gas cells 10 and 10A. Lb reflection can be suppressed.

(Modification 2)
In the gas cells 10 and 10A according to the above embodiment, the ampule 20 is used as a means for generating the alkali metal gas 13 inside the cell 12, but the present invention is not limited to such a configuration. For example, as a means for generating the alkali metal gas 13, a pill that includes an alkali metal compound and an adsorbent and has a cylindrical shape, a rectangular parallelepiped shape, a spherical shape, or the like may be used. Although not shown, when such a pill is irradiated with a continuous wave laser beam having a wavelength in the red to infrared region, an alkali metal is generated by activation of the alkali metal compound, and an impurity released at that time is generated. And impure gas is adsorbed by the adsorbent. As the alkali metal compound, when cesium is used as the alkali metal, for example, a cesium compound such as cesium molybdate or cesium chloride can be used. As the adsorbent, for example, zirconium powder, aluminum or the like can be used.

(Modification 3)
In the gas cells 10 and 10A according to the above embodiment, when the coating layer 32 is formed inside the cell 12, the material of the coating layer 32 is disposed in the reservoir 16 from the opening 18 of the cell 12, The invention is not limited to such a configuration. For example, the tubular member is filled with the material of the coating layer 32, this tubular member is placed in the reservoir 16 from the opening 18 of the cell 12, and the ampoule 20 is also placed in the reservoir 16 and the opening 18 is sealed with the lid 19. After stopping, the entire cell 12 may be heated. In this case, after the coating layer 32 is formed inside the cell 12, the tubular member filled with the material of the coating layer 32 remains in the reservoir 16.

  10, 10A, 90 ... gas cell, 11 ... wall, 12 ... cell (closed container), 13 ... alkali metal gas, 32 ... coating layer (chain saturated hydrocarbon), 50a ... first grid structure (antireflection structure) 50b ... second grid structure (antireflection structure), 52a ... first protrusion, 52b ... second protrusion, 100 ... magnetic measuring device, 101 ... atomic oscillator, 111,114 ... outer surface 112, 113 ... inner surface, f ... occupancy, h ... height, p ... period, w ... width.

Claims (10)

A closed container composed of walls,
An antireflection structure provided on the inner surface of the wall;
A chain saturated hydrocarbon covering the surface of the antireflection structure;
An alkali metal gas sealed in the closed container;
A gas cell comprising: The gas cell according to claim 1, wherein
A gas cell comprising a first grid structure in which a plurality of first ridges are arranged one-dimensionally as the antireflection structure. The gas cell according to claim 2, wherein
The occupation ratio, which is the ratio of the width to the period of the first ridges, is 0.3 or more and 0.7 or less. The gas cell according to claim 3, wherein
The gas cell according to claim 1, wherein an occupation ratio of the first ridge portion is 0.4 or more and 0.6 or less. A gas cell according to claim 3 or 4, wherein
A gas cell comprising a second grid structure in which a plurality of second ridges are arranged one-dimensionally on the outer surface of the wall. The gas cell according to claim 5, wherein
When the occupancy rate of the first ridges in the first grid structure and the occupancy rate of the second ridges in the second grid structure are the same,
The height of the said 1st protruding item | line part is smaller than the height of the said 2nd protruding item | line part, The gas cell characterized by the above-mentioned. The gas cell according to claim 5, wherein
When the height of the first ridge in the first grid structure is the same as the height of the second ridge in the second grid structure,
The gas cell characterized in that an occupancy ratio of the first ridge portion is smaller than an occupancy ratio of the second ridge portion. The gas cell according to claim 1, wherein
A gas cell comprising a moth-eye structure as the antireflection structure.   A magnetic measuring device comprising the gas cell according to claim 1.   An atomic oscillator comprising the gas cell according to any one of claims 1 to 8.

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