Gas cell for atomic clock and structure for atomic clock

Abstract

This gas cell for an atomic clock is provided with a through hole 50H. The through hole 50H contains therein a gas which contains an alkali metal. The through hole 50H has: a first part that has a first inner wall surface H1 which is at a position such that the distance thereof from a center-of-gravity position G in plan view is a first radius (R); and a second part that has a second inner wall surface H2 which is at a position such that the distance thereof from the center-of-gravity position in plan view is greater than the first radius (R) by a first dimension (ΔR). An improvement in yield is made possible by setting the first radius (R), the first dimension (ΔR), a first distance (Z) which is defined between a second transparent substrate 52 and a first transparent substrate 51 at a position in the through hole 50H, and a second dimension (ΔZ) which is along the thickness direction of a substrate 50 of the second part.

Description

Gas cell for atomic clock and structure for atomic clock

[0001] The present disclosure relates to a gas cell for an atomic clock and a structure for an atomic clock.

[0002] Atomic clocks are known as devices for measuring time accurately. There are several types of atomic clocks. In recent years, atomic clocks of a type that irradiates a gas in a gas cell with laser light, such as CPT (Coherent Population Trapping), have been gaining attention. Gas containing an alkali metal such as rubidium (Rb) or cesium (Cs) is sealed in the gas cell. Various types of measurement methods are conceivable. Physical structural components of atomic clocks, i.e., atomic clock structures equipped with a laser element, a photodetector, and a gas cell, are also being studied. Patent Documents 1 to 4 disclose atomic clocks equipped with a gas cell.

[0003] JP 2009-273088 A JP 2019-007763 A JP 2016-171419 A International Publication No. 2022 / 097557

[0004] Gas cells for atomic clocks and structures for atomic clocks with excellent yields are expected.

[0005] The atomic clock gas cell of the present disclosure includes a through-hole. The through-hole contains a gas containing an alkali metal. The through-hole includes a first portion having a first inner wall surface at a position a first diameter (R) away from a center of gravity in a plan view, and a second portion having a second inner wall surface at a position a distance from the center of gravity in a plan view that is a first dimension (ΔR) greater than the first diameter (R). The first diameter (R), the first dimension (ΔR), a first distance (Z) defined between a first transparent substrate and a second transparent substrate at the position of the through-hole, and a second dimension (ΔZ) along the thickness direction of the substrate of the second portion are set. The following conditions can be satisfied: 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50%.

[0006] The atomic clock structure of the present disclosure includes a gas cell, a laser element that directs laser light into the gas cell, and a photodetector arranged at a position where the laser light that has passed through the gas cell is incident.

[0007] FIG. 1 is an exploded perspective view of a gas cell for an atomic clock. FIG. 2(A) is a longitudinal cross-sectional view of the gas cell, and FIG. 2(B) is a horizontal cross-sectional view of the gas cell. FIG. 3 is a diagram showing the experimental results. FIG. 4 is a diagram showing the experimental results. FIG. 5 is a diagram showing the experimental results. FIG. 6 is a diagram showing the experimental results. FIG. 7 is a diagram showing the experimental results. FIG. 8 is a diagram showing the experimental results. FIG. 9(A) is a longitudinal cross-sectional view of the gas cell, and FIG. 9(B) is a horizontal cross-sectional view of the gas cell. FIG. 10(A) is a longitudinal cross-sectional view of the gas cell, and FIG. 10(B) is a horizontal cross-sectional view of the gas cell. FIG. 11(A) is a longitudinal cross-sectional view of the gas cell, and FIG. 11(B) is a horizontal cross-sectional view of the gas cell. FIG. 12(A) is a horizontal cross-sectional view of the gas cell, and FIG. 12(B) is a horizontal cross-sectional view of the gas cell. Figure 13(A) is a horizontal cross-sectional view of the gas cell, and Figure 13(B) is a horizontal cross-sectional view of the gas cell. Figure 14 is a vertical cross-sectional view of the gas cell. Figure 15(A) is a front view of the atomic clock structure, Figure 15(B) is a plan view of the atomic clock structure, and Figure 15(C) is a side view of the atomic clock structure. Figure 16(A) is a front view of the atomic clock structure, Figure 16(B) is a plan view of the atomic clock structure, and Figure 16(C) is a side view of the atomic clock structure. Figure 17(A) is a front view of the atomic clock structure, Figure 17(B) is a plan view of the atomic clock structure, and Figure 17(C) is a side view of the atomic clock structure. Figure 18(A) is a front view of the atomic clock structure, and Figure 18(B) is a plan view of the atomic clock structure.

[0008] The gas cell and atomic clock structure according to the embodiment will be described below. Note that the same elements will be denoted by the same reference numerals, and duplicated explanations will be omitted.

[0009] FIG. 1 is an exploded perspective view of a gas cell for an atomic clock.

[0010] The atomic clock structure includes a gas cell GC, a laser element optically coupled to the laser light inlet of the gas cell GC, and a photodetector optically coupled via the laser light outlet in the internal space (through-hole 50H) of the gas cell GC. A vertical-cavity surface-emitting laser (VCSEL) can be used as the laser element and a photodiode can be used as the photodetector, but other types of elements may also be used.

[0011] The gas cell GC includes a substrate 50, a first transparent substrate 51 fixed to a first surface BY1 of the substrate 50, and a second transparent substrate 52 fixed to a second surface BY2 of the substrate 50. The thickness direction of the substrate 50 is the Z-axis direction, the X-axis is perpendicular to the Z-axis, and the Y-axis is perpendicular to both the X-axis and the Z-axis. A through-hole 50H penetrating the substrate 50 is provided between the first transparent substrate 51 and the second transparent substrate 52. The through-hole 50H extends along the Z-axis direction. A gas containing an alkali metal is contained within the through-hole 50H.

[0012] This gas contains an alkali metal such as rubidium (Rb) or cesium (Cs). This gas may also contain a rare gas. The laser light emitted from the laser element is irradiated onto the gas in the through-hole 50H. If this gas contains an alkali metal, absorption of the laser light occurs according to its energy level. By controlling the energy level and frequency of the laser light, the absorption rate of the laser light in the gas changes. If the control signal given to the laser element is feedback-controlled so as to match the specific energy level difference of the alkali atoms that make up the gas, the frequency (clock) of the output signal from the feedback control circuit will be an accurate value.

[0013] The material of the substrate 50 can be an insulator (glass or resin), a semiconductor (e.g., Si), or a metal (e.g., including Cu, Al, or Fe). In this example, the material of the substrate 50 is silicon (Si). The first transparent substrate 51 and the second transparent substrate 52 are made of a material that is transparent to the laser light from the laser element. One example of the material of the first transparent substrate 51 and the second transparent substrate 52 is glass. An adhesive can be used to fix the elements, but if either the substrate 50 or the transparent substrate is made of a material that melts in response to heat, they can also be bonded by applying heat and pressure to their interface.

[0014] The planar shape (XY planar shape) of the through-hole 50H is circular. Laser light is introduced into the through-hole 50H to excite the alkali metal gas. However, since a circle does not have corners like a rectangle, reflection of the laser light by the corners is suppressed, and therefore noise generation is suppressed.

[0015] FIG. 2A is a vertical cross-sectional view (cross-sectional view taken along the arrows AA) of the gas cell, and FIG. 2B is a horizontal cross-sectional view (cross-sectional view taken along the arrows BB) of the gas cell.

[0016] The through hole 50H has two portions with different diameters. That is, the through hole 50H has a first portion P1 having a first inner wall surface H1 at a position where the distance from the center of gravity G in a plan view (when the XY plane is viewed along the Z axis) is a first diameter (R) (radius). The through hole 50H has a second portion P2 having a second inner wall surface H2 at a position (R + ΔR) where the distance from the center of gravity G in a plan view is a first dimension (ΔR) greater than the first diameter (R). The planar shape of the first portion P1 of the through hole 50H is circular, and the shape of the second portion P2 is also circular. Therefore, reflection of the laser light by the corners is suppressed, and noise generation is suppressed.

[0017] When manufacturing the gas cell GC, first, a substrate 50 having a through-hole 50H is prepared, and then the lower surface (first surface BY1) of the substrate 50 is attached and fixed to the upper surface of a first transparent substrate 51. Next, a liquid source containing an alkali metal (alkali metal azide (RbN)) is poured onto the first transparent substrate 51 in the through-hole 50H. ３ or CsN ３The liquid raw material may be a liquid (solution) of azide dissolved in water. Thereafter, a second transparent substrate 52 is attached and fixed to the upper surface (second surface BY2) of the substrate 50 so as to close the through-hole 50H.

[0018] The inventors of the present application have found that a structure with a fixed diameter for the through-hole 50H results in defective products. In other words, the resulting products fail to adequately maintain airtightness within the through-hole 50H. The defective gas cells GC have degraded characteristics and cannot be used as precision atomic clocks. After careful investigation and observation, they discovered that the liquid raw material creeps up the inner wall surface of the through-hole 50H and reaches the upper opening end surface (second surface BY2), where the alkali metals remaining on the second surface BY2 as the liquid raw material dries are left behind. The alkali metals remaining on the second surface BY2 hinder adhesion of the second transparent substrate 52, which reduces airtightness.

[0019] Therefore, in the gas cell GC according to the embodiment, the through-hole 50H has two or more diameters, and in this example, includes a first portion P1 and a second portion P2. The second portion P2, which is located at the bottom, has a shape that prevents the liquid source from creeping up.

[0020] That is, the first diameter (R), the first dimension (ΔR), the first distance (Z) defined between the first transparent substrate 51 and the second transparent substrate 52 at the position of the through-hole 50H, and the second dimension (ΔZ) of the second portion P2 along the thickness direction of the substrate 50 satisfy the following conditions: 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50%.

[0021] If the first distance (Z), which is the height of the through-hole 50H, is sufficiently high, the creeping up of alkali metals can be sufficiently suppressed, but the gas cell GC becomes larger. Therefore, the first distance (Z) is set to be equal to or less than the above-mentioned upper limit value. Note that if the effect is only to inhibit the creeping up of alkali metals, there is no need to set an upper limit for the first distance (Z). Furthermore, even if the through-hole 50H has the second portion P2, if the first distance (Z) is too low, the creeping up of alkali metals cannot be suppressed. At least, if the first distance (Z) is set to be equal to or greater than the above-mentioned lower limit value, the creeping up of alkali metals can be suppressed.

[0022] The radius of the through hole 50H is considered to have a small contribution to the creeping up of alkali metals. A suitable range for the absolute value of the first dimension (ΔR) is 1 mm≦R≦3 mm. A suitable relative range is 6%≦ΔR / R≦50%. Note that if the only effect is to inhibit the creeping up of alkali metals, there is no need for an upper limit for the first distance (Z). However, in order to prevent the gas cell GC from becoming larger and to prevent a decrease in the adhesive strength at the first surface BY1, it is preferable that the range of the first dimension (ΔR) be equal to or less than the above upper limit. If the first dimension (ΔR) is equal to or greater than the lower limit, the creeping up of alkali metals can be suppressed, and the occurrence of defective products can be significantly reduced.

[0023] In particular, when the through-hole 50H satisfies the following condition: 0.01≦(ΔR / R)×(ΔZ / Z)≦0.25, the occurrence of defective products can be significantly reduced.

[0024] In this example, the second portion P2 is provided on the substrate 50. To form this structure, after the through-hole 50H is formed in the substrate 50, a recess that is continuous with the through-hole 50H may be formed on the lower surface of the substrate 50. As a forming method, an etching method, a press working method, a cutting method, or the like may be used. Since all processing steps are applied to the substrate 50, the positional accuracy of the first portion P1 and the second portion P2 can be precisely controlled.

[0025] The inner surface of the through hole 50H, the first surface BY1, and the second surface BY2 may be subjected to a hydrophilic treatment or a cleaning treatment. These treatments remove unnecessary impurity elements, improve the surface condition, and also increase the adhesive strength.

[0026] (First Experiment) FIG. 3 is a table showing the results of the first experiment.

[0027] In the first experiment, a gas cell having the above-described structure was manufactured by the above-described method. The material of the substrate 50 was silicon, the material of the first transparent substrate 51 was glass, the material of the second transparent substrate 52 was glass, the first distance (Z) was 2 mm, the first radius (R) was 3 mm, and the first dimension (ΔR) and the second dimension (ΔZ) were changed. The liquid raw material was rubidium (Rb) azide (RbN ３ ), which was dissolved in water, and a liquid raw material with a volume of 1 μL was placed on the first transparent substrate 51 inside the through-hole 50H. The substrate and the transparent substrate were bonded using anodic bonding. In Comparative Examples 1 to 5 and Examples 1 to 20, the number of samples in each experiment was 100. The samples were divided into 6 mm squares, and each sample was observed under a microscope at 50x magnification. Products that did not experience infiltration of cutting water when divided into gas cells were judged to be good products, while products that experienced infiltration of cutting water or where isolation was clearly observed were judged to be defective products.

[0028] In Comparative Examples 1 to 5 of the first experiment, (ΔZ / Z) was changed from 0% to 5%, and (ΔR / R) was changed from -5% to 5%. In Examples 1 to 20 of the first experiment, (ΔZ / Z) was changed from 6% to 50%, and (ΔR / R) was changed from 6% to 50%.

[0029] The yields (45% to 85%) of Examples 1 to 20 of the first experiment were significantly higher than the yields (11% to 32%) of Comparative Examples 1 to 5 of the first experiment, and sufficient effects were obtained. In Examples 1 to 20 of the first experiment, 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50% were satisfied.

[0030] Furthermore, in Examples 10, 13, 14, 15, 19, and 20 of the first experiment, yields of 80% or more were obtained, and even more outstanding effects were obtained. In these examples, 0.01≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied.

[0031] (Second Experiment) FIG. 4 is a table showing the results of the second experiment.

[0032] In the second experiment, compared to the first experiment, the liquid raw material was cesium (Cs) azide (CsN ３ The only difference from the first experiment is that the first experiment was carried out using 1,2,3-trimethylsilyl methylcellulose (C10-1, C20-1, C30-1, C40-1, C50-1, C60-1, C70-1, C80-1, C9 ...

[0033] In Examples 1 to 10 of the second experiment, (ΔZ / Z) was varied from 6% to 50%, and (ΔR / R) was varied from 6% to 50%.

[0034] The yields (42% to 85%) of Examples 1 to 10 of the second experiment were significantly higher than those of Comparative Examples 1 to 5 of the first experiment, demonstrating sufficient effectiveness. Furthermore, if the liquid raw material in the Comparative Example of the first experiment were replaced with cesium, it is believed that similar yields would be achieved, given the similarity in physical properties between rubidium and cesium. In Examples 1 to 10 of the second experiment, the following conditions were satisfied: 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50%.

[0035] Furthermore, in Examples 8, 9, and 10 of the second experiment, yields of 80% or more were obtained, and even more outstanding effects were obtained. In these examples, 0.01≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied.

[0036] (Third Experiment) FIG. 5 is a table showing the results of the third experiment.

[0037] The third experiment differs from the first experiment only in that the first distance (Z) was set to 1 mm.

[0038] In Comparative Examples 1 to 5 of the third experiment, (ΔZ / Z) was changed from 0% to 5%, and (ΔR / R) was changed from -5% to 5%. In Examples 1 to 20 of the first experiment, (ΔZ / Z) was changed from 6% to 50%, and (ΔR / R) was changed from 6% to 50%.

[0039] The yields of Examples 1 to 20 in the third experiment (41% to 90%) were significantly higher than the yields of Comparative Examples 1 to 5 in the third experiment (5% to 30%), and sufficient effects were obtained. In Examples 1 to 20, 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50% were satisfied.

[0040] Furthermore, in Examples 5, 10, 15, 17, 19, and 20, yields of 80% or more were obtained, and even more significantly excellent effects were obtained. In these Examples, 0.03≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied. In Examples 5, 9, 10, 13, 14, 15, 16, 17, 18, 19, and 20, yields of 70% or more were obtained, and in these Examples, 0.01≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied.

[0041] (Fourth Experiment) FIG. 6 is a table showing the results of the fourth experiment.

[0042] In the fourth experiment, the liquid raw material was cesium (Cs) azide (CsN ３ The only difference from the third experiment is that the 1,2,3-trimethylsilyl methylcellulose was dissolved in water.

[0043] In Examples 1 to 10 of the fourth experiment, (ΔZ / Z) was changed from 6% to 50%, and (ΔR / R) was changed from 6% to 50%.

[0044] The yields (45% to 90%) of Examples 1 to 10 of the fourth experiment were significantly higher than those of Comparative Examples 1 to 5 of the third experiment, and sufficient effects were obtained. Examples 1 to 10 of the fourth experiment satisfied the conditions of 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50%.

[0045] Furthermore, in Examples 9 and 10 of the fourth experiment, a yield of 80% or more was obtained, and even more remarkably excellent effects were obtained. In these Examples, 0.04≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied. In Examples 4, 5, 8, 9, and 10, a yield of 70% or more was obtained, and in these Examples, 0.01≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied.

[0046] (Fifth Experiment) FIG. 7 is a table showing the results of the fifth experiment.

[0047] The fifth experiment differs from the first experiment only in that the first distance (Z) was set to 3 mm.

[0048] In Comparative Examples 1 to 5 of the fifth experiment, (ΔZ / Z) was changed from 0% to 5%, and (ΔR / R) was changed from -5% to 5%. In Examples 1 to 20 of the first experiment, (ΔZ / Z) was changed from 6% to 50%, and (ΔR / R) was changed from 6% to 50%.

[0049] The yields of Examples 1 to 20 in the fifth experiment (42% to 88%) were significantly higher than the yields of Comparative Examples 1 to 5 in the fifth experiment (13% to 35%), and sufficient effects were obtained. In Examples 1 to 20, 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50% were satisfied.

[0050] Furthermore, in Examples 9, 10, 15, 19, and 20, yields of 80% or more were obtained, and even more significantly excellent effects were obtained. In these Examples, 0.014≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied. In Examples 5, 9, 10, 13, 14, 15, 17, 18, 19, and 20, yields of 70% or more were obtained, and in these Examples, 0.01≦(ΔR / R)×(ΔZ / Z)≦0.25 was satisfied.

[0051] (Sixth Experiment) FIG. 8 is a table showing the results of the sixth experiment.

[0052] In the sixth experiment, the liquid raw material was cesium (Cs) azide (CsN ３ The only difference from the fifth experiment is that the above-mentioned solution was dissolved in water.

[0053] In Examples 1 to 10 of the sixth experiment, (ΔZ / Z) was changed from 6% to 50%, and (ΔR / R) was changed from 6% to 50%.

[0054] The yields (45% to 87%) of Examples 1 to 10 of the sixth experiment were significantly higher than those of Comparative Examples 1 to 5 of the fifth experiment, and sufficient effects were obtained. Examples 1 to 10 of the sixth experiment satisfied the conditions of 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50%.

[0055] Furthermore, in Example 10 of the sixth experiment, a yield of 80% or more was obtained, and an even more remarkably excellent effect was obtained. In this example, (ΔR / R) × (ΔZ / Z) = 0.25. In Examples 8, 9, and 10, a yield of 70% or more was obtained, and in these examples, 0.01 ≦ (ΔR / R) × (ΔZ / Z) ≦ 0.25 was satisfied.

[0056] In Examples 1 to 20 of the first, third, and fifth experiments, the alkali metal was rubidium, and the thickness of the opening end surface on the first portion P1 side located at the top of the through-hole 50H was 1 mm ２ The number of rubidium atoms per １５ In the measurement, the open end face was observed under a microscope, and it was assumed that at least one layer of rubidium atoms existed within the area of ​​rubidium deposition confirmed by visual observation. The density of rubidium was 1.53 g / cm ３ It is believed that when the number of rubidium atoms is small, adhesion of the second transparent substrate is not hindered, and the yield is improved.

[0057] In Examples 1 to 20 in the second, fourth, and sixth experiments, the alkali metal was cesium, and the thickness of the through-hole was 1 mm ２ The number of cesium atoms per １５ In the measurement, the open end face was observed under a microscope, and it was assumed that at least one layer of cesium atoms existed within the visually confirmed cesium adhesion area. The density of cesium was 1.93 g / cm ３ It is believed that when the number of cesium atoms is small, the adhesion of the second transparent substrate is not hindered, and the yield is improved.

[0058] The gas cell described above can be modified in many ways.

[0059] FIG. 9A is a vertical cross-sectional view of the gas cell, and FIG. 9B is a horizontal cross-sectional view of the gas cell.

[0060] In the gas cell GC of this example, the planar shape of the first portion P1 is circular, and the planar shape of the second portion P2 is elliptical. Compared to the gas cell shown in Figure 2, only the planar shape of the second portion P2 is different, and the other configurations are the same.

[0061] The first portion P1 has a first inner wall surface located at a first radius (R) from the center of gravity G in a plan view. The second portion P2 has a second inner wall surface H2 located at a distance from the center of gravity G in a plan view that is a first dimension (ΔR) greater than the first radius (R). The major axis of the ellipse of the second portion P2 is (R + ΔR), and the minor axis of the ellipse is (R). In this example, too, it is believed that a certain degree of effectiveness in suppressing the creep-up of alkali metals can be achieved if the above-mentioned relationships 1 mm ≦ Z ≦ 3 mm, 6% ≦ ΔR / R ≦ 50%, and 6% ≦ ΔZ / Z ≦ 50% are satisfied. This is because the structure of the longitudinal cross section passing through the major axis is the same as that in FIG. 2.

[0062] 2, the dimension in the X-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52) is X1, but the dimension in the X-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52) in this example is X2 (<X1). Furthermore, X2 is smaller than the dimension in the Y-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52). In other words, by reducing the dimension in the X-axis direction of the second portion P2, the gas cell GC can be made smaller.

[0063] FIG. 10A is a vertical cross-sectional view of the gas cell, and FIG. 10B is a horizontal cross-sectional view of the gas cell.

[0064] In the gas cell GC of this example, the first portion P1 has a circular planar shape, and the second portion P2 also has a circular planar shape, but the second portion P2 is provided on the first transparent substrate 51. Compared to the gas cell shown in Figure 2, only the formation position of the second portion P2 is different, and the other configurations are the same.

[0065] The first portion P1 has a first inner wall surface located at a distance of a first radius (R) from the center of gravity G in a plan view. The second portion P2, which is a recess formed in the first transparent substrate 51, has a second inner wall surface H2 located at a distance from the center of gravity G in a plan view that is a first dimension (ΔR) greater than the first radius (R). The radius of the ellipse of the second portion P2 is (R + ΔR). In this example, too, it is believed that a certain degree of effectiveness in suppressing the creep-up of alkali metals can be achieved if the above-mentioned relationships 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50% are satisfied. This is because the longitudinal cross-sectional structure of the through hole 50H is the same as that shown in FIG. 2.

[0066] 11A is a vertical cross-sectional view of the gas cell, and FIG. 11B is a horizontal cross-sectional view of the gas cell.

[0067] In the gas cell GC of this example, the planar shape of the first portion P1 is circular, and the planar shape of the second portion P2 is elliptical. Compared to the gas cell shown in Figure 10, only the planar shape of the second portion P2 is different, and the other configurations are the same.

[0068] The first portion P1 has a first inner wall surface located at a distance of a first radius (R) from the center of gravity G in a planar view. The second portion P2, which is a recess formed in the first transparent substrate 51, has a second inner wall surface H2 located at a distance from the center of gravity G in a planar view that is a first dimension (ΔR) greater than the first radius (R). The major axis of the ellipse of the second portion P2 is (R + ΔR), and the minor axis of the ellipse is (R). In this example, too, it is believed that a certain degree of effectiveness in suppressing the creep-up of alkali metals can be achieved if the above-mentioned relationships 1 mm ≦ Z ≦ 3 mm, 6% ≦ ΔR / R ≦ 50%, and 6% ≦ ΔZ / Z ≦ 50% are satisfied. This is because the structure of the longitudinal cross section passing through the major axis is the same as that in FIG. 2.

[0069] 2, the dimension in the X-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52) is X1, but in this example, the dimension in the X-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52) is X2 (<X1). In other words, by reducing the dimension in the X-axis direction of the second portion P2, the gas cell GC can be made smaller. Furthermore, X2 is smaller than the dimension in the Y-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52).

[0070] 12A is a horizontal cross-sectional view of the gas cell, and FIG. 12B is a horizontal cross-sectional view of the gas cell.

[0071] 12A, the second portion P2 is formed in the substrate 50. The first portion P1 has a circular planar shape, and the second portion P2 has an elliptical planar shape corresponding to both ends in the major axis direction. Compared to the gas cell shown in FIG. 9, only the planar shape of the second portion P2 is different; the other configurations are the same.

[0072] The first portion P1 has a first inner wall surface located at a first radius (R) from the center of gravity G in a plan view. The second portion P2 has a second inner wall surface H2 located at a distance from the center of gravity G in a plan view that is a first dimension (ΔR) greater than the first radius (R). The major axis of the ellipse of the second portion P2 is (R + ΔR), and the minor axis of the ellipse is smaller than the first radius (R). In this example, too, it is believed that a certain degree of effectiveness in suppressing the creep-up of alkali metals can be achieved if the above-mentioned relationships 1 mm ≦ Z ≦ 3 mm, 6% ≦ ΔR / R ≦ 50%, and 6% ≦ ΔZ / Z ≦ 50% are satisfied. This is because the structure of the longitudinal cross section passing through the major axis is the same as that in FIG. 9.

[0073] 12B, the second portion P2 is formed in the first transparent substrate 51. The first portion P1 has a circular planar shape, and the second portion P2 has an elliptical planar shape whose minor axis is shorter than the first radius. Compared to the gas cell shown in FIG. 11, only the planar shape of the second portion P2 is different; the other configurations are the same.

[0074] The first portion P1 has a first inner wall surface located at a first radius (R) from the center of gravity G in a plan view. The second portion P2 has a second inner wall surface H2 located at a distance from the center of gravity G in a plan view that is a first dimension (ΔR) greater than the first radius (R). The major axis of the ellipse of the second portion P2 is (R + ΔR), and the minor axis of the ellipse is smaller than the first radius (R). In this example, too, it is believed that a certain degree of effectiveness in suppressing the creep-up of alkali metals can be achieved if the above-mentioned relationships 1 mm ≦ Z ≦ 3 mm, 6% ≦ ΔR / R ≦ 50%, and 6% ≦ ΔZ / Z ≦ 50% are satisfied. This is because the structure of the longitudinal cross section passing through the major axis is the same as that in FIG. 11.

[0075] In this example, the dimension in the X-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52) is X2 (<X1), and X2 is smaller than the dimension in the Y-axis direction of the substrate 50 (first transparent substrate 51, second transparent substrate 52), making it smaller.

[0076] 13A is a horizontal cross-sectional view of the gas cell, and FIG. 13B is a horizontal cross-sectional view of the gas cell.

[0077] 13A, the second portion P2 is formed in the substrate 50. The first portion P1 has a circular planar shape, and the second portion P2 has a planar shape that protrudes outward from the position of the first inner wall surface H1 of the first portion P1. In the figure, three protruding regions are shown on one end side in the Y-axis direction and three on the other end side, for a total of six protruding regions, but this number may be less than six or greater than six.

[0078] 13B , the second portion P2 is formed in the substrate 50. The first portion P1 has a circular planar shape, and the second portion P2 has a planar shape that protrudes outward from the position of the first inner wall surface H1 of the first portion P1. In the figure, a total of four protruding regions are shown: one on one end side and one on the other end side along a straight line in the XY plane, and one on one end side and one on the other end side along a straight line perpendicular to the straight line; however, this number may be less than four or greater than four.

[0079] The structures shown in Figures 13(A) and 13(B) differ only in the planar shape of the second portion P2, and are otherwise identical to the structure shown in Figure 2. That is, the first portion P1 has a first inner wall surface located at a first radius (R) from the center of gravity G in a planar view. The second portion P2 has a second inner wall surface H2 (protruding portion) located at a distance from the center of gravity G in a planar view that is a first dimension (ΔR) greater than the first radius (R). The diameter dimension including the protruding amount of the second portion P2 is (R + ΔR). In this example, too, it is believed that a certain degree of effectiveness in suppressing alkali metal creep-up can be achieved if the above-mentioned relationships 1 mm ≤ Z ≤ 3 mm, 6% ≤ ΔR / R ≤ 50%, and 6% ≤ ΔZ / Z ≤ 50% are satisfied. This is because the structure of a vertical cross section passing through the protruding portion is the same as that in Figure 2.

[0080] FIG. 14 is a vertical cross-sectional view of the gas cell.

[0081] In the gas cell GC of this example, the first portion P1 has a circular planar shape, and the second portion P2 also has a circular planar shape. The gas cell GC is identical to the gas cell shown in FIG. 2 except that the height position of the second portion P2 is near the center of the through-hole 50H in the Z-axis direction.

[0082] The first portion P1 has a first inner wall surface located at a first radius (R) from the center of gravity G in a plan view. The second portion P2 has a second inner wall surface H2 located at a distance from the center of gravity G in a plan view that is a first dimension (ΔR) greater than the first radius (R). The radius of the ellipse of the second portion P2 is (R + ΔR). In this example, too, it is believed that a certain degree of effect in suppressing the creeping up of alkali metals can be achieved if the above-mentioned relationships 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50% are satisfied. This is because the effect of the second portion P2 in suppressing the creeping up of alkali metals is believed to be similar to that in the case of FIG. 2.

[0083] In this example, the second inner wall surface H2 of the second portion is not in contact with the first transparent substrate 51, nor is it in contact with the second transparent substrate 52. On the other hand, in the structures shown in FIGS. 2 , 9 , 10 , 11 , 12 , and 13 , the second inner wall surface H2 of the second portion is in contact with the first transparent substrate 51. When the second inner wall surface H2 of the second portion is in contact with the first transparent substrate 51, the liquid raw material easily enters the extended portion defined by the first dimension (ΔR), and a significant effect of suppressing the creep-up of alkali metal can be expected. In all of the above-described embodiments, the second dimension (ΔZ) is constant throughout the entire region defining the first dimension (ΔR), facilitating control of the processing and shape of the recess and suppressing quality variation. A structure in which the second dimension (ΔZ) varies throughout the entire region defining the first dimension (ΔR) is also conceivable.

[0084] In this structure, the planar shape (horizontal cross-sectional shape) of the second portion can also be modified to an elliptical shape or other shapes as described above.

[0085] The atomic clock structure includes any of the gas cells described above, a laser element that directs laser light into the gas cell, and a photodetector that receives the laser light that has passed through the gas cell.

[0086] 15(A) is a front view of the atomic clock structure, FIG. 15(B) is a plan view of the atomic clock structure, and FIG. 15(C) is a side view of the atomic clock structure.

[0087] The atomic clock structure 100 includes a gas cell GC into which laser light is incident in the thickness direction of a substrate 50. The gas cell GC includes a through-hole 50H. The through-hole 50H is formed at least in the substrate 50, but may be partially formed in the first transparent substrate 51 and / or the second transparent substrate 52. The through-hole 50H is an internal space IS of the substrate 50, and is filled with a gas containing an alkali metal (e.g., rubidium or cesium). A first transparent substrate 51 is bonded and fixed to the lower surface of the substrate 50. A second transparent substrate 52 is bonded and fixed to the upper surface of the substrate 50. The first transparent substrate 51 closes one open end of the through-hole 50H. The second transparent substrate 52 closes the other open end of the through-hole 50H. The gas cell GC includes a plate-shaped substrate 50 having an internal space IS filled with gas.

[0088] The material of the substrate 50 can be an insulator (glass or resin), a semiconductor (e.g., Si), or a metal (e.g., containing Cu, Al, or Fe). In this example, the material of the substrate 50 is silicon (Si). The first transparent substrate 51 and the second transparent substrate 52 are made of a material that is transparent to the laser light from the laser element 3. One example of a material for the first transparent substrate 51 and the second transparent substrate 52 is glass. An adhesive can be used to fix the elements, but if either the substrate 50 or the transparent substrate is made of a material that melts in response to heat, they can also be bonded by applying heat and pressure to their interface.

[0089] The gas cell GC has a laser light inlet optically coupled to the internal space IS in a first surface SE located at one end of the substrate 50 in the thickness direction (Z-axis direction). This laser light inlet is the opening on the light incident side of the through-hole 50H or the laser light incident surface of the first transparent substrate 51 that closes the through-hole 50H, and this opening end face is located within the first surface SE. The first surface SE includes the interface between the first transparent substrate 51 and the gas cell GC. A first spacer portion SP1 of the first holder HD1 is fixed to the first surface SE of the gas cell GC via a first resin layer 61.

[0090] The gas cell GC has a laser light emission port optically coupled to the internal space IS in a second surface SX located at the other end of the substrate 50 in the thickness direction (Z-axis direction). This laser light emission port is the opening on the light emission side of the through-hole 50H or the laser light emission surface of the second transparent substrate 52 that closes the through-hole 50H, and this opening end face is located within the second surface SX. The second surface SX includes the interface between the second transparent substrate 52 and the gas cell GC. The second spacer portion SP2 of the second holder HD2 is fixed to the second surface SX of the gas cell GC via a second resin layer 62.

[0091] The laser element 3 is fixed to the inner surface of the first holder HD1. The photodetector 4 is disposed at a position where the laser light that has passed through the gas cell GC is incident, and receives the laser light. The laser light emitted from the laser element 3 travels along the Z-axis direction (thickness direction of the substrate 50), transmits through the first transparent substrate 51, passes through the through-hole 50H formed in the substrate 50, transmits through the second transparent substrate 52, and reaches the photodetector 4.

[0092] The first spacer portion SP1 of the first holder HD1 can define the distance (including the thickness of the first resin layer 61) between the holder inner surface on which the submount 31 is provided and the first surface SE of the substrate 50 on the laser light incident side. The holder inner surface (XY plane) is the inner surface of the first main body portion B1. The pair of first spacer portions SP1 each extend from the holder inner surface (XY plane) in a direction toward the substrate 50. The submount 31 is located between the pair of first spacer portions SP1. A heat sink 11 (substrate) is provided on the underside (-Z direction side) of the first main body portion B1. The back surface (XY plane) of the first main body portion B1 of the first holder HD1 is fixed to the surface of the heat sink 11 with an adhesive or the like.

[0093] The shape of the second holder HD2 can be the same as the shape of the first holder HD1. The second spacer portion SP2 of the second holder HD2 can define the distance (including the thickness of the second resin layer 62) between the holder inner surface on which the photodetector 4 is provided and the second surface SX on the laser light emission side of the substrate 50. The holder inner surface (XY plane) is the inner surface of the second main body portion B2. The pair of second spacer portions SP2 each extend from the position of the holder inner surface (XY plane) in a direction toward the substrate 50. The photodetector 4 is located between the pair of second spacer portions SP2.

[0094] The atomic clock structure 100 includes a heat sink 11 to which a first holder HD1 is fixed, and the first holder HD1 includes a first opening OP1 that connects the space in which the laser element 3 is arranged to the outside of the first holder HD1. In other words, no holder material is located on an extension line in the X-axis direction within the first opening OP1. This also improves the lateral heat dissipation effect.

[0095] The second holder HD2 has a second opening OP2 that connects the space in which the photodetector 4 is arranged to the outside of the second holder HD2. In other words, no holder material is located on the extension line of the X-axis direction within the second opening OP2. This also improves the heat dissipation effect on the photodetector 4 side. Of course, this heat is transferred to the heat sink 11 due to the thermal conductivity of the first holder HD1 and the second holder HD2 themselves.

[0096] As described above, the atomic clock structure comprises a first holder HD1 having an inner surface to which the laser element 3 is fixed, fixed to a first transparent substrate 51, and opening in a direction perpendicular to the thickness direction of the laser element 3, and a second holder HD2 having an inner surface to which the photodetector 4 is fixed, fixed to a second transparent substrate 52, and opening in a direction perpendicular to the thickness direction of the photodetector 4.

[0097] 16(A) is a front view of the atomic clock structure, FIG. 16(B) is a plan view of the atomic clock structure, and FIG. 16(C) is a side view of the atomic clock structure.

[0098] This atomic clock structure 100 differs from the atomic clock structure 100 shown in FIGS. 15(A) to 15(C) in the direction of the opening of the holder.

[0099] In the first holder HD1, a pair of first spacer portions SP1 extend along the longitudinal direction (Y-axis direction) of the heat sink 11 in a planar view (when the XY plane is viewed from the Z-axis direction), and the space between these first spacer portions SP1 is open in the Y-axis direction, forming a first opening OP1.

[0100] In the second holder HD2, a pair of second spacer portions SP2 extend along the longitudinal direction (Y-axis direction) of the heat sink 11 when viewed in a plane, and the space between these second spacer portions SP2 is open in the Y-axis direction, forming a second opening OP2.

[0101] Other structures in this atomic clock structure 100 are the same as those in the atomic clock structure 100 shown in FIGS. 15(A) to 15(C).

[0102] 17A is a front view of the atomic clock structure, FIG. 17B is a plan view of the atomic clock structure, and FIG. 17C is a side view of the atomic clock structure.

[0103] The atomic clock structure 100 includes a first holder HD1 and a second holder HD2 fixed onto a heat sink 11. The thickness direction of the heat sink 11 is the Z-axis direction, the longitudinal direction is the Y-axis direction, and the width direction is the X-axis direction. In this example, the heat sink 11 has a larger longitudinal dimension than a width dimension in a plan view.

[0104] The first holder HD1 includes a first main body portion B1 and a pair of first spacer portions SP1 extending from the first main body portion B1 toward the substrate 50 (Y-axis direction). The lower surfaces of the first main body portion B1 and the first spacer portions SP1 are fixed to the heat sink 11. A submount 31 and a laser element 3 are disposed in the space between the pair of first spacer portions SP1. The submount 31 is fixed on the inner surface (XZ plane) of the first holder HD1. As in the above example, the laser element 3 is fixed on the submount 31. As a result, the laser element 3 is fixed to the inner surface (XZ plane) of the first holder HD1.

[0105] The second holder HD2 includes a second main body portion B2 and a pair of second spacer portions SP2 extending from the second main body portion B2 toward the substrate 50 (in the -Y-axis direction). The lower surfaces of the second main body portion B2 and the second spacer portions SP2 are fixed to the heat sink 11. The photodetector 4 is disposed in the space between the pair of second spacer portions SP2. The photodetector 4 is fixed on the inner surface (XZ plane) of the second holder HD2.

[0106] The atomic clock structure 100 includes a gas cell GC into which laser light is incident in the thickness direction of a substrate 50. The gas cell GC includes a through-hole 50H. The through-hole 50H is formed at least in the substrate 50, but may be partially formed in the first transparent substrate 51 and / or the second transparent substrate 52. The through-hole 50H is an internal space IS of the substrate 50, and is filled with a gas containing an alkali metal (e.g., rubidium or cesium). A first transparent substrate 51 is bonded and fixed to one side of the substrate 50. A second transparent substrate 52 is bonded and fixed to the other side of the substrate 50. The first transparent substrate 51 closes one open end of the through-hole 50H. The second transparent substrate 52 closes the other open end of the through-hole 50H. The gas cell GC includes a plate-shaped substrate 50 having an internal space IS filled with gas.

[0107] The material of the substrate 50 can be an insulator (glass or resin), a semiconductor (e.g., Si), or a metal (e.g., containing Cu, Al, or Fe). In this example, the material of the substrate 50 is silicon (Si). The first transparent substrate 51 and the second transparent substrate 52 are made of a material that is transparent to the laser light from the laser element 3. One example of a material for the first transparent substrate 51 and the second transparent substrate 52 is glass. An adhesive can be used to fix the elements, but if either the substrate 50 or the transparent substrate is made of a material that melts in response to heat, they can also be bonded by applying heat and pressure to their interface.

[0108] The gas cell GC has a laser light inlet optically coupled to the internal space IS in a first surface SE located at one end of the substrate 50 in the thickness direction (Y-axis direction). This laser light inlet is the opening on the light incident side of the through-hole 50H or the laser light incident surface of the first transparent substrate 51 that closes the through-hole 50H, and this opening end face is located within the first surface SE. The first surface SE includes the interface between the first transparent substrate 51 and the gas cell GC. The first spacer portion SP1 of the first holder HD1 is fixed to the first surface SE of the gas cell GC via a first resin layer 61.

[0109] The gas cell GC has a laser light emission port optically coupled to the internal space IS in a second surface SX located at the other end of the substrate 50 in the thickness direction (Y-axis direction). This laser light emission port is the opening on the light emission side of the through-hole 50H or the laser light emission surface of the second transparent substrate 52 that closes the through-hole 50H, and this opening end face is located within the second surface SX. The second surface SX includes the interface between the second transparent substrate 52 and the gas cell GC. The second spacer portion SP2 of the second holder HD2 is fixed to the second surface SX of the gas cell GC via a second resin layer 62.

[0110] The photodetector 4 is disposed at a position where the laser light that has passed through the gas cell GC is incident. The laser light emitted from the laser element 3 travels along the Y-axis direction (the thickness direction of the substrate 50), passes through the first transparent substrate 51, passes through the through-hole 50H formed in the substrate 50, passes through the second transparent substrate 52, and reaches the photodetector 4.

[0111] The first holder HD1 has a first opening OP1 that connects the space in which the laser element 3 is arranged to the outside of the first holder HD1. No holder material is located on the extension line in the Z-axis direction within the first opening OP1, but the heat sink 11 is located there. This improves the heat dissipation effect of the first holder HD1.

[0112] The second holder HD2 has a second opening OP2 that connects the space in which the photodetector 4 is arranged to the outside of the second holder HD2. No holder material is located on the extension line in the Z-axis direction within the second opening OP2, but the heat sink 11 is located there. This also improves the heat dissipation effect of the second holder HD2.

[0113] FIG. 18(A) is a front view of the atomic clock structure, and FIG. 18(B) is a plan view of the atomic clock structure.

[0114] The gas cell provided with the first and second holders is referred to as a gas cell unit UT. The gas cell unit UT can be fixed to a heat sink 11, and a heater for adjusting the temperature and a coil (or a permanent magnet) for generating a magnetic field inside the gas cell can be arranged around the gas cell unit UT.

[0115] In the atomic clock structure, a third heater H3 and a fourth heater H4 can be arranged at both ends of the gas cell unit UT in the Y-axis direction. A third coil (or permanent magnet) CL3 can be arranged outside the third heater H3. A fourth coil (or permanent magnet) CL4 can be arranged outside the fourth heater H4.

[0116] In the atomic clock structure, a fifth heater H5 and a sixth heater H6 can be arranged at both ends of the gas cell unit UT in the X-axis direction. A fifth coil (or permanent magnet) CL5 can be arranged outside the fifth heater H5. A sixth coil (or permanent magnet) CL6 can be arranged outside the sixth heater H6.

[0117] The seventh heater H7 and the eighth heater H8 can be disposed inside the gas cell unit UT. As described above, heaters and coils (or permanent magnets) can also be disposed at both ends of the gas cell unit UT in the Z-axis direction.

[0118] The arrangement of the heater and coil (permanent magnet) is not limited to the above, and several of the above elements may be selected and arranged around the gas cell unit UT as needed. The heater may be a resistance heating system, but infrared or induction heating may also be used. The heater arrangement is not limited to the above structure. The coil structure may be a solenoid coil, a spiral coil, a planar coil, or the like, and various arrangements may be adopted. The permanent magnet may also be a thin-film magnet. Known types of permanent magnets include alnico magnets (an alloy containing iron, aluminum, nickel, and cobalt), ferrite magnets, neodymium magnets (an alloy containing iron, neodymium, and boron), and samarium-cobalt magnets (an alloy containing samarium and cobalt).

[0119] The first holder HD1 and the second holder HD2 preferably have high electrical resistivity and high thermal conductivity. That is, these holders preferably have an electrical resistivity of 15 μΩcm or more and a thermal conductivity of 20 W / mK or more. Examples of materials that satisfy these conditions include silicon, alumina, silicon nitride, and silicon carbide. This allows electrode pads and wiring patterns to be formed on the holders, and heat from the holders can be transferred to the heat sink 11. That is, wiring patterns are provided on the first holder HD1, and these wiring patterns are electrically connected to the laser element 3 via bonding wires.

[0120] It is preferable that the first holder HD1 has a thermal conductivity of at least 5 W / mK or more. If the material satisfies this condition, heat can be dissipated efficiently. As a material that satisfies this condition, the first holder HD1 and the second holder HD2 can contain ceramic. As this ceramic or high resistance material (insulating material), aluminum nitride (AlN), silicon carbide (SiC), alumina (Al ２ O ３ ), silicon nitride (Si ３ N ４ The material may include at least one material selected from the group consisting of:

[0121] The first resin layer 61 and the second resin layer 62 can contain a thermosetting resin. The atomic clock structure includes a plate-shaped substrate 50 having an internal space IS filled with gas, a gas cell GC having a laser light inlet optically coupled to the internal space IS in a surface located at an end of the substrate 50 in the thickness direction, a first holder HD1 fixed to the surface of the gas cell GC, a laser element 3 fixed to the inner surface of the first holder HD1, and a photodetector 4 arranged at a position where laser light passing through the gas cell GC is incident. The atomic clock structure 100 includes a heat sink 11 to which the first holder HD1 is fixed, and the first holder HD1 has an opening OP1 that connects the space in which the laser element 3 is arranged to the outside of the first holder HD1, thereby increasing the heat dissipation effect.

[0122] As described above, the gas cell and atomic clock structure described above can be miniaturized. If an atomic clock can be miniaturized sufficiently, it can be mounted in a variety of devices. For example, a miniaturized atomic clock can be mounted in a mobile phone, an automobile, a robot, a drone, a global positioning system (GPS), a security system, or the like.

[0123] Although various exemplary embodiments have been described above, various omissions, substitutions, and modifications may be made without being limited to the above-described exemplary embodiments. Furthermore, elements from different embodiments may be combined to form other embodiments. It will be understood from the above description that various embodiments of the present disclosure have been described herein for illustrative purposes, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

[0124] 3...laser element, 4...photodetector, 11...heat sink (substrate), 50...substrate (first transparent substrate 51, second transparent substrate 52), 50H...through hole, 51...first transparent substrate, 52...second transparent substrate, 100...atomic clock structure, BY1...first surface, BY2...second surface.

Claims

1. A substrate comprising: a first transparent substrate fixed to a first surface of the substrate; and a second transparent substrate fixed to a second surface of the substrate; a through hole penetrating the substrate between the first transparent substrate and the second transparent substrate, the through hole containing a gas containing an alkali metal; the through hole comprising: a first portion having a first inner wall surface at a position distanced from a center of gravity in a plan view by a first diameter (R); and a second portion having a second inner wall surface at a position distanced from the center of gravity in a plan view by a first dimension (ΔR) greater than the first diameter (R); wherein the first diameter (R), the first dimension (ΔR), a first distance (Z) defined between the first transparent substrate and the second transparent substrate at the position of the through hole, and a second dimension (ΔZ) of the second portion along the thickness direction of the substrate satisfy the following: 1 mm≦Z≦3 mm, 6%≦ΔR / R≦50%, and 6%≦ΔZ / Z≦50%. Gas cell for atomic clock.

2. The atomic clock gas cell according to claim 1, wherein the following condition is satisfied: 0.01≦(ΔR / R)×(ΔZ / Z)≦0.

25.

3. The alkali metal is rubidium, and the thickness of the through hole is 1 mm ２ The number of rubidium atoms per １５ The atomic clock gas cell according to claim 1 , wherein the number of atoms is equal to or less than 1.

4. The alkali metal is cesium, and the thickness of the through hole is 1 mm at the opening end surface on the first portion side. ２ The number of cesium atoms per １５ The atomic clock gas cell according to claim 1 , wherein the number of atoms is equal to or less than 1.

5. The atomic clock gas cell according to claim 1, wherein the second portion is provided on the substrate.

6. The atomic clock gas cell according to claim 1, wherein the first portion has a circular planar shape, and the second portion has a circular planar shape.

7. The atomic clock gas cell according to claim 1, wherein the first portion has a circular planar shape, and the second portion has an elliptical planar shape.

8. The atomic clock gas cell according to claim 1, wherein the second portion is provided on the first transparent substrate.

9. The atomic clock gas cell according to claim 1, wherein the first portion has a circular planar shape, and the second portion has a planar shape that protrudes outward from the position of the inner wall surface of the first portion.

10. The atomic clock gas cell according to claim 1, wherein the second dimension (ΔZ) is constant over the entire area defining the first dimension (ΔR).

11. The atomic clock gas cell according to claim 1, wherein the second inner wall surface of the second portion is in contact with the first transparent substrate.

12. The atomic clock gas cell according to claim 1, wherein the second inner wall surface of the second portion is not in contact with the first transparent substrate and is not in contact with the second transparent substrate.

13. An atomic clock structure comprising: a gas cell according to any one of claims 1 to 12; a laser element for irradiating laser light onto said gas cell; and a photodetector for receiving the laser light that has passed through said gas cell.

14. An atomic clock structure as described in claim 13, comprising: a first holder having an inner surface to which the laser element is fixed, fixed to the first transparent substrate, and opening in a direction perpendicular to the thickness direction of the laser element; and a second holder having an inner surface to which the photodetector is fixed, fixed to the second transparent substrate, and opening in a direction perpendicular to the thickness direction of the photodetector.

Images