Evaluation method and atomic clock device

Abstract

To provide a method of evaluating a characteristic of a laser beam where a cost and a device size are suppressed.SOLUTION: An evaluation method evaluates a characteristic of a laser beam in an optical device. The optical device contains: a laser light source that emits the laser beam; a detector that detects a light amount of the laser beam; and an optical shutter that switches an irradiation and a cutoff of the laser beam to the detection device. An evaluation method contains steps of: transmitting a command for switching the irradiation and the cutoff to the optical shutter; acquiring a secular change of a light amount detected by the detection device during a time when a switching is completed from the transmission of the command; and evaluating the characteristic of the laser beam on the basis of the secular change to be acquired.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an evaluation method and an atomic clock device, and more particularly to an evaluation method for evaluating characteristics of laser light in an optical device and an atomic clock including a light source device that irradiates laser light to be evaluated by the evaluation method. [Background technology]

[0002] JP 2020-79854 A (patent document) discloses an atomic clock light source system for generating laser light used in an atomic clock. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-79854 A Summary of the Invention [Problem to be solved by the invention]

[0004] In devices that have a laser light source that irradiates laser light, such as an atomic clock device, the characteristics of the laser light, such as the position and angle, can change due to heat and pressure continuously applied to each component, or sudden impacts such as dropping or contact. If the characteristics of the laser light, such as the position and angle, change, malfunctions will occur in devices that use laser light, such as an atomic clock device. For this reason, it is necessary to evaluate the characteristics of the laser light.

[0005] Changes in the laser light characteristics can sometimes be detected based on signals from the device, but in order to evaluate how the laser light characteristics have changed, it was necessary to visually inspect the laser light or measure the beam shape of the laser light with a beam profiler.

[0006] When evaluating laser light visually, if the light source is installed inside the housing of the device, it is necessary to take the light source outside by removing the housing, which is costly. When evaluating by measuring the beam shape, the beam profiler can be installed inside the housing in advance, so there is no need to remove the housing. However, since the beam profiler needs to be installed on the optical axis of the laser light, a separate optical path for observation needs to be prepared, which increases the cost and size of the device.

[0007] An object of the present disclosure is to provide a method for evaluating the characteristics of laser light while reducing costs and device size. [Means for solving the problem]

[0008] The evaluation method disclosed herein evaluates characteristics of laser light in an optical device. The optical device includes a laser light source that emits laser light, a detector that detects the laser light, and an optical shutter that switches between irradiating and blocking the laser light to the detector. The evaluation method includes a step of transmitting a command to the optical shutter to switch between irradiating and blocking the laser light, a step of acquiring a change over time in the output of the detector from the time the command is transmitted until the switching is completed, and a step of evaluating the characteristics of the laser light based on the acquired change over time.

[0009] The atomic clock device of the present disclosure includes an atom generating device that emits an atomic beam or ionized atoms, a plurality of light source devices that irradiate the atoms emitted from the atom generating device with laser light, a detector that detects the laser light irradiated from each of the plurality of light source devices before the laser light is irradiated to the atoms, and a control device. Each of the plurality of light source devices includes a laser light source that emits laser light, and an optical shutter that switches between irradiating and blocking the laser light to the detector. The control device transmits a command to the optical shutter to switch between irradiation and blocking for each of the plurality of light source devices, obtains a change over time in the output of the detector from the time the command is transmitted until the switching is completed, and evaluates characteristics of the laser light based on the obtained change over time. Effect of the Invention

[0010] According to the present disclosure, the characteristics of laser light can be evaluated using optical components already included in an optical device or an atomic clock device, thereby reducing costs and device size. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of an atomic clock device. [Diagram 2] 1 is a flowchart of an evaluation method. [Diagram 3] 11A and 11B are diagrams showing a waveform indicating a change in the amount of light over time and a state from the start of blocking to the completion of blocking. [Figure 4] 11A and 11B are diagrams showing a waveform indicating a change in the amount of light over time and a state from the start of blocking to the completion of blocking. [Diagram 5] 1A and 1B are diagrams for explaining the structure of an acousto-optic element. [Figure 6] 11A and 11B are diagrams showing a waveform indicating a change in the amount of light over time and a state from the start of blocking to the completion of blocking. [Figure 7] 11A and 11B are diagrams showing a waveform indicating a change in the amount of light over time and a state from the start of blocking to the completion of blocking. [Figure 8] FIG. 13 is a schematic diagram showing a schematic configuration of an optical device according to a modified example. [Figure 9] 13 is a flowchart of an evaluation method according to a modified example. [Figure 10] FIG. 2 is a schematic diagram showing a state when laser light is diffused. [Figure 11] FIG. 2 is a schematic diagram showing a state in which laser light is focused. [Figure 12] 1 is a schematic diagram showing a state when the optical axis of a laser beam is bent. FIG. [Figure 13] FIG. 2 is a schematic diagram showing a state when the optical axis of a laser beam is translated; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0013] [Overall configuration of atomic clock device] 1 is a schematic diagram showing the general configuration of an atomic clock device. The atomic clock device 100 detects the resonance frequency specific to atoms with high accuracy, and measures time by defining the time it takes for the wave to oscillate a specific number of times as one second. The atomic clock device 100 includes an atom generating device 110, multiple light source devices 30, a vacuum vessel 130, an atom irradiation unit 134, a fluorescence detector 162, a detector 16, a control device 180, an input device 171, and a display device 172. The multiple light source devices 30 include a cooling light source 32, an excitation light source 34, a detection light source 36, and an optical lattice light source 38.

[0014] The atom generator 110 heats an atomic base material such as strontium, ytterbium, or mercury to generate an atomic gas, which is then radiated as an atomic beam to an atom irradiation unit 134 disposed within a vacuum vessel 130 .

[0015] Each of the light source devices 30 radiates a laser beam B into the vacuum vessel 130. In the following, the laser beam may be referred to as a "laser," a "beam," or a "laser beam." The laser beam B radiated into the vacuum vessel 130 is guided to the atomic irradiation unit 134 or the detector 16 by the optical path switcher 136. Although not shown, a plurality of optical path switches 136 and a plurality of detectors 16 are provided so as to correspond to each of the light source devices 30. The atomic clock device 100 does not need to include a plurality of detectors 16, and may include only one detector 16. For example, the control device 180 may control the optical path switcher 136 and the like to irradiate the detector 16 with the plurality of laser beams B emitted from the light source devices 30 one by one.

[0016] The light source device 30 includes a laser light source 12 and an optical shutter 14. In other words, it can be said that the atomic clock device 100 is equipped with an optical device 10 composed of at least the laser light source 12, the optical shutter 14, and a detector 16. The laser light source 12 emits laser light B. The optical shutter 14 is disposed on the optical path of the laser light B emitted from the laser light source 12, and switches between irradiating and blocking the laser light B emitted from the laser light source 12 to the detector 16. A mechanical shutter, an acousto-optical element, or the like can be used as the optical shutter 14.

[0017] The detector 16 is, for example, a photodiode, which detects the laser light B and outputs a detection value corresponding to the amount of light of the laser light B to the control device 180 as an output value. Since the output value output by the laser light B to the control device 180 corresponds to the amount of light, the output value is also simply referred to as the amount of light hereinafter. The response speed of the detector 16 is preferably such that the detector 16 can detect the laser light B multiple times from when the optical shutter 14 starts to switch between irradiation and blocking to when it completes the switching. Specifically, the response speed of the detector 16 is preferably less than 1 ms, and more specifically, is preferably 0.1 μs or more. The detection result of the detector 16 is used for stabilizing the amount of light of the laser light B and for noise cancellation during transmission.

[0018] The atomic clock device 100 is an optical lattice clock, and creates an optical lattice using laser light B that is controlled to a specific wavelength called the "magic wavelength" emitted from an optical lattice light source 38. Conceptually, an optical lattice is a spatial interference pattern in which depressions in the electric potential are formed at regular intervals, and atoms are trapped within these depressions.

[0019] The atomic clock device 100 decelerates the atoms in the atomic beam by cooling the atoms using the laser light B emitted from the cooling light source 32. The atomic clock device 100 traps each of the decelerated atoms one by one in an optical lattice created by the laser light B emitted from the optical lattice light source 38 to prevent interaction between the atoms. The atomic clock device 100 irradiates the atoms captured one by one by the optical lattice with the laser light B emitted from the excitation light source 34 to excite the energy level of the atom. After exciting the energy level of the atom, the atomic clock device 100 irradiates the atom with the laser light B emitted from the detection light source 36. The laser light B irradiated from the detection light source 36 generates fluorescence having an intensity proportional to the energy transition probability of the atom.

[0020] The fluorescence detector 162 receives the fluorescence generated by the detection light source 36 and detects the intensity of the received fluorescence. The fluorescence detector 162 outputs a transition probability spectrum dependent on the excitation laser frequency and represented by the detected fluorescence intensity to the control device 180. The control device 180 identifies the resonance frequency of the atom from the transition probability spectrum received from the fluorescence detector 162, and measures time based on the resonance frequency.

[0021] 1 again, the control device 180 includes a processor 182 and a memory 184. The processor 182 is, for example, a CPU, and is an arithmetic circuit that executes predetermined arithmetic processing described in a program. The memory 184 includes a non-volatile memory or a volatile memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and / or a large-capacity storage device such as a HDD (Hard Disc Drive) or an SSD (Solid State Drive). The processor 182 reads out the programs and data stored in the memory 184, controls each part that constitutes the atomic clock device 100, and executes predetermined processing upon receiving detection results from the detector 16 and the fluorescence detector 162.

[0022] An input device 171 and a display device 172 are connected to the control device 180. The input device 171 is, for example, a keyboard, a mouse, a pointing device, a touch panel, etc., and receives operations by a user. The display device 172 is, for example, a liquid crystal display (LCD) or an organic EL (Electro Luminescence) display, etc., and displays various information stored in the memory 184.

[0023] Since the atomic clock device 100 is a device for measuring time, it is necessary for it to operate stably for a long time. In addition, since the atomic clock device 100 is controlled at the atomic level, high accuracy is required, and the state of each laser light needs to be monitored. In the atomic clock device 100, which requires high accuracy, removing the housing to visually evaluate the laser light not only requires high labor costs, but also involves touching the inside of the housing, which may lead to a decrease in measurement accuracy. In addition, when a beam profiler is installed, it is necessary to provide an observation optical path for each of the multiple light source devices 30, which increases the cost and size of the device.

[0024] Therefore, there is a demand for a method for evaluating the characteristics of laser light while suppressing costs such as operating costs and device costs and the size of the device. The following describes a method for evaluating the characteristics of laser light performed in the atomic clock device 100.

[0025] [Evaluation method] Fig. 2 is a flowchart of the evaluation method. Each process shown in Fig. 2 is executed by, for example, the control device 180. Note that a part or all of the processes shown in Fig. 2 may be executed by another control device connected to the control device 180. Each process shown in Fig. 2 is executed, for example, at a predetermined cycle, as an example.

[0026] In S101, the control device 180 transmits a command to the optical shutter 14 to block irradiation of the detector 16 with laser light.

[0027] In S102, the control device 180 acquires the detection results detected by the detector 16 from the time the command is sent until the blocking is completed, and acquires the change over time in the amount of light from the time the command is sent until the blocking is completed.

[0028] In S104, the control device 180 evaluates the characteristics of the laser light based on the acquired change over time. When the incident position of the laser light on the optical shutter 14, the irradiation range, etc. change while the shutter speed of the optical shutter 14 does not change, the timing when the laser light starts to be blocked, the time required from the start of blocking the laser light to the complete blocking of the laser light, etc. change. Therefore, the control device 180 can evaluate the characteristics of the laser light based on the change over time in the amount of light from the transmission of the blocking command to the completion of blocking.

[0029] In S104, the control device 180 executes S105 to S107. In S105, the control device 180 obtains a feature amount related to the light diameter of the laser light B at the optical shutter 14 from the change over time of the obtained light amount. In S106, the control device 180 obtains a feature amount related to the incident position of the laser light B on the optical shutter 14 from the change over time of the obtained light amount. A specific method of obtaining the feature amount will be described later with reference to FIG. 3 onwards.

[0030] In S107, the control device 180 compares the reference feature amount with the obtained feature amount to evaluate the characteristics of the laser light B. The reference feature amount is each feature amount obtained from the change over time acquired at the timing when the laser light is in the reference state. The reference feature amount does not need to be obtained based on the actual measured value of the change over time, and may be obtained by calculation based on the shutter speed of the optical shutter 14, the position of the optical axis of the laser light, the beam diameter of the laser light, etc. The reference state is a state when the setting is completed to obtain the desired laser light characteristics, such as a state when the setting of the optical device 10 is completed, a state when adjustment is completed, or a state at the time of delivery.

[0031] In S110, the control device 180 outputs the evaluation result obtained in S104, and ends the process. The output destination is, for example, the display device 172, the memory 184, etc. The control device 180 may notify an error or adjust the laser light based on the evaluation result stored in the memory 184.

[0032] As described above, by using this evaluation method, in the optical device 10 in which the laser light source 12, the optical shutter 14, and the detector 16 are arranged on the optical path of the laser light, the characteristics of the laser light can be evaluated using the optical components already included in the optical device 10, and various costs such as labor costs and device costs, as well as the size of the device, can be reduced. Furthermore, since the characteristics of the laser light can be monitored, the atomic clock device 100 can achieve stable operation for a long period of time. Furthermore, the detector 16, which is used to stabilize the amount of light of the laser light B and to cancel noise during transmission, can also be used to evaluate the characteristics of the laser light, thereby reducing the device costs.

[0033] 2, the control device 180 performs the evaluation based on the change over time in the amount of light obtained by outputting a signal to switch from irradiation to blocking to the optical shutter 14. Note that the control device 180 may also perform the evaluation based on the change over time in the amount of light obtained by outputting a signal to switch from blocking to irradiation to the optical shutter 14.

[0034] In addition, in S107, the control device 180 compares the reference feature amount with the obtained feature amount to evaluate the characteristics of the laser light B. The control device 180 may evaluate the characteristics of the laser light B based on the obtained feature amount. For example, the control device 180 may evaluate the characteristics of the laser light B, such as the beam diameter and the incident position, based on actual measurement values ​​of the feature amount related to the beam diameter and the feature amount related to the incident position, and setting values ​​of the optical device 10, such as the shutter speed of the optical shutter 14.

[0035] In addition, in S107, the control device 180 performs the evaluation based on the reference change over time, but the control device 180 may evaluate the characteristics of the laser light by comparing the changes over time of the light amount acquired at different timings. This allows the control device 180 to evaluate how the characteristics have changed.

[0036] [Evaluation results obtained from changes in light intensity over time] The evaluation results obtained from the change over time of the light amount will be described. Since a mechanical shutter or an acousto-optical element can be used as the optical shutter 14, the relationship between the waveform indicating the change over time of the light amount and the beam characteristics and the evaluation results obtained from the change over time of the light amount will be described below in the cases where the optical shutter 14 is the mechanical shutter 142 and the acousto-optical element 144. In the following, the output value (light amount) obtained in the state before (or when) an opening / closing command is issued to the optical shutter 14 will be referred to as the initial value, and the output value (light amount) obtained when the optical shutter 14 receives the opening / closing command and completely blocks or opens the light will be referred to as the final value. Note that, in the following, it will be described assuming that a blocking command has been issued to the optical shutter 14, so the initial value corresponds to the output value (light amount) obtained when the optical shutter 14 is completely open, and the final value corresponds to the output value (light amount) obtained when the laser light B is completely blocked by the optical shutter 14. It is to be noted that, if the fluctuation range of the light amount becomes equal to or smaller than a predetermined value and becomes a steady value within a predetermined period after the light amount starts to change, it can be determined that the laser light B is completely blocked by the optical shutter 14.

[0037] (Mechanical shutter) With reference to Fig. 3 and Fig. 4, the relationship between the waveform showing the change over time in the amount of light and the beam characteristics when mechanical shutter 142 is used as optical shutter 14 will be described. Fig. 3 and Fig. 4 are diagrams showing the waveform showing the change over time in the amount of light and the state from the start of blocking to the completion of blocking, respectively. For the waveforms in Fig. 3 and Fig. 4, the horizontal axis is time and the vertical axis is the amount of light of laser light B detected by detector 16. The waveform shown in Fig. 3 is a waveform obtained when the beam is placed at a reference position and is in a reference state where the beam diameter is within a specified range. On the other hand, the waveform shown in Fig. 4 is a waveform obtained when both the beam position and beam diameter are in an abnormal state where they are deviated from the reference state.

[0038] Mechanical shutter 142 shown in Figs. 3 and 4 is an aperture-type shutter, and includes outer frame 142b in which circular aperture 142a is formed, and aperture 142c. Mechanical shutter 142 can concentrically increase or decrease the size of aperture 142a or close aperture 142a by opening or closing aperture 142c. Mechanical shutter 142 irradiates detector 16 with laser light B by opening aperture 142c, and blocks irradiation of detector 16 with laser light B by closing aperture 142c and closing aperture 142a. In Figs. 3 and 4, a blocking command is issued to mechanical shutter 142. Note that since mechanical shutter 142 and detector 16 are separated from each other, a time lag occurs before detector 16 detects light that has passed through mechanical shutter 142. However, for ease of explanation, the light amount at each timing shown in FIG. 3 and FIG. 4 will be explained as corresponding to the state of mechanical shutter 142 at each timing.

[0039] 3, in the reference state, mechanical shutter 142 is positioned so that laser light B passes through center O of aperture 142a. Assume that control device 180 transmits a blocking command to mechanical shutter 142 at timing t0. In response to the command from control device 180, mechanical shutter 142 gradually narrows aperture 142c from timing t0 to timings t1, t2, t3, and t4. Accordingly, aperture 142a becomes smaller, and is completely closed at timing t4.

[0040] Next, the relationship between the opening 142a (or the diaphragm 142c) and the laser light B will be described. Even if the opening 142a becomes smaller, since there is a distance between the diaphragm 142c and the outer periphery of the laser light B, the laser light B is not blocked by the diaphragm 142c for a while. Therefore, the amount of light does not change until timing ts1. After that, when the diaphragm 142c starts to block the laser light B, the amount of light reaching the detector 16 decreases, so the amount of light gradually decreases. Then, when the diaphragm 142c completely closes the opening 142a at timing t4, the laser light B is completely blocked, and the detection value detected by the detector 16 becomes a minimum.

[0041] With reference to Fig. 4, a waveform showing a change over time in the amount of light in an abnormal state will be described. In the abnormal state shown in Fig. 4, the passing position of the laser light B is a position shifted from the center O of the opening 142a. The beam diameter of the laser light B is larger than the beam diameter of the laser light B in the reference state. The states of the diaphragm 142c at each of the timings t0 to t4 in Fig. 4 are the same as the states of the diaphragm 142c at each of the timings t0 to t4 in Fig. 3.

[0042] The passing position of laser light B is shifted from center O of aperture 142a. Therefore, the distance from aperture 142c to the outer periphery of laser light B when aperture 142c is fully opened is shorter in the abnormal state than in the reference state. Therefore, in the abnormal state, laser light B is partially blocked by aperture 142c at timing t1. Laser light B is almost blocked at timing t3 before mechanical shutter 142 completely blocks laser light B, and laser light B is completely blocked at timing te2 before timing t4 when aperture 142a is completely closed, and the detection value detected by detector 16 is minimized.

[0043] The delay time ta from the timing t0 when the control device 180 transmits the cutoff command to the timing tm when the light amount changes by a predetermined rate will be described. The timing tm when the light amount changes by a predetermined rate is the timing when the change amount dax with respect to the initial value as of the light amount (light amount at the timing t0) becomes a predetermined rate with respect to the total change amount dat from the initial value as of the light amount to the closing value ae. In other words, when the change amount dax from the initial value with respect to the total change amount dat is set as the change rate X, the delay time ta can be said to be the period from the timing t0 when the control device 180 transmits the cutoff command to the timing tm when the change rate X of the light amount becomes a predetermined value. In the example shown in Figs. 3 and 4, the timing when the change rate X of the light amount becomes 50% is set as the timing tm. The timing when the change rate X of the light amount becomes a predetermined value may be any time after the timing ts when the light amount starts to change, and the predetermined value can be set arbitrarily.

[0044] The amount of light is reduced by half by blocking a predetermined range in the incidence range of laser light B by aperture 144c. The delay time ta is determined by the area of ​​laser light B blocked per unit time (hereinafter, also simply referred to as the "blocked area") and the position where laser light B enters mechanical shutter 142. In other words, if the blocked area per unit time is the same in the abnormal state and the reference state, the delay time ta corresponds to a feature corresponding to the position where laser light B enters mechanical shutter 142. Therefore, if the blocked area per unit time is the same in the abnormal state and the reference state, control device 180 can evaluate how much the incidence position is shifted in the abnormal state by comparing delay time ta1 (the time from timing t0 to timing tm1) in the reference state with delay time ta2 (the time from timing t0 to timing tm2) in the abnormal state.

[0045] In this embodiment, the blocking area per unit time differs between the abnormal state and the reference state. This is because, as shown in the lower part of each of Figs. 3 and 4, in the reference state, the laser light B is blocked from the outer periphery, whereas in the abnormal state, the laser light B is blocked from one direction. Therefore, the control device 180 may obtain a rate of change (slope) of the light amount as a feature value representing the blocking area per unit time, and correct the delay time ta with the rate of change (slope) of the light amount. The control device 180 may set the corrected delay time ta' as a feature value corresponding to the position where the laser light B enters the mechanical shutter 142. The control device 180 may compare the corrected delay time ta'1 in the reference state with the corrected delay time ta'2 in the abnormal state to evaluate how much the incident position is shifted in the abnormal state.

[0046] The change time tb from the timing ts when the laser light B starts to be blocked by the aperture 144c to the timing te when the laser light B is completely blocked will be described. If the change amount dax from the initial value as to the total change amount dat is the change rate X, the timing ts is the time when the change rate X is 0%, and the timing te is the time when the change rate X is 100%. In other words, the change time tb can be said to be the time when the change rate X increases from the first value to the second value during the period from when the light amount starts to change to when it becomes the closing value ae. In the examples shown in Figs. 3 and 4, the first value and the second value are set to 0% and 100%, respectively, but can be set arbitrarily.

[0047] The change time tb is determined by the blocking area per unit time and the light diameter at the incident position of the laser light B. In other words, if the blocking area per unit time is the same in the abnormal state and the reference state, the change time tb corresponds to a feature amount corresponding to the light diameter at the incident position of the laser light B. Therefore, if the blocking area per unit time is the same in the abnormal state and the reference state, the control device 180 can evaluate the change in the light diameter at the incident position of the laser light B by comparing the change time tb1 in the reference state (the time from timing ts1 to timing te1) with the change time tb2 in the abnormal state (the time from timing ts2 to timing te2).

[0048] In this embodiment, the blocking area per unit time differs between the abnormal state and the reference state. Therefore, the control device 180 may obtain the rate of change (slope) of the light amount as a feature quantity representing the blocking area per unit time, and correct the change time tb with the rate of change (slope) of the light amount. The control device 180 may use the corrected change time tb' as a feature quantity corresponding to the light diameter at the incident position of the laser light B. The control device 180 may compare the corrected change time tb'1 in the reference state with the corrected change time tb'2 in the abnormal state to evaluate how much the light diameter has changed in the abnormal state.

[0049] (Acousto-optical element) The relationship between the waveform showing the change over time in the amount of light and the beam characteristics when the acousto-optical element 144 is used as the optical shutter 14 will be described. FIG. 5 is a diagram for explaining the structure of the acousto-optical element. FIG. 6 and FIG. 7 are diagrams showing the waveform showing the change over time in the amount of light and the state from the start of blocking to the completion of blocking, respectively. In the waveforms in FIG. 6 and FIG. 7, the horizontal axis is time, and the vertical axis is the amount of light of the laser light B detected by the detector 16. The waveform shown in FIG. 6 is a waveform obtained when the beam is placed at a reference position and is in a reference state where the beam diameter is within a specified range. On the other hand, the waveform shown in FIG. 7 is an example of a waveform obtained when both the beam position and beam diameter are in an abnormal state where they are deviated from the reference state.

[0050] 5, the acousto-optic element 144 includes an RF signal generating circuit 144a, a piezoelectric element 144b, and an acousto-optic crystal 144c. The RF signal generating circuit 144a receives a control command from the control device 180, generates an RF signal, and sends it to the piezoelectric element 144b. When the RF signal reaches the piezoelectric element 144b, an acoustic wave is generated from the piezoelectric element 144b, and the acoustic wave propagates through the acousto-optic crystal 144c. The acousto-optic crystal 144c receives the acoustic wave and becomes a diffraction grating D due to the acousto-optic effect. When the acoustic wave reaches the irradiation position of the laser light B, the laser light B is diffracted. The transmitted light L0 transmitted through the acousto-optic crystal 144c is detected by the detector 16. The diffracted light L1 diffracted by the acousto-optic crystal 144c is detected by the auxiliary detector 16b.

[0051] That is, by propagating sound waves into acousto-optic crystal 144c, irradiation of detector 16 with laser light B is blocked, and auxiliary detector 16b is irradiated with laser light B. On the other hand, by stopping the propagation of sound waves into acousto-optic crystal 144c, detector 16 is irradiated with laser light B, and irradiation of auxiliary detector 16b with laser light B is blocked.

[0052] As described above, acousto-optic element 144 switches between irradiating and blocking laser light to detector 16 or auxiliary detector 16b. Also, sound waves gradually propagate through acousto-optic crystal 144c, and blocking or irradiation is completed when sound waves propagate to the entire area in acousto-optic crystal 144c where laser light B is incident. By acquiring the change over time in the amount of light detected by detector 16 or auxiliary detector 16b from when a command to switch between irradiation and blocking is issued until the sound waves propagate to the entire area, the position of laser light B passing through acousto-optic crystal 144c, the light diameter of laser light B, etc. are evaluated.

[0053] 6 and 7, it is assumed that the control device 180 issues a command to the acousto-optical element 144 to block the irradiation of the laser light B to the detector 16. FIGS. 6 and 7 show the change over time in the amount of transmitted light L0 detected by the detector 16 and the amount of diffracted light L1 detected by the auxiliary detector 16b. Since the acousto-optical element 144 is separated from the detector 16 and the auxiliary detector 16b, a time lag occurs before the light that has passed through the acousto-optical element 144 is detected by the detector 16 and the auxiliary detector 16b. However, for ease of explanation, it is assumed that the amount of light at each timing shown in FIGS. 6 and 7 corresponds to the state of the acousto-optical element 144 at each timing.

[0054] With reference to Fig. 6, a waveform showing a change over time in the light amount in the reference state will be described. Assume that at timing T0, the control device 180 transmits a command to the acousto-optic element 144 to block the irradiation of the laser light B to the detector 16. In response to the command from the control device 180, the RF signal generating circuit 144a generates an RF signal, an acoustic wave is generated from the piezoelectric element 144b, and the acousto-optic crystal 144c receives the acoustic wave and becomes a diffraction grating D. The acoustic wave propagates through the acousto-optic crystal 144c, and the range of the diffraction grating D gradually expands from the piezoelectric element 144b side from timing t0 to timings t1, t2, t3, and t4, and at timing T4, the entire irradiation position of the laser light B becomes the diffraction grating D.

[0055] Although the sound wave gradually propagates through the acousto-optic crystal 144c, it has not yet reached the irradiation position of the laser light B at the time T3. Since the laser light B is not diffracted at the time T3, the amount of the transmitted light L0 does not change, and the detection value of the diffracted light L1 does not change either. After that, when the sound wave reaches the end of the irradiation position of the laser light B at the time Ts1, a part of the laser light B is diffracted. As the range of the diffraction grating D expands, the amount of the transmitted light L0 decreases and the amount of the diffracted light L1 increases. After that, when the entire irradiation position of the laser light B becomes the diffraction grating D at the time T4, the laser light B incident on the acousto-optic crystal 144c is completely diffracted, the detection value of the transmitted light L0 detected by the detector 16 becomes minimum, and the amount of the diffracted light L1 detected by the auxiliary detector 16b becomes maximum.

[0056] With reference to Fig. 7, a waveform showing a change over time in the amount of light in an abnormal state will be described. In the abnormal state shown in Fig. 7, the incident position of laser light B is closer to piezoelectric element 144b than incident position P in the reference state. Also, the beam diameter of laser light B is larger than the beam diameter of laser light B in the reference state. The range of diffraction grating D at each of timings T0 to T4 in Fig. 7 is the same as the range of diffraction grating D at each of timings t0 to t4 in Fig. 8.

[0057] The incident position of the laser beam B is closer to the piezoelectric element 144b than the incident position P in the reference state. Therefore, in the abnormal state, the laser beam B is partially diffracted at the timing Ts2. Moreover, the laser beam B is already completely diffracted at the timing T3.

[0058] The delay time Ta from the timing T0 when the control device 180 transmits the cutoff command to the timing Tm when the light amount changes by a predetermined rate will be described with reference to a graph of the change over time of the transmitted light L0. The timing Tm when the light amount changes by a predetermined rate is the timing when the change amount dAx with respect to the initial value As of the light amount (light amount at the timing T0) becomes a predetermined rate with respect to the total change amount dAt from the initial value As to the end value Ae of the light amount. In other words, when the change amount dAx from the initial value with respect to the total change amount dAt is defined as the change rate X, the delay time ta can be said to be the period from the timing T0 when the control device 180 transmits the cutoff command to the timing Tm when the change rate X of the light amount becomes a predetermined value. In the example shown in FIG. 6 and FIG. 7, the timing tm is the timing when the change rate X of the light amount becomes 50%. The timing when the change rate of the light amount becomes a predetermined value may be any time after the timing ts when the light amount starts to change, and the predetermined value can be set arbitrarily.

[0059] When the diffraction grating D reaches the optical axis center of the laser beam B, the amount of light is halved. Therefore, the delay time Ta from timing T0 to timing Tm at which the amount of light is halved is the time it takes for the diffraction grating D to reach the optical axis center of the laser beam B, and corresponds to a feature value corresponding to the position at which the laser beam B is incident on the acousto-optic element 144. The control device 180 can evaluate how much the incident position has shifted in the abnormal state by comparing the delay time Ta2 (the time from timing T0 to timing Tm2) in the abnormal state with the delay time Ta1 (the time from timing T0 to timing Tm1) in the reference state.

[0060] The change time Tb from the timing Ts when the laser light B starts to be diffracted to the timing Te when the laser light B is completely diffracted will be described with reference to a graph of the change over time of the transmitted light L0. If the change amount dAx from the initial value As to the total change amount dAt is the change rate X, the time Ts is the time when the change rate X is 0%, and the time Te is the time when the change rate X is 100%. In other words, the change time Tb can be said to be the time when the change rate X increases from the first value to the second value during the period from when the light amount starts to change to when it reaches the end value Ae. In the examples shown in Figs. 6 and 7, the first value and the second value are set to 0% and 100%, respectively, but can be set arbitrarily.

[0061] The acousto-optic element 144 gradually becomes a diffraction grating D as the sound wave propagates from one direction. The propagation speed of the sound wave does not change even if the characteristics of the laser light change, so the change time Tb corresponds to a feature value corresponding to the diameter of the laser light B (light diameter at the incident position). The control device 180 can evaluate how much the light diameter has changed in the abnormal state by comparing the change time Tb2 (the time from timing Ts2 to timing Te2) in the abnormal state with the change time Tb1 (the time from timing Ts1 to timing Te1) in the reference state.

[0062] As described above, whether optical shutter 14 is mechanical shutter 142 or acousto-optical element 144, when the characteristics of the laser light such as the passing position of laser light B and the beam diameter of laser light B change, the delay time Ta from when a command is sent until the amount of light changes by a predetermined percentage and the change time Tb required from when laser light B starts to be blocked until it is completely blocked will change. By periodically acquiring data on the change in the amount of light over time, determining the delay time, change time, etc. from the data on the change in the amount of light over time, and comparing it with the delay time and change time in a reference state, it is possible to evaluate how the characteristics of the laser light have changed.

[0063] In the above description, the transmitted light L0 is taken as an example, but the characteristics of the laser light can be evaluated by calculating the delay time and change time from the change over time of the diffracted light L1 in the same manner.

[0064] [Modifications of the optical device] 3 to 7, the optical device has been described as including one optical shutter. However, the optical device may include multiple optical shutters 14. In the following, a method for evaluating laser light emitted from an optical device including multiple optical shutters will be described.

[0065] Fig. 8 is a schematic diagram showing a schematic configuration of an optical device according to a modified example. The optical device 10A has a common configuration with the optical device 10 shown in Fig. 1, except that the optical device 10A includes a mechanical shutter 142 and an acousto-optical element 144 instead of the optical shutter 14. In the optical device 10A, the laser light B irradiated from the laser light source 12 passes through the acousto-optical element 144 and the mechanical shutter 142 in order, and is detected by the detector 16. In the following description, it is assumed that when the control device 180 sends a blocking command to the acousto-optical element 144, the acousto-optical element 144 becomes a diffraction grating and diffracts the laser light B incident on the acousto-optical element 144, thereby blocking the irradiation of the laser light to the detector 16.

[0066] Fig. 9 is a flowchart of an evaluation method according to a modified example. Each process shown in Fig. 9 is executed by, for example, the control device 180. Note that a part or all of the processes shown in Fig. 9 may be executed by another control device connected to the control device 180. Each process shown in Fig. 9 is executed, for example, at a predetermined cycle, as an example. Also, the process shown in Fig. 9 is executed when the laser light B is irradiated to the detector 16.

[0067] In S101A, control device 180 transmits a command to mechanical shutter 142 to block irradiation of laser light to detector 16. At this time, control device 180 does not transmit a command to block to acousto-optic element 144. In other words, control device 180 controls each optical shutter to close mechanical shutter 142 while keeping acousto-optic element 144 open.

[0068] In S102A, control device 180 acquires the detection result detected by detector 16 between the time a command is sent to mechanical shutter 142 and the time blocking is completed, and acquires a first change in the amount of light over time between the time a command is sent and the time blocking is completed.

[0069] In S103, control device 180 transmits a command to mechanical shutter 142 to irradiate detector 16 with laser light.

[0070] In S104A, control device 180 evaluates the characteristics of the laser light based on the acquired first change over time in the amount of light. Control device 180 evaluates the incident position on mechanical shutter 142 and the beam diameter of laser light B at the incident position on mechanical shutter 142 based on the first change over time in the amount of light. The evaluation method is as described above, and therefore description will not be repeated here.

[0071] In S101B, control device 180 transmits a command to acousto-optical element 144 to block irradiation of laser light to detector 16. At this time, control device 180 does not transmit a command to block to mechanical shutter 142. In other words, control device 180 controls each optical shutter to block acousto-optical element 144 while keeping mechanical shutter 142 open.

[0072] In S102B, the control device 180 acquires the detection result detected by the detector 16 between the time when a command is sent to the acousto-optical element 144 and the time when blocking is completed, and acquires a second time-dependent change in the amount of light between the time when the command is sent and the time when blocking is completed.

[0073] In S104B, the control device 180 evaluates the characteristics of the laser light based on the acquired second change in the amount of light over time. The control device 180 evaluates the incident position on the acousto-optical element 144 and the beam diameter of the laser light B at the incident position on the acousto-optical element 144 based on the second change in the amount of light over time. The evaluation method is as described above, and therefore will not be repeated here.

[0074] In S109, the control device 180 compares the evaluation result obtained in S104A with the evaluation result obtained in S104B to evaluate the characteristics of the laser light in the optical path direction of the laser light B. Specifically, the control device 180 evaluates how the optical diameter of the laser light B changes along the emission direction of the laser light B and how the optical axis of the laser light B is shifted. A specific evaluation method will be described later with reference to Figs. 10 to 13.

[0075] In S110, the control device 180 outputs the evaluation result and ends the process. The control device 180 outputs the evaluation results obtained in S104A, S104B, and S109.

[0076] [Evaluation results obtained by comparing two evaluation results] 10 to 13, an evaluation result of the laser light characteristics in the light path direction obtained by comparing the evaluation result obtained from the first change in the light quantity over time with the evaluation result obtained from the second change in the light quantity over time will be described. Note that the first change in time is the change in time obtained when only mechanical shutter 142 is closed, and the second change in time is the change in time obtained when only acousto-optic element 144 is closed.

[0077] FIG. 10 is a schematic diagram showing a state when laser light is diffused. FIG. 11 is a schematic diagram showing a state when laser light is focused. FIG. 12 is a schematic diagram showing a state when the optical axis of laser light is bent. FIG. 13 is a schematic diagram showing a state when the optical axis of laser light is translated. The blocking directions of mechanical shutter 142 and acousto-optic element 144 shown in FIGS. 10 to 13 are the same, and both block from one direction. That is, in FIGS. 10 to 13, the following description will be given assuming that mechanical shutter 142 blocks the optical path in a manner similar to that of acousto-optic element 144 described with reference to FIGS. 6 and 7.

[0078] In Fig. 10 to Fig. 13, the dashed line indicates the laser light B in the reference state, and the solid line indicates the laser light B' in an abnormal state deviating from the reference state. Fig. 10 to Fig. 13 also show the magnitude relationship between the delay times ta1, ta2 and change times tb1, tb2 obtained from the first change over time of each light amount, and the delay times Ta1, Ta2 and change times Tb1, Tb2 subtracted from the second change over time of each light amount. The subscript "1" indicates the result obtained from the change over time of the light amount in the reference state, and the subscript "2" indicates the result obtained from the change over time of the light amount in the abnormal state.

[0079] With reference to FIG. 10, a case where the optical axis is not shifted and the laser light B is diffused like the laser light B' will be described. Since the optical axis is not shifted, the delay times Ta1 and Ta2 obtained by blocking the acousto-optic element 144 are substantially the same. The delay times ta1 and ta2 obtained by blocking the mechanical shutter 142 are substantially the same. On the other hand, the optical diameter of the cross section at the position where the acousto-optic element 144 is disposed is longer for the laser light B than for the laser light B'. Therefore, the change time Tb1 obtained by blocking the acousto-optic element 144 is longer than the change time Tb2. The optical diameter of the cross section at the position where the mechanical shutter 142 is disposed is shorter for the laser light B than for the laser light B'. Therefore, the change time tb1 obtained by blocking the mechanical shutter 142 is shorter than the change time tb2.

[0080] With reference to FIG. 11, a case where the optical axis is not shifted and the laser light B is focused like the laser light B' will be described. As in FIG. 10, since the optical axis is not shifted, the delay times Ta1 and Ta2 obtained by blocking the acousto-optical element 144 are approximately the same as the delay times ta1 and ta2 obtained by blocking the mechanical shutter 142. On the other hand, the optical diameter of the cross section at the position where the acousto-optical element 144 is disposed is shorter for the laser light B than for the laser light B'. Therefore, the change time Tb1 obtained by blocking the acousto-optical element 144 is shorter than the change time Tb2. The optical diameter of the cross section at the position where the mechanical shutter 142 is disposed is longer for the laser light B than for the laser light B'. Therefore, the change time tb1 obtained by blocking the mechanical shutter 142 is longer than the change time tb2.

[0081] As described above, when the optical axis is not misaligned, the delay time ta obtained from the first change in the light quantity over time in the reference state and the abnormal state and the delay time Ta obtained from the second change in the light quantity over time do not change. On the other hand, when the light diameter changes, the change time tb obtained from the first change in the light quantity over time in the reference state and the abnormal state and the change time Tb obtained from the second change in the light quantity over time change. The control device 180 can evaluate how the light diameter changes along the optical path direction by comparing the evaluation results of the change times tb1 and tb2 obtained from the first change in the light quantity over time with the evaluation results of the change times Tb1 and Tb2 obtained from the second change in the light quantity over time. For example, the control device 180 can evaluate whether the laser light is converging or diverging along the optical path direction, and further, how much it is converging or diverging.

[0082] With reference to FIG. 12, a case will be described in which the optical axis of laser light B becomes inclined like laser light B' without changing the optical diameter. Since the optical diameter of the cross section at the position where acousto-optic element 144 is arranged is almost the same, the change times Tb1 and Tb2 obtained by blocking acousto-optic element 144 are almost the same. The change times tb1 and tb2 obtained by blocking mechanical shutter 142 are almost the same. On the other hand, the optical axis is inclined, and the incident position on the optical shutter is different between laser light B and laser light B'. The incident position on acousto-optic element 144 is farther from the source of sound wave generation (start position of shutter) for laser light B than for laser light B'. Therefore, the delay time Ta1 obtained by blocking acousto-optic element 144 is longer than the delay time Ta2. Also, the incident position on mechanical shutter 142 is closer to the shutter for laser light B than for laser light B'. Therefore, the delay time ta1 obtained by blocking mechanical shutter 142 is shorter than the delay time ta2.

[0083] With reference to FIG. 13, a case will be described in which the optical axis of laser light B moves in parallel to laser light B' without changing the optical diameter. As in FIG. 12, since the optical diameter does not change, the change times Tb1 and Tb2 obtained by blocking acousto-optic element 144 are approximately the same as the change times tb1 and tb2 obtained by blocking mechanical shutter 142. Meanwhile, the optical axis moves in parallel to the shutter side. The incident position of laser light B to acousto-optic element 144 and the incident position of laser light B to mechanical shutter 142 are both farther from the shutter than laser light B'. Therefore, the delay time Ta1 obtained by blocking acousto-optic element 144 is longer than the delay time Ta2, and the delay time ta1 obtained by blocking mechanical shutter 142 is longer than the delay time ta2.

[0084] As described above, when the light diameter does not change, the change time tb obtained from the first change in the light quantity over time in the reference state and the abnormal state and the change time Tb obtained from the second change in the light quantity over time do not change. On the other hand, when the light axis is shifted, the delay time ta obtained from the first change in the light quantity over time in the reference state and the abnormal state and the delay time Ta obtained from the second change in the light quantity over time change. The control device 180 can evaluate how the light axis is shifted along the light path direction by comparing the evaluation results of the delay times ta1 and ta2 obtained from the first change in the light quantity over time with the evaluation results of the delay times Ta1 and Ta2 obtained from the second change in the light quantity over time. For example, the control device 180 can evaluate in which direction the light axis is tilted along the light path direction, or whether it is simply moving in parallel, and further, how far it is moving.

[0085] [Aspects] It will be understood by those skilled in the art that the above-described embodiments are specific examples of the following aspects.

[0086] (Item 1) An evaluation method according to one aspect evaluates characteristics of laser light in an optical device. The optical device includes a laser light source that emits laser light, a detector that detects the laser light, and an optical shutter that switches between irradiating and blocking the laser light to the detector. The evaluation method includes the steps of sending a command to the optical shutter to switch between irradiating and blocking the laser light, acquiring a change over time in the output of the detector from when the command was sent until the switching is completed, and evaluating the characteristics of the laser light based on the acquired change over time.

[0087] According to the evaluation method of the first aspect, the characteristics of laser light can be evaluated using optical components that are already included in the optical device, so that the cost and size of the device can be reduced.

[0088] (Item 2) In the evaluation method according to item 1, the evaluating step further includes a step of comparing each of the time-course changes obtained in the first time period and the second time period.

[0089] According to the evaluation method according to the second aspect, it is possible to evaluate how the characteristics of the laser light change between the first period and the second period.

[0090] (Item 3) In the evaluation method according to item 1 or 2, the evaluating step further includes a step of determining, from the acquired change over time, a first characteristic amount corresponding to a position where the laser light is incident on the optical shutter.

[0091] According to the evaluation method in accordance with the third aspect, it is possible to evaluate characteristics relating to the position at which the laser light enters the optical shutter.

[0092] (4) In the evaluation method according to paragraph 3, when the amount of change from the initial value to the total amount of change from the initial value to the closing value of the detector output value is defined as the rate of change, the first feature is the delay time from sending the command to the time when the rate of change of the detector output value reaches a predetermined value.

[0093] According to the evaluation method in accordance with the fourth aspect, it is possible to evaluate characteristics relating to the position at which the laser light enters the optical shutter.

[0094] (Item 5) In the evaluation method described in any one of items 1 to 4, the evaluating step further includes a step of determining a second feature corresponding to a beam diameter of the laser light at a position where the optical shutter is provided from the acquired change over time.

[0095] According to the evaluation method in accordance with the fifth aspect, it is possible to evaluate the characteristics relating to the beam diameter of the laser beam at the position where the optical shutter is provided.

[0096] (Item 6) In the evaluation method according to item 5, if the amount of change from the initial value to the total amount of change from the initial value to the closing value of the detector output value is defined as the rate of change, the second feature is the time it takes for the rate of change of the detector output value to increase from the first value to the second value during the period from when the detection output value starts to change to when it becomes the closing value.

[0097] According to the evaluation method in accordance with the sixth aspect, it is possible to evaluate the characteristics relating to the beam diameter of the laser beam at the position where the optical shutter is provided.

[0098] (Item 7) In the evaluation method according to any one of items 1 to 6, the optical shutter includes a first shutter and a second shutter. The step of transmitting a command further includes a step of transmitting a command to the first shutter to switch between irradiation and blocking while the second shutter is open, and a step of transmitting a command to the second shutter to switch between irradiation and blocking while the first shutter is open. The step of acquiring a change over time further includes a step of acquiring a first change over time in the amount of light detected by the detector during the period from when the command to switch to the first shutter is transmitted until the switching is completed, and a step of acquiring a second change over time in the amount of light detected by the detector during the period from when the command to switch to the second shutter is transmitted until the switching is completed. The step of evaluating evaluates a characteristic of the laser light along the optical path of the laser light based on the first change over time and the second change over time.

[0099] According to the evaluation method in accordance with the seventh aspect, the characteristics along the optical path of the laser light can be evaluated.

[0100] (Item 8) An atomic clock device according to one embodiment includes an atom generating device that emits an atomic beam or ionized atoms, a plurality of light source devices that irradiate the atoms emitted from the atom generating device with laser light, a detector that detects the laser light irradiated from each of the plurality of light source devices before the laser light is irradiated to the atoms, and a control device. Each of the plurality of light source devices includes a laser light source that emits laser light, and an optical shutter that switches between irradiating and blocking the laser light to the detector. The control device transmits a command to the optical shutter to switch between irradiating and blocking the laser light for each of the plurality of light source devices, obtains a change over time in the output of the detector from the time the command is transmitted until the switching is completed, and evaluates characteristics of the laser light based on the obtained change over time.

[0101] According to the atomic clock device of paragraph 8, the characteristics of each laser light emitted from a plurality of laser light sources can be evaluated using optical components already included in the atomic clock device, thereby reducing costs and device size. In addition, since the characteristics of the laser light can be monitored, the atomic clock device can achieve stable operation for long periods of time.

[0102] (Item 9) In the atomic clock device according to item 8, the optical shutter is a mechanical shutter or an acousto-optical element.

[0103] (Item 10) A program according to one aspect is a program for causing a computer to realize the method according to any one of items 1 to 9.

[0104] (Item 11) According to one aspect, a computer-readable medium stores the program described in item 10.

[0105] The embodiments disclosed herein are also intended to be combined as appropriate within the scope of technical inconsistency. The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not the description of the above embodiments, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0106] 10,10A optical device, 12 laser light source, 14 optical shutter, 16 detector, 16b auxiliary detector, 30 light source device, 32 cooling light source, 34 excitation light source, 36 detection light source, 38 optical lattice light source, 100 atomic clock device, 110 atom generator, 130 vacuum vessel, 134 atom irradiation section, 136 optical path switch, 142 mechanical shutter, 142a aperture, 142b outer frame, 142c aperture, 144 acousto-optical element, 144a signal generating circuit, 144b piezoelectric element, 144c acousto-optical crystal, 162 fluorescence detector, 171 input device, 172 display device, 180 control device, 182 processor, 184 memory, B,B' laser light, D diffraction grating, L0 transmitted light, L1 diffracted light.

Claims

1. 1. A method for evaluating characteristics of laser light in an optical device including a laser light source that emits laser light, a detector that detects the laser light, and an optical shutter that switches between irradiating and blocking the laser light to the detector, comprising: sending a command to the optical shutter to switch between illumination and blocking; acquiring a time-dependent change in the output of the detector from the time the command is sent until the switching is completed; and evaluating characteristics of the laser light based on the acquired change over time.

2. The evaluation method according to claim 1 , wherein the evaluating step further comprises a step of comparing each of the time-course changes obtained during a first period and a second period.

3. 3. The evaluation method according to claim 1, wherein the evaluating step further comprises a step of determining a first feature amount corresponding to a position at which the laser light is incident on the optical shutter from the acquired change over time.

4. Regarding the output value of the detector, the amount of change from the initial value to the total amount of change from the initial value to the final value is defined as a rate of change; The evaluation method according to claim 3 , wherein the first characteristic amount is a delay time from when the command is transmitted until when the rate of change in the output value of the detector reaches a predetermined value.

5. 3. The evaluation method according to claim 1, wherein the evaluating step further comprises a step of determining a second feature amount corresponding to a beam diameter of the laser light at a position where the optical shutter is provided, from the acquired change over time.

6. Regarding the output value of the detector, the amount of change from the initial value to the total amount of change from the initial value to the final value is defined as a rate of change; 6. The evaluation method according to claim 5, wherein the second feature is a time taken for the rate of change of the output value of the detector to increase from a first value to a second value during a period from when the output value of the detector starts to change to when the output value becomes the closing value.

7. the optical shutter includes a first shutter and a second shutter; The step of transmitting the command includes: transmitting a command to switch between illumination and blocking to the first shutter while the second shutter is open; and transmitting a command to switch between illuminating and blocking to the second shutter while the first shutter is open, The step of acquiring the change over time includes: acquiring a first time-dependent change in an output of the detector from when a command to switch to the first shutter is sent until when switching is completed; and acquiring a second time-dependent change in the output of the detector from when a command to switch to the second shutter is sent until when the switching is completed, The evaluation method according to claim 1 , wherein the evaluating step evaluates a characteristic of the laser light along an optical path of the laser light based on the first change over time and the second change over time.

8. an atom generator for emitting an atomic beam or ionized atoms; a plurality of light source devices for irradiating the atoms emitted from the atom generator with laser light; a detector for detecting the laser light irradiated from each of the plurality of light source devices before the laser light is irradiated onto the atom; a control device; Each of the plurality of light source devices includes: A laser light source that emits laser light; an optical shutter for switching between irradiating and blocking the laser light to the detector; The control device, for each of the plurality of light source devices, Sending a command to the optical shutter to switch between illumination and blocking; Obtaining a change over time in the output of the detector from the time the command is sent until the switching is completed; An atomic clock device that evaluates characteristics of the laser light based on the acquired changes over time.

9. 9. The atomic clock device according to claim 8, wherein the optical shutter is a mechanical shutter or an acousto-optical element.

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