Atomic clock device, laser system, and adjustment method

Abstract

This invention provides a technology that allows for the appropriate adjustment of the oscillation frequency of laser light emitted from a laser device. [Solution] The laser device 10 includes an optical system that includes a laser diode 30 that emits laser light and an external resonator 50 provided outside the laser diode 30 and causing the laser light emitted from the laser diode 30 to resonate. The oscillation frequency of the laser light from the laser device 10 changes based on the current flowing through the laser diode 30 and the optical system that includes the laser diode 30 and the external resonator 50. An initial value for the parameter combination is set based on first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter that adjusts the current and a second parameter that adjusts the optical system, and a predetermined target frequency.

Description

Technical Field

[0001] The present disclosure relates to an atomic clock device, a laser system, and an adjustment method.

Background Art

[0002] As a laser device, an external cavity semiconductor laser (ECDL: External Cavity Diode Laser) including a laser diode that irradiates laser light and an external resonator provided outside the laser diode and resonating the laser light irradiated from the laser diode is known. The oscillation frequency of the laser light from the laser device can change based on the current flowing through the laser diode and the distance between the laser diode and the external resonator.

[0003] Therefore, in the ECDL as described above, many parameters (hereinafter, also referred to as "parameter combinations"), such as the current flowing through the laser diode and the resonance distance based on the resonance wavelength, are adjusted so that the laser light matches a predetermined target frequency. When the oscillation frequency of the laser light is adjusted based on the parameter combination, a mode hop may occur in which the oscillation frequency changes abruptly. A mode hop is a phenomenon in which the oscillation frequency of the laser light changes discontinuously at a specific parameter combination when the parameter combination is varied. Examples of the parameters include the distance between the laser diode and the external resonator, the distance relationships of the external resonator when it includes lenses, mirrors, and spectroscopic elements, or their angles.

[0004] An ECDL has multiple resonant structures inside, and the laser light oscillates at a wavelength in which the laser light resonates simultaneously in these multiple resonant structures. Mode hopping has different dependencies on the parameter combinations used to adjust the multiple resonant structures. For this reason, mode hopping may not occur with a small change in one parameter combination, but may occur with a small change based on another parameter combination. If one tries to avoid mode hopping when adjusting the oscillation frequency, the adjustment range of the laser light oscillation frequency is limited, making it difficult to properly adjust the laser light oscillation frequency. Therefore, in an ECDL, it is necessary to adjust the laser light oscillation frequency while avoiding mode hopping. U.S. Patent No. 9,960,569 (Patent Document 1) discloses an ECDL that adjusts the laser light oscillation frequency while avoiding mode hopping. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent No. 9960569 [Overview of the project] [Problems that the invention aims to solve]

[0006] U.S. Patent No. 9,960569 discloses a technique for adjusting the oscillation frequency of a laser beam in an ECDL (External Corrugated Light) while avoiding mode hopping by simultaneously adjusting the angle of the internal diffraction grating and the mirror position of the external resonator. However, the technique disclosed in U.S. Patent No. 9,960569 requires the user to have a precise understanding of the internal structure of the ECDL in order to adjust the oscillation frequency. Furthermore, the technique disclosed in U.S. Patent No. 9,960569 requires the derivation of adjustment conditions for parameter combinations to adjust multiple resonant structures through complex calculations, thus limiting its applicability. In particular, in laser systems such as atomic clock devices that use multiple laser devices, there are individual differences in the resonant structure of each laser device, making it impossible to use common parameter combinations across multiple laser devices. Therefore, conventional adjustment methods could not properly adjust the oscillation frequency of the laser beam, and in practice, the operator had to determine the parameters through trial and error.

[0007] This disclosure was made to solve the aforementioned problem and aims to provide a technology that can appropriately adjust the oscillation frequency of laser light emitted from a laser device. [Means for solving the problem]

[0008] The atomic clock device of this disclosure comprises a vacuum vessel, an atomic generator that irradiates the vacuum vessel with an atomic beam, a laser device that excites an inter-energy level transition of atoms by irradiating the vacuum vessel with laser light while the vacuum vessel is irradiated with an atomic beam from the atomic generator, and a control device that controls the laser device. The laser device comprises an optical system including a laser diode that irradiates laser light and an external resonator provided outside the laser diode and causing the laser light irradiated from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. An initial value for the parameter combination is set based on first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and a predetermined target frequency.

[0009] This disclosure relates to a laser system for adjusting the oscillation frequency of laser light emitted from a laser device. The laser system comprises a laser device and a control device for controlling the laser device. The laser device includes an optical system that includes a laser diode for emitting laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. The control device includes the steps of acquiring first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and setting initial values ​​for the parameter combination based on the first data and a predetermined target frequency.

[0010] This disclosure relates to a method for adjusting the oscillation frequency of laser light from a laser device using a computer. The laser device includes an optical system that includes a laser diode that emits laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system that includes the laser diode and the external resonator. The process performed by the computer includes the steps of acquiring first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and setting initial values ​​for the parameter combination based on the first data and a predetermined target frequency. [Effects of the Invention]

[0011] According to this disclosure, the oscillation frequency of the laser light emitted from the laser device can be appropriately adjusted. Therefore, for example, initial values ​​that are less prone to mode hopping, even with minute parameter changes, can be set without trial and error by the operator. [Brief explanation of the drawing]

[0012] [Figure 1] This is a functional block diagram of an optical lattice atomic clock according to Embodiment 1. [Figure 2] This is a conceptual diagram of an optical lattice. [Figure 3] This is a functional block diagram of the laser system according to Embodiment 1. [Figure 4] This is a schematic diagram illustrating the laser device according to Embodiment 1. [Figure 5] This figure shows the relationship between the oscillation frequency and gain of laser light. [Figure 6] This figure shows the relationship between the final oscillation frequency of the laser light and its gain. [Figure 7] This diagram shows the relationship between the temperature of the temperature control unit of the laser device and the difference between that temperature and the target frequency. [Figure 8]It is a diagram showing the relationship between the combination of the current flowing through the laser diode and the temperature of the temperature control unit, and the frequency of the laser light. [Figure 9] It is a diagram briefly showing the combination of the current flowing through the laser diode and the temperature of the temperature control unit. [Figure 10] It is a diagram for explaining the case where the current flowing through the laser diode and the temperature of the temperature control unit are changed within the range from point C to point D. [Figure 11] It is a diagram showing the change in current with respect to time and the change in temperature of the temperature control unit in the laser device. [Figure 12] It is a diagram showing the change in the difference in the target frequency of the laser light with respect to time. [Figure 13] It is a flowchart showing the control content in the laser system. [Figure 14] It is a diagram showing the relationship between the combination of the current flowing through the laser diode according to the modification example and the temperature of the temperature control unit, and the frequency of the laser light. [Figure 15] It is a diagram showing the relationship between the combination of the current flowing through the laser diode according to the modification example and the temperature of the temperature control unit, and the oscillation state of the laser light. [Figure 16] It is a diagram showing the relationship between the combination of the current flowing through the laser diode according to the modification example and the temperature of the temperature control unit, and the light intensity of the laser light. [Figure 17] It is a diagram showing the relationship between the combination of the current flowing through the laser diode according to the modification example and the temperature of the temperature control unit, and the condition evaluation index. [Figure 18] It is a diagram showing the relationship between the combination of the current flowing through the laser diode according to the modification example and the temperature of the temperature control unit, and the condition evaluation index. [Figure 19] It is a schematic diagram for explaining the laser device according to Embodiment 2. [Figure 20] It is a schematic diagram for explaining the laser device according to Embodiment 3. [Figure 21] It is a schematic diagram for explaining the laser device according to Embodiment 4.

Embodiments for Carrying Out the Invention

[0013] This embodiment will be described in detail with reference to the drawings. Note that identical or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated in principle.

[0014] [Embodiment 1] Figure 1 is a functional block diagram of the atomic clock device 100 according to Embodiment 1. The atomic clock device 100 in Figure 1 is an optical lattice atomic clock (also simply referred to as an "optical lattice clock").

[0015] Referring to Figure 1, the atomic clock apparatus 100 comprises an atomic generator 110, a vacuum vessel 130, a detection device 140, a plurality of laser devices 10, a magnetic field generator 160, and a control device 170. The plurality of laser devices 10 include a cooling laser device 10A, an excitation laser device 10B, a detection laser device 10C, and an optical lattice laser device 10D.

[0016] The atomic generator 110 includes a heating device (oven) (not shown) and heats an atomic base material such as strontium, ytterbium, or mercury in the oven. Heating breaks the chemical bonds between atoms, isolating them and generating a collection of atoms (atomic gas). Since the heated and gasified atoms have high kinetic energy, the atomic generator 110 irradiates the atom with high-speed atomic gas as an atomic beam. The atomic beam irradiated from the atomic generator 110 is guided into the vacuum chamber 130.

[0017] The cooling laser device 10A is controlled by a control signal CTL1 from the control device 170. The cooling laser device 10A irradiates the atomic beam emitted from the atomic generator 110 with laser light (arrows AR1 and AR2 in Figure 1) that is three-dimensionally opposed to the atomic beam emitted from the atomic generator 110 inside the vacuum chamber 130. By irradiating with this cooling laser light in the opposite direction to the direction of motion of the atomic beam, the kinetic energy of the atoms is reduced (i.e., they are cooled), and as a result, the velocity of the atoms decreases.

[0018] Furthermore, a pair of opposing mirrors 131 and 132 are provided inside the vacuum chamber 130. When laser light controlled to a specific wavelength (magic wavelength) by the control signal CTL5 of the control device 170 is irradiated between mirrors 131 and 132 from the optical lattice laser device 10D, a standing wave is generated between mirrors 131 and 132 by the laser light.

[0019] Generally, atoms polarize in an electric field, generating induced dipoles. These dipoles interact with the electric field. As a result, in a spatially non-uniform laser electric field, the electrical potential for atoms becomes minimal at the points of maximum electric field intensity, and atoms are trapped at these locations. As described above, when standing waves of laser light are generated between mirrors 131 and 132, atoms are trapped at the antinodes of these standing waves. By combining these standing waves three-dimensionally, an "optical lattice" is realized in which atoms are arranged at half-wavelength intervals. Figure 2 conceptually shows an optical lattice. In Figure 2, the optical lattice 190 generated by the laser light is conceptually a spatial interference fringe with recesses of electrical potential formed at regular intervals, and atomic ATMs are trapped within these recesses.

[0020] When atoms acquire momentum (velocity), the Doppler effect can shift the resonance frequency, potentially reducing the accuracy of the measured time. By using the laser light from the cooling laser device 10A to decelerate the atomic ATM in the atomic beam, and by trapping the atomic ATM using the optical lattice 190 as shown in Figure 2, it becomes possible to search for the resonance frequency of atoms in a stationary state.

[0021] The magnetic field generator 160 is controlled by a control signal CTL4 from the control device 170, and applies a magnetic field to the moving atomic ATM by passing an electric current through electromagnetic coils (not shown) arranged around the mirrors 131 and 132 inside the vacuum chamber 130. This applied magnetic field controls the energy levels of the atomic ATM and contributes to various atomic cooling processes.

[0022] The excitation laser device 10B is controlled by a control signal CTL2 from the control device 170. The excitation laser device 10B irradiates the captured atomic ATM with pulsed laser light to excite the energy transition of the atomic ATM. Atoms generally have multiple intrinsic energy levels, and in the transition between two different energy levels, photons with a frequency corresponding to the energy difference between the energy levels are selectively absorbed.

[0023] The detection laser device 10C is controlled by a control signal CTL3 from the control device 170. The detection laser device 10C irradiates the atomic ATM with detection laser light after the energy levels of the atomic ATM have been excited by the excitation laser device 10B. The laser emitted from the detection laser device 10C generates fluorescence with an intensity proportional to the energy transition probability of the atom.

[0024] The detection device 140 receives fluorescence generated by the detection laser device 10C and detects the intensity of the received fluorescence. The detection device 140 outputs a transition probability spectrum, which depends on the excitation laser frequency and is represented by the detected fluorescence intensity, to the control device 170.

[0025] The control device 170 includes, for example, a CPU (Central Processing Unit) 171 and a memory 172. The CPU 171 comprehensively controls each component of the atomic clock device 100 by executing a program stored in the memory 172. The control device 170 identifies the resonant frequency of the atomic ATM from the transition probability spectrum received from the detection device 140. The control device 170 also stabilizes the frequency of the laser light emitted from the excitation laser device 10B based on the resonant frequency determined by calculation.

[0026] In atomic clock devices 100, including such optical lattice atomic clocks, an external resonator semiconductor laser (ECDL) may be used as the laser device 10. ECDLs include a laser diode that emits laser light and an external resonator located outside the laser diode that resonates the laser light emitted from the laser diode. In ECDLs, mode hopping can occur, where the oscillation frequency of the laser light changes abruptly. However, if mode hopping occurs during oscillation frequency adjustment, it becomes difficult to properly adjust the oscillation frequency of the laser light. Therefore, in ECDLs, it is necessary to adjust the oscillation frequency of the laser light while avoiding mode hopping.

[0027] In particular, in laser systems such as atomic clocks that use multiple laser devices, there are individual differences in the resonant structure of each of the multiple laser devices, making it impossible to use a common combination of parameters among them. Below, we will describe an atomic clock, a laser system, and an adjustment method that enable appropriate adjustment of the laser light oscillation frequency when ECDL is applied to the laser device 10.

[0028] Figure 3 is a functional block diagram of the laser system 200 according to Embodiment 1. The laser system 200 comprises a laser device 10, a splitter 11, an optical sensor 12, a control device 150, a current adjustment device 21, and a temperature adjustment device 22. The laser device 10 is, for example, an ECDL. Note that the laser device 10 may be a laser device other than an ECDL.

[0029] The laser device 10 emits (outputs) laser light when current flows through the laser diode. The splitter 11 splits the laser light emitted from the laser device 10. The optical sensor 12 converts the laser light split by the splitter 11 into an electrical signal and outputs various laser light-related information, such as the ECDL oscillation frequency, to the control device 150.

[0030] The control device 150 includes a CPU 151, a memory 152, and a storage device 153. The CPU 151 comprehensively controls each device of the laser system 200 by executing a program stored in the memory 152. The CPU 151 (control device 150) performs arithmetic processing as the computer of this disclosure. The CPU 151 can also be read as a processing circuitry whose processing is predefined by computer-readable code and / or hardwired circuitry. The memory 152 includes a storage area (e.g., a working area) for storing program code or work memory when the CPU 151 executes various programs. Examples of memory 152 include volatile memory such as DRAM and SRAM, or non-volatile memory such as ROM and flash memory.

[0031] The storage device 153 stores various programs or data executed by the CPU 151. The storage device 153 may be one or more non-transitory computer-readable media or one or more computer-readable storage media. Examples of storage devices 153 include HDDs (Hard Disk Drives) and SSDs (Solid State Drives). In this embodiment, the storage device 153 stores a data processing program 154 for executing data processing that the CPU 151 uses to process detection data acquired from the optical sensor 12.

[0032] The CPU 151 receives, for example, a signal from the optical sensor 12 regarding the emission frequency of the laser light from the laser device 10, and performs a process to bring the oscillation frequency of the laser light closer to a predetermined target frequency. The target frequency is received by the control device 150 via an input / output interface (not shown).

[0033] The current adjustment device 21 varies the current flowing through the laser device 10 (the current flowing through the laser diode 30, which will be described later) based on the current instruction value transmitted from the control device 150. The temperature adjustment device 22 varies the temperature of the temperature element of the laser device 10, which will be described later, based on the temperature instruction value transmitted from the control device 150.

[0034] An example of the structure of an ECDL will be explained using Figure 4. Figure 4 is a schematic diagram illustrating a laser device 10 according to Embodiment 1. The laser device 10 comprises a laser diode 30, a lens unit 40, an external resonator 50, a mounting unit 60, and a temperature control unit 70.

[0035] The laser diode 30 is composed of a P-type cladding layer 31, an active layer 32, an N-type cladding layer 33, and the like. In the laser diode 30, when electricity flows such that the P-type cladding layer 31 is positive and the N-type cladding layer 33 is negative, light is generated in the active layer 32. The inner end face of the active layer 32 functions as a light reflecting surface. The light that is repeatedly reflected and amplified within the active layer 32 is irradiated towards the lens portion 40 as laser light.

[0036] The laser light emitted from the laser diode 30 is focused by the lens 41 located in the lens section 40 so that each beam is parallel to the others, and then incident on the external resonator 50. The external resonator 50 functions as a circuit grating that resonates the laser light by diffracting light of a specific wavelength from the incident laser light and returning it to the laser diode 30. The resonant laser light is partially output to the outside.

[0037] In Figure 4, a volume holographic diffraction grating (VHG) is shown as the circuit grating, but it may also be a reflective type, a transmission type, etc., and the circuit grating can have any structure. The laser diode 30 is mounted on the mounting part 60 via the base part 36. The external resonator 50 is mounted on the mounting part 60 via the base part 51. The temperature control unit 70 is in contact with the lower surface of the mounting part 60 and heats or cools the mounting part 60 from below. The temperature control unit 70 is, for example, a Peltier element that functions as a temperature element. As the mounting part 60 is heated or cooled by the temperature control unit 70, the mounting part 60 expands and contracts in the direction of laser beam irradiation. The mounting part 60 is, for example, made of a metal that expands and contracts when heated or cooled. As the mounting part 60 expands and contracts, the distance between the base part 36 and the base part 51 mounted on the mounting part 60 changes. Similarly, the distance between the base portion 36 and the lens portion 40, and the distance between the lens portion 40 and the base portion 51, also change.

[0038] Thus, the optical system including the laser diode 30 and the external resonator 50 changes as the mounting portion 60 is temperature-controlled by the temperature control unit 70. In other words, the temperature control unit 70 has the function of moving the external resonator 50 relative to the laser diode 30 by temperature change. Alternatively, a piezoelectric element that expands and contracts in response to voltage changes may be used instead of a temperature element. In such a case, the piezoelectric element should be directly attached to the lower surface of the base portion 51 so that the base portion expands and contracts in the direction of laser beam irradiation. In this way, the distance between the laser diode 30 and the external resonator 50 can be adjusted by adjusting the voltage applied to the piezoelectric element. Furthermore, this disclosure is not limited to this embodiment, and if the optical system includes a light-gathering element such as a mirror, the optical system may be adjusted by changing the mirror angle with a motor element.

[0039] Next, the gain characteristics of the laser light will be explained. Figure 5 is a diagram showing the relationship between the oscillation frequency and gain of the laser light. The horizontal axis of Figure 5 represents the oscillation frequency of the laser light, and the vertical axis represents the gain of the laser light. The laser device 10 has gain characteristics of multiple factors internally, and is characterized by oscillating at the frequency in which the composite gain, obtained by taking the product of the multiple gain characteristics, is highest.

[0040] The gain characteristic L1 in Figure 5 is the gain characteristic due to the material of the laser diode 30. The gain characteristic L2 in Figure 5 is the gain characteristic due to the wavelength selectivity that reflects specific wavelengths at the reflective surface. The gain characteristic L3 in Figure 5 is the gain characteristic due to resonance within the diode. The gain characteristic L4 in Figure 5 is the gain characteristic due to the resonant structure of the external resonator. Figure 6 shows the composite gain obtained by multiplying the multiple gain characteristics in Figure 5. Figure 6 shows the relationship between the final oscillation frequency of the laser light and the gain. As shown in Figure 6, the composite gain L5 becomes the final oscillation frequency of the laser light.

[0041] Adjusting the oscillation frequency of an ECDL is difficult because it requires considering not only the resonant frequency of the external resonator but also the influence of other gain characteristics. Furthermore, in ECDLs, mode hopping, where the laser beam oscillation frequency changes abruptly, can occur. Mode hopping is explained using Figure 7.

[0042] Figure 7 shows the relationship between the temperature of the temperature control unit 70 of the laser device 10 and the difference between that temperature and the target frequency. In order to observe the occurrence of mode hopping with respect to the target frequency, it is necessary to evaluate the correspondence between the target frequency and the parameters that constitute the optical system. In this embodiment, as shown in Figure 4, the most dominant parameter for adjusting the optical system is the distance between the base unit 36 ​​and the base unit 51. For a more precise evaluation, it is also necessary to evaluate the distance between the base unit 36 ​​and the lens unit 40, and the distance between the lens unit 40 and the base unit 51 as parameters. It is optimal to observe the change in laser frequency when each of these distances is changed.

[0043] However, in this embodiment, these distances are considered to be expressible by the degree of expansion and contraction of the mounting portion 60, and furthermore, since the degree of expansion and contraction is a change due to the temperature of the mounting portion 60, temperature is used as a substitute parameter for these distances. In this way, even when there are multiple parameters that would normally need to be observed, if they are distances, heat can be used as a substitute parameter, making evaluation easier. Note that the temperature of the mounting portion 60 may have a thermal effect on the laser diode 30, but in this embodiment, since the change in laser frequency due to heat is observed, the thermal effect on the laser element is observed at the same time as the change in the optical system.

[0044] The horizontal axis of Figure 7 shows the temperature of the temperature control unit 70 of the laser device 10, and the vertical axis of Figure 7 shows the difference between the emission frequency of the laser light from the laser device 10 and the target frequency. The distance between the laser diode 30 and the external resonator 50 changes with the temperature change of the temperature control unit 70. As shown in Figure 7, there is a region in which the difference between the oscillation frequency and the target frequency changes continuously in proportion to the temperature change of the temperature control unit 70, and a region in which the difference between the oscillation frequency and the target frequency does not change proportionally to the temperature change of the temperature control unit 70 and instantaneously discretes.

[0045] The region in which the difference between the oscillation frequency and the target frequency changes continuously and proportionally is the region in which the difference between the oscillation frequency and the target frequency changes in proportion to the change in distance between the laser diode 30 and the external resonator 50. On the other hand, the region in which the difference between the oscillation frequency and the target frequency instantaneously discretes without proportionality represents the region in which the product of all gain characteristics of the ECDL has shifted to a different resonant frequency that is one or more positions away, due to gain characteristics other than the gain characteristics of the external resonator. Mode hopping occurs in this region in which the difference between the oscillation frequency and the target frequency instantaneously discretes without proportionality.

[0046] Figure 8 shows the relationship between the combination of the current flowing through the laser diode 30 and the temperature of the temperature control unit 70, and the frequency of the laser light. The temperature of the temperature control unit 70 is the same as the temperature when the laser light is indirectly conducted to the external resonator 50. The horizontal axis of Figure 8 shows the current flowing through the laser diode 30, the vertical axis shows the temperature of the temperature control unit 70, and the various shaded lines in Figure 8 show the oscillation frequency of the laser diode 30.

[0047] The oscillation frequency of the laser light from the laser device 10 changes based on a first parameter relating to the current flowing through the laser diode 30 and a second parameter relating to the optical system including the laser diode 30 and the external resonator 50. Therefore, in order to adjust the oscillation frequency of the laser light, it is necessary to adjust the parameter combination consisting of the first and second parameters so that it reaches a predetermined target frequency. In this embodiment, the temperature of the mounting section 60, which represents the distance relationship between the laser diode 30, the lens section 40, and the external resonator 50 included in the optical system, is used as the second parameter.

[0048] As shown in Figure 3, in the laser system 200 according to Embodiment 1, the current adjustment device 21 is controlled based on the current instruction value transmitted from the CPU 151 (control device 150) to vary the current flowing through the laser device 10 (the current flowing through the laser diode 30) between a lower limit and an upper limit. In addition, the laser system 200 controls the temperature adjustment device 22 based on the temperature instruction value transmitted from the CPU 151 (control device 150) to vary the temperature of the temperature control unit 70 between a lower limit and an upper limit. Through such adjustments, the laser system 200 brings the oscillation frequency of the laser light closer to the target frequency. By performing such adjustments before the laser device 10 is shipped, the laser system 200 can appropriately adjust the oscillation frequency of the laser light of the laser device 10.

[0049] In Figure 8, the change in oscillation frequency for a parameter combination of a first parameter that adjusts the current flowing through the laser diode 30 and a second parameter that adjusts the distance between the laser diode 30 and the external resonator 50, which changes with the temperature of the temperature control unit 70, is shown as first data. For example, as shown in Figure 8, when the first data is visualized, a two-dimensional table is created by extracting the maximum and minimum values ​​for the current parameter and the temperature parameter in a matrix. Three-dimensional mapping data is then created by associating the measured values ​​of the oscillation frequency for each parameter combination with this two-dimensional table.

[0050] Furthermore, because the optical system, including the laser diode 30 and the external resonator 50, is greatly affected by individual differences, it is often not possible to apply the analysis results of a pre-prepared optical model. Therefore, in this disclosure, information represented in Figure 8 is obtained for each individual laser device 10 by performing a preliminary analysis that scans the first and second parameters. This preliminary analysis only needs to be performed at least once before the device is completed, but it may also be performed after the device is completed whenever the device environment changes, such as during installation.

[0051] In the laser system 200, first data showing the change in oscillation frequency for a given parameter combination is stored in memory 152. The control device 150 uses this first data to extract boundaries where mode hopping occurs, where the oscillation frequency of the laser light changes abruptly, using image processing or other methods. For example, in Figure 8, multiple dashed lines are extracted as boundaries where mode hopping occurs.

[0052] Figure 9 is a simplified diagram showing the combination of the current flowing through the laser diode and the temperature of the temperature control unit. In Figure 9, the boundary where mode hopping occurs in Figure 8 is shown in a simplified manner, and several straight lines are extracted. The multiple straight lines are multiple linear functions that are approximately calculated based on the rate of change of temperature with respect to current. The control device 150 calculates two straight lines, such as straight lines A and B, in which a predetermined target frequency falls within the region. The calculation of the two straight lines can be done by any method, but for example, it is sufficient to select a range in which the target frequency falls within the region enclosed by the two straight lines and which is wide.

[0053] The control device 150 then sets the initial values ​​of the parameter combinations within the range enclosed by the two straight lines A and B in Figure 9. For example, the initial values ​​of the parameter combinations are set at the positions indicated by the stars in Figure 9. The initial values, which are the positions of the stars, can be determined in any way, but it is preferable to set them at a position far from each of the two straight lines. By determining the initial position in this way, the initial values ​​are not set near the boundary where mode hopping occurs, making it possible to avoid mode hopping. In this manner, the control device 150 sets the initial values ​​of the parameter combinations based on the first data stored in the memory 152 and a predetermined target frequency.

[0054] The initial values ​​of the set parameter combinations are stored in the memory 152 of the laser device 10. The initial values ​​of the parameter combinations are set similarly for each laser device 10 used in the atomic clock device 100. Subsequently, each of the multiple laser devices 10 whose initial values ​​have been adjusted is incorporated into the atomic clock device 100. Although each of the multiple laser devices 10 incorporated into the atomic clock device 100 has individual differences in its resonant structure, the accuracy of the atomic clock device 100 is increased because the initial values ​​have been adjusted for each one.

[0055] Here, when adjusting the current and temperature in the region enclosed by two straight lines (the region enclosed by two linear functions), the parameter combination can be changed as shown in Figure 10. Figure 10 is a diagram illustrating the case where the current flowing through the laser diode 30 and the temperature of the temperature control unit 70 are changed in the range from point C to point D. When adjusting the current and temperature in the region enclosed by two linear functions, if the adjustment is made in the range from point C to point D where no mode hopping occurs, a linear function like that shown in Figure 10 can be obtained.

[0056] The slope of such a linear function may be set within the range of the minimum and maximum slopes of two adjacent linear functions, or it may be set as the average value of the slopes. In other words, any method of determining the slope is acceptable as long as the slope is set within an adjustment range that does not cause mode hopping.

[0057] Next, we will explain the time variation of the parameter combinations. Figure 11 shows the change in current over time in the laser device 10 and the change in temperature of the temperature control unit 70. M1 in Figure 11 shows the change in temperature over time when the adjustment is made in the range from point C to point D in Figure 10, and M2 in Figure 11 shows the change in current over time when the adjustment is made in the range from point C to point D in Figure 10. As shown in Figure 11, when the adjustment is made in the range from point C to point D, there is a relationship in which the current decreases as the temperature increases. We will now explain the difference between the oscillation frequency and the target frequency when the adjustment is made in this way.

[0058] Figure 12 shows the change in the difference between the laser beam's frequency and the target frequency over time. As shown in Figure 12, when the parameter combination is adjusted in the range from point C to point D using the settings in Figure 11, it can be seen that the difference between the laser beam's oscillation frequency and the target frequency approaches zero over time. In other words, in the laser system 200, by adjusting the current adjustment device 21 and the temperature adjustment device 22 within a range where mode hopping does not occur, it is possible to adjust the oscillation frequency within a range where mode hopping does not occur.

[0059] Next, the control details of the laser system 200 according to Embodiment 1 will be described. Figure 13 is a flowchart showing the control details of the laser system 200. Hereafter, each step in the flowchart will be simply referred to as "S".

[0060] The control device 150 first controls the temperature control device 22 to fix the temperature T of the temperature control unit 70 at a predetermined value (S1). Next, the control device 150 controls the current control device 21 to update the current I flowing through the laser diode 30 (S2). Then, the control device 150 receives a signal from the optical sensor 12 regarding the emission frequency of the laser light from the laser device 10 and stores the oscillation frequencies at the time of S1 and S2 in the memory 152 (S3).

[0061] Next, the control device 150 determines whether the current I setting range has ended (S4). The current I setting range is predetermined to be from a lower limit to an upper limit. If the control device 150 determines that the current I setting range has ended (YES in S4), it proceeds to process S5. If the control device 150 determines in S4 that the current I setting range has not ended (NO in S4), it proceeds to process S2 and updates the current I.

[0062] In S5, the control device 150 determines whether the temperature setting range for T has ended (S5). The temperature setting range for T is predetermined to be from a lower limit to an upper limit. If the control device 150 determines that the temperature setting range for T has ended (YES in S5), it proceeds to process S7. If the control device 150 determines in S5 that the temperature setting range for T has not ended (NO in S5), it updates the temperature T (S6) and proceeds to process S1.

[0063] In S7, the control device 150 sets the maximum and minimum values ​​for current-related parameters and temperature-related parameters, extracts them in a matrix, and creates a two-dimensional table. By associating the measured oscillation frequency for each parameter combination with this two-dimensional table, it creates three-dimensional mapping data.

[0064] Next, the control device 150 calculates two boundary lines close to the target frequency from the relationship between temperature T, current I, and oscillation frequency F (S8). The process in S8 is to find two approximate boundary lines close to the target frequency, as explained in Figure 9. Next, in S9, the control device 150 calculates initial values ​​for temperature T and current I from the two boundary lines calculated in S8 so that no mode hop occurs.

[0065] Next, the control device 150 calculates the setting ranges for temperature T and current I from the initial values ​​(S10). The process in S10 is to find a linear function within the range where mode hopping does not occur, as shown in Figure 10. Then, the control device 150 stores the initial values ​​obtained in S8 and the setting range obtained in S10 in the memory 152 (S11), and terminates the process.

[0066] In this way, the control device 150 can easily adjust the oscillation frequency of the laser beam within a range where mode hopping does not occur by using the initial values ​​and setting ranges of the parameter combinations stored in the memory 152.

[0067] [Differentiation] Next, a modified version of Embodiment 1 will be described. Figure 14 is a diagram showing the relationship between the combination of the current flowing through the laser diode 30 and the temperature of the temperature control unit 70, and the frequency of the laser light, according to the modified version. In Figure 14, the current and temperature are set within a different range than in Embodiment 1. As shown in Figure 14, it can be seen that when the current and temperature are different, the position of the dashed line, which is the boundary of the mode hop, is also different.

[0068] Figure 15 shows the relationship between the combination of the current flowing through the modified laser diode 30 and the temperature of the temperature control unit 70, and the oscillation state of the laser light. Laser light exists in two forms: single-mode, where only a single specific wavelength of laser light is emitted, and multi-mode, where laser light of multiple wavelengths is emitted. In the laser device 10, a single-mode oscillation state is preferable to a multi-mode oscillation state. Such an oscillation state may be used as one indicator for parameter combinations to set initial values.

[0069] Figure 16 shows the relationship between the combination of the current flowing through the laser diode 30 and the temperature of the temperature control unit 70 in a modified example, and the light intensity of the laser beam. Light intensity is the energy per unit area. In the laser device 10, a higher light intensity is preferable to a lower one. Such light intensity can be used as one indicator for parameter combinations to set the initial value.

[0070] Figure 17 shows the relationship between the combination of the current flowing through the laser diode 30 and the temperature of the temperature control unit 70 in the modified example, and the condition evaluation index. Figure 17 shows the relationship when the oscillation frequency in Figure 14 and the oscillation state index in Figure 15 are multiplied together. In Figure 17, for example, it can be seen that the regions indicated by the two ellipses are suitable as condition evaluation indices. Therefore, the initial values ​​for the parameter combination should be set from the regions indicated by the two ellipses.

[0071] Figure 18 shows the relationship between the combination of the current flowing through the modified laser diode 30 and the temperature of the temperature control unit 70, and the condition evaluation index. In Figure 18, the relationship is further shown when the light intensity index from Figure 16 is multiplied with that of Figure 17. In Figure 18, for example, it can be seen that the region indicated by one ellipse is suitable as the condition evaluation index. Therefore, the initial value should be set from the region indicated by one ellipse that maximizes the index as a parameter combination. In this way, the calculation of the initial value becomes easy by multiplying multiple indices.

[0072] [Embodiment 2] The laser device 300A of Embodiment 2 will now be described. Figure 19 is a schematic diagram illustrating the laser device 300A according to Embodiment 2. The laser device 300A comprises a laser diode 30, lenses 41, 42, 43, a wavelength selective filter 52, a partial reflection mirror 53, and a moving mechanism 71. The configuration of the laser diode 30 is the same as in Embodiment 1.

[0073] The ECDL of the laser device 300A changes the distance between the laser diode 30 and the partial reflection mirror 53 by a moving mechanism 71 (not shown). The moving mechanism 71 is a mechanism driven by current, such as a motor. Instead of the moving mechanism 71, it may be composed of a temperature control unit 70 and a mounting unit 60 similar to those in Embodiment 1, or it may be composed of a piezoelectric element.

[0074] [Embodiment 3] The laser device 300B of Embodiment 3 will now be described. Figure 20 is a schematic diagram illustrating the laser device 300B according to Embodiment 3. The laser device 300B comprises a laser diode 30, a lens 41, a diffraction grating 54, and a rotation mechanism 72. The configuration of the laser diode 30 is the same as in Embodiment 1.

[0075] The ECDL of the laser device 300B changes the distance between the laser diode 30 and the diffraction grating 54 by a rotating mechanism 72 (not shown). The rotating mechanism 72 is preferably a drive mechanism such as a motor.

[0076] [Embodiment 4] The laser device 300C of Embodiment 4 will now be described. Figure 21 is a schematic diagram illustrating the laser device 300C according to Embodiment 4. The laser device 300C comprises a laser diode 30, a lens 41, a diffraction grating 54, a mirror 55, and a rotation mechanism 73. The configuration of the laser diode 30 is the same as in Embodiment 1.

[0077] The ECDL of the laser device 300C changes the distance between the laser diode 30 and the diffraction grating 54 by changing the position of the mirror 55 using a rotating mechanism 73 (not shown in the figure). Unlike the laser device 300B of Embodiment 3, the laser device 300C has a fixed diffraction grating structure. In this embodiment, in addition to parameters such as the distance between optical elements, the diffraction grating angle and mirror angle are newly included as parameters that constitute the optical system.

[0078] [Pattern] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0079] (Section 1) An atomic clock device according to one embodiment comprises a vacuum vessel, an atomic generator that irradiates the vacuum vessel with an atomic beam, a laser device that excites an energy level transition of atoms by irradiating the vacuum vessel with laser light while the vacuum vessel is irradiated with an atomic beam from the atomic generator, and a control device that controls the laser device. The laser device comprises an optical system including a laser diode that irradiates laser light and an external resonator provided outside the laser diode and causing the laser light irradiated from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. An initial value of the parameter combination is set based on first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and a predetermined target frequency.

[0080] According to the atomic clock device described in paragraph 1, the initial value of the parameter combination is set based on a predetermined target frequency and a first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter that adjusts the current flowing through the laser diode and a second parameter that adjusts the optical system including the laser diode and an external resonator. Therefore, the oscillation frequency of the laser light emitted from the laser device can be appropriately adjusted.

[0081] (Section 2) In the atomic clock apparatus described in Section 1, the first data is obtained by a preliminary analysis that scans the first and second parameters.

[0082] According to the atomic clock apparatus described in paragraph 2, unit 1 data can be obtained by a preliminary analysis that scans the first and second parameters.

[0083] (Section 3) In the atomic clock apparatus described in Section 1 or 2, the range in which parameter combinations can be set includes an adjustment range in which no mode hop occurs that changes the oscillation frequency. The initial value of the parameter combination is selected from among multiple parameter combinations included in the adjustment range.

[0084] According to the atomic clock device described in paragraph 3, the initial values ​​of the parameter combination can be set within an adjustment range in which no mode hop occurs, which changes the oscillation frequency.

[0085] (Section 4) In the atomic clock apparatus described in Section 3, multiple linear functions are calculated based on the first data. The adjustment range is defined based on the multiple linear functions.

[0086] According to the atomic clock apparatus described in paragraph 4, the adjustment range can be determined from multiple linear functions.

[0087] (Article 5) In the atomic clock apparatus described in any one of paragraphs 1 to 4, the oscillation state of the laser light from the laser apparatus includes a single mode in which only laser light of a specific wavelength is emitted, and a multimode in which laser light of multiple wavelengths is emitted. The initial value is set based on the oscillation state of the laser light.

[0088] According to the atomic clock device described in paragraph 5, the initial value can be set based on the oscillation state of the laser light.

[0089] (Clause 6) In the atomic clock apparatus described in any one of paragraphs 1 to 5, the initial value is set based on the light intensity of the laser beam.

[0090] According to the atomic clock device described in paragraph 6, the initial value can be set based on the light intensity of the laser beam.

[0091] (Section 7) In the atomic clock apparatus described in any one of paragraphs 1 to 6, the laser apparatus further comprises a temperature element that adjusts the optical system by applying heat to a mounting portion on which an external resonator is mounted. The second parameter includes the temperature of the temperature element.

[0092] According to the atomic clock apparatus described in paragraph 7, the optical system, including the laser diode and the external resonator, can be adjusted by changing the temperature of the temperature element.

[0093] (Section 8) In the atomic clock apparatus described in any one of paragraphs 1 to 7, the laser apparatus further comprises a piezoelectric element that adjusts the optical system by expanding or contracting based on voltage. The second parameter includes the voltage of the piezoelectric element.

[0094] According to the atomic clock apparatus described in paragraph 8, the optical system, including a laser diode and an external resonator, can be adjusted by changing the voltage of a piezoelectric element.

[0095] (Section 9) In the atomic clock apparatus described in any one of paragraphs 1 to 8, the laser apparatus further comprises a moving mechanism for changing the position of the external resonator. The second parameter includes the current of the moving mechanism.

[0096] According to the atomic clock apparatus described in paragraph 9, the distance between the laser diode and the external resonator can be adjusted by a motor.

[0097] (Section 10) A laser system according to one embodiment relates to a laser system for adjusting the oscillation frequency of laser light emitted from a laser device. The laser system comprises a laser device and a control device for controlling the laser device. The laser device comprises an optical system including a laser diode that emits laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. The control device includes the steps of acquiring first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and setting initial values ​​for the parameter combination based on the first data and a predetermined target frequency.

[0098] According to the laser system described in Section 10, the initial value of the parameter combination is set based on a first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter that adjusts the current flowing through the laser diode and a second parameter that adjusts the optical system including the laser diode and an external resonator, and a predetermined target frequency. Therefore, the oscillation frequency of the laser light emitted from the laser device can be appropriately adjusted.

[0099] (Clause 11) An adjustment method relating to one embodiment relates to an adjustment method for adjusting the oscillation frequency of laser light from a laser device using a computer. The laser device includes an optical system that includes a laser diode that emits laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system that includes the laser diode and the external resonator. The process performed by the computer includes the steps of acquiring first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and setting initial values ​​for the parameter combination based on the first data and a predetermined target frequency.

[0100] According to the adjustment method described in paragraph 11, the initial value of the parameter combination is set based on a first data showing the change in oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current flowing through the laser diode and a second parameter for adjusting the optical system including the laser diode and an external resonator, and a predetermined target frequency. Therefore, the oscillation frequency of the laser light emitted from the laser device can be appropriately adjusted.

[0101] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0102] 10, 300A, 300B, 300C Laser device, 10A Cooling laser device, 10B Excitation laser device, 10C Detection laser device, 10D Optical lattice laser device, 11 Splitter, 12 Optical sensor, 21 Current regulator, 22 Temperature regulator, 30 Laser diode, 31 P-type cladding layer, 32 Active layer, 33 N-type cladding layer, 36 Base, 40 Lens section, 41, 42, 43 Lenses, 50 External resonator, 51 Base, 52 Wavelength selective filter, 53 Partial reflection mirror, 54 Diffraction grating, 55, 131, 132 Mirrors, 60 Mounting section, 70 Temperature control section, 71 Moving mechanism, 72, 73 Rotation mechanism, 100 Atomic clock device, 110 Atomic generator, 130 Vacuum vessel, 140 Detection device, 150, 170 Control device, 152, 172 Memory, 160 Magnetic field generator, 190 Optical grating, 200 Laser system.

Claims

1. It is an atomic clock device, Vacuum container and An atomic generator that irradiates the vacuum vessel with an atomic beam, A laser device that excites an inter-energy level transition of atoms by irradiating the vacuum vessel with laser light while an atomic beam is being irradiated from the atomic generator, The laser device is equipped with a control device for controlling the laser device, The laser device includes an optical system comprising a laser diode that emits laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. An atomic clock device in which the initial value of the parameter combination is set based on first data showing the change in the oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, and a predetermined target frequency.

2. The atomic clock apparatus according to claim 1, wherein the first data is obtained by a pre-analysis that scans the first parameter and the second parameter.

3. The range in which the parameter combinations can be set includes an adjustment range in which no mode hop occurs in which the oscillation frequency changes. The atomic clock apparatus according to claim 1 or claim 2, wherein the initial value of the parameter combination is selected from among a plurality of parameter combinations included in the adjustment range.

4. Based on the first data mentioned above, several linear functions are calculated, The atomic clock apparatus according to claim 3, wherein the adjustment range is defined based on the plurality of linear functions.

5. The oscillation state of the laser light from the laser device includes a single mode in which only laser light of a specific wavelength is emitted, and a multimode in which laser light of multiple wavelengths is emitted. The atomic clock apparatus according to claim 1 or claim 2, wherein the initial value is set based on the oscillation state of the laser light.

6. The atomic clock apparatus according to claim 1 or claim 2, wherein the initial value is set based on the light intensity of the laser light.

7. The laser device further includes a temperature element that applies heat to a mounting portion on which the external resonator is mounted to adjust the optical system. The atomic clock apparatus according to claim 1 or claim 2, wherein the second parameter includes the temperature of the temperature element.

8. The laser device further comprises a piezoelectric element that adjusts the optical system by expanding or contracting based on voltage, The atomic clock apparatus according to claim 1 or claim 2, wherein the second parameter includes the voltage of the piezoelectric element.

9. The laser device further comprises a movement mechanism for changing the position of the external resonator, The atomic clock apparatus according to claim 1 or claim 2, wherein the second parameter includes the current of the moving mechanism.

10. A laser system that adjusts the oscillation frequency of laser light emitted from a laser device, The laser device and, The laser device is equipped with a control device for controlling the laser device, The laser device includes an optical system comprising a laser diode that emits laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. The control device is A step of acquiring first data showing the change in the oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, A laser system comprising the step of setting initial values ​​for the parameter combination based on the first data and a predetermined target frequency.

11. A method for adjusting the oscillation frequency of laser light from a laser device using a computer, The laser device includes an optical system comprising a laser diode that emits laser light and an external resonator provided outside the laser diode and causing the laser light emitted from the laser diode to resonate. The oscillation frequency of the laser light from the laser device changes based on the current flowing through the laser diode and the optical system including the laser diode and the external resonator. The process to be performed by the aforementioned computer is: A step of acquiring first data showing the change in the oscillation frequency with respect to a parameter combination of a first parameter for adjusting the current and a second parameter for adjusting the optical system, An adjustment method comprising the step of setting initial values ​​for the parameter combination based on the first data and a predetermined target frequency.

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