Ramsay spectrometer, optical lattice clock, and Ramsay spectroscopy method

Abstract

To achieve Ramsey spectroscopy while effectively suppressing the Doppler effect.SOLUTION: A Ramsey spectroscopic device 1 includes: an optical path 10; an optical path length stabilizing circuit 30 that stabilizes the length of the optical path 10; a modulator 20 that is optically connected to the optical path 10, generates, in a pulse shape multiple times, a resonant laser beam at a first frequency f1 that causes resonance of atoms, molecules, or ions, which are a spectroscopic target, and generates a non-resonant laser beam at a second frequency f2 that does not cause resonance; and a spectroscopic unit 200 that spectroscopically disperses the spectroscopic target. The spectroscopic unit detects a state change of the spectroscopic target according to the frequency f1 by irradiating the spectroscopic target with the resonant laser beam.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a Ramsey spectroscopy apparatus, an optical lattice clock including the Ramsey spectroscopy apparatus, and a Ramsey spectroscopy method.

Background Art

[0002] Devices using Ramsey resonance have been proposed (see, for example, Non-Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The following describes the Ramsay spectroscopy apparatus. Ramsay spectroscopy utilizes a phenomenon known as Ramsay resonance. In Ramsay resonance, an atom is pulsed with electromagnetic waves multiple times (two or more times) at intervals, and the Ramsay resonance signal is obtained by causing the electromagnetic waves and atoms to interact. Compared to Rabi spectroscopy, which does not involve multiple pulses, the Ramsay resonance signal is a sharpened signal, making it possible to read the natural frequency of an atom with high resolution. This allows for the highly accurate determination of the natural frequency of an atom.

[0006] Here, it is crucial that the multiple pulses (Ramsey pulses) irradiated are phase-continuous. This means that although the electromagnetic wave is interrupted after each pulse, the phase of the electromagnetic wave in the next pulse is as if the electromagnetic wave were continuously connected. If the phase of the Ramsey pulse is discontinuous, the reading will deviate from the original natural frequency of the atom, leading to a decrease in accuracy. Therefore, the Ramsey pulse is required to satisfy the phase-continuous condition.

[0007] A single-wavelength laser beam can be used as the electromagnetic wave for a Ramsay pulse. However, the Doppler effect, caused by changes in the length of the optical path from the laser source to the atoms, causes fluctuations in the frequency (wavelength) of the laser beam, which degrades the spectral accuracy. In particular, in configurations where the laser beam for spectroscopy is propagated to the spectroscopic unit via an optical path such as an optical fiber, the change in the length of the optical path is large, and the decrease in spectral accuracy is significant.

[0008] As a technique to suppress such Doppler effects, a technique has been proposed that detects frequency fluctuations of laser light associated with changes in optical path length and eliminates them through feedback (optical path length stabilization technique) (see, for example, Non-Patent Document 1).

[0009] Optical path length stabilization techniques require continuous irradiation with laser light, and stabilization stops when the laser light is interrupted. Therefore, they cannot be directly applied to Ramsay spectroscopy, which involves interrupting the light.

[0010] Furthermore, another challenge is that, as mentioned above, it is necessary to satisfy the phase continuity condition of the Ramsey pulse when combining optical path length stabilization technology with Ramsey spectroscopy.

[0011] This invention has been made in view of these problems, and its purpose is to achieve Ramsay spectroscopy while effectively suppressing the Doppler effect. [Means for solving the problem]

[0012] To solve the above problems, a Ramsay spectrometer in one aspect of the present invention comprises an optical path, an optical path length stabilization circuit for stabilizing the length of the optical path, a modulator optically connected to the optical path which generates multiple pulses of resonant laser light at a first frequency f1 that causes resonance in the atoms, molecules, or ions to be spectroscopically targeted, and generates non-resonant laser light at a second frequency f2 that does not cause resonance, and a spectroscopic unit for spectrally analyzing the target, wherein the spectroscopic unit detects changes in the state of the target according to the frequency f1 caused by irradiating the target with resonant laser light.

[0013] In the aforementioned Ramsay spectrometer, when n is an arbitrary natural number, and the oscillation interval of the resonant laser light is T, and times T1 and T2 are defined as times that satisfy |f1-f2|=n / T1 and |f1-f2|=(n+1) / T2, respectively, the oscillation interval T may also satisfy T1-0.25·(T2-T1)≦T≦T1+0.25·(T2-T1).

[0014] The modulator may generate resonant laser light and non-resonant laser light such that their phases are continuous in time.

[0015] The modulator may have a switching element that switches between generating resonant laser light and non-resonant laser light.

[0016] In the aforementioned Ramsay spectrometer, the difference |f1-f2| between the first frequency f1 and the second frequency f2 may satisfy |f1-f2|=n / T.

[0017] The optical path may include an optical fiber.

[0018] The optical path may include free space.

[0019] The modulator and the optical path length stabilization circuit may be integrated.

[0020] The optical path length stabilization circuit may include a PC control oscillator, a voltage control oscillator, and a multiplication circuit.

[0021] The modulator and the optical path length stabilization circuit may be independent.

[0022] The optical path length stabilization circuit may include a PLL circuit.

[0023] The Ramsey spectrometer may include a laser light source connected to one end of the optical path.

[0024] The Ramsey spectrometer may include a laser light modulator connected to the modulator for modulating the laser light emitted from the laser light source.

[0025] The laser light modulator may be an acousto-optic modulator.

[0026] Another aspect of the present invention is an optical lattice clock. This optical lattice clock includes the aforementioned Ramsey spectrometer.

[0027] Yet another aspect of the present invention is a spectroscopic method. This method is a spectroscopic method using a Ramsey spectrometer, where the Ramsey spectrometer includes an optical path, an optical path length stabilization circuit, a modulator optically connected to the optical path, and a spectroscopic unit. This spectroscopic method includes a step of stabilizing the length of the optical path using the optical path length stabilization circuit, a step of generating a pulsed resonance laser light of a first frequency f1 that causes resonance of atoms and a non-resonance laser light of a second frequency f2 that does not cause resonance using the modulator, and a step of spectroscopically analyzing the light to be spectroscopically analyzed using the spectroscopic unit.

[0028] In the spectroscopic method described above, when n is an arbitrary natural number, the oscillation interval of the resonant laser light is T, and times T1 and T2 are defined as times that satisfy |f1-f2|=n / T1|f1-f2|=(n+1) / T2, the oscillation interval T may satisfy T1-0.25·(T2-T1)≦T≦T1+0.25·(T2-T1).

[0029] In the spectroscopic method described above, the difference |f1-f2| between the first frequency f1 and the second frequency f2 may satisfy |f1-f2|=n / T.

[0030] Furthermore, any combination of the above components, as well as conversions of the expression of the present invention between devices, methods, systems, recording media, computer programs, etc., are also valid embodiments of the present invention. [Effects of the Invention]

[0031] According to the present invention, Ramsay spectroscopy can be achieved while effectively suppressing the Doppler effect. [Brief explanation of the drawing]

[0032] [Figure 1] This is a functional block diagram of the Ramsay spectrometer according to the first embodiment. [Figure 2] This graph shows the time evolution of the laser light oscillation frequency of the Ramsey resonance in the first embodiment. [Figure 3] This is a Ramsey fringe in the first embodiment. [Figure 4] This is an enlarged view of Figure 3 near the resonance frequency. [Figure 5] This diagram shows the time evolution of an RF signal. From top to bottom, the diagrams represent signal B with frequency f2, signal A with frequency f1, a signal switched from B to A at t=T using a phase-continuous switch, and a signal switched from B to A at t=T using a phase-coherent switch. [Figure 6]This figure shows the time evolution of an RF signal. (a) is a graph showing the time evolution of the oscillation frequency of the Ramsey-resonant laser light in the first embodiment. (b) is the case where the Ramsey pulse and the non-resonant wave do not satisfy the phase continuity condition. (c) is the case where the Ramsey pulse and the non-resonant wave satisfy the phase continuity condition. [Figure 7] This is a detailed functional block diagram of the Ramsay spectrometer according to the first embodiment. [Figure 8] This is a functional block diagram of the Ramsay spectrometer according to the second embodiment. [Figure 9] This is a detailed functional block diagram of the Ramsay spectrometer according to the second embodiment. [Modes for carrying out the invention]

[0033] The present invention will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and not limiting, and not all features or combinations thereof described in the embodiments are necessarily essential to the invention. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant explanations are omitted as appropriate. Furthermore, the scale and shape of each part shown in each figure are set for convenience to facilitate explanation and are not to be interpreted restrictively unless otherwise specified. In addition, when terms such as "first," "second," etc. are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are merely for distinguishing one configuration from another. Furthermore, some components that are not important for explaining the embodiments are omitted from the drawings.

[0034] [First Embodiment] Figure 1 is a functional block diagram of a Ramsay spectrometer 1 according to the first embodiment. The Ramsay spectrometer 1 comprises an optical path 10, a modulator 20 optically connected to the optical path 10, an optical path length stabilization circuit 30 for stabilizing the length of the optical path 10, an acousto-optic modulator (hereinafter also called "AOM") 40, and a spectrometer 200 for spectrally analyzing atoms to be spectroscopicized. The Ramsay spectrometer 1 is equipped with a Michelson interferometer consisting of a beam splitter 50, a reference mirror 51, and a lattice end mirror 52. An optical heterodyne detector 60 is provided before the optical path length stabilization circuit 30. In the drawing, a laser light source 100 is connected to the left end of the optical path 10, and the spectrometer 200 is connected to the right end. The modulator 20 and the optical path length stabilization circuit 30 are hardware-integrated.

[0035] The optical path 10 may be formed in part or entirely of optical fibers, or it may be formed in part or entirely of free space.

[0036] The modulator 20 generates multiple pulses of resonant laser light at a first frequency f1 that causes atomic resonance, and also generates non-resonant laser light at a second frequency f2 that does not cause resonance. That is, the difference between the first frequency f1 and the second frequency f2 is large enough not to excite the atoms that are excited by the Ramsey pulse. The atoms may be ytterbium, strontium, or cadmium.

[0037] The modulator 20 may generate resonant laser light and non-resonant laser light such that their phases are continuous in time.

[0038] The modulator 20 may have a switching element that switches between generating resonant laser light and non-resonant laser light.

[0039] The laser light source 100 may, for example, be equipped with multiple external resonator type laser diodes.

[0040] The spectroscopic unit 200 detects changes in the state of the target atom according to the frequency of the resonant laser light (first frequency f1) by irradiating the target atom with the resonant laser light arriving from the modulator 20.

[0041] As will be explained in detail below, according to this embodiment, Ramsay spectroscopy can be achieved while effectively suppressing the Doppler effect.

[0042] As an example, when n is an arbitrary natural number and the oscillation interval of the Ramsey pulse is T, the difference |f1-f2| between the first frequency f1 and the second frequency f2 is: |f1-f2|=n / T ···(1) It may satisfy the requirement.

[0043] Here, we will explain Ramsey resonance. To break the degeneracy of energy levels, a steady magnetic field is applied to align the atomic state to a certain level. In this state, the atom is irradiated with an electromagnetic pulse (called a "Ramsey pulse") for a time τ. Then, after an interval of time T, the atom is irradiated again with a Ramsey pulse for a time τ. When the atom and electromagnetic wave interact in this way, in two separate interactions, the probability of the atom transitioning to another state depends not only on the actual interaction time τ but also on the time interval T between the two interactions. As a result, the occurrence of quantum transitions becomes sensitive to changes in the frequency of the irradiated electromagnetic wave. This is called Ramsey resonance. By utilizing this phenomenon, the center frequency of transitions can be measured with high precision. The observed resonance linewidth narrows in proportion to time T. A spectrometer that uses Ramsey resonance is called a Ramsey spectrometer.

[0044] FIG. 2 is a graph showing the time variation of the oscillation frequency of the laser light of the Ramsey resonance in the present embodiment. Hereinafter, regarding time t, let t=-τ be t1, t=0 be t2, t=T be t3, and t=T+τ be t4. As shown in the figure, before time -τ (t<t1), between time 0 and time T (t2<t<t3), and after time T+τ (t4<t), the modulator oscillates an electromagnetic wave of the second frequency f2. On the other hand, between time -τ and time 0 (t1≦t≦t2), and between time T and time T+τ (t3≦t≦t4), the modulator oscillates a Ramsey pulse of the first frequency f! In this example, f1 = 80 MHz and f2 = 79 MHz. Therefore, if the difference |f1 - f2| between f1 and f2 is denoted as Δ, then Δ = 1 MHz.

[0045] FIG. 3 shows the transition probability of atoms when the electromagnetic wave oscillated as shown in FIG. 2 is irradiated on the atoms as a function of frequency detuning (the difference between the optical frequency and the resonance frequency). This graph shows fringes like interference fringes and is called a "Ramsey fringe". FIG. 4 is an enlarged view near the resonance frequency of FIG. 3. As shown in the figure, according to the Ramsey resonance, the resonance frequency can be measured with a resolution on the order of 1 / T. This indicates that the longer the interval T of the Ramsey pulses, the higher the measurement accuracy. On the other hand, as shown in FIG. 3, the full width at half maximum of the envelope of the Ramsey fringe is on the order of 1 / τ.

[0046] It is desirable that the second frequency f2 is a frequency that does not excite the atoms excited by the Ramsey pulse, that is, a non-resonance frequency.

[0047] The first Ramsey pulse (t1≦t≦t2) and the second Ramsey pulse (t3≦t≦t4) are phase coherent. Specifically, both Ramsey pulses are taken from the resonance light reference of the same atom. If the two Ramsey pulses were not phase coherent, their phase relationship would be random within [0, 2π]. Therefore, the interference fringes of the graph in FIG. 3 would be unclear and only the envelope would be observed. In this case, the measurement accuracy of the resonance frequency drops from the order of 1 / T to the order of 1 / τ.

[0048] As described above, the Ramsey resonance circuit turns on the switch of the first Ramsey pulse at t = t1 and turns it off at t = t2. Then, it turns on the switch of the second Ramsey pulse at t = t3 and turns it off at t = t4. By turning on and off this switch, the frequency switches between f1 and f2. In this case, the modulation for Ramsey resonance is FSK. Note that in FSK modulation, the power input to the AOM crystal does not change, so the crystal does not change in temperature and no chirp occurs in the frequency.

[0049] Generally, rather than irradiating an electromagnetic wave with a second frequency f2 before time - τ (t < -τ), between time 0 and time T (0 < t < T), and after time T + τ (T + τ < t), the case where no electromagnetic wave is irradiated during this period is often called Ramsey resonance (in this case, the period when no electromagnetic wave is irradiated is also called the "dark time"). In the case of Ramsey resonance with a dark time, the signal takes two values, 0 (dark time) and 1 (when the Ramsey pulse is irradiated), so the modulation is amplitude - shift keying (hereinafter referred to as "ASK" (Amplitude Shift Keying)). In ASK, contrary to FSK, the power input to the AOM crystal changes. Therefore, note that due to the change in temperature of the crystal, which causes expansion / contraction and refractive index changes, a chirp occurs in the frequency.

[0050] Figure 5 shows the time evolution of the RF signal modulating the Ramsey resonance laser light. From top to bottom, the graphs show signal B at frequency f2, signal A at frequency f1, the signal switched from B to A at t=T using a phase-continuous switch, and the signal switched from B to A at t=T using a phase-coherent switch. As mentioned above, the switch for the second Ramsey pulse is turned on at t=T(t3). This switch is a phase-coherent switch, as previously stated. Therefore, if the phase continuity condition is not required, a phase difference occurs between signal B and signal A at t=T(t3) (bottom of Figure 5). If the phases of signal B and signal A are discontinuous, high-frequency components are generated, and the control of the optical path length stabilization circuit becomes unstable. As a result, sufficient suppression of the Doppler effect cannot be achieved. Therefore, it is required that the phase continuity condition is satisfied between signal B and signal A at t=T(t3) (third from the top of Figure 5).

[0051] Figure 6 shows the time evolution of the RF signal when the Ramsey resonance shown in Figure 2 is applied. Figure 6(a) is a reproduction of Figure 2. Figure 6(b) shows the case where the first frequency f1 electromagnetic wave (Ramsey pulse) and the second frequency f2 electromagnetic wave (non-resonant wave) do not satisfy the phase continuity condition. Figure 6(c) shows the case where the first frequency f1 electromagnetic wave and the second frequency f2 electromagnetic wave satisfy the phase continuity condition. As shown in Figure 6(b), when the phase continuity condition is not satisfied, a phase jump occurs between the Ramsey pulse and the non-resonant wave. As shown in Figure 6(c), when the phase continuity condition is satisfied, no phase jump occurs between the Ramsey pulse and the non-resonant wave. This is preferable for suppressing the Doppler effect.

[0052] After the first Ramsey pulse is switched off at time t=0(t2), and before the second Ramsey pulse is switched on at time t=T(t3), the phase of signal A advances by 2π·f1·T, and the phase of signal B advances by 2π·f2·T. Therefore, for the phases of both signals to coincide at time t=T(t3), |2π·f1·T-2π·f2·T|=n·2π In other words |f1-f2|=(Δ=)n / T It is necessary and sufficient to satisfy the following condition (where n is a natural number). This embodiment satisfies this relationship. As a result, this embodiment achieves phase-coherent FSK while simultaneously satisfying the phase continuity condition when the Ramsey pulse is switched on. This makes it possible to achieve Ramsey spectroscopy while more effectively suppressing the Doppler effect.

[0053] The value of n above can be any natural number and is not restricted by any upper or lower limit. In practice, it is best to first determine the resonance frequency (f1) and the Ramsey pulse interval (T), then determine an approximate value of n corresponding to the detuning (Δ=|f1-f2|), and then select f2 according to the above formula. For example, if the resonance frequency f1=80MHz and T=1s are set, and Δ is set to approximately 1MHz, then the corresponding n would be: n=T·|f1-f2|=T·Δ=1s·1MHz=106 Since this is determined, f2 is set to 79MHz, and so on.

[0054] Here, n is a natural number, f1 is the first frequency, f2 is the second frequency, and T is the oscillation interval of the Ramsey pulse, not necessarily strictly. |f1-f2|=n / T ···(1) It is not necessary to satisfy this condition. For example, for any natural number n, the times T1 and T2 are respectively |f1-f2|=n / T1 ···(2) |f1-f2|=(n+1) / T2 ···(3) When defined as the time that satisfies the condition, the oscillation interval T is, T1-0.25 (T2-T1)≦T≦T1+0.25 (T2-T1) (4) It may also satisfy the condition. In this case, the oscillation interval T will deviate by up to ±25% from the T that satisfies equation (1). Even with this degree of deviation in the oscillation interval T, the phase between the Ramsey pulse and the non-resonant wave is practically smooth enough, the control of the optical path length stabilization circuit operates normally, the Doppler effect can be sufficiently suppressed, and sufficient spectral accuracy can be obtained.

[0055] According to this embodiment, the oscillation interval of the Ramsey pulse can be given a range of approximately ±25% from the optimal value. Therefore, the degree of design flexibility is improved.

[0056] The laser light modulator 40 is not limited to an AOM, but may be any suitable optical modulator. The detector 60 is not limited to an optical heterodyne detector, but may be any suitable detector. The laser light source 100 is not limited to a laser light source, but may be any suitable laser light source.

[0057] [Comparative Example] A comparative example to the first embodiment will now be described. As a comparative example, Non-Patent Literature 1 describes a Ramsay spectrometer for an optical lattice clock. The component configuration of this comparative example is similar to that of this embodiment, but it differs from this embodiment in that it does not use the control of |f1-f2|=n / T (phase continuity condition). Therefore, it can be seen that this embodiment has the remarkable effect of being able to achieve Ramsay spectroscopy while effectively suppressing the Doppler effect compared to the comparative example.

[0058] [First Embodiment (Re-)] Returning to the description of the first embodiment, Figure 7 is a detailed functional block diagram of the Ramsay spectrometer 1 of Figure 1. The modulator and the optical path stabilization circuit are integrated in hardware. The optical path length stabilization circuit 30 includes a pulse generator 29. The optical path length stabilization circuit 30 comprises a PC-controlled oscillator, a voltage-controlled oscillator, a multiplication circuit (phase comparison circuit), and a PLL (Phase Locked Loop) including a loop filter.

[0059] The laser beam with frequency f emitted from the laser light source 100 is split into two by the beam splitter 50. One of the split laser beams goes to the reference mirror 51, and the other goes to the AOM 40. The AOM 40 imparts the intended frequency shift fM to the latter laser beam. The laser beam, with frequency f+fM after being given the frequency shift fM by the AOM 40, is subjected to an unintended frequency shift Δf (Doppler effect due to change in the length of the optical path, usually around 1 kHz) as it passes through the optical path 10. Therefore, the frequency of the laser beam becomes f+fM+Δf. This laser beam is reflected by the lattice end mirror 52 and returns to the AOM through the same optical path as described above. In the optical path, the same unintended frequency shift as described above is given, so the frequency becomes f+fM+2·Δf. The AOM 40 again imparts the intended frequency shift fM to this laser beam. As a result, the frequency of the laser beam becomes f+2·(fM+Δf). This laser beam and the laser beam of frequency f reflected by the reference mirror 51 are input to the optical heterodyne detector 60 via the beam splitter 50. The optical heterodyne detector 60 detects these two laser beams and detects the difference frequency 2·(fM+Δf).

[0060] This difference frequency signal of 2·(fM+Δf) is input to one of the input terminals of the multiplier circuit. Meanwhile, a signal of frequency 2·fM is output from the PC-controlled oscillator and input to the other input terminal of the multiplier circuit. The output from the multiplier circuit is a signal of 2·Δf, but the RF signal of the AOM40 is controlled so that this becomes zero. This suppresses the fluctuation Δf due to the Doppler effect. By switching fM to the RF signal corresponding to the Ramsey pulse (80MHz when on, 79MHz when off), a Ramsey pulse with suppressed fluctuation Δf due to the Doppler effect can be provided.

[0061] According to this embodiment, the Doppler effect can be effectively suppressed by using a PC-controlled oscillator, a voltage-controlled oscillator, a multiplier circuit (phase comparison circuit), and a PLL (Phase Locked Loop) including a loop filter.

[0062] [Second Embodiment] Figure 8 is a functional block diagram of the Ramsay spectrometer 2 according to the second embodiment. The Ramsay spectrometer 2 comprises an optical path 10, a pulse generator 29, an optical path length stabilization circuit 30, and a laser light modulator 40. The Ramsay spectrometer 2 differs from the Ramsay spectrometer 1 in Figure 1 in that the modulator for generating Ramsay pulses and the optical path length stabilization circuit are configured independently in hardware. All other aspects are the same as the Ramsay spectrometer 1.

[0063] Figure 9 is a detailed functional block diagram of the Ramsay spectrometer 2 according to the second embodiment. The optical path length stabilization circuit 30 includes a voltage-controlled oscillator, an oscillator, a multiplier circuit (phase comparison circuit), and a PLL (Phase Locked Loop) including a loop filter.

[0064] The laser light emitted from the laser light source 100 is switched in frequency by the AOM42 to generate a Ramsey pulse. For example, the frequency is set to 80 MHz when on and 79 MHz when off. After inputting to the AOM42, the laser light of frequency f is split into two by the beam splitter 50. The subsequent operation of the Ramsey spectrometer 2 is the same as that of the Ramsey spectrometer 1 shown in Figure 7.

[0065] The difference frequency signal 2·(fM+Δf) is input to one of the input terminals of the multiplier circuit. Meanwhile, the reference frequency signal of 160MHz (=2·fM) emitted from the oscillator is input to the other input terminal of the multiplier circuit. The multiplier circuit detects the phase difference between the difference frequency 2·(fM+Δf) and the reference frequency. The loop filter controls the difference frequency 2·(fM+Δf) so that its phase difference with the reference frequency is zero, and inputs it to the voltage-controlled oscillator. The voltage-controlled oscillator oscillates a signal of fM-Δf (=80MHz-Δf). As a result, a Ramsey pulse with a suppressed contribution Δf due to the Doppler effect can be obtained.

[0066] Similar to the first embodiment, this embodiment also enables Ramsay spectroscopy while effectively suppressing the Doppler effect.

[0067] [Third Embodiment] The third embodiment is an optical lattice clock. This optical lattice clock is characterized by comprising the Ramsey spectrometer of the embodiment described above. Existing technology may be used for the basic configuration of the optical lattice clock. For example, the optical lattice clock described in Non-Patent Document 5 comprises an optical waveguide, an optical path, a laser light source, a laser cooling unit, and an optical lattice. The optical lattice clock of this embodiment can be constructed by adding the Ramsey spectrometer described above to the optical lattice clock described in Non-Patent Document 5.

[0068] According to this embodiment, it is possible to provide an optical lattice clock that enables Ramsay spectroscopy while effectively suppressing the Doppler effect.

[0069] [Fourth Embodiment] The fourth embodiment is a spectroscopic method. This spectroscopic method is characterized by using the Ramsay spectrometer of the embodiment described above. That is, the Ramsay spectrometer comprises an optical path, an optical path length stabilization circuit, a modulator optically connected to the optical path, and a spectroscopic unit. This method comprises the steps of stabilizing the length of the optical path using the optical path length stabilization circuit, generating multiple pulses of resonant laser light at a first frequency f1 that causes atomic resonance, and generating non-resonant laser light at a second frequency f2 that does not cause resonance, and spectrally analyzing the light to be spectrally analyzed using the spectroscopic unit.

[0070] According to this embodiment, Ramsay spectroscopy can be achieved while effectively suppressing the Doppler effect.

[0071] In one embodiment, n is an arbitrary natural number, and the oscillation interval of the resonant laser light is T. Time T1 and T2 respectively |f1-f2|=n / T1 |f1-f2|=(n+1) / T2 When defined as the time that satisfies the conditions, the oscillation interval T is T1-0.25 (T2-T1)≦T≦T1+0.25 (T2-T1) The modulator may be controlled to satisfy the following condition:

[0072] According to this embodiment, the oscillation interval of the Ramsey pulse can be set to a range of ±25% from the optimal value. Therefore, the degree of design flexibility is improved.

[0073] In one embodiment, when n is an arbitrary natural number and the oscillation interval of the resonant laser light is T, the difference |f1-f2| between the first frequency f1 and the second frequency f2 is, |f1-f2|=n / T The modulator may be controlled to satisfy the following condition:

[0074] According to this embodiment, Ramsay spectroscopy can be achieved while more effectively suppressing the Doppler effect.

[0075] The present invention has been described above based on embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications also fall within the scope of the present invention.

[0076] For example, although atoms were shown as the target of spectroscopy in the embodiments described above, the present invention is not limited thereto, and molecules or ions may also be used as the target of spectroscopy. [Explanation of Symbols]

[0077] 1. Ramsay spectrometer, 2. Ramsay spectrometer, 3. Ramsay spectrometer, 4. Ramsay spectrometer, 10.. Light path, 20. Modulator, 30. Optical path length stabilization circuit, 40···AOM, 42···AOM, 50-beam splitter, 51. See mirror, 52. Grid end mirror, 60. Optical heterodyne detector, 100 laser light sources, 200...Spectroscopy section, f1...the first frequency, f2...the second frequency.

Claims

1. Light path and An optical path length stabilization circuit for stabilizing the length of the optical path, A modulator optically connected to the optical path generates multiple pulses of resonant laser light at a first frequency f1 that causes resonance in the atoms, molecules, or ions to be spectrally analyzed, and generates non-resonant laser light at a second frequency f2 that does not cause resonance. The system comprises a spectrometer for spectrally analyzing the object to be spectrally analyzed, The spectroscopic unit detects a change in the state of the spectroscopic target according to the frequency f1 by irradiating the spectroscopic target with the resonant laser light, Let n be any natural number, and let T be the oscillation interval of the resonant laser light. Time T1 and T2 respectively |f1-f2|=n / T1 |f1-f2|=(n+1) / T2 When defined as the time that satisfies the condition, the oscillation interval T is, T1-0.25・(T2-T1)≦T≦T1+0.25・(T2-T1) A Ramsay spectrometer that satisfies the following conditions.

2. The Ramsay spectrometer according to claim 1, wherein the modulator generates the resonant laser light and the non-resonant laser light such that their phases are continuous in time.

3. The Ramsay spectrometer according to claim 1 or 2, wherein the modulator has a switching element that switches between generating the resonant laser light and the non-resonant laser light.

4. The Ramsey spectrometer according to claim 1, wherein the difference |f1-f2| between the first frequency f1 and the second frequency f2 satisfies |f1-f2| = n / T.

5. The Ramsay spectrometer according to any one of claims 1 to 4, wherein the optical path includes an optical fiber.

6. The Ramsay spectrometer according to any one of claims 1 to 5, wherein the optical path includes free space.

7. The Ramsay spectrometer according to any one of claims 1 to 6, wherein the modulator and the optical path length stabilization circuit are integrated.

8. The Ramsey spectrometer according to claim 7, wherein the optical path length stabilization circuit comprises a PC-controlled oscillator, a voltage-controlled oscillator, and a multiplication circuit.

9. The Ramsay spectrometer according to any one of claims 1 to 6, wherein the modulator and the optical path length stabilization circuit are independent.

10. The Ramsay spectrometer according to claim 9, wherein the optical path length stabilization circuit comprises a PLL circuit.

11. The Ramsay spectrometer according to any one of claims 1 to 10, comprising a laser light source connected to one end of the optical path.

12. The Ramsay spectrometer according to claim 11, further comprising a laser light modulator connected to the modulator and for modulating the laser light emitted from the laser light source.

13. The Ramsay spectrometer according to claim 12, wherein the laser light modulator is an acousto-optic modulator.

14. An optical lattice clock comprising the Ramsay spectrometer described in claim 1.

15. A spectroscopic method using a Ramsay spectrometer, The Ramsay spectrometer described above is Light path and Optical path length stabilization circuit, A modulator optically connected to the aforementioned optical path, A spectrometer is provided, The steps include stabilizing the length of the optical path using the optical path length stabilization circuit, The method comprises the steps of: using the modulator to generate multiple pulses of resonant laser light at a first frequency f1 that causes resonance in the atoms, molecules, or ions to be spectrally analyzed, and generating non-resonant laser light at a second frequency f2 that does not cause resonance; and using the spectroscopic unit to spectrally analyze the target object. Let n be any natural number, and let T be the oscillation interval of the resonant laser light. Time T1 and T2 respectively |f1-f2|=n / T1 |f1-f2|=(n+1) / T2 When defined as the time that satisfies the condition, the oscillation interval T is, T1-0.25・(T2-T1)≦T≦T1+0.25・(T2-T1) A spectroscopic method that satisfies the following conditions.

16. The spectroscopic method according to claim 15, wherein the difference |f1-f2| between the first frequency f1 and the second frequency f2 satisfies |f1-f2| = n / T.

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