Measuring device and measuring method

Abstract

A high-frequency magnetic field generator applies microwaves to a magnetic resonance member in which an electron spin quantum state changes in response to an AC field to be measured, and in which an electron spin quantum operation can be performed using microwaves. A high-frequency power supply causes the high-frequency magnetic field generator to generate microwaves. A light emitting device emits excitation light to be emitted onto the magnetic resonance member. A measurement control unit controls the high-frequency power supply and the light emitting device to apply microwaves and excitation light to the magnetic resonance member in a predetermined measurement sequence. In particular, the measurement control unit applies a Hahn echo pulse sequence or a pulse sequence of microwaves based on dynamic decoupling to the magnetic resonance member. At this time, the reciprocal (1 / fLOCK) of the spin lock frequency of the microwave pulse sequence is different from the period (1 / fAC) of the AC field to be measured.

Description

Measuring device and measuring method

[0001] The present invention relates to a measurement device and a measurement method.

[0002] One magnetic field measurement device performs magnetic measurements using optically detected magnetic resonance (ODMR), which utilizes the electron spin resonance of a sensing element such as a diamond structure having nitrogen and lattice defects (NV centers). In ODMR, a static magnetic field is applied to a magnetic resonance element such as a diamond having such an NV center, in addition to the magnetic field to be measured, and laser light (excitation light for initialization and measurement) and microwaves are applied in a predetermined sequence, and the amount of fluorescent light emitted from the magnetic resonance element is detected, and the magnetic flux density of the magnetic field to be measured is derived based on the amount of light (see, for example, Patent Document 1).

[0003] For example, when the measured magnetic field is an AC magnetic field, a Hahn echo (spin echo) pulse sequence is used, which includes the following steps: (a) irradiating the NV center with excitation light, (b) applying a first π / 2 microwave pulse to the NV center at a phase of 0° of the measured magnetic field, (c) applying a π microwave pulse to the NV center at a phase of 180° of the measured magnetic field, (d) applying a second π / 2 microwave pulse to the NV center at a phase of 360° of the measured magnetic field, (e) irradiating the NV center with excitation light to measure the amount of light emitted from the NV center, and (f) deriving the magnetic flux density based on the measured amount of light emitted.

[0004] Japanese Patent Application Laid-Open No. 2019-138772

[0005] As described above, when the magnetic field to be measured is an AC magnetic field, a Hahn echo (spin echo) pulse sequence, dynamic decoupling, or the like is generally used. In these methods, the spin of the NV center is inverted with a π pulse, thereby increasing the phase amount in which the effect of the magnetic field accumulates and improving sensitivity. However, it is desirable to be able to obtain even higher sensitivity.

[0006] The present invention has been made in view of the above problems, and has as its object to provide a measuring device and a measuring method that can achieve higher sensitivity.

[0007] The measurement device according to the present invention includes a magnetic resonance element whose electron spin quantum state changes in response to a measured AC field and whose electron spin quantum state can be manipulated by microwaves, a radio-frequency magnetic field generator that manipulates the electron spin quantum state of the magnetic resonance element using the microwaves, a radio-frequency power supply that causes the radio-frequency magnetic field generator to generate microwaves, a light-emitting device that emits excitation light to be irradiated onto the magnetic resonance element, a light-receiving device that receives fluorescence emitted by the magnetic resonance element in response to the excitation light and generates a detection signal corresponding to the intensity of the fluorescence, a measurement controller that controls the radio-frequency power supply and the light-emitting device to apply the microwaves and excitation light to the magnetic resonance element in a predetermined measurement sequence, and a measurement processor that derives a measurement value based on the detection signal. The measurement controller applies a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling to the magnetic resonance element. The reciprocal of the spin-locking frequency of the microwave pulse sequence is different from the period of the measured AC field.

[0008] The measurement method according to the present invention includes: (a) performing electron spin quantum manipulation of a magnetic resonance component, the electron spin quantum state of which changes in response to a measured AC field and which is capable of electron spin quantum manipulation using microwaves, using the microwaves in accordance with a predetermined measurement sequence, and irradiating the magnetic resonance component with excitation light to be irradiated thereon; (b) receiving fluorescence emitted by the magnetic resonance component in response to the excitation light and generating a detection signal corresponding to the intensity of the fluorescence; and (c) deriving a measurement value based on the detection signal. In the measurement sequence, a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling is applied to the magnetic resonance component. The reciprocal of the spin locking frequency of the microwave pulse sequence is different from the period of the measured AC field.

[0009] According to the present invention, a measuring device and a measuring method that can achieve higher sensitivity are provided.

[0010] Fig. 1 is a block diagram showing the configuration of a measurement device according to a first embodiment of the present invention. Fig. 2 is a diagram showing an example of a measurement sequence in the first embodiment. Fig. 3 is a diagram showing a measurement sequence for a spin-lock frequency f ＬＯＣＫ and the frequency f of the AC field to be measured ＡＣ 4 is a diagram illustrating the relationship between the frequency f of the AC field to be measured and the maximum value max|dS / dB| of the derivative (dS / dB) of the intensity S of the detection signal with respect to the magnetic flux density B of the AC field to be measured. ＡＣ 5 is a diagram illustrating the distribution of the detected signal strength S (relative value) with respect to the frequency f of the AC field to be measured in the first embodiment. ＡＣ FIG. 6 is a diagram illustrating the maximum slope value max|dS / dB| with respect to the frequency fs / sampling frequency fs in the second embodiment. FIG. 7 is a diagram illustrating the detection signal appearing in the observable band in the second embodiment. FIG. 8 is a diagram illustrating a case where a band corresponding to a range from half the sampling frequency fs (fs / 2) to the sampling frequency fs is attenuated in the filter processing. FIG. 9 is a diagram illustrating a case where a band corresponding to a range from 0 to half the sampling frequency (fs / 2) is attenuated in the filter processing. FIG. 10 is a diagram illustrating a measurement sequence (dynamic decoupling) in the third embodiment. FIG. 11 is a diagram illustrating a case where a frequency fs / sampling frequency fs of the AC field to be measured in the third embodiment is attenuated in the filter processing. ＡＣ 12 is a diagram illustrating an example of a measurement sequence according to the fourth embodiment. FIG. 13 is a diagram illustrating a maximum gradient max|dS / dB| with respect to a frequency f ＡＣ 14 is a diagram illustrating the sensitivity corresponding to the first detected value, the second detected value, and the measurement value in the fourth embodiment. FIG. 15 is a diagram illustrating the sensitivity corresponding to the frequency f of the AC field to be measured in the fourth embodiment. ＡＣ 16 is a diagram (1 / 2) for explaining the maximum slope max|dS / dB| with respect to the frequency f ＡＣ 17 is a diagram (2 / 2) illustrating the maximum value of the slope max|dS / dB| with respect to the frequency fＡＣ 18 is a diagram (1 / 2) for explaining the maximum slope max|dS / dB| with respect to the frequency f ＡＣ 10 is a diagram (2 / 2) illustrating the maximum value of the gradient max|dS / dB| with respect to

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] Embodiment 1.

[0013] 1 is a block diagram showing the configuration of a measurement device according to a first embodiment of the present invention. The measurement device shown in FIG. 1 includes a sensor unit 10, a high-frequency power supply 11, a light-emitting device 12, and a light-receiving device 13.

[0014] The sensor unit 10 detects a measured field (e.g., a magnetic field such as the strength and direction of the magnetic field) at a predetermined position (e.g., on or above the surface of an object to be inspected). The measured field may be an AC field of a single frequency or an AC field of a predetermined period having multiple frequency components.

[0015] In this embodiment, the sensor unit 10 includes a magnetic resonance member 1, a high-frequency magnetic field generator 2, and a magnet 3, and detects the field to be measured by ODMR.

[0016] The magnetic resonance component 1 has a crystalline structure, and the electron spin quantum state changes in response to the field to be measured (here, the magnetic field), and the electron spin quantum state can be manipulated (based on Rabi oscillation) by microwaves with a frequency corresponding to the alignment direction of defects and impurities in the crystal lattice. That is, the magnetic resonance component 1 is placed at the position where the magnetic field is to be measured.

[0017] In this embodiment, the magnetic resonance component 1 is a photodetector magnetic resonance component having a plurality (i.e., an ensemble) of specific color centers, each of which has an energy level that can be Zeeman split and can assume a plurality of orientations with different energy level shift widths upon Zeeman splitting.

[0018] Here, the magnetic resonance component 1 is a component such as diamond that includes multiple NV (Nitrogen Vacancy) centers as a single type of specific color center. In the case of NV centers, the ground state is a triplet state of ms = 0, +1, -1, and the ms = +1 level and the ms = -1 level are Zeeman split. When the NV centers transition from the excited state of the ms = +1 and ms = -1 levels to the ground state, a certain proportion of them emit fluorescence, while the remaining proportion of the NV centers transition from the excited state (ms = +1 or ms = -1) to the ground state (ms = 0) without radiation.

[0019] The color center included in the magnetic resonance member 1 may be a color center other than the NV center.

[0020] The radio frequency magnetic field generator 2 applies microwaves to the magnetic resonance member 1 to perform electron spin quantum manipulation in the magnetic resonance member 1. The radio frequency power supply 11 generates a microwave current and conducts it through the radio frequency magnetic field generator 2, causing the radio frequency magnetic field generator 2 to generate microwaves.

[0021] For example, the high-frequency magnetic field generator 2 is a plate-shaped coil that includes a substantially circular coil portion that emits microwaves and terminal portions that extend from both ends of the coil portion and are fixed to a substrate. The coil portion conducts two parallel currents at both end surfaces at a predetermined interval so as to sandwich the magnetic resonance component 1, thereby emitting the microwaves. Here, although the coil portion is a plate-shaped coil, microwave current flows through the end surfaces of the coil portion due to the skin effect, forming two currents. As a result, microwaves of spatially uniform intensity are applied to the magnetic resonance component 1.

[0022] In the case of NV centers, color centers are formed in diamond crystals by defects (vacancies) (V) and nitrogen (N) as impurities, and there are four possible positions of adjacent nitrogen (N) relative to the defects (vacancies) (V) in the diamond crystal (i.e., the arrangement direction of the vacancy-nitrogen pair), and the sublevels (i.e., the energy levels from the ground state) after Zeeman splitting corresponding to each of these arrangement directions are different from each other. Therefore, in the characteristics of the fluorescence intensity after Zeeman splitting by a static magnetic field with respect to the microwave frequency, four different dip frequency pairs (fi+, fi-) appear corresponding to each direction i (i = 1, 2, 3, 4). Here, the frequency (wavelength) of the microwave described above is set corresponding to one of the dip frequencies of these four dip frequency pairs.

[0023] The magnet 3 applies a static magnetic field (a direct current magnetic field) to the magnetic resonance member 1, and Zeeman-splits the energy levels of a plurality of specific color centers (here, a plurality of NV centers) in the magnetic resonance member 1. Here, the magnet 3 is a ring-shaped permanent magnet, such as a ferrite magnet, an alnico magnet, or a samarium-cobalt magnet.

[0024] In this embodiment, the direction of application of the static magnetic field is the same as the direction of application of the magnetic field to be measured, and application of the static magnetic field enhances the change in fluorescence intensity at the dip frequency, thereby increasing sensitivity.

[0025] Furthermore, in this embodiment, the magnetic resonance member 1 includes a plurality of color centers (here, NV centers) capable of quantum manipulation of electron spins by microwaves, and the magnet 3 applies a substantially uniform static magnetic field to a predetermined region (irradiation region of excitation light) of the magnetic resonance member 1. For example, the static magnetic field is applied so that the difference or ratio between the maximum and minimum values ​​of the static magnetic field strength in the predetermined region is equal to or less than a predetermined value.

[0026] Furthermore, in the magnetic resonance component 1, the crystals of the magnetic resonance component 1 are formed and the orientation of the magnetic resonance component 1 is set so that the arrangement direction of the above-mentioned defects and impurities approximately coincides with the direction of the above-mentioned static magnetic field (and the direction of the applied magnetic field).

[0027] Furthermore, in this embodiment, an optical system is provided from the light-emitting device 12 to the magnetic resonance component 1 in order to irradiate excitation light onto the magnetic resonance component 1, and an optical system is provided from the magnetic resonance component 1 to the light-receiving device 13 in order to detect fluorescence from the magnetic resonance component 1.

[0028] The light-emitting device 12 includes a laser diode or the like as a light source, which emits laser light of a predetermined wavelength as excitation light to be irradiated onto the magnetic resonance component 1. The light-receiving device 13 includes a photodiode, a phototransistor, or the like as a light-receiving element, which receives fluorescence emitted by the magnetic resonance component 1 in response to the excitation light, and generates a fluorescence sensor signal PL corresponding to the intensity of the fluorescence. This fluorescence is focused toward the light-receiving device 13 by an optical system such as a compound parabolic concentrator (CPC).

[0029] The light receiving device 13 includes a light receiving element that generates an electrical signal corresponding to the incident light by the photoelectric effect, receives the fluorescence emitted by the magnetic resonance component 1 in response to the excitation light, and generates a detection signal corresponding to the intensity of the fluorescence. The light receiving device 13 may include a signal processing unit that performs predetermined signal processing on the electrical signal output from the light receiving element to generate a detection signal, or the electrical signal output from the light receiving element may be used as the detection signal.

[0030] For example, the signal processing may involve common mode rejection using a reference signal based on a reference light branched from the excitation light.

[0031] Furthermore, the measuring device shown in FIG. 1 includes an analog-to-digital converter 21 that digitizes the detection signal, and a processing unit 31 that controls the measuring device and performs signal processing.

[0032] The analog-to-digital converter 21 samples and digitizes the detection signal at a predetermined sampling frequency fs, and outputs the digitized detection signal to the arithmetic processing device 31 .

[0033] The arithmetic processing device 31 includes, for example, a computer, and executes a signal processing program on the computer to operate as various processing units. In this embodiment, the arithmetic processing device 31 causes the computer to operate as a measurement control unit 41 and a measurement processing unit 42, and also includes a non-volatile storage device 43.

[0034] A signal processing program is stored in the storage device 43, and the computer is equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and operates as the measurement control unit 41 and measurement processing unit 42 by loading the signal processing program into the RAM and executing it on the CPU.

[0035] The measurement control unit 41 (a) controls the high-frequency power supply 11 and the light-emitting device 12 to apply microwaves and excitation light to the magnetic resonance component 1 in a predetermined measurement sequence, and (b) acquires the detection signals digitized as described above, stores them in RAM or the storage device 43, and causes the measurement processing unit 42 to derive measurement values ​​of the AC field to be measured. The measurement processing unit 42 derives the measurement values ​​based on the digitized detection signals.

[0036] However, in the case of a conventional Hahn echo pulse sequence (spin echo pulse sequence) or conventional dynamic decoupling, the reciprocal of the spin lock frequency of the microwave pulse sequence, 1 / f ＬＯＣＫ ) is the period of the AC field to be measured (1 / f ＡＣ ) of the spin lock frequency of the microwave pulse sequence in the measurement sequence. ＬＯＣＫ ) is the period of the AC field to be measured (1 / f ＡＣ ) where f ＬＯＣＫ is the spin lock frequency, and f ＡＣ is the frequency of the AC field to be measured.

[0037] 2 is a diagram showing an example of a measurement sequence. Fig. 2 shows the timing of microwave pulses with respect to the AC magnetic field to be measured and the timing of excitation light irradiation (twice, for initialization and measurement) in the measurement sequence of embodiment 1. As shown in Fig. 2, for each measurement, fluorescence is detected during the excitation light irradiation period.

[0038] In particular, the measurement control unit 41 applies a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling to the magnetic resonance element 1. At this time, the reciprocal of the spin lock frequency (1 / f ＬＯＣＫ ) is the period (1 / f ＡＣ In the first embodiment, a microwave pulse sequence based on a Hahn echo sequence (spin echo pulse sequence) is applied to the magnetic resonance component 1 .

[0039] The reciprocal of the spin lock frequency (1 / f ＬＯＣＫ ) is the time length from the end of the first π / 2 pulse to the beginning of the second π / 2 pulse, as shown in FIG. 2, for example. In the first embodiment, the measurement control unit 41 applies a microwave pulse sequence based on the Hahn echo pulse sequence to the magnetic resonance element 1 in the measurement sequence. However, the reciprocal of the spin lock frequency (1 / f ＬＯＣＫ ) is the period (1 / f ＡＣ ) shorter.

[0040] FIG. 3 shows the spin lock frequency f ＬＯＣＫ and the frequency f of the AC field to be measured ＡＣ and the maximum value max|dS / dB| of the derivative (dS / dB) of the detection signal intensity S with respect to the magnetic flux density B of the AC field to be measured.

[0041] As shown in FIG. 3, the strength S of the detected signal is ＡＣ , and f ＬＯＣＫ is a function of f ＡＣ and f ＬＯＣＫIn the equation shown in Fig. 3, γ is the gyromagnetic ratio (a constant), and φ0 is the phase shift between the microwave pulse sequence and the AC field to be measured.

[0042] Here, as shown in FIG. 3, for example, dS / dB represents a slope, and the larger dS / dB is, the higher the sensitivity is. Therefore, under the condition where max|dS / dB| is maximized, f ＡＣ and f ＬＯＣＫ is preferably set.

[0043] FIG. 4 shows the frequency f ＡＣ 4 is a diagram illustrating the distribution of the detected signal strength S (relative value) with respect to the frequency f of the AC field to be measured in the first embodiment. ＡＣ 10 is a diagram illustrating the maximum value of the gradient max|dS / dB| with respect to

[0044] For example, as shown in FIG. 4, the detected signal strength S varies depending on the magnitude of the phase shift between the AC field to be measured and the measurement sequence. For example, as shown in FIGS. 4 and 5, the maximum value of the detected signal strength S is f ＡＣ ga f ＬＯＣＫ If it is the same as f ＡＣ ga f ＬＯＣＫ It should be noted that FIG. 5 shows the relationship between f and ＡＣ The maximum value of the slope max|dS / dB| at each value is shown.

[0045] That is, the maximum value (max|dS / dB|) of the differential (dS / dB) of the intensity S of the detection signal with respect to the magnetic flux density B of the AC field to be measured is the spin lock frequency f ＬＯＣＫ is the frequency f of the AC field to be measured ＡＣ The spin lock frequency f is set to be larger when ＬＯＣＫ and the wave number f of the AC field to be measured ＡＣ The frequency f of the AC field to be measured is set. ＡＣ is preferably set at (or near) the peak frequency of the characteristic curve in FIG.

[0046] Also, the frequency f of the AC field to be measured ＡＣ If there is a possibility that a fluctuation or deviation of a predetermined width may occur in the characteristic curve, a measurement band of a predetermined width is set that includes the peak frequency of the characteristic curve in Fig. 5. By setting the measurement band in this way, it is possible to perform measurements under conditions that provide a good maximum slope (max|dS / dB|) (i.e., sensitivity).

[0047] Next, the operation of the measurement device according to the first embodiment will be described.

[0048] The sensor unit 10 is disposed at a measurement position of the AC field to be measured (here, an AC magnetic field). Note that the sensor unit 10 may be scanned to perform measurements at a plurality of measurement positions.

[0049] The measurement control unit 41 executes measurement sequences successively as shown in FIG. 2, for example, and performs each measurement sequence (f ＡＣ Higher f ＬＯＣＫ In the Hahn echo sequence, the light emitting device 12 emits excitation light and the high frequency magnetic field generator 2 emits microwaves.

[0050] As a result, during the irradiation period of the excitation light during measurement, a detection signal is obtained by the light receiving device 13, and the detection signal is sampled and digitized by the analog-to-digital converter 21 to be continuously generated.

[0051] Upon receiving this detection signal, the measurement processing unit 42 derives a measurement value of the AC field to be measured from the detection signal using a known method.

[0052] As described above, according to the first embodiment, the radio-frequency magnetic field generator 2 applies microwaves to the magnetic resonance component 1, whose electron spin quantum state changes in response to the AC field to be measured and whose electron spin quantum state can be manipulated by microwaves. The radio-frequency power supply 11 causes the radio-frequency magnetic field generator 2 to generate microwaves. The light-emitting device 12 emits excitation light to be irradiated onto the magnetic resonance component 1. The measurement control unit 41 controls the radio-frequency power supply and the light-emitting device to apply microwaves and excitation light to the magnetic resonance component 1 in a predetermined measurement sequence. In particular, the measurement control unit 41 applies a microwave pulse sequence based on a Hahn echo pulse sequence (or dynamic decoupling) to the magnetic resonance component 1. In this case, the reciprocal of the spin-locking frequency of the microwave pulse sequence is different from the period of the AC field to be measured.

[0053] This allows the measurement of the AC field to be measured with higher sensitivity than with a conventional Hahn echo sequence (or conventional dynamic decoupling).

[0054] Embodiment 2.

[0055] 6 is a diagram illustrating sampling of the detection signal in embodiment 2. In embodiment 2, for example, as shown in FIG. 6, the analog-to-digital converter 21 samples and digitizes the detection signal at a predetermined sampling frequency fs under the undersampling condition, and outputs the digitized detection signal to the arithmetic processing device 31. Due to the undersampling condition, in embodiment 2, the observable band based on the detection signal is a band from 0 to fs / 2.

[0056] FIG. 7 is a diagram illustrating a detection signal that appears in the observable band in the second embodiment. For example, as shown in FIG. 7 , if the detection signal contains unnecessary components in addition to the components of the AC field to be measured, the unnecessary components may enter the observable band due to aliasing. Therefore, in the second embodiment, in order to attenuate such unnecessary components, a filter process is performed on the detection signal to attenuate bands other than a predetermined measurement band. This measurement band is set according to the sampling frequency fs. Note that this filter process may be performed by an analog circuit on the detection signal as an analog signal, or by a digital signal processor or the measurement processing unit 42 described above on the detection signal as a digital signal.

[0057] 8 is a diagram illustrating a case where the band corresponding to the range from half the sampling frequency fs (fs / 2) to the sampling frequency fs is attenuated in the above-mentioned filtering process. For example, the spin lock frequency f is attenuated so that the above-mentioned measurement band corresponds to the range from 0 to half the sampling frequency fs and includes the peak frequency at which the maximum value (max|dS / dB|) of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is reached. ＬＯＣＫ In this case, aliasing is suppressed, and as shown in FIG. 8, for example, the measurement band is set in the range between a frequency that is an integer (n-1) times the sampling frequency fs ((n-1)fs) and a frequency that is an integer (n-1) times the sampling frequency fs plus half the sampling frequency fs ((n-1)fs+fs / 2), thereby enabling detection signals to be detected with good sensitivity in the observable band.

[0058] 9 is a diagram illustrating a case where the band corresponding to the range from 0 to half the sampling frequency (fs / 2) is attenuated in the above-mentioned filtering process. For example, the spin lock frequency f is attenuated so that the above-mentioned measurement band corresponds to the range from half the sampling frequency fs to the sampling frequency fs and includes the peak frequency at which the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is maximized. ＬＯＣＫIn this case, assuming that aliasing is utilized, the measurement band is set in the range between a frequency obtained by adding half the sampling frequency fs to an integer (n-1) times the sampling frequency fs ((n-1)fs+fs / 2) and a frequency obtained by an integer multiple n of the sampling frequency fs (nfs), as shown in FIG. 9 , thereby detecting the detection signal with good sensitivity in the observable band. Note that in this case, due to aliasing, the detection signal is detected at a frequency that is symmetrical with respect to (n-1 / 2)×fs.

[0059] The other configurations and operations of the measuring device according to the second embodiment are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0060] As described above, according to the second embodiment, the unnecessary components are suppressed in the measurement band with good sensitivity by the above-mentioned filtering process.

[0061] Embodiment 3.

[0062] 10 is a diagram illustrating a measurement sequence (dynamic decoupling) in the third embodiment. In the third embodiment, dynamic decoupling is used as the measurement sequence, for example, as shown in FIG. 10. Examples of dynamic decoupling include XY8-k and CPMG (Carr-Purcell-Meiboom-Gill).

[0063] In this measurement sequence, the measurement control unit 41 applies a microwave pulse sequence based on dynamic decoupling to the magnetic resonance component 1. However, the reciprocal of the spin lock frequency (1 / f ＬＯＣＫ ) is the period (1 / f ＡＣ ) is longer than the reciprocal of the spin lock frequency (1 / f ＬＯＣＫ ) is the time length from the center of the first π pulse to the center of the last π pulse among three consecutive π pulses in the N π pulses in the pulse sequence, for example, as shown in FIG.

[0064] FIG. 11 shows the frequency f of the AC field to be measured in the third embodiment. ＡＣ 10 is a diagram illustrating the maximum value of the gradient max|dS / dB| with respect to

[0065] In the case of dynamic decoupling, for example, as shown in FIG. 11, the frequency f ＡＣ Although the characteristic of the maximum slope max|dS / dB| for ＬＯＣＫ Therefore, the frequency f of the AC field to be measured ＡＣ is the spin lock frequency f ＬＯＣＫ That is, the reciprocal of the spin lock frequency of the microwave pulse sequence (1 / f ＬＯＣＫ ) is the period (1 / f ＡＣ ) is set longer.

[0066] The other configurations and operations of the measurement device according to the third embodiment are the same as those of the first or second embodiment, and therefore the description thereof will be omitted.

[0067] Embodiment 4.

[0068] FIG. 12 is a diagram showing an example of a measurement sequence in the fourth embodiment. In the fourth embodiment, for example, as shown in FIG. 12 , the measurement control unit 41 controls the high-frequency power supply 11 and the light-emitting device 12 to apply microwaves and excitation light to the magnetic resonance component 1 in a first measurement sequence (first half sequence) and to apply microwaves and excitation light to the magnetic resonance component 1 in a second measurement sequence (second half sequence). The first measurement sequence and the second measurement sequence are respectively similar to the measurement sequences in the first embodiment. However, the phase of the final microwave pulse in the second measurement sequence is inverted relative to the phase of the final microwave pulse in the first measurement sequence. In the fourth embodiment, the measurement control unit 41 applies a microwave pulse sequence based on a Hahn echo pulse sequence to the magnetic resonance component 1 in each of the first measurement sequence and the second measurement sequence. Here, the first and second measurement sequences are consecutive. Note that in the first embodiment, the final microwave pulse in the second measurement sequence is in phase with the final microwave pulse in the first measurement sequence.

[0069] Here, for the final π / 2 pulse in the microwave pulse sequence, the final pulse in the first half sequence rotates the spin state by π / 2 (counterclockwise) around the positive direction of the y-axis on the Bloch sphere, and the final pulse in the second half sequence rotates the spin state by π / 2 (counterclockwise) around the negative direction of the y-axis on the Bloch sphere. As a result, the rotation angles of the spin states at the end of the pulse sequence differ by 180 degrees, so the positive and negative signs of the detected values ​​are reversed. Note that in the case shown in Figure 12, the final pulses in the first half sequence and the second half sequence rotate the spin state around the y-axis, but instead, they may rotate the spin state around the x-axis (in opposite directions to each other).

[0070] The measurement processing unit 42 (a) acquires the detection signals of the first measurement sequence and the detection signals of the second measurement sequence, (b) derives the detection values ​​of the measured AC field (i.e., the first detection value and the second detection value, which are the measurement values ​​for each measurement sequence) based on those detection signals using an existing method, and (c) derives the difference between the first detection value and the second detection value as the measurement value of the measured AC field.

[0071] FIG. 13 shows the frequency f of the AC field to be measured in the fourth embodiment. ＡＣ 14 is a diagram illustrating the sensitivity corresponding to the frequency f of the AC field to be measured in the fourth embodiment. FIG. 14 is a diagram illustrating the first detected value, the second detected value, and the measured value in the fourth embodiment. FIG. 14 shows the waveform when measurements are continuously repeated (first and second measurement sequences). FIG. 15 and FIG. 16 are diagrams illustrating the sensitivity corresponding to the frequency f of the AC field to be measured in the fourth embodiment. ＡＣ 15 and 16, the case of the first embodiment (i.e., a case where one measurement value is obtained in one measurement sequence) is referred to as a single sequence, and the case of the fourth embodiment (i.e., a case where one measurement value is obtained in two measurement sequences) is referred to as a double sequence.

[0072] In the fourth embodiment, the phase of the final pulse of the microwave in the second measurement sequence is inverted relative to the phase of the final pulse of the microwave in the first measurement sequence, so that the frequency f ＡＣ is approximately an integer multiple of the sampling frequency fs, the phase of the AC field to be measured relative to the microwave pulse sequence is approximately in phase between the first half sequence and the second half sequence, as shown in FIG. 13, for example, and the positive and negative signs of the detected values ​​are reversed, so that the amplitude of the measured value (difference between detected values) is approximately twice the amplitude of each detected value, as shown in FIGS. 14, 15, and 16, for example.

[0073] On the other hand, the frequency f of the AC field to be measured ＡＣis approximately a half-integer multiple of the sampling frequency fs, the phase of the AC field to be measured relative to the microwave pulse sequence is approximately opposite in phase between the first half sequence and the second half sequence, as shown in FIG. 13, and the positive and negative signs of the detected values ​​are reversed, as shown in FIGS. 15 and 16, so the measured value (difference between the detected values) approaches zero.

[0074] Therefore, the sensitivity (maximum slope max|dS / dB|) is determined by the frequency f ＡＣ is the spin lock frequency f ＬＯＣＫ The sensitivity is higher than when the frequency of the AC field to be measured is set to f ＡＣ is set within the measurement band adjacent to the maximum peak frequency (27 kHz in FIG. 15, 24 kHz in FIG. 16).

[0075] In this case, if the detection signal is digitized under undersampling conditions as in embodiment 2, the frequency of the maximum peak in the observable band (0 to fs / 4) will correspond to 0 Hz in the observable band, so the measurement band (for example, measurement band #1 and measurement band #2 in Figures 15 and 16) is set so as not to include the maximum peak frequency.

[0076] In the case of FIG. 15 (i.e., when the sampling frequency fs is 9 kHz), the maximum peak frequency in the double sequence (the magnetic field frequency f at which the maximum gradient max|dS / dB| is maximized) ＡＣ ) coincides with the peak frequency in the single sequence, but even if the maximum peak frequency in the double sequence does not coincide with the peak frequency in the single sequence due to the sampling frequency fs, etc., by appropriately setting the measurement band as described above, the magnetic field frequency f ＡＣ is the spin lock frequency f ＬＯＣＫ 16, even when the peak frequency of 27 kHz in the single sequence is located in a notch portion of the frequency characteristics of the double sequence, magnetic field measurement can be performed with the high sensitivity as described above by setting the measurement band adjacent to the maximum peak frequency of 24 kHz.

[0077] On the other hand, if a desired measurement band is already known, the sampling frequency fs can be set so that the maximum peak frequency is located within or adjacent to that measurement band, thereby enabling magnetic field measurements to be performed with the high sensitivity described above.

[0078] The other configurations and operations of the measuring device according to the fourth embodiment are the same as those of any of the other embodiments, and therefore a description thereof will be omitted.

[0079] As described above, in the fourth embodiment, the amplitude of the measured value is increased, and therefore the magnetic field is measured with good sensitivity. Furthermore, since the difference between the two detected values ​​of the first and second sequences is derived as described above, the in-phase noise components contained in the two detected values ​​are suppressed.

[0080] Embodiment 5.

[0081] In the fifth embodiment, the measurement control unit 41 applies a microwave pulse sequence based on dynamic decoupling, such as that shown in FIG. 10, to the magnetic resonance element 1 in each of the first and second measurement sequences. However, as in the fourth embodiment, the phase of the final microwave pulse in the second measurement sequence is inverted relative to the phase of the final microwave pulse in the first measurement sequence. Here, the first and second measurement sequences are continuous. Note that, in the third embodiment, the final microwave pulse in the second measurement sequence has the same phase as the final microwave pulse in the first measurement sequence.

[0082] As in the third embodiment, the reciprocal of the spin lock frequency of the microwave pulse sequence (1 / f ＬＯＣＫ ) is the period (1 / f ＡＣ ) is longer than the reciprocal of the spin lock frequency (1 / f ＬＯＣＫ ) is the time length from the center of the first π pulse to the center of the last π pulse among three consecutive π pulses in the N π pulses in each of the first and second pulse sequences.

[0083] 17 and 18 show the frequency f ＡＣ 18 is a diagram illustrating the maximum slope value max|dS / dB| with respect to π pulse number N, the sampling frequency fs is 9 kHz, and the spin lock frequency f ＬＯＣＫ 17 and 18, the case of embodiment 3 (i.e., the case where one measurement value is obtained in one measurement sequence) is referred to as single sequence, and the case of embodiment 5 (i.e., the case where one measurement value is obtained in two measurement sequences) is referred to as double sequence.

[0084] In the case of dynamic decoupling, the frequency of the AC field to be measured, f ＡＣ 17 and 18, the characteristic of the maximum slope max|dS / dB| for ＬＯＣＫ Therefore, the frequency f of the AC field to be measured ＡＣ is the spin lock frequency f ＬＯＣＫ That is, the reciprocal of the spin lock frequency of the microwave pulse sequence (1 / f ＬＯＣＫ ) is the period (1 / f ＡＣ ) is set longer.

[0085] The other configurations and operations of the measuring device according to the fifth embodiment are the same as those of the fourth embodiment, and therefore the description thereof will be omitted.

[0086] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, it is intended that such changes and modifications be included within the scope of the claims.

[0087] The present invention is applicable to, for example, a measurement device that uses optically detected magnetic resonance.

Claims

a light-emitting device that emits excitation light to be irradiated onto the magnetic resonance element; a light-receiving device that receives fluorescence emitted by the magnetic resonance element in response to the excitation light and generates a detection signal corresponding to the intensity of the fluorescence; a measurement control unit that controls the high-frequency power supply and the light-emitting device to apply the microwaves and the excitation light to the magnetic resonance element in a predetermined measurement sequence; and a measurement processing unit that derives measurement values ​​based on the detection signal, wherein the measurement control unit applies the microwave pulse sequence based on a Hahn echo pulse sequence or dynamic decoupling to the magnetic resonance element, and wherein the reciprocal of the spin-locking frequency of the microwave pulse sequence is different from the period of the AC field to be measured.

2. A measurement method comprising the steps of: performing electron spin quantum manipulation of a magnetic resonance component, the electron spin quantum state of which changes in response to a measured AC field and which can be manipulated by microwaves, using microwaves in accordance with a predetermined measurement sequence; emitting excitation light to be irradiated onto the magnetic resonance component; receiving fluorescence emitted by the magnetic resonance component in response to the excitation light and generating a detection signal corresponding to the intensity of the fluorescence; deriving a measurement value based on the detection signal; applying a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling to the magnetic resonance component in the measurement sequence; and wherein the reciprocal of the spin locking frequency of the microwave pulse sequence is different from the period of the measured AC field.

3. A measurement method according to claim 2, characterized in that the reciprocal of the spin lock frequency and the period of the AC field to be measured are set so that the maximum value of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is larger when the reciprocal of the spin lock frequency of the microwave pulse sequence coincides with the period of the AC field to be measured.

4. A measurement method according to claim 2 or 3, characterized in that in the measurement sequence, a microwave pulse sequence based on a Hahn echo pulse sequence is applied to the magnetic resonance component, and the reciprocal of the spin lock frequency of the microwave pulse sequence is shorter than the period of the AC field to be measured.

5. A measurement method according to claim 2 or 3, characterized in that in the measurement sequence, a microwave pulse sequence based on dynamic decoupling is applied to the magnetic resonance component, and the reciprocal of the spin lock frequency of the microwave pulse sequence is longer than the period of the AC field to be measured.

6. A measurement method according to claim 2 or claim 3, characterized in that: the detection signal is sampled at a sampling frequency under sampling conditions; a measurement value is derived based on the sampled detection signal; the detection signal is subjected to a filter process to attenuate bands other than a predetermined measurement band; the measurement band corresponds to the spin lock frequency; and the spin lock frequency is set so that the measurement band corresponds to a range from 0 to half the sampling frequency and is a band including a peak frequency that is the maximum value of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured.

7. A measurement method according to claim 2 or claim 3, characterized in that: the detection signal is sampled at a sampling frequency under sampling conditions; a measurement value is derived based on the sampled detection signal; the detection signal is subjected to a filter process to attenuate bands other than a predetermined measurement band; the measurement band corresponds to the spin lock frequency; and the spin lock frequency is set so that the measurement band corresponds to a range from half the sampling frequency to the sampling frequency and is a band including a peak frequency that is the maximum value of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured.

8. A measurement method according to claim 2 or 3, characterized in that: the high-frequency power supply and the light-emitting device are controlled to apply the microwave and the excitation light to the magnetic resonance element in a first measurement sequence, and the microwave and the excitation light are applied to the magnetic resonance element in a second measurement sequence; the phase of the final pulse of the microwave in the second measurement sequence is inverted relative to the phase of the final pulse of the microwave in the first measurement sequence; deriving a first detection value based on the detection signal in the first measurement sequence, and deriving a second detection value based on the detection signal in the second measurement sequence; and deriving a difference between the first detection value and the second detection value as the measurement value.

9. A measurement method according to claim 8, comprising: sampling the detection signal at a sampling frequency under sampling conditions; deriving a measurement value based on the sampled detection signal; filtering the detection signal to attenuate bands other than a predetermined measurement band; and setting the sampling frequency so that a maximum peak frequency for a maximum value of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is located within or adjacent to the measurement band.

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