Optical nuclear magnetic resonance device

Abstract

Provided is an optical nuclear magnetic resonance device in which it is possible to shorten the time required for initialization by shaping the spatial distribution of the intensity of a laser radiated at a diamond (sensor material) from a Gaussian shape to a spatially uniform top-hat shape, thereby shortening the measurement time.　An optical nuclear magnetic resonance device 1 comprises: a sensor material 101 having electron spins that cause electron spin resonance; a laser 102 that is radiated at the sensor material 101 in order to control the direction of the electron spins of defects contained in the sensor material 101 and to measure the direction of the electron spins; a beam shaping element 105 for controlling the laser; a detector for measuring fluorescence emitted from the sensor material as a result of the irradiation by the laser 102; a microwave radiating device 103 for radiating microwaves at the sensor material 101; a permanent magnet or an electromagnet 106 for applying a static magnetic field to the sensor material 101; and a control unit 108 for controlling the laser 102, the microwave radiating device 103, and the beam shaping element 105 so as to homogenize the two-dimensional intensity distribution of the laser 102.

Description

optical nuclear magnetic resonance apparatus

[0001] The present invention relates to a measurement device that uses diamond as a sensor material.

[0002] In recent years, optical nuclear magnetic resonance technology using diamond has been proposed. Electron spins present on nitrogen-vacancy complex defects (hereinafter referred to as NV centers) in diamond have the property of absorbing light with a wavelength of 532 nm and emitting red fluorescence. The intensity of this red fluorescence is determined by the direction of the electron spin. Furthermore, in the absence of an externally applied static magnetic field, when irradiated with microwaves of approximately 2.87 GHz, these electron spins absorb the microwaves and enter an excited state, i.e., their direction changes. Accordingly, the intensity of the red fluorescence when irradiated with light of approximately 532 nm decreases. This is called the electron spin resonance phenomenon. On the other hand, when an externally applied static magnetic field is present, the wavelength of the microwave absorbed is proportional to the value of the applied static magnetic field, and the microwave wavelength at which the electron spin resonance phenomenon occurs shifts from approximately 2.87 GHz. Therefore, by measuring the wavelength dependence of the red fluorescence intensity when irradiated with light of approximately 532 nm, the magnetic field strength felt by the NV centers in diamond can be quantified. Furthermore, the wavelength of the microwaves at which this electron spin resonance phenomenon occurs does not depend solely on the strength of the magnetic field, but also changes depending on the strength of the electric field felt by the diamond and the temperature at which it is placed. This means that it is possible to measure not only the strength of the magnetic field, but also the strength of the electric field and temperature.

[0003] Furthermore, by irradiating microwaves and approximately 532 nm irradiation light in pulsed irradiation rather than continuously in time, magnetic field strength, temperature, and electric field strength can be detected with higher sensitivity. Furthermore, when measuring magnetic field strength, this pulse irradiation method makes it possible to detect not only static magnetic fields but also AC magnetic fields of specific frequencies. In this case, the measurement sequence for laser and microwave is a sequence in which pulsed laser irradiation and pulsed microwave irradiation are alternately repeated. Here, the role of the pulsed laser can be divided into two regions in time: the first half and the second half. The first half is a region in which the intensity of red fluorescence is measured to identify the direction of the electron spin on the NV center, and the second half is a region in which the laser initializes the electron spin on the NV center, i.e., aligns the direction of all spins in the same direction. Here, if molecules containing hydrogen, fluorine, etc. are present near the NV center of diamond, the AC nuclear magnetic field formed by the atomic nuclei of hydrogen, fluorine, etc. can be detected. The detection of this nuclear magnetic field is the nuclear magnetic resonance method, and in this specification, it is referred to as the optical nuclear magnetic resonance method to distinguish it from the conventional nuclear magnetic resonance method. In optical nuclear magnetic resonance, the frequency of the nuclear magnetic field can be calculated by converting the time change of the detected alternating current nuclear magnetic field into frequency. From this frequency, the molecular structure of molecules containing hydrogen, fluorine, etc. can be determined. Furthermore, from the magnitude of the detected nuclear magnetic field, it is possible to quantify the amount of molecules present. This optical nuclear magnetic resonance method is known to have better detection sensitivity than ordinary nuclear magnetic resonance. Patent Document 1 describes a method for obtaining magnetic field strength by using a CCD camera to capture the dependence of the intensity of red fluorescence emitted when a diamond containing an NV center is irradiated with light of approximately 532 nm on the irradiated microwave frequency.

[0004] US Patent Application Publication No. 20220050153

[0005] Patent Document 1 describes a method for detecting the intensity of red fluorescence emitted from diamond and a method for analyzing the acquired data. However, no consideration is given to the influence of the spatial uniformity of the laser intensity irradiated onto the diamond, which induces the emission of red fluorescence, on the measurement data.

[0006] However, as mentioned above, the electron spins on the NV center must be initialized before measurement. It is known that insufficient initialization reduces the sensitivity of magnetic field strength, electric field strength, and temperature measurement. The time required for this initialization increases with the intensity of the laser beam with a wavelength of approximately 532 nm. However, the two-dimensional spatial distribution of this laser intensity usually has a Gaussian shape, with the light intensity being strong near the center of the laser beam and decreasing with distance from the center. In other words, initialization is faster near the center of the laser beam and slower with distance. Hereinafter, this area away from the center will be referred to as the "tail." Therefore, the irradiation time required for sufficient initialization throughout the entire laser spot area irradiated on the diamond is determined by the initialization time of the tail of the laser beam. Previously, this spatial distribution of laser intensity was not taken into consideration. In other words, the initialization time was determined by the tail area of ​​the laser beam.

[0007] Therefore, the present invention provides an optical nuclear magnetic resonance apparatus that can shorten the time required for initialization by changing the spatial distribution of the laser intensity irradiated onto diamond (sensor material) from a Gaussian shape to a spatially uniform top-hat shape, thereby shortening the measurement time.

[0008] In order to solve the above problems, the optical nuclear magnetic resonance apparatus of the present invention is characterized by comprising: a sensor material having electron spins that cause electron spin resonance; a laser that is irradiated onto the sensor material to control the direction of the electron spins of defects contained in the sensor material and to measure the direction of the electron spins; a beam shaping element for controlling the laser; a detector that measures fluorescence emitted from the sensor material by irradiation with the laser; a microwave irradiating device that irradiates the sensor material with microwaves; a permanent magnet or electromagnet that applies a static magnetic field to the sensor material; and a control unit that controls the laser, microwave irradiating device, and beam shaping element to homogenize the two-dimensional intensity distribution of the laser.

[0009] According to the present invention, it is possible to provide an optical nuclear magnetic resonance apparatus that can change the spatial distribution of the laser intensity irradiated on diamond (sensor material) from a Gaussian shape to a spatially uniform top-hat shape, thereby shortening the time required for initialization and shortening the measurement time. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments.

[0010] 1 is a schematic diagram of an optical nuclear magnetic resonance apparatus according to a first embodiment of the present invention; FIG. 2 is a diagram of the beam shaping element in FIG. 1; FIG. 3 is an explanatory diagram showing the sequence of laser pulses and microwave pulses irradiated onto diamond (sensor material); FIG. 4 is an explanatory diagram showing the change in red fluorescence per laser pulse and the amount of measurement signal when initialization is sufficient; FIG. 5 is an explanatory diagram showing the change in red fluorescence per laser pulse when initialization is insufficient; FIG. 6 is an explanatory diagram showing the correlation between the number of laser pulses and the red fluorescence intensity when the initialization time is changed to 1000 μsec and 300 μsec, and when the beam shaping element of the present invention is used or not; and FIG. 7 is an explanatory diagram explaining the dependence of the red fluorescence intensity of the 28th laser pulse in FIG. 5 on the time (initialization time) of the second half of the laser pulse, when the beam shaping element of the present invention is used or not.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. This embodiment includes a process for shaping the spatial intensity distribution of a laser irradiated onto a diamond (sensor material) containing an NV center from a normal Gaussian shape to a spatially uniform top-hat shape by using an optical element such as a DOE (Diffractive Optical Element) and a beam expander. According to this embodiment, the diameter of the laser irradiated onto the diamond (sensor material) can be expanded or reduced by the beam expander to a diameter optimal for the optical element such as the DOE.

[0012] In this embodiment, the laser beam expanded or reduced by the beam expander can be shaped into a top-hat beam with a spatially uniform intensity distribution by passing it through an optical element such as a DOE. Therefore, according to this embodiment, it is possible to irradiate the diamond (sensor material) with a laser beam with a spatially uniform intensity, thereby shortening the initialization time and, as a result, shortening the total measurement time.

[0013] The measurements targeted in this embodiment include magnetic field strength measurement, its application, optical nuclear magnetic resonance measurement, temperature measurement, and electric field strength measurement. Furthermore, although a diamond (sensor material) containing an NV center is described as the sensor material, any diamond (sensor material) containing various centers responsive to magnetic fields, temperatures, and electric fields, such as a diamond (sensor material) containing an SiV center or a diamond (sensor material) containing a GeV center, may be used. Furthermore, although a DOE is used as an example of the element for shaping the laser, any optical element capable of shaping the laser into a top-hat shape, such as a fly's eye lens or a diffuser, may be used. Hereinafter, an embodiment of the present invention will be described using the drawings, taking an optical nuclear magnetic resonance apparatus as an example.

[0014] In this embodiment, a diamond containing an NV center is used as a sensor material, a DOE is used as an optical element for shaping a laser, and optical nuclear magnetic resonance measurement is used as an example for measurement. Figure 1 is a schematic diagram of an optical nuclear magnetic resonance apparatus according to a first embodiment of the present invention. As shown in Figure 1, the optical nuclear magnetic resonance apparatus 1 includes a diamond (sensor material) 101, a laser 102 having a wavelength of approximately 532 nm that is irradiated onto the diamond (sensor material) 101, a microwave irradiation device 103 that irradiates microwaves onto the diamond (sensor material) 101, red fluorescence 104 emitted from the diamond (sensor material) 101, a beam shaping element 105 for shaping the laser into a top hat shape, a permanent magnet or electromagnet 106 installed nearby to apply a static magnetic field to the diamond (sensor material) 101, a detector 107 for detecting the red fluorescence 104, and a control unit 108. The control unit 108 outputs a command value for a microwave pulse to the microwave irradiation device 103 that irradiates microwaves, and a command value for a laser pulse to a laser irradiation device (not shown), as will be described in detail later. The control unit 108 also controls the beam shaping element 105 and receives as input the detected values ​​from the detector 107. Here, the control unit 108 is realized by, for example, a processor such as a CPU (not shown), a ROM for storing various programs, a RAM for temporarily storing data in the calculation process, and a storage device such as an external storage device, and the processor such as the CPU reads and executes the various programs stored in the ROM and stores the calculation results, which are the execution results, in the RAM or the external storage device.

[0015] Here, in this embodiment, the laser 102 is irradiated onto the diamond (sensor material) 101 via the microwave irradiation device 103, but it is not necessarily required to irradiate the diamond (sensor material) 101 via the microwave irradiation device 103. The microwave irradiation device 103 may be installed in a position where it can irradiate the diamond (sensor material) 101 with microwaves, and may be composed of a printed circuit board or a metal wire. Furthermore, the permanent magnet or electromagnet 106 is not limited in its position relative to the diamond (sensor material) 101, as long as it is positioned so that it can apply a static magnetic field parallel to the bond axis of the NV center contained in the diamond (sensor material) 101. Furthermore, since the red fluorescence 104 emitted from the diamond (sensor material) 101 is emitted in all directions from the diamond (sensor material) 101, the detector 107 may be positioned anywhere as long as it can detect the red fluorescence 104. Furthermore, other optical elements such as lenses may be included before and after the beam shaping element 105 and in front of the detector 107. The wavelength of the laser 102 is not limited to 532 nm, but may be any wavelength at which the NV center contained in the diamond (sensor material) 101 emits red fluorescence.

[0016] The beam shaping element 105 shown in FIG. 1 will be described. FIG. 2 is a configuration diagram of the beam shaping element in FIG. 1. As shown in FIG. 2, the beam shaping element 105 has a DOE 201 and a beam expander 202. The laser 102 passes through the DOE 201 and the beam expander 202 that constitute the beam shaping element 105. The beam expander 202 has a function of expanding or reducing the spot diameter of the laser 102, and the spot diameter may be optimized in accordance with the specifications of the DOE 201 installed downstream. The beam expander 202 may be of either the typical Galilean type or Keplerian type. Furthermore, a configuration in which other optical elements such as lenses are disposed between the beam expander 202 and the DOE 201 may also be used.

[0017] Here, the DOE 201 will be described. The laser 102 expanded or reduced by the beam expander 202 has a divergence angle, albeit small. The laser 102 is shaped into a top-hat shape by passing through the DOE 201, and the uniformity and size of the top-hat shape are affected by the spot diameter of the laser 102 incident on the DOE 201. Therefore, in order to optimize the uniformity and size, it is desirable that the DOE 201 have a mechanism that can move it upstream and downstream. The control unit 108 controls the mechanism that can move it upstream and downstream.

[0018] FIG. 3 is an explanatory diagram showing the sequence of laser pulses and microwave pulses irradiated onto diamond (sensor material). That is, FIG. 3 is a diagram outlining the optical nuclear magnetic resonance measurement sequence. A laser 102 is irradiated onto diamond (sensor material) 101 as a pulse by an AOM (Acoustic Optical Modulator) or the like (not shown). As shown in FIG. 3, the pulse of this laser 102 can be divided into two temporal regions: a first half 301 of the laser pulse and a second half 302 of the laser pulse. The first half 301 of the laser pulse is a read region for measuring red fluorescence 104 emitted from diamond (sensor material) 101 with a detector 107. The second half 302 of the laser pulse is an initialization region for initializing the direction of the electron spin of the NV center in diamond (sensor material) 101. After the first half 301 of this laser pulse and the second half 302 of the laser pulse, the laser is cut off, and a microwave pulse 303 is irradiated from the microwave irradiation device 103 onto the diamond (sensor material) 101. Note that this microwave pulse may be composed of a large number of pulse groups, but any pulse group may be used. Subsequently, the microwave pulse is cut off, and a laser pulse is again irradiated onto the diamond (sensor material) 101. As explained above, the sequence in which the laser pulse and the microwave pulse are alternately and repeatedly irradiated onto the diamond (sensor material) 101 is the optical nuclear magnetic resonance measurement sequence.

[0019] 4A is an explanatory diagram showing the change in red fluorescence for each laser pulse and the amount of measurement signal when initialization is sufficient. That is, FIG. 4 is a diagram explaining the intensity of red fluorescence 104 measured by the detector 107 according to the optical nuclear magnetic resonance measurement sequence of FIG. 3, and corresponds to the case where the initialization of the electron spin of the NV center in the diamond (sensor material) 101 is sufficient. The first half 401 of the red fluorescence intensity when initialization is sufficient indicates the intensity of the red fluorescence 104 emitted during the first half 301 of the laser pulse, and the second half 402 of the red fluorescence intensity when initialization is sufficient indicates the intensity of the red fluorescence 104 emitted during the second half 302 of the laser pulse. Note that in the case of FIG. 4A where initialization is sufficient, the intensity of red fluorescence 104 in the second half 402 of the red fluorescence intensity when initialization is sufficient does not change with each laser pulse and is a constant value. The difference in intensity of red fluorescence 104 between the start point of first half 401 of red fluorescence intensity when initialization is sufficient and the latter half 402 of red fluorescence intensity when initialization is sufficient corresponds to optical nuclear magnetic resonance signal intensity 403. Note that there is also an analysis method in which the signal intensity is the product of the period of first half 401 of red fluorescence intensity when initialization is sufficient and signal intensity 403, rather than the difference between the start point of first half 401 of red fluorescence intensity when initialization is sufficient and the latter half 402 of red fluorescence intensity when initialization is sufficient, but either method may be used.

[0020] 4B is an explanatory diagram showing the change in red fluorescence for each laser pulse when initialization is insufficient. That is, FIG. 4B is a diagram explaining the intensity of red fluorescence 104 measured by the detector 107 according to the optical nuclear magnetic resonance measurement sequence of FIG. 3, and corresponds to a case where initialization of the electron spin of the NV center in the diamond (sensor material) 101 is insufficient. The first half 404 of the red fluorescence intensity when initialization is insufficient indicates the intensity of red fluorescence 104 emitted during the first half 301 of the laser pulse, and the second half 405 of the red fluorescence intensity when initialization is insufficient indicates the intensity of red fluorescence 104 emitted during the second half 302 of the laser pulse. When initialization is insufficient as in FIG. 4B, the intensity of red fluorescence 104 at the beginning of the first half 404 of the red fluorescence intensity when initialization is insufficient and the second half 405 of the red fluorescence intensity when initialization is insufficient decrease with each laser pulse. That is, when initialization is insufficient, the intensity of red fluorescence 104 at the start of first half 404 of the red fluorescence intensity increases with each laser pulse, while when initialization is insufficient, the intensity of red fluorescence 104 in second half 405 of the red fluorescence intensity decreases with each laser pulse. As shown in Figure 4B, when initialization is insufficient, the optical nuclear magnetic resonance signal intensity decreases with each laser pulse, and therefore it is understood that sufficient initialization is important.

[0021] Figure 5 is an explanatory diagram showing the correlation between the number of laser pulses and the red fluorescence intensity when the initialization time is changed to 1000 μsec and 300 μsec, and when the beam shaping element of the present invention is used or not. That is, Figure 5 is a graph plotting the intensity of red fluorescence 104 measured for each laser pulse in the latter half 402 of the red fluorescence intensity when initialization is sufficient or in the latter half 405 of the red fluorescence intensity when initialization is insufficient. The measurement conditions in Figure 5 were an incident laser intensity of 15 mW and an interval between laser pulses of 100 μsec. The laser pulse number dependence 501 of the latter half of the red fluorescence intensity is a measurement value measured when the initialization time is 1000 μsec and the beam shaping element 105 is not used, while the laser pulse number dependence 502 of the latter half of the red fluorescence intensity is a measurement value measured when the initialization time is 1000 μsec and the beam shaping element 105 is used. Furthermore, the laser pulse number dependence 503 of the latter half of the red fluorescence intensity is a measurement value obtained when the initialization time is 300 μsec and the beam shaping element 105 is not used, while the laser pulse number dependence 504 of the latter half of the red fluorescence intensity is a measurement value obtained when the initialization time is 300 μsec and the beam shaping element 105 is used. The laser pulse number dependence 501 of the latter half of the red fluorescence intensity and the laser pulse number dependence 502 of the latter half of the red fluorescence intensity are almost the same and constant, indicating that an initialization time of 1000 μsec is sufficient. On the other hand, the laser pulse number dependence 503 of the latter half of the red fluorescence intensity decreases with each laser pulse, indicating that an initialization time of 300 μsec is insufficient. However, the laser pulse number dependence 504 of the latter half of the red fluorescence intensity is the same value as the laser pulse number dependence 501 of the latter half of the red fluorescence intensity and the laser pulse number dependence 502 of the latter half of the red fluorescence intensity and is almost constant, indicating that sufficient initialization is achieved by using the beam shaping element 105, even when the initialization time is 300 μsec.

[0022] FIG. 6 illustrates the dependence of the red fluorescence intensity at the 28th laser pulse in FIG. 5 on the time (initialization time) of the second half of the laser pulse, with and without the use of the beam shaping element of the present invention. That is, FIG. 6 plots the intensity of red fluorescence 104 detected upon irradiation of the 28th laser pulse versus the initialization time. Here, the measurement conditions in FIG. 6 were the same as those in FIG. 5 , with an incident laser intensity of 15 mW and an interval between laser pulses of 100 μs. The dependence 601 of the red fluorescence intensity at the 28th pulse on the time (initialization time) of the second half of the laser pulse corresponds to the case where the beam shaping element 105 is not used, while the dependence 602 of the red fluorescence intensity at the 28th pulse on the time (initialization time) of the second half of the laser pulse corresponds to the case where the beam shaping element 105 is used. First, in the dependence 601 of the red fluorescence intensity at the 28th pulse on the time (initialization time) of the second half of the laser pulse, it can be seen that the shorter the initialization time, the more significantly the intensity of red fluorescence 104 decreases, indicating insufficient initialization. However, since the value remains nearly constant when the initialization time is 1000 μsec or longer, it can be seen that sufficient initialization cannot be achieved unless the initialization time is set to 1000 μsec or longer when the beam shaping element 105 is not used. On the other hand, the time (initialization time) dependence 602 of the red fluorescence intensity of the 28th pulse in the latter half of the laser pulse remains nearly constant regardless of the initialization time, so it can be determined that the initialization is sufficient. Therefore, it is clear that the time required for initialization can be shortened by using the beam shaping element 105.

[0023] That is, according to this embodiment, it is possible to provide an optical nuclear magnetic resonance apparatus that can shorten the measurement time by shaping the spatial distribution of the laser intensity irradiated on the diamond (sensor material) from a Gaussian shape to a spatially uniform top-hat shape, thereby shortening the time required for initialization. Specifically, according to this embodiment, by shaping the laser into a top-hat shape, the spatial distribution of the laser intensity can be made uniform, thereby shortening the time required for initialization of the electron spin of the NV center in the diamond (sensor material). It is clear that this shortens the total measurement time of optical nuclear magnetic resonance.

[0024] It should be noted that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0025] 1... Optical nuclear magnetic resonance apparatus 101... Diamond (sensor material) 102... Laser 103... Microwave irradiation device 104... Red fluorescence 105... Beam shaping element 106... Permanent magnet or electromagnet 107... Detector 108... Control unit 201... DOE (Diffractive Optical Element) 202... Beam expander 301... First half of laser pulse 302... Second half of laser pulse 303... Microwave pulse 401... First half of red fluorescence intensity when initialization is sufficient 402... Second half of red fluorescence intensity when initialization is sufficient 403... Signal intensity 404... First half of red fluorescence intensity when initialization is insufficient 405... Second half of red fluorescence intensity when initialization is insufficient 501, 502, 503, 504... Dependence of second half of red fluorescence intensity on laser pulse number 601, 602...Dependence of red fluorescence intensity at pulse number 28 on the time (initialization time) in the latter half of the laser pulse

Claims

1. An optical nuclear magnetic resonance apparatus comprising: a sensor material having electron spins that cause electron spin resonance; a laser that is irradiated onto the sensor material to control the direction of the electron spins of defects contained in the sensor material and to measure the direction of the electron spins; a beam shaping element for controlling the laser; a detector for measuring fluorescence emitted from the sensor material by irradiation with the laser; a microwave irradiation device that irradiates the sensor material with microwaves; a permanent magnet or electromagnet that applies a static magnetic field to the sensor material; and a control unit that controls the laser, microwave irradiation device, and beam shaping element so as to homogenize the two-dimensional intensity distribution of the laser.

2. An optical nuclear magnetic resonance apparatus according to claim 1, characterized in that the beam shaping element shapes the spatial distribution of the laser intensity from a non-uniform Gaussian shape to a uniform top-hat shape.

3. An optical nuclear magnetic resonance apparatus according to claim 2, characterized in that the beam shaping element comprises at least one of a diffractive optical element, a diffuser and a fly's eye lens, and a beam expander for optimizing the spot diameter of the incident laser on at least one of the diffractive optical element, the diffuser and the fly's eye lens.

4. An optical nuclear magnetic resonance apparatus according to claim 3, characterized in that the detector detects an alternating magnetic field emitted by the nuclear spins of elements contained in the sample to be measured.

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