Optical nuclear magnetic resonance apparatus

Abstract

To provide an optical nuclear magnetic resonance apparatus that can shorten measuring time.SOLUTION: An optical nuclear magnetic resonance apparatus 1 comprises: a sensor material 101 having electron spin which causes electron spin resonance; a laser 102 with which the sensor material 101 is irradiated in order to control a direction of electron spin of a defect included in the sensor material 101 and measure a direction of electron spin; a beam shaping element 105 for controlling laser; a detector which measures fluorescence emitted from the sensor material by irradiation of the laser 102; a microwave irradiation device 103 which irradiates the sensor material 101 with microwave; a permanent magnet or an electromagnet 106 which apply a static magnetic field to the sensor material 101; and a control part 108 which controls the laser 102, the microwave irradiation device 103 and the beam shaping element 105 so as to uniformize two-dimensional intensity distribution of the laser 102.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a measuring device using diamond as a sensor material.

Background Art

[0002] In recent years, an optical nuclear magnetic resonance technique using diamond has been proposed. The electron spin existing on the nitrogen-vacancy composite defect (hereinafter referred to as the NV center) present in diamond has 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. Further, when this electron spin is irradiated with microwaves of about 2.87 GHz in the absence of an externally applied static magnetic field, it absorbs this microwave and enters an excited state, that is, its direction changes. Along with this, the intensity of the red fluorescence when irradiated with light having a wavelength of about 532 nm decreases. This is called the electron spin resonance phenomenon. On the other hand, when an externally applied static magnetic field is present, since the wavelength of the absorbed microwave is proportional to the value of the applied static magnetic field, the wavelength of the microwave at which the electron spin resonance phenomenon occurs changes from about 2.87 GHz. Therefore, by measuring the wavelength dependence of the intensity of the red fluorescence when irradiated with light having a wavelength of about 532 nm, the magnetic field strength felt by the NV center of diamond can be quantified. Further, since the wavelength of the microwave at which this electron spin resonance phenomenon occurs depends not only on the magnetic field strength but also on the electric field strength felt by the diamond and the temperature at which it is placed, in addition to the magnetic field strength, it is also possible to measure the electric field strength and temperature.

[0003] Furthermore, by using pulsed irradiation instead of continuous irradiation of microwaves and irradiation light of approximately 532 nm, the magnetic field strength, temperature, and electric field strength can be detected with higher sensitivity. Also, regarding the measurement of the magnetic field strength, when using this pulsed irradiation method, it becomes possible to detect not only static magnetic fields but also alternating magnetic fields of a specific frequency. In this case, the measurement sequence regarding the laser and microwaves is a sequence that alternately repeats pulsed laser irradiation and pulsed microwave irradiation. Here, the role of the pulsed laser can be divided into two regions in terms of time, the first half is a region for measuring the intensity of red fluorescence for identifying the direction of electron spins on the NV center, and the second half is a region for initializing the electron spins on the NV center by the laser, that is, aligning the directions of all spins in the same direction. Here, when molecules containing hydrogen, fluorine, etc. are present near the NV center of the diamond, an alternating nuclear magnetic field formed by the nuclei of hydrogen, fluorine, etc. can be detected. This detection of the nuclear magnetic field is the nuclear magnetic resonance method, and in this specification, in order to distinguish it from the normal nuclear magnetic resonance method, it is described as the optical nuclear magnetic resonance method. In the optical nuclear magnetic resonance method, the frequency of the nuclear magnetic field can be calculated by converting the time change of the detected alternating nuclear magnetic field into frequency. From this frequency, the molecular structure of molecules containing hydrogen, fluorine, etc. can be determined. Also, it becomes possible to quantify the abundance of the molecules from the magnitude of the detected nuclear magnetic field. This optical nuclear magnetic resonance method is known to have higher detection sensitivity than the normal nuclear magnetic resonance method. Patent Document 1 describes a method of obtaining the magnetic field strength by acquiring the irradiation microwave frequency dependence of the intensity of red fluorescence emitted when diamond containing an NV center is irradiated with light of approximately 532 nm using a CCD camera.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 has been given to the influence of the spatial uniformity of the laser intensity irradiated on the diamond, which induces the emission of red fluorescence, on the measurement data.

[0006] However, as described above, at the time of measurement, an operation for initializing the electron spin on the NV center is required. It is known that when this initialization is insufficient, the sensitivity of magnetic field strength, electric field strength, and temperature measurement decreases. The time required for this initialization becomes shorter as the laser intensity of about 532 nm wavelength is stronger. However, usually, the spatial distribution of this laser intensity in two dimensions has a Gaussian shape, and the light intensity is strong near the center of the laser beam and weakens as it moves away from the center. That is, the initialization is fast near the center of the laser beam and slow as it moves away from the center. Hereinafter, the portion away from this center will be described as the skirt. Therefore, the irradiation time required to perform sufficient initialization throughout the laser spot region irradiated on the diamond is determined by the initialization time of the skirt of the laser beam. Conventionally, the spatial distribution of this laser intensity has not been taken into consideration. That is, the initialization time has been rate-determined in the skirt region of the laser beam.

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

Means for Solving the Problems

[0008] In order to solve the above problems, an optical nuclear magnetic resonance apparatus according to the present invention includes a sensor material having an electron spin that causes electron spin resonance, control of the direction of the electron spin of defects contained in the sensor material, and a laser that irradiates the sensor material to measure the direction of the electron spin, 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 for irradiating the sensor material with microwaves, a permanent magnet or an electromagnet that applies a static magnetic field to the sensor material, and a control unit that controls the laser, the microwave irradiation device, and the beam shaping element so as to equalize the two-dimensional intensity distribution of the laser.

Effects of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6

Embodiment for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, the spatial intensity distribution of the laser irradiating the diamond (sensor material) containing the NV center is shaped from a normal Gaussian shape into a spatially uniform top-hat type 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 irradiating the diamond (sensor material) can be enlarged or reduced to an optimum diameter for an optical element such as a DOE by the beam expander.

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

[0013] Note that the measurements targeted in this embodiment are magnetic field strength measurements, optical nuclear magnetic resonance measurements which are an application thereof, temperature measurements, or electric field strength measurements. Furthermore, although a diamond (sensor material) containing an NV center is described as the sensor material, a 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. Also, although a DOE is described as an example of the element for shaping the laser, any optical element capable of shaping the laser into a top-hat type, such as a fly-eye lens or a diffuser, may be used. Hereinafter, examples of the present invention will be described using drawings, taking an optical nuclear magnetic resonance apparatus as an example.

Examples

[0014] In this embodiment, diamond containing NV centers is used as the sensor material, a DOE is used as the optical element for shaping the laser, and optical nuclear magnetic resonance measurement is taken as an example for the measurement. FIG. 1 is a schematic configuration diagram of an optical nuclear magnetic resonance apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the optical nuclear magnetic resonance apparatus 1 includes a diamond (sensor material) 101, a laser 102 with a wavelength of about 532 nm that irradiates the diamond (sensor material) 101, a microwave irradiation device 103 that irradiates the diamond (sensor material) 101 with microwaves, red fluorescence 104 emitted from the diamond (sensor material) 101, a beam shaping element 105 for shaping the laser into a top-hat type, a permanent magnet or an electromagnet 106 installed in the vicinity 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 of a microwave pulse to the microwave irradiation device 103 that irradiates microwaves, which will be described in detail later, and a command value of a laser pulse to a laser irradiation device (not shown). Further, the control unit 108 controls the beam shaping element 105 and inputs a detection value from the detector 107. Here, the control unit 108 is realized by, for example, a processor such as a CPU (not shown), a ROM that stores various programs, a RAM that temporarily enables data in the calculation process, and a storage device such as an external storage device. The processor such as the CPU reads and executes various programs stored in the ROM, and stores the calculation result, which is the execution result, 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 pass through the microwave irradiation device 103. Further, the microwave irradiation device 103 may be installed in a position where it can irradiate the diamond (sensor material) 101 with microwaves, and it may be composed of a printed circuit board or a metal wire. Furthermore, the permanent magnet or electromagnet 106 may be arranged in a position where it can apply a static magnetic field parallel to the coupling axis of the NV centers contained in the diamond (sensor material) 101, and there is no limitation on the position with respect to the diamond (sensor material) 101. And since the red fluorescence 104 emitted from the diamond (sensor material) 101 is emitted in all directions from the diamond (sensor material) 101, the arrangement of the detector 107 is arbitrary as long as the red fluorescence 104 can be detected. Also, other optical elements such as lenses may be included before and after the beam shaping element 105 and in front of the detector 107. Note that the wavelength of the laser 102 is not limited to 532 nm, and any wavelength at which the NV centers contained in the diamond (sensor material) 101 emit red fluorescence may be used.

[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 make up the beam shaping element 105. Here, the beam expander 202 has a function of expanding or contracting the spot diameter of the laser 102, and the spot diameter may be optimized according to the specifications of the DOE 201 installed downstream. Note that the beam expander 202 may be of a typical Galilean type or Keplerian type. Also, it may be configured to arrange other optical elements such as lenses between the beam expander 202 and the DOE 201.

[0017] Here, DOE201 will be described. The laser 102 expanded or reduced by the beam expander 202 has a slight divergence angle. The laser 102 is shaped into a top-hat type by passing through the DOE201, but its uniformity and size are affected by the spot diameter of the laser 102 incident on the DOE201. Therefore, in order to optimize the uniformity and size, it is desirable for the DOE201 to have a mechanism that can be moved upstream and downstream. Note that the control unit 108 controls the mechanisms that can be moved upstream and downstream.

[0018] FIG. 3 is an explanatory diagram showing the sequence of laser pulses and microwave pulses for irradiating diamond (sensor material). That is, FIG. 3 is a diagram for explaining the outline of the measurement sequence of optical nuclear magnetic resonance. The laser 102 is irradiated as a pulse onto the diamond (sensor material) 101 by an AOM (Acoustic Optical Modulator) (not shown). As shown in FIG. 3, the pulse of this laser 102 can be temporally distinguished into the following two regions: the first half 301 of the laser pulse and the second half 302 of the laser pulse. The first half 301 of the laser pulse is a reading region for measuring the red fluorescence 104 emitted from the diamond (sensor material) 101 by the 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 the 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 blocked, and the 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 number of pulse groups, and any pulse group may be used. Subsequently, the microwave pulse is blocked, and the laser pulse is irradiated onto the diamond (sensor material) 101 again. As described above, the sequence of alternately and repeatedly irradiating the diamond (sensor material) 101 with the laser pulse and the microwave pulse becomes the measurement sequence of optical nuclear magnetic resonance.

[0019] FIG. 4A is an explanatory diagram showing the change in red fluorescence for each laser pulse and the signal amount of measurement when initialization is sufficient. That is, FIG. 4 is a diagram for explaining the intensity of red fluorescence 104 measured by detector 107 according to the measurement sequence of the optical nuclear magnetic resonance of FIG. 3, corresponding to the case where the electron spin of the NV center in diamond (sensor material) 101 is sufficiently initialized. 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. In the case of FIG. 4A where initialization is sufficient, the intensity of the red fluorescence 104 in the second half 402 of the red fluorescence intensity when initialization is sufficient becomes a constant value without changing for each laser pulse. The difference in the intensity of the red fluorescence 104 between the starting point of the first half 401 of the red fluorescence intensity when initialization is sufficient and the second half 402 of the red fluorescence intensity when initialization is sufficient corresponds to the signal intensity 403 of the optical nuclear magnetic resonance. There is also an analysis method that uses the product of the period of the first half 401 of the red fluorescence intensity when initialization is sufficient and the signal intensity 403 as the signal intensity instead of the difference between the starting point of the first half 401 of the red fluorescence intensity when initialization is sufficient and the second half 402 of the red fluorescence intensity when initialization is sufficient, but either method is acceptable.

[0020] FIG. 4B is an explanatory diagram showing the change in red fluorescence for each laser pulse when the initialization is insufficient. That is, FIG. 4B is a diagram explaining the intensity of the red fluorescence 104 measured by the detector 107 according to the measurement sequence of the optical nuclear magnetic resonance 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 insufficient. The first half 404 of the red fluorescence intensity when the initialization is insufficient indicates the intensity of the red fluorescence 104 emitted during the first half 301 of the laser pulse, and the second half 405 of the red fluorescence intensity when the initialization is insufficient indicates the intensity of the red fluorescence 104 emitted during the second half 302 of the laser pulse. When the initialization is insufficient as shown in FIG. 4B, the intensity of the red fluorescence 104 between the initial stage of the first half 404 of the red fluorescence intensity when the initialization is insufficient and the second half 405 of the red fluorescence intensity when the initialization is insufficient decreases for each laser pulse. That is, the intensity of the red fluorescence 104 at the starting point of the first half 404 of the red fluorescence intensity when the initialization is insufficient increases for each laser pulse, while the intensity of the red fluorescence 104 in the second half 405 of the red fluorescence intensity when the initialization is insufficient decreases for each laser pulse. As shown in this FIG. 4B, when the initialization is insufficient, since the signal intensity of the optical nuclear magnetic resonance decreases for each laser pulse, it is understood that it is important to perform the initialization sufficiently.

[0021] FIG. 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, FIG. 5 is a graph obtained by measuring and plotting the intensity of the red fluorescence 104 in the latter half 402 of the red fluorescence intensity when the initialization is sufficient or in the latter half 405 of the red fluorescence intensity when the initialization is insufficient for each laser pulse. Here, the conditions at the time of measurement in FIG. 5 are that the incident laser intensity is 15 mW and the interval between laser pulses is 100 μsec. The laser pulse number dependency 501 of the latter half of the red fluorescence intensity is a measured value when the initialization time is 1000 μsec and the beam shaping element 105 is not used, and the laser pulse number dependency 502 of the latter half of the red fluorescence intensity is a measured value when the initialization time is 1000 μsec and the beam shaping element 105 is used. Also, the laser pulse number dependency 503 of the latter half of the red fluorescence intensity is a measured value when the initialization time is 300 μsec and the beam shaping element 105 is not used, and the laser pulse number dependency 504 of the latter half of the red fluorescence intensity is a measured value when the initialization time is 300 μsec and the beam shaping element 105 is used. Since the laser pulse number dependency 501 of the latter half of the red fluorescence intensity and the laser pulse number dependency 502 of the latter half of the red fluorescence intensity are almost the same value and a constant value, it can be seen that the initialization time of 1000 μsec is sufficient. On the other hand, since the value of the laser pulse number dependency 503 of the latter half of the red fluorescence intensity decreases for each laser pulse, it can be seen that the initialization time of 300 μsec is insufficient. However, since the laser pulse number dependency 504 of the latter half of the red fluorescence intensity is a value equivalent to the laser pulse number dependency 501 of the latter half of the red fluorescence intensity and the laser pulse number dependency 502 of the latter half of the red fluorescence intensity and is almost a constant value, it can be seen that sufficient initialization can be achieved even when the initialization time is 300 μsec by using the beam shaping element 105.

[0022] FIG. 6 is a diagram for explaining the dependence of the red fluorescence intensity at the 28th laser pulse in FIG. 5 on the time (initialization time) in the second half of the laser pulse with and without using the beam shaping element of the present invention. That is, FIG. 6 is a diagram plotting the intensity of the red fluorescence 104 detected at the time of the 28th laser pulse irradiation against the initialization time. Here, the conditions at the time of measurement in FIG. 6 are the same as those in FIG. 5, where the incident laser intensity is 15 mW and the interval between laser pulses is 100 μs. The dependence 601 of the red fluorescence intensity at the 28th pulse on the time (initialization time) in the second half of the laser pulse corresponds to the case without using the beam shaping element 105, and the dependence 602 of the red fluorescence intensity at the 28th pulse on the time (initialization time) in 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) in the second half of the laser pulse, it can be understood that the shorter the initialization time, the more significantly the intensity of the red fluorescence 104 decreases, indicating an increase in insufficient initialization. However, since it becomes almost a constant value when the initialization time is 1000 μsec or more, it can be seen that sufficient initialization cannot be performed unless the initialization time is set to 1000 μsec or more when the beam shaping element 105 is not used. On the other hand, in the dependence 602 of the red fluorescence intensity at the 28th pulse on the time (initialization time) in the second half of the laser pulse, since it becomes almost a constant value regardless of the initialization time, 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 the present embodiment, it is possible to provide an optically detected nuclear magnetic resonance apparatus that can shorten the time required for initialization and the measurement time by shaping the spatial distribution of the laser intensity irradiated on diamond (sensor material) from a Gaussian shape to a spatially uniform top-hat shape. Specifically, according to this embodiment, by shaping the laser into a top-hat type, the spatial distribution of the laser intensity can be made uniform, so that the time required for the initialization of the electron spin of the NV center in diamond (sensor material) can be shortened. Thus, it is obvious that the total measurement time of the optical nuclear magnetic resonance can be shortened.

[0024] Note that the present invention is not limited to the above-described embodiments, and various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.

Explanation of Reference Numerals

[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 the number of laser pulses on the second half of the red fluorescence intensity 601, 602… Dependence of the red fluorescence intensity in the second half of the laser pulse (initialization time) on the number of pulses, 28th pulse

Claims

1. A sensor material having electron spins that cause electron spin resonance, a laser that irradiates the sensor material to control the orientation of the electron spins of the defects contained in the sensor material and to measure the orientation 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 for irradiating the sensor material with microwaves, a permanent magnet or an electromagnet for applying a static magnetic field to the sensor material, and a control unit for controlling the laser, the microwave irradiation device, and the beam shaping element so as to equalize the two-dimensional intensity distribution of the laser. An optically detected nuclear magnetic resonance apparatus characterized by comprising.

2. The optically detected nuclear magnetic resonance apparatus according to claim 1, wherein the beam shaping element shapes the spatial distribution of the laser intensity from a non-uniform Gaussian shape to a uniform top-hat type. An optically detected nuclear magnetic resonance apparatus characterized by this.

3. The optically detected nuclear magnetic resonance apparatus according to claim 2, wherein the beam shaping element is at least one of a diffractive optical element, a diffuser, and a fly-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-eye lens. An optically detected nuclear magnetic resonance apparatus characterized by having.

4. The optically detected nuclear magnetic resonance apparatus according to claim 3, wherein the detector detects an alternating magnetic field emitted by nuclear spins of elements contained in a sample to be measured. An optically detected nuclear magnetic resonance apparatus characterized by this.

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