Method for forming vacancy defects and method for producing diamond

Abstract

To form high-density vacancy defects in diamond.SOLUTION: The present invention discloses a method for forming vacancy defects inside diamond, the method including the steps of: shaping a pulse wave form of laser having a transparent wavelength with respect to an absorption wavelength of diamond to compensate for temporal dispersion on a phase of pulse light of laser; and emitting the pulse light of laser subjected to dispersion compensation into the diamond plural times.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for forming vacancy defects in diamond, a method for producing diamond having vacancy defects, and diamond having vacancy defects formed therein. [Background technology]

[0002] Diamond has excellent optical, electrical, and thermal properties, and is expected to be applied to optical elements and electronic devices. In particular, in recent years, nitrogen-vacancy centers called NV centers (Nitrogen Vacancy centers) that exist inside diamond have attracted attention. NV centers consist of pairs of nitrogen impurities inside diamond and adjacent vacancy defects, and when an electron is captured in the vacancy, they exhibit a magnetic property called electron spin. The electron spin in the NV center has a long coherence time even at room temperature, and the spin state can be controlled and detected at room temperature, so it is expected to be applied to quantum computing and as a highly sensitive quantum sensor for magnetic and electric fields.

[0003] Examples of conventional reports on the formation of NV centers in diamond include the following Non-Patent Documents 1 and 2. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] VV Kononenko, II Vlasov, EV Zavedeev, AA Khomich, and VI Konov, “Correlation between surface etching and NV center generation in laser-irradiated diamond”, Appl. Phys. A 124, 226 (2018). https: / / doi.org / 10.1007 / s00339-018-1646-x [Non-Patent Document 2] VV Kononenko, II Vlasov, VM Gololobov, TV Kononenko, TA Semenov, AA Khomich, VA Shershulin, VS Krivobok, and VI Konov, “Nitrogen-vacancy defects in diamond produced by femtosecond laser nanoablation technique”, Applied Physics Letters 111, 081101 (2017). https: / / doi.org / 10.1063 / 1.4993751 Summary of the Invention [Problem to be solved by the invention]

[0005] Ensemble NV centers, which are a collection of many NV centers, are important for applications to quantum computing. Ensemble NV centers have the advantage of improving the performance of quantum sensors by increasing the signal strength. In addition, when an ensemble NV center is a collection of NV centers with four different orientations, it has the advantage of being able to determine the three-dimensional vector components of a magnetic field by utilizing the difference in Zeeman splitting width due to the difference in orientation.

[0006] Therefore, in quantum sensor applications, it is effective to form a large number of NV centers (ensemble NV centers) in diamond and increase the concentration of NV centers in order to improve the measurement sensitivity of the sensor. However, no quantitative evaluation of the concentration of NV centers created by laser irradiation has been performed so far, and it has not been possible to obtain a high concentration (e.g., about 10 15 cm -3 ~10 16 cm -3There have been no reports to date on the formation of NV centers at high concentrations (or higher). In order to apply the NV centers in diamond to quantum sensors and other applications, a method is needed to form NV centers at a high concentration that can be used in quantum sensors.

[0007] The present invention aims to form a high concentration of vacancy defects in diamond. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention includes, for example, the following aspects. (Section 1) A method for forming vacancy defects in a diamond, comprising the steps of: A step of shaping a pulse waveform of a laser having a wavelength transparent to the absorption wavelength of the diamond to compensate for temporal dispersion in the phase of the pulse light of the laser; irradiating the dispersion-compensated pulsed laser light into the diamond a plurality of times; The method includes: (Section 2) The number of pulsed lights focused and irradiated inside the diamond is 5×10 7 The method according to item 1, which is as described above. (Section 3) The number of pulsed lights focused and irradiated inside the diamond is 2.5×10 8 The method according to item 2, which is as described above. (Section 4) the pulse energy of the laser is in the range of 60 nJ to 200 nJ; 4. The method according to any one of items 1 to 3, wherein the pulse width of the laser is 40 femtoseconds or less. (Section 5) 5. The method according to claim 4, wherein the pulse energy of the laser is in the range of 150 nJ to 200 nJ. (Section 6) 6. The method according to any one of items 1 to 5, wherein in the step of compensating for dispersion, a time delay is generated between a first sub-pulse light having a first polarization component and a second sub-pulse light having a second polarization component intersecting the first polarization component by performing phase modulation on the pulsed light. (Section 7) Preparing a diamond; forming vacancy defects inside the diamond by any one of the methods of items 1 to 6; A method for producing diamond, comprising: (Section 8) The concentration of vacancies formed inside is 1×10 15 cm -3 That's all there is to diamonds. (Section 9) The concentration of the vacancy defects is 3×10 15 cm -3 Item 9. A diamond as described in item 8 above. (Section 10) The concentration of the vacancy defects is 1×10 16 cm -3 Item 10. A diamond as described in item 9 above. Effect of the Invention

[0009] According to the present invention, a high concentration of vacancy defects can be formed in diamond. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram showing a schematic configuration of an optical system used when performing a void defect forming method according to an embodiment of the present invention. [Diagram 2] 2 is an example of a time waveform of pulsed light output from a laser. [Diagram 3] FIG. 2 is a diagram showing a schematic configuration of a pulse shaper shown in FIG. [Figure 4] FIG. 13 is a diagram showing a schematic configuration when dispersion compensation of pulsed light is set in a pulse shaper. [Diagram 5]FIG. 13 is a diagram for explaining the results of verification according to the embodiment, and is a graph showing the change in concentration of NV centers with respect to the number of pulsed beams for each pulse energy. [Figure 6] FIG. 1 is a diagram for explaining the verification results according to the embodiment, in which (a) is a pulse sequence by the Hahn echo method based on the optically detected magnetic resonance (ODMR) method used to measure the transverse relaxation time T2, and (b) to (e) are measurement signals by the Hahn echo method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same reference numerals denote the same or similar components, and therefore, redundant description of the same or similar components will be omitted.

[0012] According to a first aspect of the present invention there is provided a method of forming vacancy defects in a diamond. In one embodiment the method comprises the steps of: A step of shaping a pulse waveform of a laser having a wavelength transparent to the absorption wavelength of diamond to compensate for temporal dispersion of the phase of the pulse light of the laser; irradiating the inside of the diamond with a plurality of pulsed dispersion-compensated laser beams; Includes.

[0013] In one embodiment of the method, the number of pulsed lights focused and irradiated inside the diamond is 5×10 7 Preferably, the number of pulsed lights focused and irradiated inside the diamond is 2.5×10 8 That's all.

[0014] In one embodiment of the method, the laser pulse energy is in the range of 60 nJ to 200 nJ and the laser pulse width is less than or equal to 40 femtoseconds. More preferably, the laser pulse energy is in the range of 150 nJ to 200 nJ.

[0015] In one embodiment of a method, in the step of compensating for dispersion, phase modulation is performed on the pulsed light to generate a time delay between a first sub-pulse light consisting of a first polarization component and a second sub-pulse light consisting of a second polarization component that intersects the first polarization component.

[0016] According to a second aspect of the present invention, there is provided a method for producing diamond. In one embodiment, the method comprises the steps of: Preparing a diamond; forming vacancy defects within a diamond by a method provided according to a first aspect of the present invention; Includes.

[0017] According to a third aspect of the present invention, there is provided a diamond. The diamond according to one embodiment has a concentration of vacancy defects formed therein of 1×10 15 cm -3 Preferably, the concentration of vacancies is 3×10 15 cm -3 More preferably, the concentration of vacancies is 1×10 16 cm -3 That's all.

[0018] In the embodiment of the present invention described later, the number of pulsed lights irradiated onto the diamond sample is set to 5×10 5 ~5×10 8 Even if the NV center is formed by increasing the lattice relaxation time T 2 does not vary significantly within the range of about 1.6±0.2 microseconds to about 2.4±0.2 microseconds, and graphitization of diamond is suppressed.

[0019] [Optical system] FIG. 1 is a diagram showing a schematic configuration of an optical system used when carrying out a void defect forming method according to one embodiment of the present invention.

[0020] The optical system 10 mainly comprises a laser 1 used as a light source for modifying a sample 9, a pulse shaper 2 that shapes the pulse waveform of the laser light, and an objective lens 3 that focuses and irradiates the waveform-shaped pulse light inside the sample 9. The pulse light Lp irradiated from the laser 1 has its pulse waveform shaped by the pulse shaper 2 to control its pulse width, and is focused by the objective lens 3 to irradiate a predetermined depth inside the sample 9. The sample 9 is modified by the irradiation of the laser light. The traveling direction of the pulse light Lp irradiated from the laser 1 is appropriately adjusted by a total reflection mirror 4.

[0021] The optical system 10 may further include a dichroic mirror 5 and a photodetector 6 such as an avalanche-type photodiode as components for observing the modified sample 9. An optical system for irradiating the sample 9 with the pulsed light Lp output from the laser 1 through the pulse shaper 2 and an optical system for observing the reflected light from the sample 9 through the photodetector 6 are confocal optical systems. Such an optical system 10 may be configured using, for example, a confocal fluorescence microscope. Note that, when modifying the inside of the sample 9, the optical system 10 does not need to include the dichroic mirror 5 and the photodetector 6, and does not need to configure a confocal optical system.

[0022] FIG. 2 is an example of the time waveform of the pulsed light Lp output by the laser, and is also an example of an intensity autocorrelation waveform. The vertical axis of FIG. 2 indicates normalized light intensity. Unless otherwise specified in the following description of this specification, the pulse width is a value after time waveform shaping by the pulse shaper 2, Pulse width = full width at half maximum (FWHM) of intensity autocorrelation waveform / 1.5426 The pulse waveform is calculated as follows: 2 It is assumed to be of type.

[0023] In this embodiment, synthetic diamond is used for the sample 9. In this embodiment, the sample 9 is, for example, a type Ib HPHT single crystal synthetic diamond with a high concentration of nitrogen impurity, and illustratively, the nitrogen concentration of the synthetic diamond used for the sample 9 is about 33 ppm. The sample 9 is placed on a three-axis stage (not shown), and the area (XY plane) on the sample 9 where the laser light is irradiated and the position (Z axis) of the sample 9 along the irradiation axis of the laser light are adjustable. The laser light can be irradiated to the sample 9 in the atmosphere at room temperature. Exemplarily, room temperature means a temperature range of about 1°C to 30°C, including the normal temperature range of about 15°C to 25°C, but is not limited to these temperature ranges.

[0024] The laser 1 outputs pulsed light Lp with a pulse width on the order of femtoseconds. The pulsed light Lp output by the laser 1 has a wavelength transparent to the absorption wavelength of the sample 9. As a result, the laser 1 causes modification of the sample 9 in the vicinity of the focal point of the laser by nonlinear absorption, enabling spatially selective position control including the depth direction of the sample 9. The pulsed light Lp having a wavelength transparent to the absorption wavelength of the sample 9 means that the wavelength band of the pulsed light Lp is a wavelength band in which no spectral lines appear in the absorption spectrum of the sample 9 even when the sample 9 is irradiated with the pulsed light Lp. The energy of the pulsed light Lp irradiated to the sample 9 is absorbed nonlinearly by the crystal lattice of the sample 9. In this embodiment, the pulsed light Lp is linearly polarized, and the laser 1 uses a regenerative amplification type titanium sapphire laser that outputs pulsed light with a center wavelength of about 800 nm.

[0025] In this embodiment, the pulse energy of the laser is preferably in the range of about 60 nJ to 200 nJ, and the pulse width is about 40 femtoseconds. As described later, the pulse width of the laser can be shaped by the pulse shaper 2, and the illustrated pulse width of about 40 femtoseconds is the value after time waveform shaping by the pulse shaper 2. In this embodiment, the repetition frequency when outputting the pulsed light is about 250 kHz.

[0026] In this embodiment, the laser light is irradiated onto the sample 9 for a longer time than in the past (for example, about 1 second). The time for irradiating the laser light onto the sample 9 is about 2 seconds to about 5000 seconds. That is, in this embodiment, the laser 1 is about 5×10 5 1.25 x 10 9 The laser outputs a plurality of pulsed light Lp.

[0027] The pulse shaper 2 shapes the pulse waveform of the laser light to control the pulse width. The phase φ of the pulse light can be approximated by a polynomial through Taylor expansion.

number

[0028] The objective lens 3 condenses and irradiates the pulsed light after time waveform shaping inside the sample 9. In this embodiment, the objective lens 3 has a magnification of about 50 times (numerical aperture NA=0.80) and focuses at a depth of about 15 μm from the surface of the sample 9.

[0029] [Pulse Shaper and Dispersion Compensation] Pulse Shaper Fig. 3 is a diagram showing a schematic configuration of the pulse shaper shown in Fig. 1. The pulse shaper 2 includes a polarization control unit 21, mirrors 22, 23, and 24, a dispersive element 25, a focusing element 26, and a spatial light modulator (SLM) 27. The pulse shaper 2 passes the input pulsed light Lp through the dispersive element 25 and the spatial light modulator 27 in this order, thereby modulating the phase of the pulsed light Lp for each wavelength.

[0030] The pulse shaper 2 performs phase modulation on the pulsed light Lp output from the laser 1, thereby generating a time delay between a first sub-pulse light consisting of a first polarization component and a second sub-pulse light consisting of a second polarization component that intersects with the first polarization component.

[0031] The polarization control unit 21 is an optical element that is optically coupled to the laser 1 and rotates the polarization plane of the input pulsed light Lp. The polarization control unit 21 is composed of, for example, a wave plate such as a λ / 2 plate, a polarizing element, and the like. As a result, the pulsed light Lp includes a first polarization component along a first polarization direction and a second polarization component along a second polarization direction that intersects with the first polarization direction. In one embodiment, the first polarization direction and the second polarization direction are orthogonal to each other.

[0032] The mirrors 22, 23, and 24 are optical elements that direct the traveling direction of the input pulsed light Lp toward the dispersive element 25. The mirrors 22, 23, and 24 are, for example, total reflection mirrors. The mirrors 22, 23, and 24 can be omitted depending on the relative positional relationship with the dispersive element 25.

[0033] The dispersion element 25 is an optical element that disperses the pulsed light Lp for each wavelength. The dispersion element 25 is configured by, for example, a diffraction grating or a prism. Since the diffraction angle differs for each wavelength in a diffraction grating, when the pulsed light Lp having wavelength components in a wide band is incident on the diffraction grating, each wavelength component is diffracted in a different direction from each other.

[0034] The focusing element 26 is an optical element that focuses each wavelength component of the pulsed light Lp outputted from the dispersion element 25 while expanding, at different positions on the spatial light modulator 27. The focusing element 26 is formed of, for example, a cylindrical lens. The focusing element 26 has a refractive power (lens power) in a plane including the wavelength dispersion direction by the dispersion element 25, and has no refractive power in a plane perpendicular to the wavelength dispersion direction.

[0035] The spatial light modulator 27 is a phase modulation type spatial light modulator, and modulates the pulsed light Lp dispersed by the dispersion element 25 for each wavelength. In this embodiment, the spatial light modulator 27 is configured by a liquid crystal type (Liquid Crystal on Silicon: LCOS) spatial light modulator. The modulation surface of the spatial light modulator 27 includes a plurality of modulation regions corresponding to the plurality of wavelength components, respectively, and these modulation regions are aligned in the wavelength dispersion direction by the dispersion element 25. When each wavelength component of the pulsed light Lp is input to the corresponding modulation region, it is modulated independently according to the modulation pattern of the modulation region.

[0036] The pulsed light Lp input to the spatial light modulator 27 rotates with respect to the polarization direction in which the spatial light modulator 27 provides the modulation action as a result of the rotation of the polarization plane by the polarization control unit 21. As a result, among the polarization components of the pulsed light Lp, the polarization components along the polarization direction in which the spatial light modulator 27 provides the modulation action are modulated by the spatial light modulator 27, and the time waveform changes.

[0037] ·Dispersion compensation FIG. 4 is a diagram showing a schematic configuration when dispersion compensation of pulsed light is set in a pulse shaper.

[0038] As shown in Fig. 4, when setting dispersion compensation of the pulsed light in the pulse shaper, a focusing optical system 81, a wavelength conversion element 82, and a spectrometer 83 are optically coupled to the rear stage of the optical system including the laser 1 and pulse shaper 2 of the optical system shown in Fig. 1. Dispersion compensation of the pulsed light is set in the pulse shaper 2 by a control unit 84.

[0039] The light collecting optical system 81 is provided between the spatial light modulator 27 and the wavelength conversion element 82, and collects the pulsed light Lp toward the wavelength conversion element 82.

[0040] The wavelength conversion element 82 changes the intensity spectrum of the light emitted in accordance with the phase of the pulsed light Lp. The wavelength conversion element 82 may be made of, for example, GaAs, GaP, ZnTe, KDP, BBO, BIBO, LiNbO 3A nonlinear optical crystal such as KTP, LBO, or CLBO can be used. Several kinds of light, such as the second harmonic, the third harmonic, and higher harmonic, are emitted from the wavelength conversion element 82. These several kinds of light emitted from the wavelength conversion element 82 can be separated by a wavelength filter.

[0041] The spectroscope 83 detects the intensity spectrum of light emitted from the wavelength conversion element 82 by irradiating the wavelength conversion element 82 with the pulsed light Lp. The detected intensity spectrum of light is output to the control unit 84 as a detection signal.

[0042] The control unit 84 controls the polarization control unit 21 and the spatial light modulator 27 based on the detection signal output from the spectrometer 83. The control unit 84 is an arithmetic device such as a general-purpose computer or a personal computer (PC). The control unit 84 changes the polarization direction of the pulsed light Lp by controlling the rotation angle of the polarization plane in the polarization control unit 21. The control unit 84 also changes the time waveform of the pulsed light Lp by controlling the phase pattern of the spatial light modulator 27.

[0043] In this embodiment, the pulse shaper 2 controls and compensates for temporal dispersion in the phase of the pulsed light based on the MIIPS (Multiphoton Intrapulse Interference Phase Scan) method, thereby aligning the phase of the pulsed light irradiated from the laser 1 to generate a Fourier transform limited pulse with a further shortened laser pulse width.

[0044] In the MIIPS method, second harmonics of the pulsed light Lp are generated by passing the pulsed light Lp through a wavelength conversion element 82 such as a nonlinear optical crystal, and the phase dispersion of the second harmonics is measured by a spectrometer 83. The pulse shaper 2 generates a Fourier transform limited pulse by compensating for the phase dispersion measured by the spectrometer 83. In this embodiment, the pulse shaper 2 compensates for the phase dispersion and matches the phase of the pulsed light Lp, for example, by modulating the phase of the pulsed light Lp so that the intensity of the second harmonic is maximized.

[0045] It is sufficient to perform the measurement of phase dispersion using the wavelength conversion element 82, the spectrometer 83, and the control unit 84 shown in FIG. 4 and the setting of dispersion compensation for the pulse shaper 2 once before configuring the optical system 10 shown in FIG. 1.

[0046] The following examples of the present invention will make the features of the present invention clearer. EXAMPLES

[0047] In this embodiment, the optical system according to the above-mentioned embodiment of the present invention is constructed using a confocal fluorescence microscope.The wavelength conversion element, spectrometer and control unit described in the above-mentioned embodiment are used to measure phase dispersion, and dispersion compensation is set for the pulse shaper so as to generate a Fourier transform limit pulse based on the MIIPS method.The optical system equipped with the pulse shaper with dispersion compensation setting is used to irradiate the pulsed light of a laser onto diamond, and NV center is formed inside the diamond.

[0048] In this example, NV centers were formed inside diamond by the vacancy defect formation method according to the above-described embodiment of the present invention. The formation of NV centers was performed by various combinations of laser light irradiation time and pulse energy. The concentration of NV centers was estimated from the measured values ​​of the intensity of the fluorescence emitted from the NV centers. The intensity of the fluorescence emitted from the NV centers was measured using a photodiode.

[0049] In this embodiment, two items were verified. In verification 1, it was verified whether the concentration of the formed NV center was improved compared to the conventional reports. In verification 2, it was verified whether the formed NV center was graphitized in diamond.

[0050] <Verification 1> Concentration of NV centers was compared between the NV centers formed inside diamond by the vacancy defect forming method according to the present embodiment and the NV centers formed on the surface or inside diamond in the conventional report as a comparative example. The graph of the comparison result is shown in FIG.

[0051] The concentrations in the comparative examples were estimated based on the values ​​of fluorescence intensity described in conventional reports. In estimating the concentrations in the comparative examples, conditions and values ​​not described in the reports were assumed. The conventional reports cited as comparative examples are the two above-mentioned Non-Patent Documents 1 and 2. In the following explanation, 1 ppm = 1.76 × 10 17 cm -3 It is.

[0052] Comparative Example 1 As Comparative Example 1, the maximum fluorescence intensity reported in Non-Patent Document 1 was approximately 2.3 (pulse light number approximately 1.68 × 10 7 ) to estimate the concentration of NV centers at 7.2 × 10 14 cm -3 In Non-Patent Document 1, the NV center is formed on the surface by surface ablation.

[0053] Regarding Non-Patent Document 1, the concentration of NV centers was estimated as follows. Nitrogen concentration of diamond sample: 0.5 ppm (calculated from absorption coefficient at 270 nm) Fluorescence intensity in the area not exposed to pulsed light (Original PL signal): approx. 0.28 Maximum fluorescence intensity: Approximately 2.3 (number of pulsed lights: Approximately 1.68 x 10 7 ) Assuming that the NV concentration in the non-exposed area is 0.1% of the nitrogen concentration in the diamond sample, the maximum concentration in the exposed area is 7.2 × 10 14 cm -3 It was estimated that.

[0054] Comparative Example 2 As Comparative Example 2, the maximum fluorescence intensity reported in Non-Patent Document 2 was approximately 0.87 (pulse light number approximately 8.39 × 10 4 ) to estimate the concentration of NV centers at 5.4 × 10 14 cm -3 In Non-Patent Document 2, the NV center is formed on the surface by surface ablation.

[0055] Regarding Non-Patent Document 2, the concentration of NV centers was estimated as follows. Nitrogen concentration of diamond sample: 0.5 ppm (calculated from absorption coefficient at 270 nm) Fluorescence intensity in the area not exposed to pulsed light (Original PL signal): approx. 0.14 Maximum fluorescence intensity: Approximately 0.87 (number of pulsed lights: Approximately 8.39 × 10 4 ) Assuming that the NV concentration in the non-exposed area is 0.1% of the nitrogen concentration in the diamond sample, the maximum concentration in the exposed area is 5.4 × 10 14 cm -3 It was estimated that.

[0056] FIG. 5 is a diagram for explaining the verification results according to the embodiment, and is a graph showing the change in the concentration of NV centers with respect to the number of pulsed light for each pulse energy. The data of four types of line graphs plotted in the figure using four different symbols are the measured values ​​of the concentration of NV centers formed inside diamond by the vacancy defect formation method according to the embodiment. The data plotted in the figure using two different types of enclosed symbols are the estimated values ​​of the concentration of NV centers according to the comparative example.

[0057] Based on the graph in Figure 5, which compares the NV center concentrations, we investigated the conditions of the laser light irradiation time and pulse energy for forming a high concentration of NV centers. The target concentration of NV centers to be formed was about 10 15 cm -3 ~10 16 cm -3 It was decided.

[0058] First, we report an overview of the measurement results of this example. In this example, as the number of pulsed light irradiated to the diamond sample was increased, the concentration of NV centers first increased, then saturated or slightly decreased. After that, the number of pulsed light irradiated was increased to obtain measurement data, and when the number of pulsed light was about 2.5 × 10 7 pieces~approx. 5×10 7 At each measurement point, the concentration of NV centers is approximately 3–4×10 15 cm -3 The number of pulsed lights was further increased to obtain measurement data, and in this embodiment, the final value was about 5×10 8 By irradiating a diamond sample with pulsed light, the maximum concentration of NV centers was increased to approximately 3 × 10 16 cm -3 The NV centers were formed without annealing the diamond after irradiating the diamond sample with a laser pulse.

[0059] In addition, in these measurement results, the behavior in which the concentration of NV centers saturates or decreases with an increase in the number of pulsed light can be interpreted from the perspective of competition between the formation and annihilation of NV centers.

[0060] The measurement results of the concentration of the NV center in this example were compared with the estimated values ​​of the concentrations of the NV center in Comparative Examples 1 and 2. The observation results were as follows.

[0061] In this example, the diamond sample was subjected to a pulse energy of about 60 nJ and a laser beam of about 2.5 × 10 6By irradiating the material with 10 pulses of light, the concentration of NV centers was reduced to approximately 1×10 15 cm -3 The obtained concentration value is higher than any of the estimated values ​​of the NV center concentration shown in Comparative Examples 1 and 2, and is about 10, which is the lower limit of the target concentration value at which high sensitivity can be expected in quantum sensors. 15 In addition, when the pulse energy was about 100 nJ, about 150 nJ, and about 200 nJ, the 6 By irradiating the material with 10 pulses of light, the concentration of NV centers was reduced to approximately 1×10 15 cm -3 Diamonds having the above properties were obtained.

[0062] In this example, the diamond sample had a particle size of about 5 × 10 7 By irradiating the material with 10 pulses of light, the concentration of NV centers was increased to approximately 3×10 15 cm -3 The obtained diamonds had a concentration of NV centers of 10 or more. This concentration of NV centers was obtained for all pulse energies. The obtained concentration value was the concentration at which the concentration of NV centers, once saturated, began to increase again. This number of pulsed light irradiations was a number that was not achieved in either Comparative Example 1 or 2. The obtained concentration value is higher than any of the estimated values ​​of the NV center concentration shown in Comparative Examples 1 and 2, and is approximately 10, which is the lower limit of the target concentration value at which high sensitivity can be expected in quantum sensors. 15 had been achieved.

[0063] In this example, the diamond sample had a particle size of about 2.5 × 10 8 By irradiating the material with 10 pulses of light, the concentration of NV centers was reduced to approximately 1×10 16 cm -3The diamonds thus obtained had a concentration of NV centers equal to or greater than 10. This concentration of NV centers was obtained at all pulse energies. This number of pulsed light irradiations was not achieved in either Comparative Example 1 or 2. The obtained concentration value is higher than any of the estimated values ​​of the NV center concentration shown in Comparative Examples 1 and 2, and is approximately 10, which is the target concentration value for which high sensitivity can be expected in quantum sensors. 16 had been achieved.

[0064] According to this embodiment, the maximum radiation dose of about 5×10 was measured for a diamond sample with a pulse energy of about 150 nJ or about 200 nJ. 8 By irradiating the material with 10 pulses of light, the concentration of NV centers increased to a maximum of approximately 3 × 10 16 cm -3 This number of pulsed light irradiations was not achieved in either Comparative Example 1 or 2, and the obtained concentration was also not achieved in either Comparative Example 1 or 2.

[0065] <Verification 2> Regarding the NV center formed inside the diamond by the vacancy defect forming method according to the present embodiment, it was examined whether the diamond was graphitized or not.

[0066] The verification was carried out by the known Optically Detected Magnetic Resonance (ODMR) method, which measured the transverse relaxation time T 2 If the diamond is graphitized when the NV center is formed in the diamond, the transverse relaxation time T 2 decreases.

[0067] For the verification, the concentration, i.e. the number of pulsed light to be irradiated, was set to about 5×10 5 pieces~approx. 5×10 8 The laser pulse energy irradiated to the diamond samples was approximately 150 nJ.

[0068] FIG. 6 is a diagram for explaining the verification results according to the embodiment. (a) shows the transverse relaxation time T 2 The pulse sequence is based on the Hahn echo technique using optically detected magnetic resonance (ODMR) for the measurement of (a) to (e). (b) to (e) are the measurement signals using the Hahn echo technique.

[0069] As shown in the measurement signals in (b) to (e), the number of pulsed light beams irradiated onto the diamond sample was set to 5 × 10 5 pieces~5×10 8 Even if the NV center is formed by increasing the number of 2 does not vary significantly within the range of about 1.6±0.2 microseconds to about 2.4±0.2 microseconds. Furthermore, the transverse relaxation time T 2 The time t1, t2, and t3 were approximately 1.6±0.2 microseconds, which were almost the same value. This confirmed that the vacancy defect formation method according to this embodiment suppresses graphitization of diamond, which may occur when forming NV centers.

[0070] The number of pulsed light beams irradiated onto the diamond sample was 7.5 × 10 8 When the number of pulsed light was increased beyond this number, a decrease in the concentration of NV centers was confirmed, and when the number of pulsed light irradiated was further increased, the area near the focal point clearly turned black, confirming that the diamond sample was graphitized.

[0071] In addition, the number of pulses of light that were observed to graphitize the diamond sample was confirmed while increasing the number of pulses of light irradiated to the diamond sample. When the pulse energy was about 60 nJ, the number of pulses was about 1.75 × 10 9 It was confirmed that the diamond sample was graphitized when irradiated with pulsed light of about 1.25 × 10 9 In this case, no graphitization of the diamond samples was observed.

[0072] Similarly, for a pulse energy of about 100 nJ, the9 It was confirmed that the diamond sample was graphitized when irradiated with pulsed light of about 7.5 × 10 8 In these cases, no graphitization of the diamond sample was observed. For a pulse energy of about 200 nJ, the graphitization rate was about 1 × 10 9 It was confirmed that the diamond sample was graphitized when irradiated with pulsed light of about 7.5 × 10 8 In this case, no graphitization of the diamond samples was observed.

[0073] As described above, according to the present invention, a high concentration of NV centers can be formed in diamond. Conventionally, it has not been easy to form NV centers in diamond without graphitizing the diamond, and it has been difficult to form a high concentration of NV centers in diamond. According to the present invention, the concentration of the formed NV centers is about 10, which is a concentration that can be expected to increase the sensitivity of quantum sensors. 15 cm -3 ~10 16 cm -3 This high concentration suppresses graphitization of diamond even when NV centers are formed.

[0074] Furthermore, according to the present invention, NV centers can be formed in diamond without annealing the diamond after irradiating the diamond with a pulsed laser beam. If the annealing step becomes unnecessary, a low-temperature process can be adopted when industrially manufacturing a quantum sensor element containing an NV center, and the quantum sensor element can be manufactured at room temperature in the atmosphere.

[0075] [Other formats] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0076] In the above embodiment, diamond is used as the sample 9, and a nitrogen-vacancy center called an NV center is formed inside the diamond as a color center, but the color center formed inside the diamond is not limited to the NV center. Instead of the NV center, a silicon-vacancy center or a germanium-vacancy center may be formed inside the diamond.

[0077] In the above embodiment, the pulse width of the pulsed light Lp generated by the laser 1 and the pulse shaper 2 is on the order of femtoseconds, but the pulse width of the laser irradiated to modify the diamond is not limited to the order of femtoseconds. As long as a high concentration of NV centers can be preferentially formed inside the diamond, the pulse width can be within the order of femtoseconds (10 -15 seconds), e.g. attoseconds (10 -18 Diamond can be irradiated with a laser having a pulse width on the order of 100 .mu.m (s).

[0078] The concentration of nitrogen impurity contained in sample 9 is not limited to the concentration exemplified in the above embodiment. For example, in the application to quantum sensor, the concentration of nitrogen impurity contained in synthetic diamond may be less than about 33 ppm (for example, less than about 1 ppm) as exemplified above, and the synthetic diamond used is not limited to type Ib, but may be type IIa. [Explanation of symbols]

[0079] 1 Laser (light source) 2 Pulse Shaper 3 Objective Lens 4 Total reflection mirror 5 Dichroic mirror 6 Photodetector (photodiode) 9. Samples 10 Optical system 21 Polarization control section (wave plate) 22, 23, 24 Mirrors (total reflection mirrors) 25 Dispersive element (diffraction grating) 26 Condenser element (cylindrical lens) 27 Spatial light modulator (LCOS-SLM) 81 Condensing optical system 82 Wavelength conversion element (nonlinear optical crystal) 83 Spectrometer 84 Control Unit Lp Pulsed Light

Claims

1. A method for forming vacancy defects in a diamond, comprising the steps of: A step of shaping a pulse waveform of a laser having a wavelength transparent to the absorption wavelength of the diamond to compensate for temporal dispersion in the phase of the pulse light of the laser; irradiating the dispersion-compensated pulsed laser light into the diamond a plurality of times; The method includes:

2. The number of pulsed lights focused and irradiated inside the diamond is 5×10 ７ The method according to claim 1 .

3. The number of pulsed lights focused and irradiated inside the diamond is 2.5×10 ８ The method according to claim 2 .

4. The pulse energy of the laser is in the range of 60 nJ to 200 nJ; The method according to any one of claims 1 to 3, wherein the pulse width of the laser is 40 femtoseconds or less.

5. 5. The method of claim 4, wherein the laser pulse energy is in the range of 150 nJ to 200 nJ.

6. 6. The method according to claim 1, wherein in the step of compensating for dispersion, a time delay is generated between a first sub-pulse light consisting of a first polarization component and a second sub-pulse light consisting of a second polarization component intersecting the first polarization component by performing phase modulation on the pulsed light.

7. Preparing a diamond; forming vacancy defects inside the diamond by any one of the methods of claims 1 to 6; A method for producing diamond, comprising:

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