WO2018174909A1

WO2018174909A1 - Magnetometer with a waveguide

Info

Publication number: WO2018174909A1
Application number: PCT/US2017/024171
Authority: WO
Inventors: Nicholas Mauriello LUZOD
Original assignee: Lockheed Martin Corporation
Priority date: 2017-03-24
Filing date: 2017-03-24
Publication date: 2018-09-27

Abstract

A diamond can be used in a magnetometer to determine the strength of a magnetic field applied to the diamond. The diamond includes a first portion comprising a plurality of nitrogen vacancy (NV) centers dispersed throughout the first portion. The diamond also includes a second portion adjacent to the first portion. The second portion does not contain NV centers. The second portion is configured to facilitate transmission of light generated by the NV centers of the first portion away from the first portion.

Description

MAGNETOMETER WITH A WAVEGUIDE

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application is related to U.S. Patent Application No. 15/468,641 filed March 24, 2017, entitled "MAGNETOMETER WITH A

WAVEGUIDE", the content of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Magneto-optical defect center materials such as diamonds with nitrogen vacancy centers can be used to determine an applied magnetic field by transmitting light into the diamond and measuring the responsive light that is emitted . The loss of light in such systems may be detrimental to measurements and operations.

SUMMARY

[0003] An illustrative magneto-optical defect center material may include a first portion comprising a plurality of defect centers dispersed throughout the first portion. The magneto-optical material also may include a second portion adjacent to the first portion. The second portion may not contain significant defect centers. The second portion may be configured to facilitate transmission of light generated by the defect centers of the first portion away from the first portion.

[0004] Some illustrative magneto-optical defect center materials may include a first portion that can have a plurality of defect centers dispersed throughout the first portion. The materials may also include a second portion adjacent to the first portion. The second portion may not contain defect centers. The second portion may be configured to facilitate transmission of light generated by the defect centers of the first portion away from the first portion.

[0005] Some illustrative magnetometers may include a diamond. The diamond may include a first portion and a second portion. The first portion may include a plurality of nitrogen vacancy (NV) centers, and the second portion may not have substantial NV centers. The second portion may be configured to facilitate transmission of light generated from the NV centers of the first portion away from the first portion. The magnetometer may further include a light source that may be configured to transmit light into the first portion of the diamond. The magnetometer may further include a photo detector configured to detect light transmitted through at least one side of the second portion of the diamond. The magnetometer may also include a processor operatively coupled to the photo detector. The processor may be configured to determine a strength of a magnetic field based at least in part on the light detected by the photo detector.

[0006] Some illustrative magneto-optical defect center materials include means for absorbing first light with a first frequency and transmitting second light with a second frequency. The materials may also include means for directing the second light that may be adjacent to the means for absorbing the first light and transmitting the second light. The means for directing the second light may not absorb the first light. The means for directing the second light may be configured to facilitate transmission of the second light away from the means for absorbing the first light and transmitting the second light.

[0007] Some illustrative methods include receiving, at a plurality of defect centers of a first portion of a magneto-optical defect center material, first light with a first frequency. The plurality of defect centers may be dispersed throughout the first portion. The method can also include transmitting, from the plurality of defect centers, second light with a second frequency. The method may further include facilitating, via a second portion of the magneto-optical defect center material, the second light away from the first portion. The second portion may be adjacent to the first portion. The second portion may not contain defect centers.

[0008] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the following drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 illustrates an NV center in a diamond lattice in accordance with some illustrative embodiments.

[0010] Figure 2 illustrates an energy level diagram showing energy levels of spin states for an NV center in accordance with some illustrative embodiments.

[0011] Figure 3 is a schematic diagram illustrating a NV center magnetic sensor system in accordance with some illustrative embodiments.

[0012] Figure 4 is a graph illustrating the fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field in accordance with some illustrative embodiments.

[0013] Figure 5 is a graph illustrating the fluorescence as a function of an applied RF frequency for four different NV center orientations for a non-zero magnetic field in accordance with some illustrative embodiments.

[0014] Figure 6 is a schematic diagram illustrating a magnetic field detection system in accordance with some illustrative embodiments.

[0015] Figure 7 is a diagram illustrating possible paths of light emitted from a material with defect centers in accordance with some illustrative embodiments.

[0016] Figure 8A is a diagram illustrating possible paths of light emitted from a material with defect centers and a rectangular waveguide in accordance with some illustrative embodiments.

[0017] Figure 8B is a three-dimensional view of the material and rectangular waveguide of Figure 8A in accordance with some illustrative embodiments.

[0018] Figure 9A is a diagram illustrating possible paths of light emitted from a material with defect centers and an angled waveguide in accordance with some illustrative embodiments.

[0019] Figure 9B is a three-dimensional view of the material and angular waveguide of Figure 9A in accordance with some illustrative embodiments. [0020] Figure 1 OA is a diagram illustrating possible paths of light emitted from a material with defect centers and a three-dimensional waveguide in accordance with some illustrative embodiments.

[0021] Figure 1 OB is a three-dimensional view of the material and a three- dimensional waveguide of Figure 10A in accordance with some illustrative embodiments.

[0022] Figures 10C-10F are two-dimensional cross-sectional drawings of a three-dimensional waveguide in accordance with some illustrative embodiments.

[0023] Figure 1 1 is a diagram illustrating a material attached to a waveguide in accordance with some illustrative embodiments.

[0024] Figure 12 is a flow chart of a method of forming a material with a waveguide in accordance with some illustrative embodiments.

[0025] Figure 13 is a flow chart of a method of forming a material with a waveguide in accordance with some illustrative embodiments.

[0026] The foregoing and other features of the present disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

DETAILED DESCRIPTION

[0027] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

[0028] Magneto-optical defect center materials such as diamonds with nitrogen vacancy (NV) centers can be used to detect magnetic fields. Green light which enters a diamond structure with NV centers interacts with NV centers, and red light is emitted from the diamond. The amount of red light emitted can be used to determine the strength of the magnetic field. The efficiency and accuracy of sensors using magneto-optical defect center materials such as diamonds with NV centers (DNV sensors) is increased by transferring as much light as possible from the NV centers to the photo sensor that measures the amount of red light. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC) and other materials with nitrogen, boron, or other chemical defect centers.

[0029] In various embodiments described herein, the material with the defect centers may be formed in a shape that directs light from the defect centers towards the photo diode. When excited by the green light photon, a defect center emits a red light photon. But, the direction that the red light photon is emitted from the defect center is not necessarily the direction that the green light photon was received. Rather, the red light photon can be emitted in any direction. When the red photon reaches the interface between the diamond and the surrounding medium, the photon may transmit through the interface or reflect back into the diamond, depending, in part, on the angle of incidence at the interface. The phenomenon by which the photon may reflect back into the diamond is referred to as total internal reflection (TIR). Thus, the sides of the diamond can be angled and polished to reflect red light photons towards the photo sensor.

[0030] The NV center in a diamond comprises a substitutional nitrogen or boron atom in a lattice site adjacent a carbon vacancy as shown in Figure 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice. [0031] The NV center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NVo, while the negative charge state uses the nomenclature NV, which is adopted in this description.

[0032] The NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

[0033] The NV center has rotational symmetry, and as shown in Figure 2, has a ground state, which is a spin triplet with A₂ symmetry with one spin state m_s = 0, and two further spin states m_s = +1, and m_s = -1. In the absence of an external magnetic field, the m_s = ±1 energy levels are offset from the m_s = 0 due to spin-spin interactions, and the m_s = ±1 energy levels are degenerate, i.e., they have the same energy. The m_s = 0 spin state energy level is split from the m_s = ±1 energy levels by an energy of 2.87 GHz for a zero external magnetic field.

[0034] Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m_s = ±1 energy levels, splitting the energy levels ms = ±1 by an amount 2gμBB_z, where g is the g-factor, μβ is the Bohr magneton, and B_z is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter and will not affect the computational and logic steps in the systems and methods described below.

[0035] The NV center electronic structure further includes an excited triplet state E with corresponding m_s = 0 and m_s = ±1 spin states. The optical transitions between the ground state A₂ and the excited triplet E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet E and the ground state A₂, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

[0036] There is, however, an alternative non-radiative decay route from the triplet E to the ground state A₂ via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the m_s = ±1 spin states of the excited triplet E to the intermediate energy levels is significantly greater than the transition rate from the m_s = 0 spin state of the excited triplet E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet A₂ predominantly decays to the m_s = 0 spin state over the m_s = ±1 spins states. These features of the decay from the excited triplet E state via the intermediate singlet states A, E to the ground state triplet A₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m_s = 0 spin state of the ground state A₂. In this way, the population of the m_s = 0 spin state of the ground state A₂ may be "reset" to a maximum polarization determined by the decay rates from the triplet E to the intermediate singlet states.

[0037] Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet E state is less for the m_s = ±1 states than for the m_s = 0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m_s = ±1 states of the excited triplet E state will decay via the non- radiative decay path. The lower fluorescence intensity for the m_s = ±1 states than for the m_s = 0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m_s = ±1 states increases relative to the m_s = 0 spin, the overall fluorescence intensity will be reduced.

[0038] Figure 3 is a schematic diagram illustrating a conventional NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the m_s = ±1 states, and to measure the magnetic field based on the energy difference between the m_s = +1 state and the m_s = -1 state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source 330, which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

[0039] The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground m_s = 0 spin state and the m_s = +1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground m_s = 0 spin state and the m_s = +1 spin state, reducing the population in the m_s = 0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance occurs between the m_s = 0 spin state and the m_s = -1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m_s = 0 spin state and the m_s = -1 spin state, or between the m_s = 0 spin state and the m_s = +1 spin state, there is a decrease in the fluorescence intensity.

[0040] The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m_s = 0 spin state of the ground state A₂ to a maximum polarization, or other desired polarization.

[0041] For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the m_s = ±1 spin states have the same energy) photon energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in Figure 4 for different magnetic field components B_z along the NV axis, where the energy splitting between the m_s = -1 spin state and the m_s = +1 spin state increases with B_z. Thus, the component B_z may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence. The excitation scheme utilized during the measurement collection process (i.e., the applied optical excitation and the applied RF excitation) may be any appropriate excitation scheme. For example, the excitation scheme may utilize continuous wave (CW) magnetometry, pulsed magnetometry, and variations on CW and pulsed magnetometry (e.g., pulsed RF excitation with CW optical excitation). In cases where Ramsey pulse RF sequences are used, pulse parameters π and τ may be optimized using Rabi analysis and FID-Tau sweeps prior to the collection process, as described in, for example, U.S. Patent Application No. 15/003,590, which is incorporated by reference herein in its entirety.

[0042] In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. Figure 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component B_z along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

[0043] While Figure 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC) and other materials with nitrogen, boron, or other defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

[0044] Figure 6 is a schematic diagram of a system 600 for a magnetic field detection system according to some embodiments. The system 600 includes an optical excitation source 610, which directs optical excitation to an NV diamond material 620 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 630 provides RF radiation to the NV diamond material 620. A magnetic field generator 670 generates a magnetic field, which is detected at the NV diamond material 620.

[0045] The magnetic field generator 670 may generate magnetic fields with orthogonal polarizations, for example. In this regard, the magnetic field generator 670 may include two or more magnetic field generators, such as two or more Helmholtz coils. The two or more magnetic field generators may be configured to provide a magnetic field having a predetermined direction, each of which provide a relatively uniform magnetic field at the NV diamond material 620. The

predetermined directions may be orthogonal to one another. In addition, the two or more magnetic field generators of the magnetic field generator 670 may be disposed at the same position, or may be separated from each other. In the case that the two or more magnetic field generators are separated from each other, the two or more magnetic field generators may be arranged in an array, such as a one-dimensional or two-dimensional array, for example.

[0046] The system 600 may be arranged to include one or more optical detection systems 605, where each of the optical detection systems 605 includes the optical detector 640, optical excitation source 610, and NV diamond material 620. Furthermore, the magnetic field generator 670 may have a relatively high power as compared to the optical detection systems 605. In this way, the optical systems 605 may be deployed in an environment that requires a relatively lower power for the optical systems 605, while the magnetic field generator 670 may be deployed in an environment that has a relatively high power available for the magnetic field generator 670 so as to apply a relatively strong magnetic field.

[0047] The system 600 further includes a controller 680 arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system 600. The second magnetic field generator 675 may be controlled by the controller 680 via an amplifier 660, for example. [0048] The RF excitation source 630 may be a microwave coil, for example. The RF excitation source 630 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground m_s = 0 spin state and the m_s = ±1 spin states as discussed above with respect to Figure 3.

[0049] The optical excitation source 610 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 610 induces fluorescence in the red from the NV diamond material 620, where the fluorescence corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. The optical excitation light source 610, in addition to exciting fluorescence in the NV diamond material 620, also serves to reset the population of the m_s = 0 spin state of the ground state A₂ to a maximum polarization, or other desired polarization.

[0050] The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The controller may include a processor 682 and a memory 684, in order to control the operation of the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675 to be controlled. That is, the controller 680 may be programmed to provide control.

[0051] Figure 7 illustrates a magneto-optical defect center material 720 with a defect center 715 and an optical detector 740. In an illustrative embodiment, the magneto-optical defect center material 720 is a diamond material, and the defect center 715 is an NV center. In alternative embodiments, any suitable magneto-optical defect center material 720 and defect center 715 can be used. An excitation photon travels along path 705, enters the material 720 and excites the defect center 715. The excited defect center 715 emits a photon, which can be in any direction. Paths 710, 711 , 712, 713, and 714 are example paths that the emitted photon may travel. In the embodiments of Figure 7, one defect center 715 is shown for illustrative purposes. However, in alternative embodiments, the material may include multiple defect centers 715. Also, the angles and specific paths in Figure 7 are meant to be illustrative only and not meant to be limiting. In alternative embodiments, additional, fewer, and/or different elements may be used.

[0052] In the embodiments illustrated in Figure 7, there is no object between the material 720 and the optical detector 740. Thus, air or a vacuum is between the material 720 and the optical detector 740. The air or vacuum surrounds the material 720. In alternative embodiments, obj ects such as waveguides may be between the material 720 and the optical detector 740. Regardless of whether an object is between the material 720 and the optical detector 740, the refractive index of the material is different than the refractive index of whatever is between the material 720 and the optical detector 740.

[0053] In the embodiments shown in Figure 7 in which the same material (e.g., air or a vacuum) surrounds the material 720 on all sides and has a different refractive index than the material 720, the path of the emitted light may change direction at the interface between the material 720 and the surrounding material depending upon the angle of incidence and the differences in the refractive indexes. In some instances, depending upon the differences in the refractive indexes, the angle of incidence, and the surface of the interface (e.g., smooth or rough), the photon may reflect off of the surface of the material 720. In general, as the angle of incidence becomes more orthogonal, as the differences in the refractive indexes gets closer to zero, and as the surface of the interface is more rough, the higher the chance that the emitted photon will pass through the interface rather than reflect off of the interface. In the examples of Figure 7, all of paths 710, 711 , 712, 713, and 714 travel through the interface (i.e., a side surface of the material 720). However, in other instances, the photon may reflect off of one or more surfaces of the material 720 before passing through the interface. Because the emitted photon can be emitted in any three- dimensional direction, only a small fraction of the possible beam paths exit the surface of the material 720 facing the optical detector 740. [0054] Figure 8 A is a diagram illustrating possible paths of light emitted from a material with defect centers and a rectangular waveguide in accordance with some illustrative embodiments. Figure 8A illustrates a material 820 with a defect center 815 and an optical detector 840. In an illustrative embodiment, the magneto-optical defect center material 820 is a diamond material, and the defect center 815 is an NV center. In alternative embodiments, any suitable magneto-optical defect center material 820 and defect center 815 can be used. Attached to the material 820 is a waveguide 922. An excitation photon travels along path 805, enters the material 820 and excites the defect center 815. The excited defect center 815 emits a photon, which can be in any direction. Paths 810, 81 1, 812, 813, and 814 are example paths that the emitted photon may travel. In the embodiments of Figure 8A, one defect center 815 is shown for illustrative purposes. However, in alternative embodiments, the material may include multiple defect centers 815. Also, the angles and specific paths in Figure 8 are meant to be illustrative only and not meant to be limiting. Figure 8B is a three-dimensional view of the material and rectangular waveguide of Figure 8A in accordance with an illustrative embodiment. As shown in Figure 8B, the material 820 and the waveguide 822 are a cuboid. In altemative embodiments, additional, fewer, and/or different elements may be used.

[0055] The embodiments shown in Figure 8A includes a waveguide 822 attached to the material 820. In an illustrative embodiment, the waveguide 822 is a diamond, and there is no difference in refractive indexes between the waveguide 822 and the material 820. In altemative embodiments, the waveguide 822 may be of any material with the same or similar refractive index as the material 820. Because there is little or no difference in refractive indexes, light passing through the interface 824 does not bounce back into the material 820 or change velocity (e.g., including direction). Accordingly, because light passes freely through the interface 824, more light is emitted from the material 820 toward the optical detector 840 than in the embodiments of Figure 7. That is, light emitted in a direction toward a side of the material 820 that is not the interface 824 may bounce back into the material 820 depending upon the angle of incidence, etc., as described above. Such light, therefore, has a chance to be bounced into the direction of the interface 824 and toward the optical detector 840. In general, light (e.g., via path 812) that contacts a sidewall of the waveguide 822 will be reflected back into the waveguide 822 as opposed to transitioning outside of the waveguide 822 because of the angle of incidence. That is, such light will generally have a low angle of incidence, thereby increasing the chance that the light will bounce back into the waveguide 822.

Similarly, light that hits the end face of the waveguide 822 (i.e., the face of the waveguide 822 facing the optical detector 840) will generally have a high angle of incidence, and, therefore, a higher chance of passing through the end of the waveguide 822 and pass onto the surface of the optical detector.

[0056] In some illustrative embodiments, the material 820 includes NV centers, but the waveguide 822 does not include NV centers. Light emitted from an NV center can be used to excite another NV center. The excited NV center emits light in any direction. Accordingly, if the waveguide 822 includes NV centers, light that passed through the interface 824 may excite an NV center in the waveguide 822, and the NV center may emit light back towards the material 820 or in a direction that would allow the light to pass through a side surface of the waveguide 822 (e.g., as opposed to the end face of the waveguide 822 and toward the optical detector 840). In some instances, light may be absorbed by defects that are not NV centers, and such defects may not emit a corresponding light. In such instances, the light is not transmitted to a light sensor.

[0057] Accordingly, efficiency of the waveguide 822 is increased when the waveguide 822 does not include nitrogen vacancies. In this context, efficiency of the system is determined by the amount of light that is emitted from the defect centers compared to the amount of light that is detected the optical detector 840. That is, in a system with 100% efficiency, the same amount of light that is emitted by the defect centers passes through the end face of the waveguide 822 and is detected by the optical detector 840. In an illustrative embodiment, a system with the waveguide 822 that has nitrogen vacancies has a mean efficiency of about 4.5%, whereas a system with the waveguide 822 that does not have nitrogen vacancies has a mean efficiency of about 6.1 %.

[0058] Figure 9A is a diagram illustrating possible paths of light emitted from a material with defect centers and an angled waveguide in accordance with some illustrative embodiments. Figure 9A illustrates a material 920 with a defect center 915 and an optical detector 940. In an illustrative embodiment, the magneto-optical defect center material 920 is a diamond material, and the defect center 915 is an NV center. In alternative embodiments, any suitable magneto-optical defect center material 920 and defect center 915 can be used. The material 920 with the waveguide 922 has a higher efficiency than the embodiments of Figure 8. In an illustrative embodiment with a diamond and waveguide similar to the material 920 and the waveguide 922 of Figure 9, the system has a mean efficiency of about 9.8%.

[0059] In an illustrative embodiment, the shape of the material 920 and the waveguide 922 in Figure 9A is two-dimensional. That is, the surfaces of the material 920 and the waveguide 922 that are orthogonal to the viewing direction of Figure 9 are flat with each side in a plane that is parallel to one another, and each side spaced from one another. Figure 9B is a three-dimensional view of the material and angular waveguide of Figure 9A in accordance with an illustrative embodiment.

[0060] As shown in Figure 9A, the material 920 and the waveguide 922 are defined, in one plane, by sides 951, 952, 953, 954, 955, and 956. The angles between sides 951 and 952, between sides 952 and 953, between sides 953 and 954, and between sides 956 and 951 are obtuse angles (i.e., greater than 90°). The angles between sides 954 and 955 and between sides 955 and 956 are right angles (i.e., 90°). The material 920 with nitrogen vacancies does not extend to sides 954, 955, and 956. In alternative embodiments, any suitable shape can be used. For example, the waveguide can include a compound parabolic concentrator (CPC). In another example, the waveguide can approximate a CPC.

[0061] Figure 1 OA is a diagram illustrating possible paths of light emitted from a material with defect centers and a three-dimensional waveguide in accordance with some illustrative embodiments. Figure 10A illustrates a material 1020 with a defect center 1015 and an optical detector 1040. In an illustrative embodiment, the magneto-optical defect center material 1020 is a diamond material, and the defect center 1015 is an NV center. In alternative embodiments, any suitable magneto- optical defect center material 1020 and defect center 1015 can be used. Attached to the material 1020 is a waveguide 122. An excitation photon travels along path 1005, enters the material 1020, and excites the defect center 1015. The excited defect center 1015 emits a photon, which can be in any direction. Paths 1010, 101 1, 1012, and 1013 are example paths that the emitted photon may travel. In the embodiments of Figure 10, one defect center 1015 is shown for illustrative purposes. However, in alternative embodiments, the material may include multiple defect centers 1015. Also, the angles and specific paths in Figure 10 are meant to be illustrative only and not meant to be limiting. In alternative embodiments, additional, fewer, and/or different elements may be used.

[0062] In an illustrative embodiment, the material 1020 includes defect centers, and the waveguide 1022 is made of diamond but does not include defect centers. In an illustrative embodiment, the angles formed by sides 1055 and 1056 and by sides 1056 and 1057 are right angles, and the other angles formed by the other sides are obtuse angles. In an illustrative embodiment, the cross-sectional shape of the material 1020 and the waveguide 1022 of Figure 10A is the shape of the material 1020 and the waveguide 1022 in two, orthogonal planes. That is, the material 1020 and the waveguide 1022 have one side 1052, one side 1056, two sides 1051 , two sides 1053, two sides 1054, two sides 1055, two sides 1057, and two sides 1058. The three- dimensional aspect can be seen in Figure 10B.

[0063] Figures 10C-10F are two-dimensional cross-sectional drawings of a three-dimensional waveguide in accordance with some illustrative embodiments. The three-dimensional waveguide in Figures 10C-10F can be the same waveguide as in Figures 10A and/or 10B. Dimensions 1061, 1062, 1063, 1064, 1065, 1066, 1067, 1068, 1069, and 1070 are provided as illustrative measurements in accordance with some embodiments. In alternative embodiments, any other suitable dimensions may be used. In an illustrative embodiment, the dimension 1061 is 2.81 mm, the dimension 1062 is 2.00 mm, the dimension 1063 is 0.60 mm, the dimension 1064 is 1.00 mm, the dimension 1065 is 3.00 mm, the dimension 1066 is 0.50 mm, the dimension 1067 is 1.17 mm, the dimension 1068 is 2.0 mm, the dimension 1069 is 0.60, and the dimension 1070 is 1.75 mm.

[0064] In an illustrative embodiment, the three-dimensional material 1020 and waveguide 1022 of the system of Figures 10A-10F had a mean efficiency of 55.1%. The shape of the configuration of Figures 10A and 10B can be created using diamond shaping and polishing techniques. In some instances, the shapes of Figures 10A-10F can be more difficult (e.g., more steps, more sides, etc.) than other configurations (e.g., those of Figures 8A, 8B, 9A, and 9B). As explained above, the material and the waveguide of the configurations of Figures 8 A, 8B, 9A, 9B, and 10A-10F include the material with the defect centers and the material without the defect centers (i.e., the waveguide). In some embodiments, the material with the defect centers is synthesized via any suitable method (e.g., chemical vapor deposition), and the waveguide is synthesized onto the material with the defect centers. In alternative embodiments, the material with the defect centers is synthesized onto the waveguide.

[0065] In alternative embodiments, the material and the waveguide can be synthesized (or otherwise formed) independently and attached after synthesis. For example, Figure 1 1 is a diagram illustrating a material attached to a waveguide in accordance with some illustrative embodiments. The material 1120 can be fused to the waveguide 1 122. In an illustrative embodiment, the material 1 120 and the waveguide 1 122 are fused together using optical contact bonding. In alternative embodiments, any suitable method can be used to fuse the material 1120 and the waveguide 1 122.

[0066] In an illustrative embodiment, the refractive index of the material 1120 and the waveguide 1122 are the same. Accordingly, as discussed above, more of the light that is emitted from the defect centers is directed towards the optical detector 1140 with the waveguide 1122 than without.

[0067] In an illustrative embodiment, because the waveguide 1 122 is synthesized separately from the material 1 120, the waveguide 1 122 can be manufactured into any suitable shape. In the embodiments shown in Figure 1 1, the waveguide 1 122 is a paraboloid. For example, the waveguide 1122 can be a compound parabolic concentrator. In an illustrative embodiment, the material 1120 is a cube. In such an embodiment, the length of the diagonal of one of the sides is the same as the length of the diameter of the paraboloid at the end of the waveguide 1 122 attached to the material 1120. In alternative embodiments, any other suitable shape can be used, such as any of the shapes shown in Figures 8 A, 8B, 9A, 9B, and 10A- 10F.

[0068] In the embodiments of Figures 7, 8A, 9A, and 10A, the light used to excite the corresponding defect centers is orthogonal to the respective side of the material that the light enters. In some instances, light entering the material through the interface at an orthogonal angle is the most efficient direction to get the light into the material. In other instances, a larger incidence angle may be more efficient than an orthogonal angle, depending upon the polarization of the light with respect to the surface orientation. In alternative embodiments, the light can enter the material at any suitable angle, even if at a less efficient angle. For example, the angle of the light entering the material can be parallel to a plane of the respective optical detector (e.g., as in Figure 7). Such an angle can be chosen based on, for example, a configuration of a magnetometer system (e.g., a DNV system) or other system constraints.

[0069] Figure 12 is a flow chart of a method of forming a material with a waveguide in accordance with an illustrative embodiment. In alternative

embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow chart and/or arrows is not meant to be limiting with respect to the order or flow of operations. For example, in alternative embodiments, two or more operations may be performed simultaneously.

[0070] In an operation 1205, a material with defect centers is synthesized. For example, the material can be a diamond material, and the defect centers can be NV centers. In an illustrative embodiment, chemical vapor deposition can be used to create the material with defect centers. In alternative embodiments, any suitable method for synthesizing the material with defect centers can be used.

[0071] In an operation 1210, a waveguide is synthesized. For example, the waveguide can be the same material as the material with the defect centers but without the defect centers (e.g., diamond material without NV centers or other defect centers). In an illustrative embodiment, chemical vapor deposition is used to synthesize the waveguide onto the material with defect centers. For example, chemical vapor deposition can be used to form the material in the operation 1205 in the presence of nitrogen or other element or material, and the waveguide can be synthesized by continuing to deposit carbon on the material but without the nitrogen or other element or material.

[0072] In an operation 1215, the material and waveguide can be cut and polished. For example, the material and waveguide can be cut and polished into one of the shapes shown in Figures 8A, 8B, 9A, 9B, 10A- 10F. In an illustrative embodiment, after the material and waveguide is cut and polished, the material and waveguide can be used in a magnetometer such as a DNV sensor.

[0073] Figure 13 is a flow chart of a method of forming a material with a waveguide in accordance with some illustrative embodiments. In altemative embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow chart and/or arrows is not meant to be limiting with respect to the order or flow of operations. For example, in alternative embodiments, two or more operations may be performed simultaneously.

[0074] In an operation 1305, a material with defect centers is synthesized. In an illustrative embodiment, the material is diamond and the defect centers are NV centers. For example, a material can be formed using chemical vapor deposition in the presence of nitrogen or other defect material, thereby forming a material with defect centers. In altemative embodiments, any suitable method can be used to create a material with defect centers. In an operation 1310, the material with defect centers is cut and polished. The material with defect centers can be cut into any suitable shape, such as a cube, a cuboid, etc.

[0075] In an operation 1315, a waveguide is synthesized. For example, a material without defect centers can be formed using any suitable method, such as chemical vapor deposition. In an operation 1320, the waveguide can be cut and polished. For example, the waveguide can be cut into the shape of the waveguide 822 of Figures 8 A and 8B, the waveguide 922 of Figures 9A and 9B, the waveguide 1022 of Figures 10A-10F, or the waveguide 1 122 of Figure 11. In altemative

embodiments, the waveguide can be cut into any suitable shape.

[0076] In an operation 1325, the material with the defect centers is fused to the waveguide. For example, optical contact bonding can be used to fuse the material with the defect centers with the waveguide. In alternative embodiments, an adhesive or other suitable bonding agent can be used to attach the material with the defect centers to the waveguide. In such embodiments, the substance used to fix the material with the defect centers to the waveguide can have a refractive index that is the same as or similar to the refractive index of the material. In an illustrative embodiment, after the material and waveguide are fixed together, the material and waveguide can be used in a magnetometer such as a DNV sensor.

[0077] In an illustrative embodiment, any of the operations described herein can be implemented at least in part as computer-readable instructions stored on a computer-readable memory. Upon execution of the computer-readable instructions by a processor, the computer-readable instructions can cause a node to perform the operations.

[0078] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being "operably couplable," to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

[0079] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0080] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Further, unless otherwise noted, the use of the words "approximate," "about," "around,"

"substantially," etc., mean plus or minus ten percent.

[0081] The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A diamond comprising: a first portion comprising a plurality of nitrogen vacancy (NV) centers dispersed throughout the first portion; and a second portion adjacent to the first portion, wherein the second portion does not contain NV centers, and wherein the second portion is configured to facilitate transmission of light generated by the NV centers of the first portion away from the first portion.

2. The diamond of claim 1 , wherein all sides of the diamond are polished.

3. The diamond of claim 1 , wherein the second portion is configured to facilitate transmission of the light from the first portion through a side of the second portion that is opposite the first portion.

4. The diamond of claim 1, wherein the first portion of the diamond comprises a first side along a first plane, wherein the second portion of the diamond comprises a second side along a second plane, and wherein the first plane is orthogonal to the second plane.

5. The diamond of claim 4, wherein light that travels through the first side excites at least a portion of the NV centers, and wherein more light emitted from the NV centers travels through the second side than any other side of the diamond.

6. The diamond of claim 1 , wherein the second portion comprises a first side and a second side, wherein the first side and the second side are on opposite sides of the second portion, wherein the first portion is adjacent to the second portion along the first side, wherein an outside surface of the diamond is covered by a plurality of flat surfaces, wherein one of the plurality of the flat surfaces is the second side of the second portion, and wherein more light emitted from the NV centers travels through the second side than through any other one of the plurality of flat surfaces.

7. A magneto-optical defect center material comprising: a first portion comprising a plurality of defect centers dispersed throughout the first portion; and a second portion adjacent to the first portion, wherein the second portion does not contain defect centers, and wherein the second portion is configured to facilitate transmission of light generated by the defect centers of the first portion away from the first portion.

8. The magneto-optical defect center material of claim 7, wherein all sides of the magneto-optical defect center material are polished.

9. The magneto-optical defect center material of claim 7, wherein the second portion is configured to facilitate transmission of the light from the first portion through a side of the second portion that is opposite the first portion.

10. The magneto-optical defect center material of claim 7, wherein the first portion of the magneto-optical defect center material comprises a first side along a first plane, wherein the second portion of the magneto-optical defect center material comprises a second side along a second plane, and wherein the first plane is orthogonal to the second plane.

11. The magneto-optical defect center material of claim 10, wherein light that travels through the first side excites at least a portion of the defect centers, and wherein more light emitted from the defect centers travels through the second side than any other side of the magneto-optical defect center material.

12. The magneto-optical defect center material of claim 7, wherein the second portion comprises a first side and a second side, wherein the first side and the second side are on opposite sides of the second portion, wherein the first portion is adjacent to the second portion along the first side, wherein an outside surface of the magneto-optical defect center material is covered by a plurality of flat surfaces, wherein one of the plurality of the flat surfaces is the second side of the second portion, and wherein more light emitted from the defect centers travels through the second side than through any other one of the plurality of flat surfaces.

13. A magnetometer comprising: a magneto-optical defect center material comprising a first portion and a second portion, wherein the first portion comprises a plurality of defect centers, wherein the second portion does not comprise defect centers, and wherein the second portion is configured to facilitate transmission of light generated at the defect centers of the first portion away from the first portion; a light source configured to transmit light into the first portion of the magneto- optical defect center material; a photo detector configured to detect light transmitted through at least one side of the second portion of the magneto-optical defect center material; and a processor operatively coupled to the photo detector, wherein the processor is configured to determine a strength of a magnetic field based at least in part on the light detected by the photo detector.

14. The magnetometer of claim 13, wherein all sides of the magneto- optical defect center material are polished.

15. The magnetometer of claim 13, wherein the second portion of the magneto-optical defect center material is configured to facilitate transmission of the light from the first portion through a side of the second portion that is opposite the first portion.

16. The magnetometer of claim 13, wherein the first portion of the magneto-optical defect center material comprises a first side along a first plane, wherein the second portion of the magneto-optical defect center material comprises a second side along a second plane, and wherein the first plane is orthogonal to the second plane.

17. The magnetometer of claim 16, wherein light that travels through the first side excites at least a portion of the defect centers, and wherein more light emitted from the defect centers travels through the second side than any other side of the magneto-optical defect center material.

18. The magnetometer of claim 13, wherein the second portion comprises a first side and a second side, wherein the first side and the second side are on opposite sides of the second portion, wherein the first portion is adjacent to the second portion along the first side, wherein an outside surface of the magneto-optical defect center material is covered by a plurality of flat surfaces, wherein one of the plurality of the flat surfaces is the second side of the second portion, and wherein more light emitted from the defect centers travels through the second side than through any other one of the plurality of flat surfaces.

19. The magnetometer of claim 13, wherein the photo detector has a sensing surface within a plane that is parallel to a direction that the light source is configured to transmit light.

20. A magneto-optical defect center material comprising: means for absorbing first light with a first frequency and transmitting second light with a second frequency; and means for directing the second light that is adj acent to the means for absorbing the first light and transmitting the second light, wherein the means for directing the second light does not absorb the first light, and wherein the means for directing the second light is configured to facilitate transmission of the second light away from the means for absorbing the first light and transmitting the second light.

21. The magneto-optical defect center material of claim 20, wherein all sides of the magneto-optical defect center material are polished.

22. The magneto-optical defect center material of claim 20, wherein the means for directing the second light is configured to facilitate transmission of the light from the means for absorbing the first light and transmitting the second light through a side of the means for directing the second light that is opposite the means for absorbing the first light and transmitting the second light.

23. The magneto-optical defect center material of claim 20, wherein the means for absorbing the first light and transmitting the second light comprises a first side along a first plane, wherein the means for directing the second light of the magneto-optical defect center material comprises a second side along a second plane, and wherein the first plane is orthogonal to the second plane.

24. The magneto-optical defect center material of claim 20, wherein the means for directing the second light comprises a first side and a second side, wherein the first side and the second side are on opposite sides of the means for directing the second light, wherein the means for absorbing the first light and transmitting the second light is adjacent to the means for directing the second light along the first side, wherein an outside surface of the magneto-optical defect center material is covered by a plurality of flat surfaces, wherein one of the plurality of the flat surfaces is the second side of the means for directing the second light, and wherein more of the second light travels through the second side than through any other one of the plurality of flat surfaces.

25. A method comprising: receiving, at a plurality of defect centers of a first portion of a magneto-optical defect center material, first light with a first frequency, wherein the plurality of defect centers are dispersed throughout the first portion; transmitting, from the plurality of defect centers, second light with a second frequency; and facilitating, via a second portion of the magneto-optical defect center material, the second light away from the first portion, wherein the second portion is adjacent to the first portion, wherein the second portion does not contain defect centers.

26. The method of claim 25, further comprising reflecting the second light off of polished sides of the first portion, through the first portion, and into the second portion.

27. The method of claim 26, further comprising transmitting the second light through a side of the second portion that is at an opposite side of the second portion from the first portion.

28. The method of claim 25, further comprising: transmitting the first light through a first side of the first portion along a first plane; and transmitting the second light through a second side of the second portion along a second plane, wherein the first plane is orthogonal to the second plane.

29. The method of claim 28, wherein more of the second light travels through the second side than any other side of the magneto-optical defect center material.