Sensor system for sensing a magnetic field or magnetic-field-dependent measurement variable

Abstract

The invention relates to a sensor system (1) for sensing a magnetic-field parameter of an external magnetic field, comprising: an NV diamond (2); a microwave source (3) which is designed to generate an electromagnetic field; a microwave structure (30) which is arranged and designed to shape the electromagnetic field generated by the microwave source (3) in such a way that a microwave field is produced within the NV diamond (2); an excitation light source (4) which is arranged and designed to direct an excitation light beam (5) onto the NV diamond (2) such that an optical field is formed within the NV diamond (2) along a beam axis of the excitation light beam (5); at least one detector (6) which is arranged and designed to detect an optical signal emitted by the NV diamond (2) as a result of irradiation with the excitation light beam (5); and a magnetic-field generating device (12) which is arranged and designed to generate, within the NV diamond (2), a directed internal static magnetic field (20) which exhibits improved homogeneity within the NV diamond (2) along a first preferred axis (21). Within the NV diamond (2), the beam axis of the excitation light beam (5) is aligned along the first preferred axis (21).

Description

[0001] R. 417124

[0002] - 1 -

[0003] Description

[0004] title

[0005] Sensor system for detecting a magnetic field or a magnetic field-dependent measurement quantity

[0006] The present invention relates to a sensor system for detecting a magnetic field or a magnetic field-dependent measured quantity.

[0007] Background of the invention

[0008] To detect a magnetic field, so-called NV magnetic field sensors are used. These sensors consist of a diamond whose crystal lattice has defects in the form of NV centers. In an NV center, a nitrogen atom occupies the lattice site of a carbon atom, with a defect located in the immediate vicinity of the nitrogen atom—again occupying the lattice site of a carbon atom. If such a crystal lattice is irradiated with excitation radiation with a wavelength between 490 nm and 575 nm, an electronic transition from a ground state occurs in the crystal lattice. 3 A2 into an excited state 3 E induced. From the excited state 3 E relaxes the NV center back to its ground state by emitting fluorescence radiation in a wavelength range between 600 nm and 850 nm. 3 A2. The basic state 3 A2 has three magnetic substates with m s =0, m s=±1. The states with m s =0 and m s The values ​​=±1 differ by an energy difference of 2.87 GHz (zero field splitting). The excited state 3 E also has three magnetic substates with m s =0, m s =±1. If the NV center is now in the ground state 3 When exposed to microwave radiation at a frequency of 2.87 GHz, the NV center oscillates between the m s =0, 3 A2 - Basic state and the m s =±1 , 3 A2 ground state. Upon irradiation with the excitation radiation, the NV center is now partially removed from the m s =±1 , 3 A2 - Ground state in the excited m s =±1 , 3 It enters an E-state. From there, it relaxes back into the m predominantly without radiation and without maintaining spin. s =0, 3 A2 - Ground state. Simultaneously, the excited state relaxes. s =0, 3E also emits fluorescence radiation into the m s =0, 3 A2 - R. 417124

[0009] - 2 -

[0010] Ground state. If the amplitude of the fluorescence radiation is measured as a function of the frequency of the microwave radiation during irradiation with the excitation radiation, a sudden drop in the amplitude of the fluorescence radiation (a so-called dip or resonance) occurs at a frequency of 2.87 GHz. The drop in the amplitude of the fluorescence radiation can be explained by the fact that – when irradiated with microwave radiation at a frequency of 2.87 GHz – the transition between the ground state and the excitation state occurs. s =0, 3 A2 ground state and the m s =±1 , 3 The A2 ground state is induced, which is excited by the excitation radiation in a spin-conserving manner, but is radiationless and not spin-conserving in the m s =0, 3The A2 ground state can relax. Therefore, if microwave radiation of a precisely matching frequency is applied, the m s =0, 3 A2 ground state, during the m s =±1 , 3 A2 ground state is filling up.

[0011] In a magnetic field, the m s =±1 , 3 A2 ground state into two states with spin quantum number m s =1 and m s =-1 (Zeeman effect). If the amplitude of the fluorescence radiation is measured while changing the frequency of the microwave radiation, two dips are obtained if the axes of the NV centers point in the same direction. The frequencies at which these dips occur depend on the size of the splitting of the m s =±1 , 3A2 ground state and thus depends on the field strength and direction of the magnetic field. In the diamond crystal lattice, there are four different possible orientations for the axes of the NV centers. If the NV axes are aligned according to these four possibilities—in which case there are four differently oriented NV axes in the crystal lattice of the NV diamond—then measuring the amplitude of the fluorescence radiation while changing the frequency of the microwave radiation yields eight dips, i.e., the two resonances corresponding to the states with spin quantum number m. s =1 and m sThe values ​​of -1 are split into four states. The projection of the magnetic field onto the respective NV centers is recorded in each case. To determine not only the field strength but also the direction of an external magnetic field, a static magnetic field, referred to below as the internal static magnetic field, is therefore necessary. The field strength of the internal static magnetic field must be large enough that the individual resonances, which correspond to the respective orientations of the NV axes, R. 417124

[0012] - 3 - do not overlap, and thus an external magnetic field is simply measured in addition to the internal magnetic field. If the resonances are very close together, it is possible that the respective line widths are larger than the splitting.

[0013] One such NV magnetic field sensor is described, for example, in US 2019 / 0018091 A1. The NV magnetic field sensor has several permanent magnets that generate an internal, static magnetic field. The permanent magnets are arranged in a Halbach configuration. The excitation radiation is directed perpendicular to the plane of the Halbach configuration onto the NV diamond.

[0014] The sensitivity of the NV magnetic field sensor depends significantly on the homogeneity of the internal, static magnetic field at the location of the NV diamond. In most cases, this homogeneity is directly dependent on the size of the magnetic field generating device. Therefore, as a general rule, the largest possible magnetic field generating devices are used. However, for many applications, the most compact magnetic field sensor possible is advantageous. To design the NV magnetic field sensor to be both as compact and as sensitive as possible, it is therefore necessary to improve its sensitivity in other ways.

[0015] Disclosure of the invention

[0016] The invention relates to a sensor system for detecting a magnetic field parameter of an external magnetic field, e.g., the magnetic field strength of the external magnetic field. Such a sensor system comprises a diamond with at least one NV center (NV diamond). The sensor system further comprises a microwave source, an excitation light source, and a detector. The microwave source is arranged and configured to generate an electromagnetic field within the NV diamond. The sensor system further comprises a microwave structure arranged and configured to shape the electromagnetic field generated by the microwave source such that a microwave field is generated within the NV diamond. R. 417124

[0017] - 4 - is generated. The excitation light source can be, for example, a diode laser. The excitation light source is specifically designed to generate an excitation light beam with a wavelength between 490 nm and 575 nm. The excitation light source is further arranged and configured to direct the excitation light beam onto the NV diamond, so that an optical field forms along a beam axis of the excitation light beam within the NV diamond, whereby, as a result of the irradiation with the excitation light beam, the NV diamond emits an optical signal, in particular fluorescence radiation in a wavelength range between 600 nm and 850 nm. A beam-shaping (e.g., a lens) or beam-guiding (e.g., a deflecting mirror) optical element can be arranged between the excitation light source and the NV diamond.The detector is designed and arranged to detect the optical signal emitted by the NV diamond as a result of irradiation with the excitation light beam. In particular, the detector can be designed as a photodiode capable of detecting radiation in a wavelength range of the fluorescence radiation emitted by the NV diamond, especially between 600 nm and 850 nm.

[0018] The sensor system further comprises a magnetic field generation device, which is arranged and configured to generate a directed, internal, static magnetic field within the NV diamond, exhibiting increased homogeneity along a first preferred axis within the NV diamond. Within the NV diamond, the beam axis of the excitation light beam is aligned along this first preferred axis.

[0019] In this process, a volume region of the NV diamond in which the optical field, the microwave field, and the internal static magnetic field overlap is referred to as the active volume. The shape and size of the active volume of the sensor system according to the invention are designed such that—with the same sensitivity compared to a conventional sensor system—the requirements for the homogeneity of the internal static magnetic field are reduced, or, with the same homogeneity of the internal static magnetic field, the sensitivity of the sensor system according to the invention is improved compared to a conventional sensor system.

[0020] The position of the first preferred axis relative to the magnetic field generating device as a reference system depends on the type of magnetic field generating device. The inventors have recognized that by aligning the first preferred axis of the R. 417124

[0021] - 5 - the active volume assumes a shape and size that is particularly advantageous with regard to the properties of the sensor system due to the inner, static magnetic field along the beam axis of the excitation light beam.

[0022] According to a further development of the invention, the magnetic field generating device is designed as a Halbach arrangement with at least one permanent magnet. The permanent magnet can, for example, be designed as a ring magnet, in which case the direction of magnetization changes continuously along the ring circumference at twice the polar angle (M = A (cos2)). <p, sin2<p, 0)). Die Richtung des inneren, statischen Magnetfelds verläuft dabei in und / oder parallel zu der Ebene, in der der Ringmagnet angeordnet ist. An einer vordefinierten Winkelkoordinate cpo = 0 zeigt das innere, statische Magnetfeld in Richtung (A, 0, 0). Dabei ist durch das Vorzeichen der Konstanten A die Polarität definiert, d.h. ob das interne Magnetfeld in positive oder negative x-Richtung zeigt. An dieser Winkelkoordinate cpo zeigt die Magnetisierungsrichtung ebenfalls in die Richtung (A, 0, 0) und damit radial nach außen.Here, the direction of the static, internal magnetic field and the magnetization direction coincide, i.e., the static, internal magnetic field points radially outwards at this angular coordinate.

[0023] Alternatively, the Halbach arrangement can also comprise at least three individual magnets arranged along an imaginary circle. Each individual magnet possesses a single magnetic dipole moment—and thus only one magnetization direction. The magnetic dipole moments of the individual magnets are aligned according to the Halbach arrangement. The orientations of the dipole moments correspond to the Halbach principle; that is, the following applies to the orientation of each individual magnet: i: m; = A (cos2 <p, sin2<p, 0), wobei das interne Magnetfeld in die Richtung (A,0,0) zeigt. Das Vorzeichen der Konstanten A definiert dabei die Polarität. Dies gilt auch dann, wenn sich an der Position <pi = 0 kein Einzelmagnet befindet.

[0024] The at least three individual magnets are arranged in a first plane, resulting in a single-layer arrangement of individual magnets. Alternatively, the ring magnet can be the sole permanent magnet arranged in the first plane. In this case, the first preferred axis lies in the first plane and is perpendicular to the direction of the internal, static magnetic field R. 417124

[0025] - 6 - aligned The beam axis of the excitation light beam runs along the first preferred axis.

[0026] The active volume of such a sensor system is designed to utilize a comparatively large proportion of the internal, static magnetic field, which exhibits increased homogeneity. Furthermore, the Halbach configuration allows for a compact sensor system, resulting in an overall compact sensor system with high sensitivity.

[0027] According to a further development of the invention, the magnetic field generating device, designed as a Halbach arrangement, has, in addition to the first plane, a second plane arranged parallel to the first plane. In the second plane, another ring magnet can be arranged, the magnetization direction of which changes continuously with twice the polar angle. Ring sections or individual magnets arranged one above the other, i.e., perpendicular to the plane of the ring, have the same magnetization direction or the same magnetic dipole moment. Alternatively, at least three further individual magnets arranged along an imaginary circle in accordance with the Halbach arrangement can also be provided in the second plane. In this case as well, the magnetic dipole moments or the magnetizations of the individual magnets or ring sections arranged one above the other point in the same direction.In such a two-plane Halbach arrangement, the first preferred axis runs in a median plane that is parallel to the first plane and midway between the first and second planes, and perpendicular to the direction of the internal static magnetic field. The internal static magnetic field points in the direction (A,0,0), where the sign of the constant A defines the polarity. If—in the case of individual magnets used as permanent magnets—the magnetic dipole moment of one of the at least three individual magnets is directed radially outward, i.e., in the positive or negative x-direction, this corresponds to the direction of the internal static magnetic field. Similarly, if ring magnets are used as permanent magnets, the direction of the internal static magnetic field coincides with the magnetization direction at the angular coordinate cpo = 0.

[0028] Compared to the single-plane Halbach arrangement, the two-plane Halbach arrangement has the advantage that the generated, internal, static magnetic field exhibits increased homogeneity over a larger area. By adding an R. 417124

[0029] - 7 - In the second plane, a second preferred axis is created along which the internal static magnetic field also exhibits increased homogeneity, but along a shorter, second path. This allows for a more flexible arrangement of the remaining components of the sensor device relative to the internal static magnetic field. Furthermore, the permanent magnets can be positioned above and below at least some of the other components of the sensor system, thus providing more space for these components. Alternatively or additionally, this method can also enable a sensor system with a larger active volume.

[0030] In a further development of the invention, the magnetic field generating device is configured as an Aubert arrangement. The Aubert arrangement comprises at least two permanent magnets arranged in a first plane and a second plane parallel to the first plane. The permanent magnets can be configured as ring magnets, with the magnetization direction of one of the two ring magnets pointing radially outwards, while the magnetization direction of the other of the two ring magnets points radially inwards. In this case as well, the magnetization direction of the ring magnets changes continuously with the circumference, but with the simple polar angle (M (cos φ)). <p, sin <p, 0)). Alternativ können auch in jeder der beiden Ebene jeweils mindestens zwei, entlang einer gedachten Kreislinie angeordnete Einzelmagnete vorgesehen sein, deren magnetische Dipolmomente in der ersten Ebene jeweils nach außen und in der zweiten Ebene jeweils nach innen zeigen.In such an arrangement of permanent magnets, the first preferred axis runs in and / or parallel to the first plane and thus perpendicular to the direction of the internal, static magnetic field. The Aubert arrangement of permanent magnets is rotationally symmetric. The axis of rotation runs perpendicular to both planes and through the respective centers of the circles. Accordingly, the generated static, internal magnetic field is also rotationally symmetric and aligned along the axis of rotation, so that the first preferred axis can run perpendicular to the internal, static magnetic field in any direction.

[0031] Comparing Aubert arrays with Halbach arrays using the same number of individual magnets and the same radius in which the individual magnets are arranged, Aubert arrays produce more homogeneous magnetic fields than corresponding Halbach arrays. Furthermore, Aubert arrays are less sensitive to the position of the individual magnets than R. 417124.

[0032] - 8 - also with regard to the magnitude and orientation of the magnetic dipole moments of the individual magnets used. Thus, the actual dipole moments of the individual magnets often deviate from the dipole moments specified by the manufacturer. Aubert arrays are less sensitive to these deviations.

[0033] If the magnetic field generating device comprises an arrangement of permanent magnets in two planes, the NV diamond can be positioned centrally between the two planes. The two planes are then arranged at a distance d from each other, with the NV diamond being positioned, in particular, at a distance d / 2 from the two planes.

[0034] The magnetic field generating device can also be configured as a Helmholtz coil pair. The Helmholtz coil pair can comprise two identical coils arranged concentrically. When current flows through them, the internal, static magnetic field is generated perpendicular to the plane of the coil windings. Like the Aubert arrangement of permanent magnets, the Helmholtz coil pair is rotationally symmetrical. The axis of rotation passes through the centers of the concentrically arranged coils. The first preferred axis is perpendicular to the axis of rotation and thus to the direction of the internal, static magnetic field. Due to the rotational symmetry, the first preferred axis can point in any direction perpendicular to the axis of rotation.

[0035] Permanent magnets have the advantage over Helmholtz coil pairs that they are independent of an external power supply, so that the corresponding sensor devices can be designed to be more compact and energy-saving.

[0036] The directed, internal, static magnetic field also exhibits increased homogeneity, particularly along a second preferred axis. A first segment along the first preferred axis, along which the internal, static magnetic field exhibits increased homogeneity, is longer than the second segment along the second preferred axis, along which the internal, static magnetic field also exhibits increased homogeneity.

[0037] In the case that the magnetic field generating device is configured as a Halbach arrangement with a single first plane, the second preferred axis runs parallel to the first plane and perpendicular to the first preferred axis, i.e., in the direction of the internal, static magnetic field. R. 417124

[0038] - 9 -

[0039] If the magnetic field generating device is designed as a two-plane Halbach arrangement, the second preferred axis runs along the z-axis. The z-axis runs perpendicular to both planes and through the centers of the circles that correspond to the respective imaginary circles along which the individual magnets of the first and second planes are arranged.

[0040] In a further development of the invention, the excitation light beam is configured, at least approximately, as a Gaussian beam. This beam has a minimal cross-sectional area at its waist. The internal, static magnetic field preferably overlaps with a region around the waist of the Gaussian excitation light beam. In this region, the excitation light beam exhibits a particularly high intensity, enabling it to excite a very high proportion of the NV centers of the NV diamond it detects. It is understood that the beam axis of the excitation light beam is aligned along the first preferred axis. In this way, the sensitivity of the sensor system can be further increased.

[0041] The beam cross-section can be elliptically shaped at and / or near the beam waist. According to a further development of the invention, the principal axis, i.e., the longer of the two axes, of the elliptical beam cross-section is aligned along the second preferred axis, while the optical axis of the excitation light beam is aligned along the first preferred axis. This makes it possible to optimally utilize that portion of the internal, static magnetic field which exhibits the increased homogeneity.

[0042] The increased homogeneity is particularly high between 10 PPM and 10,000 PPM, preferably between 200 PPM and 2,000 PPM, where PPM stands for "parts per million". The following applies to the volume under consideration:

[0043] 1000,000 * || B(x,y,z)- || / || || < Homogeneity value in PPM, where ||.|| is the norm of the respective vector and the average vectorial value of the magnetic field in the considered volume.

[0044] The internal magnetic field along the first and / or second preferred axis can assume a value between 99.9% and 100.1% of an average vector field. The average field strength typically has a value between 10 pT and 10 R. 417124

[0045] - 10 - mT, particularly between 0.5 mT and 2 mT. The increased homogeneity can thus be defined as a maximum deviation from the mean vectorial field by a value of 0.1% of the mean vectorial field. This corresponds to a deviation of the magnetic field by a value of 0.1% of the mean vectorial field and a homogeneity of 1000. This is a vectorial deviation, meaning that a deviation can exist in the considered volume even if the field strength has the same value everywhere in this volume, but the direction of the magnetic field varies. The internal, static magnetic field exhibits this increased homogeneity along the first preferred axis along the first segment.

[0046] The shape of the volume exhibiting increased homogeneity, and thus the length of the first and second sections, depends on the following parameters: the type of magnetic field generation device, the size of the magnetic field generation device, the number of individual magnets (if individual magnets are permanent magnets), and the mechanical and magnetic tolerances of the magnetic field generation device. These parameters are interdependent, so the sensor system must be treated as a system with mutually influencing requirements. If the homogeneity is to be increased to a predetermined level, the radius of the circle in the magnetic field generation device, configured as a Haibach or Aubert arrangement, can be increased, for example. Alternatively, positional, rotational, and magnetic tolerances of the permanent magnets (i.e.,The absolute value of the dipole moment for individual magnets, the magnetization in the continuous case, and / or the magnetization angle deviation compared to the nominal (ideal) magnetic field generating device can be reduced. With other parameters remaining the same (including the same number of individual magnets per plane), switching from a single-plane to a two-plane magnetic field generating device can also increase homogeneity. Alternatively or additionally, the number of individual magnets per plane can be increased. These aspects of the magnetic field generating device design must be systematically evaluated, as an improvement (deterioration) of one parameter decreases (increases) the requirements for the other parameters. R. 417124.

[0047] - 11 -

[0048] The first section is particularly between 100 pm and 5000 pm, preferably between 400 pm and 1200 pm, and corresponds in particular to the thickness of the NV diamond. According to the invention, it is aligned along the propagation direction of the excitation light beam. The second section, along which the internal, static magnetic field exhibits increased homogeneity along the second preferred axis, is particularly between 5 pm and 600 pm, preferably between 30 pm and up to 300 pm. The second section corresponds in particular to the beam diameter of the excitation light beam or is at least aligned along the longer axis of the cross-section of the excitation light beam.

[0049] Brief description of the drawings

[0050] Fig. 1 shows a schematic structure of a sensor system according to an embodiment of the invention;

[0051] Fig. 2 shows a magnetic field generating device in which 12 individual magnets are arranged in a Halbach arrangement encompassing a single plane;

[0052] Fig. 3 shows a magnetic field generating device in which 24 individual magnets are arranged in a two-plane Halbach arrangement;

[0053] Fig. 4 shows the position of an NV diamond relative to a beam axis of an excitation light beam and an internal, static magnetic field, such as can be generated by the magnetic field generating device shown in Fig. 2 or 3;

[0054] Fig. 5 shows a magnetic field generating device in which 24 individual magnets are arranged in an Aubert arrangement.

[0055] Embodiments of the invention R. 417124

[0056] - 12 -

[0057] Figure 1 shows an overview of a sensor system 1 for detecting a magnetic field parameter of an external magnetic field. The sensor system 1 comprises a diamond crystal with low-voltage defects (low-voltage diamond 2), a microwave source 3, an excitation light source 4, at least one detector 6, at least one reference detector (not shown), and a magnetic field generation device 12. Optical filters (not shown) may be arranged on the detector 6 and / or the reference detector, each configured to block wavelength ranges that are not intended to be, or cannot be, detected by the detector 6 and / or the reference detector. The detector 6 and / or the reference detector may be configured as photodiodes. The excitation light source 4 is configured to emit an excitation light beam 5. The wavelength of the excitation light beam 5 is, in particular, in a range between 490 nm and 575 nm.The low-voltage diamond 2 and the excitation light source 4 are aligned and arranged relative to each other such that the low-voltage diamond 2 can be irradiated with the excitation light beam 5. The excitation light beam 5 can be directed onto the low-voltage diamond 2, for example, via a partially reflective mirror, whereby the reflected portion of the excitation light beam 5 is directed onto the low-voltage diamond 2 and the transmitted portion of the excitation light beam 5 is directed onto the reference detector. The microwave source 3 is configured to emit an electromagnetic field that can be directed to a microwave structure 13. The microwave structure 13 is arranged and configured to shape the electromagnetic field in such a way that a microwave field is generated in the low-voltage diamond 2. Detector 6 is designed to detect fluorescence radiation, e.g. in a wavelength range between 600 nm and 850 nm, and is designed, e.g., as a photodiode.The detector 6 can be mounted directly on a side face of the NV diamond 2. Optionally, a filter can be arranged between the NV diamond 2 and the detector 6, configured to separate the fluorescence radiation from the excitation light beam. Multiple detectors, in particular multiple photodiodes, can also be provided to detect either only the fluorescence radiation or simultaneously the fluorescence radiation and the excitation light beam 5. Optionally, filters can be placed upstream of the at least one detector 6 and / or the at least one reference detector, filtering out predetermined wavelength ranges from the incoming radiation.

[0058] - 13 - filter out. The magnetic field generating device 12 is designed and arranged to generate a static, internal magnetic field B in the NV diamond 2.

[0059] The magnetic field generating device 12 can, for example, have two layers of a total of four permanent magnets 7, arranged such that the NV diamond 2 is located at the center of the magnetic field generating device 12. The permanent magnets 7 can be designed – as shown in Fig. 1 – as individual magnets 9 with a magnetic dipole moment or as ring magnets with a continuously changing magnetization direction.

[0060] Figure 2 shows the magnetic field generating device 12 as provided in one embodiment of the invention. The permanent magnets 7 are configured as individual magnets 9. In a first plane 14, 12 individual magnets 9 are arranged according to a Halbach arrangement 10. The magnetic dipole moments of the individual magnets 9 typically have the same magnitude. The individual magnets 9 are arranged along a circular path 25, which defines a circle with radius R. The direction of the magnetic dipole moments m of the individual magnets 9 changes along the circumferential direction with twice the polar angle m (cos 2). <p, sin 2<p, 0). Dabei ist der Polarwinkel der Winkel in der xy-Ebene, wobei die xy-Ebene die Ebene 14, in der die Einzelmagnete 9 (oder der Ringmagnet) angeordnet sind, bezeichnet.

[0061] The magnetic field generating device 12 can alternatively also include a ring magnet. In this case, the direction of the magnetization M changes with twice the polar angle. The z-component of the magnetization of the ring magnet is zero or nearly zero.

[0062] In such arrangements, the static magnetic field inside the ring magnet or the ring-shaped arrangement of individual magnets 9 is formed. In Fig. 2, the internal, static magnetic field points in the x-direction (viewed from right to left in the plane of the drawing) in the direction of the magnetic dipole moment of the individual magnet whose magnetic dipole moment points radially outwards. In this case, this corresponds to the position of R. 417124

[0063] - 14 -

[0064] single magnet, which is at a polar angle <p0von 0° angeordnet ist. Außerhalb des Ringmagneten oder der ringförmigen Anordnung von Einzelmagneten 9 verschwindet das statische Magnetfeld.

[0065] In this process, individual magnets shown in Fig. 2 can be omitted; for example, only magnets with polar angles can be used. <p von 90°, 180° und 270° Einzelmagnete entlang der Kreislinie 25 angeordnet sein. Dabei sind der NV- Diamant 2, die Mikrowellenstruktur 13 und die Anregungslichtquelle 4 insbesondere innerhalb der Magnetfelderzeugungsvorrichtung 12 angeordnet.

[0066] The inner, static magnetic field exhibits increased homogeneity along a first preferred axis 21; that is, in particular, along the first preferred axis and along a first segment, the field of the inner, static magnetic field deviates from the mean, vectorial field by, for example, a maximum of 0.1%. The first preferred axis is perpendicular to the direction of the inner, static magnetic field, i.e., in this case, in the y-direction. The inner, static magnetic field exhibits maximum homogeneity in a volume around the center of the arrangement. The center of the arrangement corresponds to the origin r. c = (0,0,0). If the individual magnets have a height h in the z-direction, then the center of the arrangement lies at a height h / 2 directly above (i.e., without offset in the x- and / or y-direction) the center of circle 25 in which the individual magnets 9 are arranged. The first preferred axis thus runs in the y-direction and through the center of the arrangement.

[0067] Figure 3 shows the magnetic field generating device 12 as provided in a further embodiment of the invention. In the first plane 14 and in a second plane 16, 12 individual magnets 9 are arranged according to the Halbach arrangement 10. The magnetic dipole moments of the individual magnets 9 typically have the same magnitude.

[0068] The permanent magnets can alternatively be configured as ring magnets. In this case, the magnetization – considered along the circumference of the ring magnets – has the same value. Here, m represents the magnetic dipole moment of the individual magnet, M the magnetization, and V the volume of the individual magnet. R. 417124

[0069] - 15 -

[0070] The individual magnets 9 of a plane are each arranged in a single plane along a circular line 15, 25, which defines a circle with radius R. The direction of the magnetic dipole moments m of the individual magnets 9 (or the magnetization in the case of a ring magnet) changes along the circumferential direction with twice the polar angle m <* (cos 2 <p, sin 2<p, 0). Dabei ist der Polarwinkel der Winkel in der xy-Ebene. Die erste und zweite Ebene sind senkrecht zur z-Achse ausgerichtet Im Fall, dass es sich bei den Permanentmagneten um Ringmagnete handelt, sind diese ebenfalls senkrecht zur z-Achse angeordnet Die z-Komponente der magnetischen Dipolmomente der Einzelmagnete 9 oder der Magnetisierung des Ringmagneten ist dabei null oder beinahe null.

[0071] In such an arrangement, the inner, static magnetic field results inside the ring magnet or the ring-shaped arrangement of individual magnets 9. Outside the ring magnet or the ring-shaped arrangement of individual magnets 9, the static magnetic field disappears.

[0072] The first and second planes are arranged concentrically and offset from each other by a distance d along the z-axis. The magnetic dipole moments of individual magnets 9, arranged directly above one another, are directed in the same direction. The homogeneity of the generated, internal, static magnetic field is maintained within a volume around the center of the arrangement r. c = (0,0,0) at most, where r c This concerns the origin of the coordinate system. The center of the arrangement is located on the z-axis, at a distance d / 2 from the two layers. The z-axis runs through the centers of the circles bounded by circles 15 and 25, on which the individual magnets of the first and second layers are arranged. The direction of the inner, static magnetic field B is perpendicular to the z-axis and points in the direction of those magnetic dipole moments that point radially outwards. The NV diamond – not shown in Fig. 3 – is at the center of the magnetic field generating device r. c = (0,0,0) positioned. The above statements apply analogously to the case where the permanent magnets are designed as ring magnets. R. 417124

[0073] - 16 -

[0074] The first preferred axis 21 runs here – just as in the previous embodiment – ​​through the center of the arrangement, in this case the origin of the coordinate system, in the y-direction, i.e., perpendicular to the direction of the inner, static magnetic field. The inner, static magnetic field exhibits increased homogeneity along the first preferred axis; in particular, the vector field strength of the inner, static magnetic field deviates from its mean vector field strength by, for example, a maximum of 0.1% along the first preferred axis and along the first segment.

[0075] Figure 4 illustrates the relative position between the internal static magnetic field 20, the beam axis 35 of the excitation light beam 5, and the NV diamond 2. The illustrated internal static magnetic field 20 could, for example, be the static magnetic field generated by a Halbach array. The excitation light beam 5 generates an optical field that, within the NV diamond 2, interacts with the internal static magnetic field generated by the magnetic field generation device 12.

[0076] 20 and the microwave field (not shown here) overlap. The first preferred axis 21 runs in the y-direction and, according to the invention, coincides with the beam axis 35 of the excitation light beam 5. The first preferred axis

[0077] The 21 is perpendicular to the direction of the internal, static magnetic field B, which in this case runs in the x-direction. The region of the internal, static magnetic field 20, which exhibits increased homogeneity, has the form of a disk 23 that is curved on both sides, i.e., in both the negative and positive z-directions, and whose maximum diameter in the y-direction is larger than its maximum diameter in the x-direction. This, in turn, is larger than its maximum diameter in the z-direction. The curved disk 23 is mirror-symmetric with respect to the xz-plane. The first preferred axis 21 runs along the maximum diameter of the disk 23, which, according to the invention, coincides at least approximately with the beam axis 35.

[0078] Along the first preferred axis 21, the inner, static magnetic field exhibits increased homogeneity along a first segment, i.e., the field deviates within this first segment, in particular by, for example, a maximum of 0.1% from the mean, vectorial field. The first segment is specifically R. 417124

[0079] - 17 -

[0080] Values ​​between 100 pm and 5000 pm, preferably between 400 pm and 1200 pm, are used. In particular, the first segment corresponds to the thickness of the NV diamond.

[0081] The magnetic field generating device 12 can have a second preferred axis 22. Along the second preferred axis 22, the internal static magnetic field exhibits increased homogeneity along a second segment, i.e., the vectorial internal static magnetic field deviates along this second segment, in particular by, for example, a maximum of 0.1% from the mean vectorial field. The second segment assumes values ​​between 5 pm and 600 pm, preferably between 30 pm and 300 pm, and corresponds in particular to the beam diameter of the excitation light beam within the NV diamond or is at least aligned along the longer axis of the cross-section of the excitation light beam. In the single-plane Halbach arrangements, the second preferred axis 22 runs perpendicular to the first preferred axis 21 and in the xy-plane, i.e., in this case in the y-direction and perpendicular to the beam axis 35 of the excitation light beam 5.In Halbach arrangements with two planes, the second preferred axis 22 runs along the z-axis.

[0082] The excitation light beam 5 is typically designed as a Gaussian beam and has a minimal beam cross-section at its beam waist. The beam cross-section of the excitation light beam 5 can be elliptical in a region around the beam waist, wherein, according to the invention, the second preferred axis is aligned along the long axis of the elliptical beam cross-section.

[0083] Fig. 5 shows a magnetic field generating device 12 as provided in a further embodiment of the invention. The individual magnets 9 are arranged as an Aubert arrangement 11. Here too, the magnetic field generating device 12 has two layers 14, 16, in which the individual magnets 9 are arranged along the imaginary circles 15, 25. The two layers 14, 16 are arranged concentrically to each other and offset from each other along the z-axis. The individual magnets 9 of the first layer 14 each have a magnetic dipole moment which, viewed from the center of the circle bounded by a first imaginary circle 15, is R. 417124

[0084] - 18 - points outwards, i.e., the direction of the magnetic dipole moments of the individual magnets 9 in the xy-plane varies with the simple polar angle m <* ± (cos <p, sin <p, 0). Die z-Komponente der magnetischen Dipolmomente ist dabei null oder nahezu null.

[0085] The individual magnets of the second layer 16 each have a magnetic dipole moment which, viewed from the center of a circle bounded by a second imaginary circle 25, points inwards, i.e., here too the direction of the magnetic dipole moments of the individual magnets 9 varies with the simple polar angle m <* + (cos <p, sin <p, 0). Die Homogenität des erzeugten, inneren, statischen Magnetfelds ist in einem Volumen um den Mittelpunkt der Anordnung und Ursprung des Koordinatensystems r c = (0,0,0) at its maximum. The origin of the coordinate system lies on the z-axis between the two planes and at a distance d / 2 from both planes. The NV diamond (not shown in Fig. 5) is also located here. The generated magnetic field B is therefore aligned along the z-axis.

[0086] To ensure that the total dipole moment m per layer is equal to zero (m = Jm; = 0), the Aubert arrangements can have more than two individual magnets or exactly two individual magnets per layer.

[0087] Alternatively, concentrically arranged ring magnets offset along the z-axis can also be configured as an Aubert arrangement. In this case, the magnetization of one of the two ring magnets is directed outwards, while the magnetization of the other is directed inwards. The condition that the total dipole moment m per position is zero is satisfied if the absolute value, i.e., the magnitude, of the magnetization does not change along the circumferential direction.

[0088] The Aubert arrangement is rotationally symmetric with respect to the z-axis. The first preferred axis 21 runs perpendicular to the direction of the internal, static magnetic field, i.e., within the xy-plane. Due to the rotational symmetry of the Aubert arrangement, the internal, static magnetic field is also rotationally symmetric. The beam axis 36 of the excitation light beam R. 417124

[0089] - 19 -

[0090] 5 therefore always coincides with the first preferred axis, as long as it lies in the xy-plane of the Aubert arrangement.

Claims

R. 417124 - 20 - Claims 1. Sensor system (1) for detecting a magnetic field parameter of an external magnetic field with • an NV diamond (2), • a microwave source (3) designed to generate an electromagnetic field, • a microwave structure (30) which is arranged and designed to shape the electromagnetic field generated by the microwave source (3) in such a way that a microwave field is created in the NV diamond (2), • an excitation light source (4) which is arranged and designed to direct an excitation light beam (5) onto the NV diamond (2) such that an optical field is formed along a beam axis of the excitation light beam (5) within the NV diamond (2), • at least one detector (6) which is arranged and designed to detect an optical signal emitted by the NV diamond (2) as a result of irradiation with the excitation light beam (5), • a magnetic field generating device (12) which is arranged and designed to generate a directed, internal, static magnetic field (20) within the NV diamond (2) which has increased homogeneity within the NV diamond (2) along a first preferred axis (21), characterized in that the beam axis of the excitation light beam (5) is aligned along the first preferred axis (21) within the NV diamond (2).

2. Sensor system (1) according to claim 1, wherein the magnetic field generating device (12) is designed as a Halbach arrangement with at least one permanent magnet and wherein the first preferred axis (21) is perpendicular to the direction of the inner, static magnetic field (20). R. 417124 - 21 - 3. Sensor system (1) according to claim 2, wherein the at least one permanent magnet of the Halbach arrangement is arranged in a first plane and the first preferred axis (21) runs in the first plane.

4. Sensor system (1) according to claim 1, wherein the magnetic field generating device (12) is designed as an Aubert arrangement, wherein the Aubert arrangement has at least two permanent magnets arranged in a first and in a second plane parallel to the first plane, and wherein the first preferred axis (21) is parallel to the first plane.

5. Sensor system (1) according to one of claims 2 to 4, wherein the magnetic field generating device (12) has at least three permanent magnets designed as individual magnets in each plane.

6. Sensor system (1) according to one of the preceding claims, wherein the directed, internal, static magnetic field along a second preferred axis (22) has increased homogeneity.

7. Sensor system (1) according to claim 6, wherein a second path running along the second preferred axis and along which the directed, internal, static magnetic field has increased homogeneity is shorter than a first path running along the first preferred axis and along which the internal, static magnetic field has increased homogeneity.

8. Sensor system (1) according to one of the preceding claims, wherein the excitation light beam is designed at least approximately as a Gauss beam and has an elliptical beam cross-section at and / or near its beam waist and wherein the principal axis of the elliptical beam cross-section is aligned along the second preferred axis.

9. Sensor system (1) according to one of the preceding claims, wherein the internal magnetic field along the first and / or second preferred axis and along the first and / or second segment, along which the internal magnetic field exhibits increased homogeneity, assumes a value between 99.9% and 100.1% of its mean vectorial magnetic field.

Images