Sensor unit and sensor arrangement containing a crystal with colour centres

Abstract

The invention relates to a sensor unit (1), in particular for magnetic field measurement, comprising: a crystal, in particular a diamond crystal (2), which has a measurement region (3) with colour centres, in particular with NV centres, wherein the colour centres emit fluorescent light (15) when excited with excitation light (6), and a fluorescence detector (16) for detecting the fluorescent light (15). The sensor unit (1) has a housing (4) in which the crystal and the fluorescence detector (16) are arranged. The housing (4) preferably has at least one coupling element (25) for mechanically coupling the housing (4) to at least one housing of a further sensor unit.

Description

[0001] Q.ANT GmbH 08.12.2025

[0002] 34089064WO

[0003] Sensor unit and sensor arrangement

[0004] The present invention relates to a sensor unit, in particular for magnetic field measurement, comprising: a crystal, in particular a diamond crystal, having a measuring area with color centers, in particular with NV centers, wherein the color centers emit fluorescent light when excited with excitation light, and a fluorescence detector for detecting the fluorescent light. The invention also relates to a sensor arrangement comprising such a sensor unit and at least one further such sensor unit.

[0005] Crystals doped with color centers are typically used as sensor elements in quantum sensor units. In particular, a diamond crystal doped with color centers, usually nitrogen vacancy centers (hereinafter referred to as nitrogen vacancy, NV, centers), can be used as a sensor element. NV centers in diamond exhibit a characteristic electronic structure that changes when certain measured quantities, such as an external magnetic field, temperature, pressure, or electric field, are altered.The color centers are excited by irradiation with excitation light in the optical range and typically by irradiation with a microwave field with varying frequency in the microwave range, and the fluorescence light induced in the color centers is detected by a fluorescence detector and demodulated and analyzed in an evaluation unit in order to determine a physical measurement quantity, for example an external magnetic field.

[0006] Quantum sensor units exploit the extreme sensitivity of such quantum systems or sensor elements, thus enabling very precise measurements of physical quantities, such as magnetic fields. However, when measuring quantities with extremely small values, e.g., biomagnetic fields generated during muscle contraction, even quantum sensors face a significant challenge in distinguishing the smallest signal levels of the desired signal from ambient interference. One way to differentiate between the desired signal and interference is to use a sensor array comprising two or more sensor units, arranged, for example, at a fixed distance from each other. When using more than two sensor units, these can be arranged in a multidimensional array.In such a sensor arrangement, interference fields are detected equally by all sensor units of the sensor arrangement, while the useful signal is detected with different strengths in the individual sensor units of the sensor arrangement, e.g., due to different distances of the quantum sensors to the source (e.g., a muscle that generates a biomagnetic field), and can thus be distinguished from the interference signals that are the same in all sensor units.

[0007] To develop a sensor array with multiple sensor units, which can be arranged, for example, in a grid pattern, a compact sensor design with at least one crystal near the point to be measured and a means of combining multiple sensor units is required. Especially in unshielded environments, a gradiometric approach is often necessary, in which interference signals are eliminated from the sensor signal by calculating a gradient of the measured quantity, such as a magnetic field gradient (see, for example, DE102021206954A1). This patent describes, among other things, a magnetic field gradiometer array comprising a plurality of magnetic field gradiometers arranged along an axis or in a plane. A three-dimensional magnetic field gradiometer array can comprise a plurality of such stacked magnetic field gradiometer arrays.

[0008] Using a sensor array with multiple gradiometers leads to a significant increase in the complexity of the sensor array's design and higher costs, as at least two crystals, e.g., two diamonds, are required per gradiometer, and sufficient laser power must be available for each gradiometer. Furthermore, the optical path for the two crystals should be as identical as possible to ensure the same light-induced noise in both gradiometer arms. Compact, miniaturized sensor units are particularly advantageous for use in sensor arrays with multiple sensor units.

[0009] US2016146904A1 describes a miniaturized vector magnetometer in which a micro-diamond crystal with NV centers is embedded in a bonding material to form a micro-diamond sensor. A micro-sensor assembly is provided by integrating the micro-diamond sensor with a radio frequency source, a micro-light source, a reference bias magnet, and one or more micro-photodetectors. The integration can consist of the miniaturized vector magnetometer having a multilayer structure, with each layer containing at least one of the components listed above.

[0010] US2022075013A describes a sensor for measuring an external magnetic field, comprising: an optical resonator, a laser medium which, together with the optical resonator, exhibits a laser threshold, a laser pump, and a radio frequency driver applied to the laser medium such that the laser threshold varies with a change in the external field. The laser pump signal and its fluctuations can be monitored and, together with the laser output, used for noise reduction. The laser medium can consist of negatively charged NV centers in diamond.

[0011] Object of the invention

[0012] The invention is based on the objective of providing a sensor unit which simplifies the formation of a sensor arrangement together with at least one further sensor unit, as well as providing a sensor arrangement with at least two such sensor units.

[0013] Subject matter of the invention

[0014] According to a first aspect, this problem is solved by a sensor unit of the type mentioned above, which has a housing in which the crystal and the fluorescence detector are arranged, wherein the housing has at least one coupling element for mechanically coupling the housing with at least one housing of another sensor unit.

[0015] By arranging the fluorescence detector and the crystal in a common housing, a compact sensor unit design can be achieved. Components not strictly necessary within the sensor unit or sensor head, such as control or evaluation units, can be located outside the housing, thus facilitating miniaturization of the sensor unit. The sensor unit described here—especially if the housing has at least one coupling element—is suitable for expansion by connecting or assembling multiple sensor units into a sensor array. In particular, one-, two-, or three-dimensional grid arrangements of the sensor units can be created.

[0016] The housing of each sensor unit preferably has at least one coupling element that allows several sensor units, generally with identical housings, to be assembled or stacked on top of each other, thus creating a sensor arrangement in the form of a modular system. In the simplest case, the coupling element forms a spacer that enables several sensor units to be stacked on top of and / or next to each other at a predetermined distance.

[0017] The coupling element can also be in the form of a connector. The sensor unit housing may have two or more different types of coupling elements. For example, one or a first group of coupling elements may form the male part of a connector, and a second coupling element or a second group of coupling elements may form the corresponding female part of the connector. The first and second coupling elements may be located on opposite sides of the sensor unit to enable mechanical coupling of two or more sensor units in a modular sensor array along a spatial direction. The coupling elements allow for the specification or adjustment of a defined distance between the sensor units, which can be advantageous, for example, for implementing a "virtual" gradiometer array.In the event that two sensor units are plugged into each other or mechanically coupled using coupling elements, the offset magnetic field (su) generated by a magnetic field generator in one sensor unit can also be used for both sensor units if it extends into the housing of the adjacent sensor unit.

[0018] In one embodiment, the coupling element serves as an interface for exchanging signals between the sensor unit and at least one other sensor unit. In this case, the coupling element(s) can be used to transmit signals from one sensor unit to another. The interface can be implemented using cables routed through the coupling elements or by incorporating fixed conductor structures within the coupling elements and contacts on their outer surfaces. For example, microwave signals or detector signals can be transmitted from one sensor unit to another via the coupling elements.

[0019] In another embodiment, the sensor unit has a feed device, in particular an optical fiber, for supplying the excitation light, which couples the excitation light into the housing. The feed device is typically an optical fiber or a fiber optic connector through which the excitation light is guided into the housing. At the exit end of the feed device, in the form of the optical fiber, a collimation optic, for example in the form of a GRIN lens, can be provided to collimate the excitation light.

[0020] The excitation light is generated by an excitation light source and coupled into the feed device. If a sensor array with multiple sensor units is used, the excitation light from a high-power excitation light source can be split between two or more feed devices, e.g., in the form of optical fibers, and fed to two or more sensor units.

[0021] In an alternative embodiment, an excitation light source for emitting the excitation light is arranged within the housing. Integrating the excitation light source into the housing allows for increased sensitivity through improved optical excitation. The excitation light source can be, for example, a diode laser or a laser diode (e.g., in its own housing), or an LED. Integrating the excitation light source into the sensor unit has the advantage of avoiding intensity noise in the excitation light or the excitation beam, which can be generated, for example, by mechanical vibrations in an optical fiber. This simplifies the use of the sensor unit in applications where the sensor unit is in motion.

[0022] The excitation light source integrated into the sensor unit housing can be connected to a Peltier element, which serves to stabilize the temperature of the excitation light source. Alternatively or additionally, a thermal heat sink can be provided to dissipate the heat generated by the excitation laser source and any Peltier element used. The heat sink and / or the Peltier element can, for example, be mounted on the outside of the housing.

[0023] In a further embodiment, the sensor device comprises a polarization filter for filtering the excitation light, which is arranged in the excitation light beam path upstream of the crystal, preferably between the crystal and the feed device or between the crystal and the excitation light source. Providing a polarization filter for filtering the excitation light is advantageous because the intensity of the fluorescence light produced in the crystal doped with color centers, e.g., in the diamond crystal doped with NV centers, depends on the polarization direction of the excitation light. It is therefore advantageous to first pass the excitation light or the excitation light beam through a polarization filter in order to minimize effects of polarization noise from the excitation light source or induced by the optical fibers used.Without this measure, polarization fluctuations in the crystal lead to intensity fluctuations of the fluorescence light and thus to signal fluctuations in the fluorescence detector. These fluctuations do not occur in balanced detection (su) in the polarization-insensitive reference path and therefore not in the reference detector. Thus, polarization fluctuations in the excitation light lead to uncorrelated noise components that cannot be compensated for by balanced detection of fluorescence and excitation light. The polarization filter typically serves to generate a defined polarization state of the excitation light, i.e., an elliptical, circular, or linear polarization state.

[0024] In another embodiment, the sensor unit has a reference detector arranged in the housing for detecting excitation light, which is arranged in the beam path of the excitation light after the crystal, or the sensor unit has a further fluorescence detector for detecting fluorescence light from another measuring area of ​​the crystal or from another crystal arranged in the housing.

[0025] In the first case, balanced detection can be implemented using the reference detector. This involves subtracting the electrical detector signal of the fluorescence detector from the electrical detector signal of the reference detector to reduce the influence of excitation light intensity noise on the measurement. Balanced detection in each sensor unit compensates for effects caused by different excitation light beam paths when the excitation light is generated by a single excitation light source and distributed across multiple sensor units. Differences in signal noise resulting from the use of different excitation light sources in two or more sensor units can also be compensated for by balanced detection or a corresponding readout circuit.

[0026] This allows, in particular, the expansion of the sensor unit into a sensor array forming a gradiometric array, without requiring alignment of the optical path of the individual sensor units, since the influence of laser noise in each sensor unit is minimized by the balanced evaluation circuit. Balanced detection thus also enables the distribution of the excitation light from a single excitation light source across multiple sensor units, which are used at different locations to measure a quantity, such as the magnetic field. The output signals of each balanced readout circuit for a given individual sensor unit can also be processed in another balanced readout circuit to enable further processing of the differential signal.

[0027] In the case described above, i.e., if the sensor unit has an additional fluorescence detector and an additional measuring range, a gradiometer, in particular a magnetic field gradiometer, can be implemented with the sensor unit, as described in DE102021206954A1 cited at the outset, which is incorporated in its entirety by reference into this application. In this case, the additional fluorescence detector serves to detect fluorescence light from a further measuring range that is spaced apart from the measuring range whose fluorescence light is detected by the fluorescence detector described above.

[0028] The fluorescence detector, or additional fluorescence detector(s), used to detect the fluorescent light can be a photodiode. The photodiode can be directly printed or coated with a filter layer that prevents the excitation light, typically in the green wavelength range (between 515 and 560 nm), from being measured. Alternatively or additionally, a filter plate with a suitable coating can be used. The coating must be selected so that the fluorescent light, typically in the red wavelength range (between 600 and 850 nm), is transmitted, while the green excitation light and the infrared light (wavelength typically 1042 nm) generated during the non-radiative transition are reflected.

[0029] As described above, another fluorescence detector in the form of a photodiode can be used to detect fluorescence light from a measuring area of ​​a second crystal if a gradiometer is to be formed with the sensor unit.

[0030] The reference detector, which serves as a reference for the balanced readout circuit, can also be designed as a photodiode. The photodiode can be protected from incident fluorescent light and infrared light by a filter (either directly applied or as a separate filter plate), so that only the excitation light is detected.

[0031] Dielectric filters (Bragg filters), plasmonic filters, or dye filters can be used as filters. The filters or filter elements can be macroscopic, but they can also be printed, layered, etc.

[0032] The detector photodiode is ideally a silicon pn diode. The photodiodes can be mounted on a plastic block, which, for example, transmits the signal from the photodiodes to an evaluation circuit or amplifier stage via contacts in the base of the housing. This plastic block can be made adjustable by manufacturing the contacts as flat or strip-like surfaces. For this purpose, the plastic block can be moved within a recess in a base plate located in the housing during adjustment and subsequently fixed in place.

[0033] In another embodiment, the sensor unit comprises at least one optical element arranged in the housing for guiding the excitation light and / or the fluorescence light. The housing of the sensor unit typically has one or more optical elements for guiding the excitation light onto the measuring area of ​​the crystal containing the color centers. Similarly, the housing typically also has one or more optical elements for guiding the fluorescence light generated during excitation onto the fluorescence detector. It is possible that the excitation light and / or the fluorescence light is guided by free-jet propagation within the housing. In this case, the optical elements can be, for example, beam deflectors, prisms, or mirrors for free-jet guidance.In the event that the excitation light and / or the fluorescence light is not guided in free jet propagation in the housing, waveguides and / or coupling structures (gratings) can also be used for light guidance, see also DE102021206954A1.

[0034] To minimize the distance between the crystal, especially a diamond crystal, and the measuring point, the sensor unit or the beam path through the optical elements can be designed to shine excitation light laterally into the crystal. This means the beam direction of the excitation light shining into the crystal is essentially perpendicular to the axis of fluorescence detection or to the beam direction of the detected fluorescence light. In this way, the crystal can be positioned close to the wall of the housing and thus close to the measuring point.

[0035] The crystal, e.g., the diamond crystal, can be shaped to achieve optimal absorption of the excitation light and optimal fluorescence yield. For example, the crystal can be shaped like a truncated pyramid. Furthermore, the crystal can be bonded or overprinted into a printed, optically transparent holder, which simultaneously ensures optimal alignment of the diamond with the offset magnetic field (su). This printed optic can also be designed to enhance the collection of the fluorescence light or to improve the focusing of the excitation light onto the diamond (lensing effect). A metalenser, a collimating lens, a compound parabolic concentrator, etc., can also be used as a collection optic.

[0036] If the crystal is a diamond, it preferably has a concentration of NV centers of 0.01–10 ppm, ideally 0.1–1 ppm. Furthermore, the use of an isotopically pure C12 diamond is advantageous. This ensures a narrower magnetic resonance linewidth and thus higher magnetic field sensitivity during magnetic field measurements.

[0037] In another embodiment, the sensor unit has a microwave emitter arranged in the housing for imparting a microwave field to the measuring area. The microwave field, which is used to change the spin state of the electrons, can be radiated to the crystal within the sensor unit by a microwave emitter in the form of an antenna or resonator structure. The microwave emitter can, for example, be a strip-line resonator, which can be optically transparent. However, other antenna structures such as split-ring resonators, Helmholtz antennas (see, for example, DE102022205469A1), microcoils, or omega resonators can also be used as microwave emitters. The generation of the microwave frequency can also be carried out within the housing of the sensor unit, for example, by means of a microwave emitter.The microwave frequency can be generated by an ASIC or, alternatively, it can be generated in an electronic unit and transmitted to the sensor unit via cable. The number of microwave frequencies can be selected to allow for temperature compensation by simultaneously exciting the m = +1 and m = -1 junctions of the crystal, as well as determining the direction of the magnetic field to be measured. Ideally, SDR (Signal-Defined Radio) generators are used for microwave generation. It is not essential that the microwave emitter be located inside the housing; it is also possible for the microwave emitter to be located outside the housing. For example, if a sensor array with multiple sensor units is used, a common microwave emitter can be provided for all sensor units or for a group of several sensor units.

[0038] In another embodiment, the sensor unit includes a magnetic field generator for producing an offset magnetic field in the measuring area of ​​the crystal. The bias or offset magnetic field, which is generally required to separate the transitions of the different orientations of the crystal's color centers, is located within the housing of the sensor unit in this embodiment. Alternatively, the magnetic field generator can be located outside the housing of the sensor unit. Particularly in a sensor arrangement comprising multiple sensor units, a single magnetic field generator can be provided that covers the area of ​​all sensor units in the sensor arrangement.

[0039] Permanent magnets, such as those in a Halbach ring or Halbach sphere arrangement, disc magnets, or coil arrangements like Helmholtz coil arrangements or coil pairs can be used to generate the offset magnetic field. It is also possible for the offset magnetic field to be generated by an external magnetic field generator that is not part of the sensor arrangement. For example, this could be a magnetic field generator used to create a magnetic field for an MRI scan, which also requires a constant magnetic field.

[0040] The magnetic field generator is preferably configured to produce an offset magnetic field whose orientation is parallel to the propagation direction of the excitation light in the diamond crystal. In this way, the effects of polarization changes in the excitation light or the excitation light source, e.g., in the form of a laser, can be minimized.

[0041] Another aspect of the invention relates to a sensor arrangement comprising: a sensor unit and at least one further sensor unit, which are configured as described above. The sensor units of the sensor arrangement do not necessarily have to be identical in construction; however, it is advantageous if the sensor units or the housings of the sensor units are compatible with each other, so that the sensor units can be easily mechanically connected or coupled. The individual housing(s) are typically designed such that the assembly of two or possibly more than two sensor units is possible.

[0042] In one embodiment, the at least one coupling element of the sensor unit housing is designed to mechanically couple the sensor unit housing to the housing of at least one further sensor unit at a predetermined, preferably adjustable, distance. The mechanical connection or coupling of the housings at the coupling elements allows for a fixed or, if necessary, variably adjustable distance between the housings and, in particular, between the crystals arranged in the sensor unit housings.

[0043] The adjustable distance is particularly advantageous when a gradiometric arrangement is to be implemented with the sensor array comprising at least two sensor units, since in this case the optimal distance between the crystals or sensor units depends on their distance to the signal source and to the respective sources of interference. The coupling or holding elements for variable distance adjustment can be designed in various ways, e.g., by a manually lockable telescopic arrangement or by a variable spindle drive that can optionally be operated automatically by an electric motor, thus enabling automatic changes to the distance between adjacent sensor units.

[0044] It is generally possible for the coupling element(s) to be integrally molded onto the housing or permanently attached to it. However, it is also possible for the coupling element(s) to be detachably attached to the housing. This allows for the use of different coupling elements, particularly those of varying lengths, to achieve the variably adjustable distance between the housings. Using these coupling elements, the sensor units can be arranged in a one-, two-, or three-dimensional grid configuration.

[0045] In another embodiment, the sensor arrangement comprises a control unit for controlling the sensor unit, a further control unit for controlling the further sensor unit, and / or a central control unit for controlling the sensor units of the sensor arrangement. It is generally possible to use a single central control unit to control all sensor units of the sensor arrangement, which can also be used for data processing of the data provided by the sensor units. It is also possible for each individual sensor unit or a respective group of sensor units to have its own control unit. These control units can generally be controlled by the central control unit; however, the central control unit can also be omitted if necessary.

[0046] In the respective control unit and / or in the central control unit, the signals from the sensor units can be used, for example, to demonstrate temporal and spatial correlations of magnetic field changes. Algorithms can also be used to facilitate targeted data processing and the detection of weak signals by examining multiple spatially (and temporally) separated measurements. Depending on the application, the direction of the magnetic field to be measured can also be determined by one or more sensor units.

[0047] In a further embodiment, the sensor unit additionally comprises at least one evaluation unit configured to determine a gradient of a measured quantity, in particular a magnetic field, from detector signals of the sensor unit and detector signals of the other sensor unit. The evaluation unit can be part of a control unit for the two sensor units or – if the sensor arrangement has more than two sensor units – part of the central control unit.

[0048] In the embodiment described here, at least two sensor units are connected to form a "virtual" gradiometer. Using appropriate position-variable mechanical coupling elements, this allows for easy adjustment of the distance between the two sensor units combined into a gradiometric unit to the expected magnetic field gradient of the magnetic field source to be measured (e.g., activated muscles). The sensor unit located closest to the magnetic field source observes both the source's magnetic field and surrounding interference or stray fields, while the second sensor unit, located further away from the source, observes only the stray fields. The difference between the two detector signals then leads to a significant improvement in the signal-to-noise ratio of the source magnetic field being measured. The detector signals can be those of the respective fluorescence detectors.In the case of balanced detection, the detector signals are those obtained by calculating the difference. Typically, the strength of the magnetic field at the position of the crystal's measuring area is determined from the detector signals of each sensor unit, and the measured values ​​of the respective sensor units are subtracted from each other to determine the magnetic field gradient.

[0049] In this advanced version, the sensor array additionally includes a clock for the synchronous readout of detector signals from the sensor unit and the other sensor unit in detected fluorescence light. The detector signals are typically those generated by the fluorescence detectors or those produced during balanced detection. To ensure gradiometric functionality, it is typically necessary to time-synchronize the acquisition of the magnetic field signals in both sensor units of this "virtual" gradiometer; that is, the detected signals must be read out synchronously. This can be achieved by using a central, high-precision clock. This clock is typically part of the central control unit of the sensor array and can, for example, be a [missing information - likely a specific type of clock].It can be implemented as a temperature-controlled quartz oscillator, a miniaturized atomic clock, or a MEMS-based micromechanical silicon oscillator.

[0050] It is fundamentally possible for the sensor arrangement to include sensor units designed to determine different physical quantities, for example, sensor units for determining temperature, pressure, magnetic field, etc. These quantities can also be determined by measuring crystals that exhibit defects in the form of color centers, particularly diamond crystals with NV color centers. Different types of sensor units (for determining magnetic fields, pressure, temperature, etc.) can be combined individually or in a cluster or group.

[0051] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those listed below can be used individually or in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples illustrating the invention.

[0052] They show:

[0053] Fig. 1 is a schematic representation of a sensor unit for magnetic field measurement with a housing in which a diamond crystal is arranged, wherein an optical fiber serves to supply excitation light into the housing, Fig. 2 is a schematic representation analogous to Fig. 1 with a polarization filter for filtering the excitation light,

[0054] Fig. 3 is a schematic representation analogous to Fig. 2, in which the sensor unit has an excitation light source integrated into the housing, as well as

[0055] Fig. 4 shows a schematic representation of a sensor arrangement with a plurality of sensor units arranged in a grid arrangement.

[0056] In the following description of the drawings, identical reference symbols are used for identical or functionally equivalent components.

[0057] Fig. 1 shows a sensor unit 1 (sensor head) for measuring magnetic fields. The sensor unit 1 has an optical crystal in the form of a diamond crystal 2, which has a measuring range 3 with color centers in the form of NV centers. The diamond crystal 2 is shaped like a truncated pyramid and is doped with the NV centers throughout its entire volume. The sensor unit 1 has a housing 4 in which the diamond crystal 2 is arranged. A base plate 5 in the form of a circuit board is arranged in the housing 4, on which the diamond crystal 2 is fixed.

[0058] In the example shown in Fig. 1, excitation light 6 for exciting the NV centers is supplied to the housing 4 via a feed device 7 in the form of an optical fiber. In the example shown, a Grin lens is attached to the exit surface of the optical fiber to collimate the excitation light 6 and form a collimated excitation light beam that propagates through the housing 4 in free-jet propagation. The feed device 7 can have a socket into which the optical fiber can be inserted. It is also possible that such a socket forms the feed device for supplying the excitation light 6 into the housing 4.

[0059] For guiding the excitation light 6 within the housing 4, the sensor unit 1 has three optical elements in the form of beam deflectors 8, 9, 10, each designed as a right-angled prism and deflecting the excitation light 6 by 90°. The beam deflectors 8, 9, 10 are mounted in the housing 4 in such a way that the excitation light 6, or the excitation light beam, can be adjusted onto the diamond crystal 2, and that the beam deflectors 8, 9, 10 can subsequently be fixed in place (e.g., by clamping or gluing). In the example shown, the beam deflectors 8, 9, 10 are positioned in recesses 11, 12, 13 of the base plate 5, which allow rotation of the beam deflectors 8, 9, 10 while still ensuring pre-alignment.

[0060] In the example shown, the excitation light 6 passes through a side face of the truncated cone-shaped diamond crystal 2. The volume of the diamond crystal 2 illuminated by the excitation light 6 forms the measuring area 3. The diamond crystal 2 is located close to the housing 4. The diamond crystal 2 is bonded to a microwave emitter 14, which is designed as an optically transparent strip-line resonator, to impart a microwave field to the measuring area 3. Alternatively, the diamond crystal 2 can also be aligned and attached to a printed holding device (not shown).

[0061] When the NV centers in the measuring range 3 are excited, they emit fluorescence light 15, which is detected by a fluorescence detector 16. The detected fluorescence light 15 is emitted by the diamond crystal 2 at an angle of approximately 90° to the direction of propagation of the excitation light 6 entering it. In the example shown, an optical filter 17 is arranged between the diamond crystal 2 and the fluorescence detector 16. This filter reflects radiation in the wavelength range of the excitation light 6, e.g., at 520 nm, as well as infrared radiation at approximately 1042 nm, which is generated during a low-radiation transition in the diamond crystal 2. Other components, such as collimation optics for collimating the fluorescence light 15, can also be arranged between the diamond crystal 2 and the fluorescence detector 16. It is possible that the collimation optics are provided with a filter layer.This allows the distance between the diamond crystal 2 and the fluorescence detector 16 to be reduced, resulting in an increase in the fluorescence collection. In the example shown in Fig. 1, the fluorescence detector 16 is designed as a photodiode soldered onto a plastic block 18, which transmits a detector signal from the fluorescence detector 16 to the base plate 5 and from there to a photodetector circuit or an evaluation unit. This circuit can be housed either in the casing 4 of the sensor unit 1 or in an external casing belonging to an external control unit (su). In the latter case, the detector signal can be routed through the bottom of the casing 4. The base plate 5 has a recess or cavity 19 for aligning the diamond crystal 2 or the assembly with the fluorescence detector 16 and the filter 17.

[0062] Part of the excitation light 6 passes through the diamond crystal 2, is deflected by the third beam deflector 10, and strikes a reference detector 20. The reference detector 20 detects the excitation light 6 and generates a detector signal that can be used for balanced evaluation. An optical filter 21, which serves as a low-pass filter, is positioned in front of the reference detector 20. The reference detector 20 is in the form of a photodiode and is soldered onto a plastic block 22, which conducts the detector signal from the reference detector 20 to the base plate 5 and from there to a photodetector circuit or an evaluation unit. The base plate 5 has a recess 23 for aligning the reference detector 20 using the plastic block 21.

[0063] The sensor unit 1 also includes a magnetic field generator 24 arranged in the housing 4 for generating a static offset magnetic field in the measuring area 3 of the diamond crystal 2. In the example shown, the magnetic field generator 24 is designed as a disc magnet. Alternatively, for example, a Haibach arrangement of permanent magnets or a pair of coils can also be used as the magnetic field generator 24.

[0064] The sensor unit 1 shown in Fig. 1 is designed for balanced evaluation, in which a difference is calculated between the detector signal of the fluorescence detector 16 and the detector signal of the reference detector 20 to enable noise suppression. Alternatively, the sensor unit 1 can be configured as a gradiometer and include a further fluorescence detector for detecting fluorescence light from another measuring area of ​​the diamond crystal 2 or from another crystal arranged in the housing 4. The basic design of such a gradiometer, in which the beam is guided by waveguides, is described in DE 102021206954A1 cited above.

[0065] In the example shown, the housing 4 has coupling elements 25 on its outer surface for mechanically coupling the housing 4 to a housing of another sensor unit, which is not shown in Fig. 1. In the example shown, the coupling elements 25 are part of the housing 4, i.e., permanently connected to the housing 4. The coupling elements 25 make it possible to position or hold the housing 4 at a predetermined distance A from a housing 4a of another sensor unit 1a of a sensor arrangement 30, as shown in Fig. 4. In this way, two or more sensor units 1 can be mechanically coupled to each other. When using more than two sensor units, a multidimensional sensor array can be arranged in the same way.

[0066] The coupling elements 25 can also serve to adjust a distance A between the housings 4, 4a of adjacent sensor units 1, 1a, ... . For this purpose, the coupling elements 25 can, for example, be designed to be telescopic. In the sensor arrangement 30 shown in Fig. 4, the coupling elements 25 serve to stack the sensor units 1, 1a, ... , 1n on top of each other. It is possible that the housings 4, 4a, ... , 4n of the sensor units 1, 1a, ... , 1n have stacking aids on their side facing away from the coupling elements 25, which prevent the housings 4, 4a, ... , 4n from slipping laterally. It is also possible that the offset magnetic field generated by the magnetic field generator 24 in the sensor unit 1 is used by one or more neighboring sensor units 1a, ... so that no magnetic field generator needs to be provided in this sensor unit 1a or in these sensor units 1a, ...

[0067] The housings 4, 4a, ..., 4n may have coupling elements (not shown) on their undersides, facing away from the upper surfaces with the coupling elements 25 shown in Fig. 1. In this case, the coupling elements 25 on the upper surface of each lower sensor unit 1, 1a, 1n can be mechanically coupled to the coupling elements on the underside of each upper sensor unit 1, 1a, 1n, for example via a plug connection. Such coupling can enable the exchange of signals between sensor unit 1 and the further sensor unit 1a, ... connected to it via the coupling elements 25. In this way, for example, detector signals can be exchanged, but it is also possible to transmit a microwave signal, which is required for generating the microwave field, via the coupling elements 25. For the transmission or data exchange, the coupling elements 25 can be, for example,have electronic contacts or cables can be routed through the coupling elements 25.

[0068] Fig. 2 shows a sensor unit 1 that differs from the sensor unit 1 shown in Fig. 1 in that a polarization filter 26 is arranged in the beam path of the excitation light 6. The polarization filter 26 is arranged between the diamond crystal 2 and the feed device 7 in the form of the optical fiber and filters the excitation light 6 before it enters the diamond crystal 2. The polarization filter 26 generates excitation light 6 with a defined polarization state (linearly, circularly, or elliptically polarized). The polarization filter 26 prevents the occurrence of uncorrelated noise components.

[0069] Polarization fluctuations at the fluorescence detector 16 and at the reference detector 20.

[0070] Fig. 3 shows a sensor unit 1, which differs from the sensor unit 1 shown in Fig. 2 in that the feed device 7 in the form of the optical fiber is replaced by an excitation light source 27, which is arranged in the housing 4. The excitation light source 27 can be a laser diode or an LED, which in the example shown is integrated into its own housing. In the example shown, the excitation light source 27 integrated into the housing 4 of the sensor unit 1 is connected to a Peltier element 28, which serves to temperature stabilize the excitation light source 27 and is attached to the outside of the housing 4. In the example shown, the sensor unit 1 also has a thermal heat sink 29, which dissipates the waste heat generated by the excitation light source 27 and, if applicable, by the Peltier element 28, and is also attached to the outside of the housing 4 of the sensor unit 1.

[0071] Fig. 4 shows the sensor arrangement 30 described above, which comprises the sensor unit 1 described above and a predetermined number of further sensor units 1, 1a, ... 1n, stacked one above the other in a two-dimensional grid arrangement. It is understood that the sensor units 1, 1a, ... 1n can also be arranged in a two- or three-dimensional grid arrangement. Alternatively or additionally, the sensor units 1, 1a, ... 1n can also be arranged side by side.

[0072] In the sensor arrangement 30 shown in Fig. 4, each of the sensor units 1, 1a, ..., 1n has its own control unit 31, 31a, ..., 31n, which serves to control the corresponding sensor unit 1, 1a, ..., 1n. The control units 31, 31a, ..., 31n can be used, among other things, to monitor the respective sensor unit 1, 1a, ..., 1n with regard to temperature, for tracking, and for data analysis, for example, for evaluating or processing the detector signals of the fluorescence detector 16 and the reference detector 20. It is also possible that the respective control unit 31, 31a, ..., 31n is configured to determine the magnetic field or the magnetic field strength based on the detector signals. The control units 31 , 31 a, ... , 31 n have for this purpose a plurality of electronic components, e.g. in the form of electronic circuits or in the form of suitable hardware and / or software.

[0073] If the excitation light 6 is supplied to all or some of the sensor units 1, 1a, ..., 1n via a supply device 7 from an external excitation light source, as shown in Fig. 1 or Fig. 2, each sensor unit 1, 1a, ..., 1n can have its own excitation light source. However, it is also possible for one excitation light source to generate the excitation light 6 for several or all of the sensor units 1, 1a, ..., 1n. In this case, the excitation light 6 from the excitation light source is distributed among the sensor units 1, 1a, ..., 1n.

[0074] As can also be seen in Fig. 4, the sensor arrangement 30 has a central control unit 32 for all sensor units 1, 1a, ..., 1n. The central control unit 32 is in signal communication with the sensor units 1, 1a, ..., 1n via an I / O interface 33. The central control unit 32 has an evaluation unit 34 which enables the realization of a virtual gradiometer by calculating a magnetic field gradient from the detector signals of sensor unit 1 and the detector signals of at least one further sensor unit 1a, ..., 1n. In the example shown, the evaluation unit 34 uses for this purpose the measured value of the magnetic field B, Ba, ... , Bn determined in a respective control unit 31 , 31a, ... , 31 n at the position of the crystal 2, 2a, ... , 2n of the respective sensor unit 2, 2a, ..., 2n, more precisely, the evaluation unit 34 calculates the difference between any two measured values ​​B, Ba, ... , Bn of the magnetic field for this purpose. A prerequisite for the realization of such a "virtual" gradiometer is a clock generator 35, which enables synchronous readout of the detector signals of sensor unit 1 and at least one further sensor unit 1a, ... , 1n. Synchronization is necessary to be able to compare the measured values ​​B, Ba, ... Bn of the individual sensor units 1 , 1a, ... , 1n without any time offset.

[0075] As can also be seen in Fig. 4, the central control unit 32 is connected to a power supply in the form of an external battery 36 and delivers its output, in particular the measured values, to an application system 37. The central control unit 32 can also perform other tasks, for example the calibration of the sensor arrangement 30, an alarm function or a software-implemented low impedance amplifier, LIA.

Claims

23 Patent claims 1. Sensor unit (1), in particular for measuring magnetic fields, comprising: a crystal (2), in particular a diamond crystal, which has a measuring area (3) with color centers, in particular with NV centers, wherein the color centers emit fluorescence light (15) when excited with excitation light (6), a fluorescence detector (16) for detecting the fluorescence light (15), characterized in that the sensor unit (1) has a housing (4) in which the crystal and the fluorescence detector (16) are arranged, wherein the housing (4) has at least one coupling element (25) for mechanically coupling the housing (4) with at least one housing (4a, ... ) of a further sensor unit (1a, ... ).

2. Sensor unit according to claim 1, wherein the coupling element (25) is designed as an interface for exchanging signals between the sensor unit (1) and the at least one further sensor unit (1a, ...).

3. Sensor unit according to claim 1 or 2, further comprising: a feed device (7), in particular an optical fiber, for feeding the excitation light (6) into the housing (4).

4. Sensor unit according to claim 1 or 2, in which an excitation light source (27) for emission of the excitation light (6) is arranged in the housing (4).

5. Sensor unit according to one of the preceding claims, further comprising: a polarization filter (26) for polarization filtering of the excitation light (6), which is arranged in the beam path of the excitation light (6) in front of the crystal (2), preferably between the crystal (2) and the feed device (7) or between the crystal (2) and the excitation light source (27).

6. Sensor unit according to one of the preceding claims, further comprising: a reference detector (20) arranged in the housing (4) for detection of excitation light (6) which is arranged in the beam path of the excitation light (6) after the crystal (2), or a further fluorescence detector for detecting fluorescence light of a further measuring area of ​​the crystal (2) or of a further crystal arranged in the housing.

7. Sensor unit according to one of the preceding claims, further comprising: at least one optical element (8, 9, 10) arranged in the housing (4) for guiding the excitation light (5) and / or the fluorescence light (15).

8. Sensor unit according to one of the preceding claims, further comprising: a microwave emitter (14) arranged in the housing (4) for imparting a microwave field to the measuring area (3).

9. Sensor unit according to one of the preceding claims, further comprising: a magnetic field generator (24) arranged in the housing (4) for generating an offset magnetic field in the measuring area (3).

10. Sensor arrangement (30) comprising: a sensor unit (1 ) and at least one further sensor unit (1 a, ... , 1 n) configured according to one of the preceding claims.

11. Sensor arrangement according to claim 10, wherein the at least one coupling element (25) of the housing (4) of the sensor unit (1 ) is designed for mechanical coupling of the housing (4) of the sensor unit (1 ) with a housing (4a) of the at least one further sensor unit (1 a, ... , 1 n) at a predetermined, preferably adjustable distance (A).

12. Sensor arrangement according to claim 10 or 11, further comprising: a control unit (31 ) for controlling the sensor unit (1 ), a further control unit (31 a, ... ) for controlling the further sensor unit (31 a, ... ) and / or a central control unit (32) for controlling the sensor units (1 , 1 a, ... ) of the sensor arrangement (30).

13. Sensor arrangement according to one of claims 10 to 12, further comprising: at least one evaluation unit (34) configured to generate at least one gradient of a sensor unit from detector signals of the sensor unit (1) and detector signals of at least one further sensor unit (1a, ... ). sensor arrangement (30) to determine the measured quantity, in particular a magnetic field (B, Ba, ... , Bn).

14. Sensor arrangement according to claim 13, further comprising: a clock generator (35) for synchronously reading out detector signals of the sensor unit (1) and the at least one further sensor unit (1a, ... ).

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