Optical sensor unit with lattice

Abstract

The invention relates to a sensor unit (1) having an optical system (2), an excitation light source (3), a first signal detector (4) and a reference detector (4), the optical system (2) having a lattice (6) with at least one defect, and the excitation light source (3) being configured to emit excitation radiation (7). The optical system (2) and the excitation light source (3) are arranged and cooperate with each other in such a way that a first portion of the excitation radiation causes emission of fluorescent radiation (8) in the lattice (6) and a second portion (10) of the excitation radiation is transmitted or reflected by the optical system (2). The first signal detector (5) is configured to at least partially detect the fluorescent radiation (8), and the reference detector (4) is arranged and configured such that the reference detector can at least partially detect a second portion (10) of the excitation radiation transmitted or reflected by the optical system (2). The invention also relates to a method for operating such a sensor unit (1).

Description

Technical Field

[0001] The present invention relates to a sensor unit for detecting a magnetic field and a method for detecting a magnetic field performed using such a sensor unit. Background Art

[0002] So-called NV magnetometers are used as sensor units for detecting magnetic fields. These NV magnetometers consist of diamond whose crystal lattice contains defects in the form of NV centers. In an NV center, a nitrogen atom occupies a lattice site of a carbon atom, wherein the defect is directly adjacent to the nitrogen atom – also located at a lattice site of a carbon atom. If this lattice is irradiated with excitation radiation with a wavelength between 490 nm and 575 nm, a change from the ground state to the ground state is induced in the lattice. 3 A2 to excited state 3 Electronic transition of E. NV center from excited state 3 E relaxes back to the ground state 3 A2, emits fluorescence radiation in the wavelength range between 650nm and 750nm. Ground state 3 A2 has three magnetic substates, m s =0,m s = ±1. m s =0 and m s = ±1 state energy difference is 2.87GHz (Zero Field Splitting). Excited state 3 E also has three magnetic substates, m s =0,m s = ±1. If we now make 3 When the NV center of A2 is exposed to a microwave field with a frequency of 2.87 GHz, the NV center will s =0, 3 A2 ground state and m s = ±1, 3 Under the irradiation of the exciting radiation, the NV center will now partially oscillate from the m s = ±1, 3 The A2 ground state is placed in m s = ±1, 3 E excited state. From there, the center relaxes back to the ground state mainly in a non-radiative manner. If the amplitude of the fluorescence radiation is measured as a function of the microwave field frequency, the amplitude of the fluorescence radiation suddenly drops (the so-called "dip") at a frequency of 2.87 GHz. This drop in the amplitude of the fluorescence radiation can be explained by the fact that under irradiation with a microwave field at a frequency of 2.87 GHz, the fluorescence radiation at m s =0, 3 The A2 ground state is optically excitable and can relax to m while emitting fluorescence radiation. s= ±1, 3 The number of NV centers in the A2 ground state is reduced.

[0003] Under an external magnetic field, the ground state m s = ±1, 3 A2 splits into spin quantum number m s =1 and m s = -1 (Zeemann effect). If we now measure the amplitude of the fluorescence radiation while varying the frequency of the microwave field, we obtain two dips. The frequency at which these dips occur depends on m s = ±1, 3 The magnitude of the splitting of the A2 ground state depends, therefore, on the strength of the external magnetic field. In this way, the strength of the external magnetic field can be determined.

[0004] This is described, for example, in DE 10 2014 2019 550 A2, which discloses a combined sensor for measuring pressure and / or temperature and / or magnetic field. The combined sensor comprises a diamond structure with NV centers as a sensitive component. Summary of the Invention

[0005] According to the present invention, a sensor unit having the features of claim 1, comprising an optical system, an excitation light source, a first signal detector, and a reference detector, and a method for operating such a sensor unit are provided. Advantageous embodiments are the subject matter of the dependent claims and the subsequent description.

[0006] The sensor unit according to the present invention comprises an optical system, an excitation light source, a first signal detector, and a reference detector. The optical system comprises a crystal lattice in which at least one defect is arranged. The crystal lattice can be a diamond lattice having at least one NV center as a defect, i.e., a defect and a nitrogen atom adjacent to the defect, which occupies a lattice position of a carbon atom. The sensor unit can comprise a microwave structure configured to emit microwave radiation, in particular microwave radiation in the frequency range between 2.7 and 3.1 GHz. The optical system and the microwave structure can be arranged and coordinated with one another such that the microwave radiation emitted by the microwave structure can excite spin states in the crystal lattice. The sensor unit according to the present invention also comprises an excitation light source configured to emit excitation radiation. The optical system and the excitation light source are arranged and coordinated with one another such that a first portion of the excitation radiation causes the crystal lattice to emit fluorescence radiation, and a second portion of the excitation radiation is transmitted or reflected by the optical system. The first signal detector is configured to at least partially detect the emitted fluorescence radiation. The reference detector is arranged and configured such that it can at least partially detect a second portion of the excitation radiation that is transmitted or reflected by the optical system.

[0007] Because the reference detector is arranged so as to at least partially detect the second portion of the excitation radiation transmitted or reflected by the optical system, the excitation radiation detected by the reference detector contains information about the excitation light source and the optical system. Consequently, not only interfering components introduced into the excitation radiation by the excitation light source, such as power fluctuations in the excitation radiation, are detected, but also interfering components introduced via the optical system into the portion of the excitation radiation detected by the reference detector are detected. These interfering components can be taken into account when evaluating the fluorescence radiation detected by the first signal detector.

[0008] This arrangement of the reference detector also eliminates the need for optical elements to deflect or shape the transmitted or reflected excitation radiation, thereby avoiding the introduction of further interfering components into the excitation radiation detected by the reference detector.

[0009] With this arrangement of the reference detector, the emitted fluorescent radiation can therefore be detected very precisely while keeping the structure of the sensor unit very compact.

[0010] The excitation light source can be designed as a laser diode, so that the excitation radiation is laser radiation. Of the photons introduced into the optical system, only a portion—the first portion of the excitation radiation—will induce electronic transitions in the optical system. Photons whose energies do not correspond to the energy difference between the electronic states involved in the transition are transmitted by the optical system. Photons whose energies correspond to the energy difference between the electronic states involved in the transition but do not induce electronic excitation are also transmitted because, for example, they do not encounter NV centers on their path through the optical system. These photons form the second portion of the excitation radiation.

[0011] Furthermore, the reference detector and the first signal detector can be arranged and configured such that the fluorescence radiation can be transmitted by the reference detector and detected by the first signal detector. The reference detector is transparent within the wavelength range of the fluorescence radiation. This enables a linear arrangement of the optical system, the reference detector, and the signal detector, which allows for a very narrow configuration without the need for optical elements to split or deflect the signal or excitation radiation.

[0012] The fluorescence radiation emitted by the optical system is non-directional, that is, it emits it with equal intensity in all directions, so that the first signal detector can be arranged at any solid angle relative to the optical system without incurring signal losses. In contrast, the excitation radiation is directional radiation, which is emitted, for example, by a laser diode.

[0013] The first signal detector can also be arranged outside the direct optical path of the second portion of the excitation radiation transmitted or reflected by the optical system. In this case, the direct optical path is the path that the excitation radiation takes or will take if the excitation radiation is not reflected, scattered or absorbed by any other element except the optical system. In this case, the reference detector can be opaque in the wavelength range of the fluorescence radiation, so that a wider selection of detector types can be used as the reference detector. Alternatively or additionally, an optical filter can be set up and arranged so that it absorbs the fluorescence radiation before it reaches the reference detector.

[0014] The sensor unit can have at least one second signal detector, which is set up to at least partially detect the fluorescent radiation. In this case, the at least one second signal detector can be arranged so that a first part of the fluorescent radiation can be detected by the first signal detector and a second part of the fluorescent radiation can be transmitted by the first signal detector and detected by the second signal detector. In this case, the first signal detector is preferably transparent or partially transparent in the wavelength range in which the second signal detector can detect the radiation. In this way, different wavelength ranges of the signal can be evaluated and the amount of information of the measurement can therefore be increased. To this end, different detector systems and / or detector types that are sensitive to different wavelength ranges can be used for the first and second signal detectors, which in turn increases the amount of information of the measurement. From this, possible detector-specific measurement artifacts or other detector-specific problems can also be inferred.

[0015] Alternatively or additionally, the sensor unit can have at least one third signal detector, which is arranged outside the direct beam path of the second portion of the excitation radiation transmitted or reflected by the optical system. In this way, the sensitive area, i.e., the area suitable for detecting signals, can be increased, thereby improving the signal yield.

[0016] The sensor unit can have an optical system in the shape of a cuboid or cube. This enables a particularly compact and simple structure of the sensor unit.

[0017] In a sensor unit having a cubic or cuboid optical system, a reference detector can be arranged such that it detects excitation radiation transmitted through a first cubic or cuboid surface, and at least one of the signal detectors from the group consisting of the first, second, and third signal detectors is arranged such that it detects fluorescence radiation emitted by a second cubic or cuboid surface. In particular, the excitation light source, the optical system, and the reference detector can be arranged along an imaginary line, with the optical system arranged between the excitation light source and the reference detector. One of the signal detectors can also be arranged behind the reference detector along this imaginary line, as viewed in the beam direction of the excitation radiation.

[0018] Such an arrangement of signal detector and reference detector is also conceivable for optical systems having at least two surfaces which are at an angle other than 90° to one another.

[0019] When the sensor unit includes at least four signal detectors, these signal detectors and the reference detector can be arranged so that the optical system is completely surrounded by the detectors. In this case, the optical system is largely or completely isolated from the environment, and thereby also isolated from radiation that may impinge on the optical system from the environment. In this way, signal measurement can be achieved while largely or completely eliminating interference from the environment of the sensor unit. At least one of the signal detectors and / or the reference detector can also be mounted directly on the optical system. In particular, when all signal detectors and the reference detector are mounted directly on the optical system, very precise measurements can be achieved while maintaining a very compact structure of the sensor unit.

[0020] The sensor unit can also include an optical system in the shape of a cuboid or cube, wherein the first signal detector is arranged so that it can detect fluorescence radiation from a first surface area of ​​a first cube or cuboid surface, and at least one fourth signal detector is arranged so that it can detect fluorescence radiation from a second surface area of ​​the first cube or cuboid surface. Alternatively, while maintaining the same arrangement of the signal detectors, at least two of the surfaces of the optical system can be angled at 90° relative to each other, such that the optical system is designed as a truncated pyramid, for example. With this configuration, the signal detectors are arranged side by side or above and below each other, parallel to or approximately parallel to one of the cube, cuboid, or other surfaces, allowing the field strength of the magnetic field to be measured to be measured at different locations. Thus, the spatial distribution of the magnetic field to be measured can also be detected. This arrangement thus forms a gradiometer, which can detect the magnetic field direction of the magnetic field to be measured in addition to the field strength.

[0021] The fluorescence radiation can be spectrally split using a grating or prism before it strikes the signal detectors, so that each signal detector detects a different wavelength range of the fluorescence radiation. In this case, the grating or prism is positioned between the optical system and the signal detectors. In particular, the signal detectors can be sensitive to different wavelength ranges.

[0022] The reference detector can also be arranged within the housing of the excitation light source. In this case, the reference detector detects scattered light resulting from reflection or scattering on optical elements or other components within the housing of the excitation light source. Information about the excitation radiation can also be extracted from this scattered light, thereby improving measurement accuracy.

[0023] Further advantages and configurations of the invention are apparent from the description and the accompanying drawings.

[0024] It will be understood that the features mentioned above and still to be explained below can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of protection of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A sensor unit is shown, in which a reference detector is arranged such that it can detect excitation radiation reflected at the optical system.

[0026] Figure 2 A sensor unit is shown in which the first signal detector is arranged outside the direct beam path of the excitation radiation.

[0027] Figure 3 A sensor unit is shown in which a first signal detector is arranged in the direct beam path of the excitation radiation.

[0028] Figure 4 A sensor unit with two signal detectors is shown, wherein a first signal detector is arranged in the direct beam path of the excitation radiation and a second signal detector is arranged outside the direct beam path of the excitation radiation.

[0029] Figure 5 A sensor unit with three signal detectors is shown.

[0030] Figure 6 A sensor unit with a cuboid-shaped optical system is shown.

[0031] Figure 7 A sensor unit with a cuboid-shaped optical system is shown, wherein two signal detectors are arranged parallel to one of the cuboid surfaces. DETAILED DESCRIPTION

[0032] Figure 1A sensor unit 1 is shown, which comprises an optical system 2, an excitation light source 3, a reference detector 4 and a signal detector 5. The excitation light source 3 can be designed as a laser diode, for example. The optical system can be designed as a diamond, which has defects in the form of NV centers. In this case, NV centers are defects that are directly adjacent to nitrogen atoms occupying lattice positions in the diamond lattice. In the excitation light source 3, excitation radiation 7 is generated in the form of a laser beam with a wavelength between 490 nm and 575 nm. This laser beam is aligned with the optical system 2. The optical system then emits fluorescence radiation 10 in a wavelength range between 650 nm and 750 nm, which is detected by the first signal detector 5. A portion of the excitation radiation 13 is reflected by the optical system 2 and impinges on the reference detector 4.

[0033] Figure 2 A sensor unit 1 is shown, which comprises an optical system 2, an excitation light source 3, a reference detector 4 and a signal detector 5. Excitation radiation 7 is generated in the excitation light source 3. This excitation radiation is directed onto the optical system 2. This optical system then emits fluorescence radiation 10, which is detected by a first signal detector 5. A portion of the excitation radiation 8 is transmitted by the optical system 2 and impinges on the reference detector 4. The first signal detector 5 is arranged outside the direct beam path of the excitation radiation 7. In this case, the direct beam path is the path that the excitation radiation 7 takes or would take if it is not or could not be reflected, scattered or absorbed by any other element except the optical system 2.

[0034] Figure 3 A sensor unit 1 is shown, which has an excitation light source 3, an optical system 2, a reference detector 4 and a signal detector 5. Figure 1 A sensor unit 1 is shown in FIG. 1 , in which a signal detector 5 is arranged in the direct beam path of excitation radiation 7, 8. Excitation radiation 7, 8 is directional radiation, emitted, for example, by a laser diode. Fluorescence radiation 10 is emitted by an optical system 2 and transmitted by a reference detector 4. The transmitted fluorescence radiation 9 is detected by a first signal detector 5. Reference detector 4 is transparent in the wavelength range of fluorescence radiation 9, 10.

[0035] Figure 4 The sensor unit 1 is shown in which the second signal detector 11 is arranged in the direct optical path of the excitation radiation 7, 8. The first and second signal detectors 5, 11 are sensitive to different wavelength ranges of the fluorescence radiation 9, 12, so that different wavelength ranges of the fluorescence radiation can be evaluated. It should be understood that the first signal detector 5 is transparent in the wavelength range to which the second signal detector 11 is sensitive.

[0036] Figure 5The sensor unit 1 is shown, which also has an excitation light source 3, an optical system 2 and a reference detector 4. In this embodiment, the first signal detector 5 is arranged outside the direct beam path of the excitation radiation 7, 8. The second signal detector 11 is arranged in the direct beam path of the excitation radiation 7, 8.

[0037] Figure 6 shows a sensor unit 1, which is different from Figure 5 The sensor unit in FIG. 1 further comprises a third signal detector 14 , which is likewise arranged outside the direct beam path of the excitation radiation 7 , 8 .

[0038] Figure 7 The sensor unit 1 is shown, in which the optical system 2 is designed as a cuboid. The reference detector 4 is arranged parallel to one of the cuboid surfaces 15 in the direct beam path of the excitation radiation 7. The signal detectors 5, 14 are arranged parallel to four of the six cuboid surfaces 16. In this case, these detectors 4, 5, 14 are designed to be flat and have the same or approximately the same surface shape and size as the cuboid surfaces 15, 16 respectively adjacent thereto. Figure 7 , for the sake of clarity, the detectors 4, 5, 14 are shown at a distance from the surface of the optical system 2. However, the detectors 4, 15, 14 may also be directly adjacent to the cuboid surface, so that the sensor unit 1 forms a completely or almost completely encapsulated system.

[0039] Figure 8 A sensor unit 1 is shown, wherein a first signal detector 5 and a fourth signal detector 21 are arranged parallel to the same cuboid surface 17, so that the first signal detector and the fourth signal detector can detect fluorescent radiation from different parts of the optical system 2. In this way, the magnetic field strength at different positions can be detected, and thereby the magnetic field gradient can be detected. It should be understood that more than two signal detectors can also be arranged along the cuboid surface. Multiple signal detectors can also be arranged on different cuboid surfaces. These signal detectors can also be directly adjacent to the cuboid surface, so that the sensor unit 1 again forms a mostly or completely encapsulated system.

[0040] Here, the fluorescence radiation can be spectrally split by means of a grating or a prism before it strikes the signal detectors 5, 21, so that each signal detector 5, 21 detects a different wavelength range of the fluorescence radiation. In this case, the grating or the prism is arranged between the optical system 2 and the signal detectors 5, 21.

Claims

1. A sensor unit (1) comprising an optical system (2), an excitation light source (3), a first signal detector (4) and a reference detector (4), wherein: The optical system (2) has a crystal lattice (6) with at least one defect, The excitation light source (3) is configured to emit excitation radiation (7), Wherein, the optical system (2) and the excitation light source (3) are arranged and coordinated with each other so that: o a first portion of the excitation radiation causes emission of fluorescent radiation (8) in the crystal lattice (6), o a second portion (10) of the excitation radiation is transmitted or reflected by the optical system (2), wherein The first signal detector (5) is configured to at least partially detect the fluorescent radiation (8), It is characterized by: The reference detector (4) is arranged and configured such that it can at least partially detect a second portion (10) of the excitation radiation that is transmitted or reflected by the optical system (2).

2. The sensor unit (1) according to claim 1, wherein The reference detector (4) and the first signal detector (5) are arranged and set up so that the fluorescent radiation (8) can be transmitted by the reference detector (4) and the transmitted fluorescent radiation (9) can be detected by the first signal detector (5), wherein the reference detector (4) is transparent in the wavelength range of the fluorescent radiation (8, 9).

3. The sensor unit (1) according to claim 1, wherein The first signal detector (5) is arranged outside the direct optical path of the second portion (10) of the excitation radiation transmitted or reflected by the optical system (2).

4. The sensor unit (1) according to claim 1, comprising at least one second signal detector (11) which is configured to at least partially detect the fluorescence radiation (8, 9, 12, 13), and wherein: The at least one second signal detector (11) is set up and arranged so that: the first part (12) of the fluorescent radiation can be detected by the first signal detector (5), and the second part (13) of the fluorescent radiation can be transmitted by the first signal detector (5) and detected by the second signal detector (11).

5. The sensor unit (1) according to any one of claims 1 to 4, comprising at least one third signal detector (14), which is arranged outside the optical path of the second part (10) of the excitation radiation transmitted or reflected by the optical system (2).

6. The sensor unit (1) according to any one of claims 1 to 5, wherein The optical system (2) is designed in the shape of a cuboid or a cube.

7. The sensor unit (1) according to claim 6, wherein The reference detector (4) is arranged such that it can detect excitation radiation (10) transmitted through a first cube or cuboid surface (15), and at least one signal detector from the group of signal detectors (4, 11, 14) consisting of a first, a second and a third signal detector (4, 11, 14) is arranged such that it can detect fluorescence radiation (8) emitted by a second cube or cuboid surface (16).

8. The sensor unit (1) according to any one of the preceding claims, wherein The optical system (2) is designed in the shape of a cuboid or a cube, and the first signal detector (4) is arranged so that the first signal detector can detect fluorescent radiation from a first surface area (17) of the cube or cuboid surface, and at least one fourth signal detector (21) is arranged so that the fourth signal detector can detect fluorescent radiation from a second surface area (18) of the cube or cuboid surface.

9. A method for operating a sensor unit (1) according to any one of claims 1 to 8.

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