Method for manufacturing a sensor element, sensor element and machine for additive manufacturing

Abstract

The invention relates to a method for manufacturing a sensor element comprising a crystal (11) with at least one color center (10) and at least one optic, comprising: arranging the crystal (11) in a processing volume (7) of a machine (1) for additive manufacturing, exciting the at least one color center (10) with a light beam, in particular with a laser beam (4), which is directed into the processing volume (7) and focused in the processing volume (7), detecting fluorescence light (13) generated when the at least one color center (10) is excited with the laser beam (4), determining a position (P(x,y,z)) of the color center (10) in the processing volume (7) based on the detected fluorescence light (13), and forming the at least one optic on the crystal (11) by additive manufacturing taking into account the determined position (P(x,y,z)) of the at least one color center (10).The invention also relates to a sensor element produced by the method, and to a machine (1) for additive manufacturing designed to carry out the method.

Description

[0001] The present invention relates to a method for manufacturing a sensor element comprising a crystal with at least one color center, in particular a diamond crystal with at least one NV center, and at least one optical element. The invention also relates to a sensor element manufactured by the method and to a machine for additive manufacturing.

[0002] Sensor elements play a central role in many technical applications and can be used in optical sensors, for example in the form of quantum sensors, to determine various physical quantities. Sensor elements for quantum sensors typically feature crystals doped with color centers. In particular, such a sensor element can utilize a diamond crystal doped with color centers, usually nitrogen-vacancy (NV) centers. NV centers in diamond exhibit a characteristic electronic structure that changes when certain measured quantities are altered, such as an external magnetic field, temperature, pressure, or electric current. In an optical sensor containing such a crystal, the color centers are activated by irradiation with excitation light in the optical, typically visible, wavelength range.Irradiation with a microwave field of varying frequency can manipulate the ground state of the NV center. The fluorescence light induced in the color centers by the optical excitation is detected and analyzed, as described, for example, in US 2016 / 0356863 A1.

[0003] Manufacturing sensor elements for quantum sensors presents various challenges, such as miniaturization, scalability, cost-efficiency, robustness, and assembly and interconnection technology. Additive manufacturing processes can, in principle, be used to produce optics, e.g., lenses, for such sensor elements. It is well-established to monitor additive manufacturing processes and adjust their process parameters as needed.

[0004] German patent DE 102011009624 A1 describes a method and a device for process monitoring of an additive manufacturing process in which a component is formed from a multitude of layers in a build chamber based on a three-dimensional data model, with each subsequent layer being fixed to a preceding layer by means of a high-energy beam. During layer deposition, the component is at least optically monitored, and the build chamber is thermally monitored. The acquired data can be evaluated during the manufacturing process, and if a maximum permissible deviation is exceeded, the process parameters can be changed accordingly. The properties of each layer can be monitored using a light source that emits light waves and a light sensor that detects the reflected light.

[0005] German patent DE 102014112155 A1 describes a method for monitoring the production of a component from a powdered starting material by laser sintering. In this method, excitation radiation is injected into the powdered starting material in the area of ​​a feed path, and the radiation emitted by the powdered starting material is received by a sensor that records the radiation spectrum. The recorded spectrum is examined for the presence of spectral lines that identify at least one marker substance present in the starting material. After the excitation radiation has been injected into the material hardened by laser sintering, a spectrum of the radiation emitted by the hardened material can be recorded, and this spectrum can be examined for the presence of spectral lines that identify at least one parameter change in the hardened material compared to the starting material. Object of the invention

[0006] The invention is based on the objective of improving a method for manufacturing a sensor element, as well as providing a sensor element manufactured using the method and a machine for manufacturing such a sensor element. Subject matter of the invention

[0007] This task is solved by a method of the type mentioned above, comprising: arranging the crystal in a processing volume of an additive manufacturing machine, exciting the at least one color center with a light beam, in particular with a laser beam, which is directed into the processing volume and focused in the processing volume, detecting fluorescence light generated when exciting the at least one color center, determining a position of the at least one color center in the processing volume based on the detected fluorescence light, and forming the at least one optic on the crystal by additive manufacturing, taking into account the determined position of the at least one color center.

[0008] The method proposes first determining the position of the color center within the machine's processing volume, i.e., locating the color center. A given color center can typically be located within the processing volume with an accuracy on the order of approximately 1 µm. 3 or less precisely localized. The determined position of the color center is typically stored; that is, a coordinate data set is created in the coordinate system of the sintering laser for the respective localized color center. This can be easily achieved by selecting the wavelength of the sintering laser so that it falls within the absorption band of the color center (approximately 510–610 nm for NV centers).

[0009] The position of the color center within the processing volume, or the coordinate data set, is taken into account when forming the optics on or around the crystal, and the optics produced by additive manufacturing are adapted to the position of the color center. The position of the crystal within the processing volume is assumed to be known in the method described here, or can be precisely determined using the laser beam or, for example, a suitable detector such as a camera. Since the position of the crystal within the processing volume is known, the optics can be formed on or around the crystal—more precisely, on a surface of the crystal or around the crystal—by additive manufacturing. The optics are applied to the surface of the crystal in the additive manufacturing machine using 3D printing. Alternatively, the crystal can also be enclosed or surrounded by the optics.Additive manufacturing can be done layer by layer, but this is not absolutely necessary (su).

[0010] Using the known position of the color center within the processing volume, as well as its position relative to the surface of the crystal on which the optics are formed, the optics, and thus the resulting sensor element, can be optimized during their fabrication. The sensor element, which comprises the crystal and at least one optical component, can be designed to suit the specific sensor concept employed, thereby optimizing it for various purposes (e.g., high sensitivity, high integrability, cost-sensitive applications, etc.). For example, the collection efficiency or the volume of the optics can be optimized.

[0011] Using the method described above, it is possible to use very small crystals for the fabrication of the sensor element. This is particularly advantageous when using diamond crystals, as their high purity makes them expensive to produce. Furthermore, the spatial resolution of the sensor can be increased by reducing the diamond volume. The optics can also be designed so that only a single color center within the sensor element is excited. This can make the measurement more sensitive than when a cluster of color centers is excited. This also improves thermal management and reduces heat dissipation requirements, which in turn enhances the spatial resolution of the sensor element. The method described here is easily scalable and does not require active crystal alignment, as the position of the NV center is taken into account in the production data for the optics.

[0012] To excite the color centers, the light beam must have a suitable excitation wavelength. For the excitation of NV centers in a diamond crystal, the excitation wavelength is typically in the green wavelength range, i.e., between 510 nm and 610 nm.

[0013] In one variant, the laser beam is directed into the processing volume to excite at least one color center and to form at least one optical element. In this case, the same laser beam is used for both exciting the color center(s) and for the additive manufacturing of the optical element. Alternatively, a separate light source can be used to excite the color center. The light beam generated by this light source, which can also be a laser beam, is directed into the processing volume and focused there. In this case, a laser beam from a laser source whose wavelength is not suitable for exciting the color centers can be used for additive manufacturing. However, using two different light or laser sources is generally not recommended.

[0014] In another variant, when forming the at least one optical element, the determined position of the at least one color center is taken into account to define the position of the optical element on or around the crystal, its orientation relative to the crystal, its geometry, and / or an optical path. The position of the optical element on the crystal refers to its position on the crystal surface where it is formed. In an alternative embodiment, where the crystal is at least partially enclosed by the optical element, the position of the optical element relative to the crystal refers to its orientation relative to a crystal axis. For example, the position of the optical element can be chosen so that it is centered with respect to the respective color center. It is also possible to consider the positions of several color centers when determining the position of the optical element.This is typically also the case when the orientation of the optics is determined relative to the crystal. For example, if several color centers are arranged in a grid or array (e.g., in a 3 x 3 array of color centers), the orientation of the optics can be aligned with the grid of color centers. With such an array arrangement, information about the spatial distribution of the magnetic field can be obtained.

[0015] The position of the color center can also be considered when defining the geometry of the optics. For example, the focal length of the optics can be determined based on the distance between the color center and the surface on which the optics are fabricated. The focal length is determined by the geometry of the optics, such as the radius of curvature in the case of a lens. The optical path can also be optimized depending on the position of the color center. For example, the focal length and position of the optics can be adjusted to improve the sensitivity and efficiency (i.e., less laser power is required to achieve the same laser intensity at the color center) of the sensor element. Particularly in the case of an optical path, it can be advantageous to enclose the crystal, at least partially or completely, with the optics.

[0016] The type of optics formed on the crystal is essentially arbitrary. In the simplest case, the optics consist of one or more lenses, for example, in the form of microlenses. The optics can also be a raster arrangement of lenses. However, it is also possible to form optics with more complex geometries on the crystal or to mold them onto the crystal. For example, the optics can be a concentrator optic for focusing radiation. Optics in the form of optical filter elements can also be formed on the crystal. Furthermore, optics can be attached to the crystal as beam guides in the form of fibers. When the crystal is at least partially or completely enclosed by the optics, or optical element, it can be, in particular, an optical collector or beam guide. The optics can also be designed for direct coupling to a waveguide.

[0017] In another variant, an optical system is integrated into the crystal. This system consists of an input coupling optic for coupling an excitation laser beam into the crystal, or an output coupling optic for coupling fluorescence light out of the crystal. The input coupling optic serves to concentrate the excitation laser beam at the position of the color center. The output coupling optic serves to focus the fluorescence light emitted from the color center in order to maximize the yield of the portion of the fluorescence light captured by a detector. In the simplest case, the input and output coupling optics can be designed as lenses, for example, as microlenses; however, they can also have more complex geometries.

[0018] In another variant, at least two optics are formed on different surfaces of the crystal. It is possible and practical to form one or more optics on multiple surfaces of the crystal using additive manufacturing. Furthermore, it is possible to form the optics on the surfaces without changing the crystal's position within the processing volume; that is, no repositioning of the crystal is required. If the crystal needs to be repositioned within the processing volume to form two or more optics, the process described above can be repeated. In this case, the respective color center is detected again, or a new color center is detected if necessary.However, it is also possible that the position of the color center (relative to the crystal) is stored and used after the crystal is repositioned to form further optics without having to determine the position of the color center again.

[0019] In another variant, the crystal is held against a holding tool during optic fabrication. This tool is preferably movable (i.e., displaceable and / or rotatable) in three spatial directions. Particularly when forming optics on multiple surfaces of the crystal, it is generally advantageous to be able to reposition and align the crystal within the processing volume using the holding tool. This repositioning typically occurs after each optic has been fully formed and before another optic is formed on the crystal.

[0020] In another variant, the crystal is fixed to the surface of a holding element during the optical formation process, particularly partially embedded in the holding element, which is preferably manufactured using additive manufacturing. The surface of the holding element is a predefined, e.g., flat, surface to which the crystal can be fixed with a defined orientation. The crystal can be fixed to the surface by a material bond, e.g., by adhesive bonding. If the holding element is manufactured using additive manufacturing, the crystal can be partially embedded in the holding element, and the position of the color center(s) need not be known for this embedding. The holding element can also be an optical element. In this case, the holding element can be formed on the crystal using the method described above.

[0021] The holding element can also have a recess or similar feature that serves as a support or mounting surface for the crystal, allowing it to be positioned and fixed in a desired orientation before the optics are formed. In the step of arranging the crystal within the processing volume described above, the crystal can then be attached to or fixed to the holding element manually or automatically.

[0022] In a further development of this variant, the crystal is embedded between the optics and the holding element during the optical process. In this variant, the optics are printed over the entire crystal, enclosing it. In this way, the optics and the holding element, which may also be designed as optics, protect the crystal and its color centers from damage, thus increasing mechanical stability. The sensor element therefore becomes more tolerant of mechanical shocks, vibrations, thermal changes, and other effects.

[0023] In another variant, additive manufacturing is achieved through the selective curing of a typically liquid or viscous material, preferably by bath-based photopolymerization, in particular by two-photon lithography or stereolithography. The material that selectively cures upon laser beam irradiation can be, for example, a light-curing polymer or resin. In bath-based photopolymerization, photopolymers, or more precisely, a bath of photopolymers, are used that cure selectively under light irradiation. In stereolithography, the photopolymers are selectively cured in thin layers, similar to additive manufacturing in a powder bed that is selectively melted by a laser beam.

[0024] In two-photon lithography, the material requires that two photons be absorbed simultaneously for it to harden. The necessary photon density can only be generated at the focal point of the laser beam, and typically only using an ultrashort pulsed laser beam with pulse durations in the femtosecond range. Consequently, the material is hardened only at the focal point and not along the entire light path, as is the case with single-photon polymerization.

[0025] It is possible to excite or determine the position of the color center before the curing material is fed into the additive manufacturing machine. It is also possible to perform color center excitation when the crystal is partially or completely covered by the curing material. In this case, when exciting the color center with the light or laser beam, its parameters, especially its intensity, are selected so that the light or laser beam does not cause the material to cure. If the additive manufacturing process uses two-photon polymerization, the two-photon absorption process makes it unlikely that the laser beam will interact with the resin or polymer during color center excitation and be scattered or absorbed in the material bath. In particular, the light or laser beam can be...The laser beam used to excite the color center should be emitted with a significantly shorter pulse duration and / or intensity than is required to trigger the two-photon absorption process.

[0026] Another aspect of the invention relates to a sensor element produced by the method described above. The sensor element, comprising the crystal and one or more optics, can be integrated into an optical sensor that includes further components, such as an excitation laser, a detector for detecting fluorescence light generated during the excitation of the at least one color center, and a microwave generator for generating a microwave field at the location of the color center. Such an optical sensor can be used to determine various measured quantities, for example, the strength and, if applicable, the orientation of a magnetic field.

[0027] Another aspect of the invention relates to an additive manufacturing machine comprising: a processing volume in which a crystal with at least one color center, in particular a diamond crystal with at least one NV center, can be arranged; an irradiation device for shining a light beam, in particular a laser beam, into the processing volume and for focusing the light beam, in particular the laser beam, in the processing volume in order to excite at least one color center in the crystal; a detector for detecting fluorescence light generated when the at least one color center is excited by the laser beam; and an evaluation device for determining the position of the at least one color center in the processing volume based on the detected fluorescence light, wherein the machine is configuredTaking into account the determined position of at least one color center, at least one optical element is to be formed on or around the crystal by additive manufacturing.

[0028] The additive manufacturing machine is designed to carry out the process described above for manufacturing the sensor element. To locate and excite at least one color center, the laser beam can three-dimensionally scan a volume region of the processing volume in which the crystal is or can be arranged. A scanner unit and a focusing unit of the irradiation unit can be appropriately controlled to move the laser beam's focus position within this volume region. This scanning movement of the laser beam allows for the localization of multiple color centers within the crystal. The position of at least one color center within the crystal is taken into account when designing the optics.

[0029] The detector is designed to detect the fluorescence light generated by a specific color center during excitation. In the simplest case, the detector is a photodiode, i.e., a non-spatially resolved detector. However, it is also possible to use a spatially resolved detector, such as a camera, to detect the fluorescence light, possibly in combination with the photodiode. The position of the color center corresponds to the focus position of the laser beam at the moment of maximum fluorescence detection, or to a slightly different position, which can be determined, for example, through calibration.

[0030] In another embodiment, the irradiation device is designed to direct the laser beam into the processing volume and focus it within the volume, both for exciting the at least one color center and for the additive manufacturing of the optics. In this case, a material that can be selectively cured using the laser beam is typically introduced into the processing volume. Alternatively, a powder bed can be used, which is selectively melted by the laser beam. The laser beam has a wavelength that enables the excitation of the color center and—typically with different laser parameters (so)—serves to selectively cure the material introduced into the processing volume.

[0031] In another embodiment, the machine has a holding tool for holding the crystal within the processing volume, wherein the holding tool is preferably movable in three spatial directions within the processing volume. As described above, it is advantageous for the crystal to be held by a holding tool when the color center(s) are localized or when the optical formation takes place within the processing volume. The holding tool can be designed to be displaceable and / or rotatable in three spatial directions, but this is not mandatory.

[0032] 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.

[0033] They show: Fig. 1 A schematic representation of an additive manufacturing machine with a processing volume in which a diamond crystal with a color center is arranged, during the determination of the position of the color center, Fig. 2 a schematic representation of the diamond crystal of Fig. 1, which is held by a holding tool and on which three optics in the form of lenses are formed, Fig. 3a,b a schematic representation of a diamond crystal partially embedded in a holding element or embedded between the holding element and an optic, as well as Fig. 4 A schematic representation of a sensor element integrated into an optical sensor, which has a diamond crystal with multiple color centers and with multiple optics.

[0034] In the following description of the drawings, identical reference symbols are used for identical or functionally equivalent components.

[0035] Fig. Figure 1 shows a machine 1 for additive manufacturing, which includes an irradiation unit 2. The irradiation unit 2 has a laser source 3 for generating a laser beam 4 with a laser wavelength λ. LThe laser beam 4 is fed to a scanner unit 5 of the irradiation unit 2, which has two scanner mirrors to deflect the laser beam 4 in two spatial directions. A focusing unit 6 of the irradiation unit 2 serves to focus the laser beam at a focus position F(x,y,z) in a processing volume 7, which is formed in a container 8 that is also part of the machine 1.

[0036] At the in Fig. In the example shown, a material 9 in the form of a liquid or viscous polymer is introduced into the processing volume 7. This material can be cured using the laser beam 4 to produce components via additive manufacturing. In the example described here, the curing of the material 9 requires a two-photon absorption process; that is, the additive manufacturing process is two-photon lithography. In two-photon lithography, the material is cured at the focus position F(x,y,z) when the laser beam 4 is generated by the laser source 3 in the form of ultrashort laser pulses and a material-dependent intensity value is exceeded at the focus position F(x,y,z).

[0037] At the in Fig. In the machine 1 described above, the laser beam 4 is used not only for the additive manufacturing of components, but also for the excitation of a color center, more precisely an NV center 10, in a diamond crystal 11, which is arranged in the processing volume 7. The machine 1 includes a detector 12 in the form of a photodiode, which serves to detect fluorescence light 13 generated during excitation with the laser beam 4. An optical filter 14 in the form of a wavelength filter serves to filter laser radiation that was scattered at the color center 10 or deflected towards the detector 12 during excitation with the laser beam 4.

[0038] An evaluation unit 15, which in the example shown is part of the irradiation unit 2, serves to determine the position P(x,y,z) of the color center 10 in the diamond crystal 11 based on the detected fluorescence light 13. For this purpose, the evaluation unit 15 determines the focus position F(x,y,z) of the laser beam 4 at the time of detection of the fluorescence light 13 and identifies it with the position P(x,y,z) of the color center 10. To determine the position P(x,y,z) of the color center 10 or of other color centers present in the diamond crystal 11, the three-dimensional volume of the diamond crystal 10 is scanned using the laser beam 4, as shown in Fig. 1 is indicated by an arrow. In the example described here, the wavelength λ L of the laser beam 4 in the green wavelength range between 515 nm and 570 nm.

[0039] As in Fig. As can be seen in Figure 2, three optics 16, 16', 16" are formed on the crystal 11 in machine 1, which in the example shown are designed in the form of lenses. The optics 16, 16', 16" are manufactured by additive manufacturing, whereby the material 9 in the processing volume 7 is selectively cured using the laser beam 4. During the additive manufacturing of the optics 16, 16', 16" the position P(x,y,z) of the color center 10 is taken into account. More precisely, the location or position of each optic 16, 16', 16" on a surface 11a-c of the crystal 11, where the respective optic 16, 16', 16" is formed, is determined depending on the calculated position P(x,y,z). In the example shown in Figure 2, the optics 16, 16', 16" are formed by selectively curing the material 9 in the processing volume 7 using the laser beam 4. Fig. In the example shown, the optics 16, 16', 16" are aligned in the form of lenses such that a center line 17, running centrally through each optic 16, 16', 16" intersects the color center 10 in the crystal 11. The geometry of the optics 16, 16', 16"—more precisely, the lens curvature—is also determined depending on the position P(x,y,z) of the color center 10, such that the color center 10 is located at a distance equal to the focal length from the respective optics 16, 16', 16"

[0040] As in Fig. As can also be seen in Figure 2, the crystal 11 is held in a holding tool 18, which is either temporarily inserted into the machine 1 for additive manufacturing, more precisely into the processing volume 7, or is permanently attached to the machine 1. In the example shown, the holding tool 18 is designed to be freely positioned in space. For this purpose, the holding tool 18 can be moved in three spatial directions x, y, z and additionally rotated about the three spatial directions x, y, z using actuators (not shown). This is advantageous because repositioning is usually required for the formation of the optics 16' on the underside 11c of the crystal 11, since the laser beam 4 would have to be focused through the volume of the crystal 11 onto the underside 11c of the crystal 11. For repositioning, the crystal 11 can be moved in the example shown.The holding tool 18 is rotated 180° around the x-axis of an xyz coordinate system.

[0041] The use of a holding tool 18 may be dispensed with if the crystal 11 is fixed to a holding element 19, as is the case in Fig. 3a is shown. In the Fig. In the example shown in Figure 3a, the crystal 11 is partially embedded in the holding element 19. To enable this partial embedding, the holding element 19 is also manufactured using additive manufacturing. The holding element 19 with the crystal 11 can be positioned in the processing volume 7 by placing the holding element 19 on the bottom of the container 8 or on a platform that may be located in the container 8. Subsequently, the color center 10 in the diamond crystal 11 is detected in the manner described above, and an optic 16 is formed on a surface 19a of the holding element 19, to which the diamond crystal 11 is fixed, as shown in Figure 3a. Fig. Figure 3b shows the diamond crystal 11 being embedded between the retaining element 19 and the optics 16, forming a sensor element 20 together with the optics 16 and the retaining element 19.

[0042] Fig. Figure 4 shows a sensor element 20 comprising a plate-shaped diamond crystal 11 with a plurality of color centers 10, integrated into an optical sensor 21. Optics 16, 16' in the form of microlenses are formed on two parallel surfaces 11a, 11b of the plate-shaped diamond crystal 11. The position of the optics 16, 16' on the respective surfaces 11a, 11b was determined as described in [reference to relevant section]. Fig. 2 described, depending on the respective position P(x,y,z) of the color centers 10. Each of the optics 16, 16' is assigned to one of the color centers 10 and centered with respect to the respective assigned color center 10. The focal length of the respective optic 16, 16' is adapted to the distance to the respective color center 10. For the optics 16 at the in Fig. The upper surface 11a of the crystal 11 consists of output coupler optics which collect the fluorescence light generated upon excitation of the respective color center 10 and direct it to a respective detector 12, which, as in Fig. 1 is designed as a photodiode. An optical filter 14 serves as in Fig. 1 for filtering excitation light that has not contributed to the excitation of the respective color center 10.

[0043] As in Fig.As shown in Figure 4 as an example for one of the color centers 10, an excitation light source 3' is used in the optical sensor 21 to generate an excitation light beam 4' which is directed centrally onto an optic 16' on the underside 11b of the crystal 11. The optic 16' serves as a coupling optic and is designed in the form of a microlens to focus the excitation light beam 4' at the position P(x,y,z) of the color center 10. The optical sensor 21 can have one or more excitation light sources 3' to excite all or, if necessary, only individual color centers 10 of the crystal 11. Accordingly, one or more detectors 12 can be provided in the optical sensor 21 to detect fluorescence light 13 generated during excitation.

[0044] The optical sensor 21 includes further components, such as a microwave generator that serves to generate a microwave field in the region of the color centers 10 in order to determine a measurand, for example, the strength of a magnetic field, in a known manner. The optical sensor 21 can also be configured as an array. In this case, a grid arrangement of color centers 10, for example, in the form of 3 x 3 color centers arranged at equal intervals in a Cartesian grid, can be excited, and the fluorescence light 13 generated by each color center 10 during excitation can be detected to determine a spatial distribution of the magnetic field. It is understood that the optical sensor 21 can also be configured to determine other measurands.

[0045] It is understood that other optics than (micro-)lenses can also be formed on the crystal 11 of the sensor element 20, the formation of which can be adapted or optimized depending on the determined position P(x,y,z) of a respective color center 10. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2016 / 0356863 A1

[0002] DE 102011009624 A1

[0004] DE 102014112155 A1

[0005]

Claims

[1] Method for producing a sensor element (20) comprising a crystal (11) with at least one color center (10), in particular a diamond crystal with at least one NV center, and at least one optic (16, 16', 16"), comprising: Arranging the crystal (11) in a processing volume (7) of a machine (1) for additive manufacturing, Excitation of the at least one color center (10) with a light beam, in particular with a laser beam (4), which is irradiated into the processing volume (7) and focused in the processing volume (7), Detecting fluorescent light (13) generated upon excitation of the at least one color center (10), Determining a position (P(x,y,z)) of the color center (10) in the processing volume (7) based on the detected fluorescent light (13), and forming the at least one optic (16, 16', 16") on or around the crystal (11) by additive manufacturing, taking into account the determined position (P(x,y,z)) of the at least one color center (10). [2] Method according to claim 1, wherein the laser beam (4) is irradiated into the processing volume (7) for exciting the at least one color center (10) and for forming the at least one optical system (16, 16', 16"). [3] Method according to claim 1 or 2, wherein, when forming the at least one optical system (16, 16', 16"), the determined position (P(x, y, z)) of the at least one color center (10) is taken into account to determine a position of the optical system (16, 16', 16") on or around the crystal (11), an alignment of the optical system (16, 16', 16") relative to the crystal (11), a geometry of the optical system (16, 16', 16") and / or an optical path. [4] Method according to one of the preceding claims, in which an optic in the form of a coupling optic (16') for coupling a laser beam (4') into the crystal (11) or an optic in the form of a coupling optic (16) for coupling out fluorescent light (13) from the crystal (11) is formed on the crystal (11). [5] Method according to one of the preceding claims, in which at least two optics (16, 16', 16") are formed on different surfaces (11a-c) of the crystal (11). [6] Method according to one of the preceding claims, wherein, during the formation of the at least one optic (16, 16', 16"), the crystal (11) is held on a holding tool (18) which is preferably movable in three spatial directions. [7] Method according to one of the preceding claims, in which the crystal (11) is fixed to a surface (19a) of a holding element (19) during the formation of the optics (16), in particular is partially embedded in the holding element (19), wherein the holding element (19) is preferably produced by additive manufacturing. [8] Method according to claim 7, wherein the crystal (11) is embedded between the optics (16) and the holding element (19) by forming the optics (16). [9] Method according to one of the preceding claims, in which the additive manufacturing is carried out by selective curing of a material (9), preferably by bath-based photopolymerization, in particular by two-photon lithography or by stereolithography. [10] Sensor element (20) manufactured by a method according to any one of the preceding claims. [11] Machine (1) for additive manufacturing, comprising: a processing volume (7) in which a crystal (11) with at least one color center (10), in particular a diamond crystal with at least one NV center, can be arranged, an irradiation device (2) for irradiating a light beam, in particular a laser beam (4), into the processing volume (7) and for focusing the light beam, in particular the laser beam (4), in the processing volume (7) in order to excite at least one color center (10) in the crystal (11), a detector (12) for detecting fluorescent light (3) generated when the at least one color center (10) is excited with the laser beam (4), and an evaluation device (15) for determining a position (P(x,y,z)) of the at least one color center (10) in the processing volume (7) based on the detected fluorescent light (13), wherein the machine (1) is designed, taking into account the determined position (P(x,y,z)) of the at least one color center (10), to form at least one optic (16, 16', 16") on or around the crystal (11) by additive manufacturing. [12] Machine according to claim 11, wherein the irradiation device (2) is designed to irradiate the laser beam (4) into the processing volume (7) and to focus it in the processing volume (7) both for the excitation of the at least one color center (10) and for the additive manufacture of the optics (16, 16', 16"). [13] Machine according to claim 11 or 12, further comprising: a holding tool (18) for holding the crystal (11) in the processing volume (7), wherein the holding tool (18) is preferably movable in three spatial directions (x, y, z) in the processing volume (7).

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