Method and device for calibrating a pyrometer
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- AIXTRON LTD
- Filing Date
- 2026-01-20
- Publication Date
- 2026-07-30
Smart Images
Figure EP2026051235_30072026_PF_FP_ABST
Abstract
Description
Description Method and apparatus for calibrating a pyrometer field of technology
[0001] The invention relates to a method and a device for calibrating a pyrometer. State of the art
[0002] To calibrate a pyrometer, the emission zone of a calibration element is heated to a reference temperature. The pyrometer's beam path is directed toward the emission zone. The pyrometer can then be adjusted to the reference temperature. Ideally, the spectral specific emission of the emission zone should correspond to that of a blackbody, and the emissivity of the emission zone should be one. In practice, hollow bodies with a small opening are used for this purpose. The walls of the hollow body are heated to the reference temperature so that the small opening forms an emission zone.
[0003] Alternative calibration elements, such as light-emitting diodes (LEDs), are used to emit light of a specific wavelength, which can then be used to calibrate the pyrometer. It is crucial that the spectral distribution of the light emitted by the LED is precisely matched to the spectral sensitivity of the pyrometer being calibrated. Heating elements or filaments are also used as light sources, but their spectral distribution typically deviates from the blackbody curve because the actual filament temperature differs from the nominal temperature of the calibration element. This is necessary because the emissivity is typically significantly reduced compared to 1. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0004] In general, it is difficult to artificially produce the spectral specific emission of a blackbody.
[0005] When operating a CVD reactor used to coat substrates in a process chamber, the temperature of a susceptor, the surface temperature of the substrate, or the temperature of the deposited layer is measured using a pyrometer. This pyrometer must be calibrated at regular intervals. The CVD reactor is operated in a cleanroom; therefore, the pyrometer used for calibration must be cleanroom-compatible.
[0006] German patent DE 10 2020 111 293 A1 describes a method for determining the temperature of a wafer in a coating process using emission-corrected pyrometry. An LED is used as the light source.
[0007] US patent 2013 / 0294476 A1 discloses a device for calibrating a pyrometer, using a light-imitation plate that simulates thermal radiation. The plate is a transparent body. The light sources are LEDs.
[0008] US patent 2004 / 02227906 A1 describes an infrared projector that can project infrared light onto an infrared detector.
[0009] JP S 58-34769 B2 describes a radiation thermometer for measuring a surface temperature using the radiation energy emanating from that surface. 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 Summary of Invention
[0010] The invention is based on the objective of providing a cleanroom-compatible method for calibrating a pyrometer and a calibration element that can be used in this process.
[0011] The problem is solved by the invention specified in the claims, wherein the dependent claims represent not only advantageous further developments of the invention specified in the dependent claims, but also independent solutions to the problem.
[0012] First and foremost, a calibration element is proposed that incorporates two or more individual light sources. These individual light sources are arranged within an optical device, such as an integrating sphere, in such a way that the light sources are not directly visible through an opening in the integrating sphere. Only the light reflected from the frosted (non-reflective) walls of the integrating sphere is visible. Alternatively, the mixed light used to calibrate the pyrometer can be observed through a ground glass screen, or the light from the two light sources can be focused onto a common point, which then forms an emission zone that emits the light with which the pyrometer is to be calibrated. The mixed light can also be generated and / or guided into the pyrometer to be calibrated using optical fibers or fiber couplers.When using an integrating sphere, the emission zone is formed by an opening.
[0013] The two or more individual light sources form radiating surfaces with different emissivities ε1, ε2. The individual light sources are operated at different temperatures TI, T2. The temperatures are chosen such that the shape of the cumulative emissivity curve 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01 The spectral specific emissivity of the radiating surfaces is as identical as possible to the curve of a blackbody radiation pattern of a blackbody with the reference temperature TO. Here, the focus is placed more on the spectral distribution than on the absolute intensity. Thus, it is also possible to approximate the spectral profile of the blackbody radiation pattern with emissivities higher or lower than 1. If the emissivity value deviates from 1, but the spectral profile conforms to the Planck distribution, then it is graybody radiation. Generally, a graybody radiation pattern is approximated for temperature TO and emissivity E0. An optimization calculation is performed to determine the characteristic temperatures TI and T2 at which the light sources are operated.In this optimization calculation, a summation curve of the spectral specific emissivities of at least two radiating surfaces is calculated using the Planck equation. The radiating surfaces are chosen such that the sum of their emissivities ε1, ε2 > ε0, where the gray-body radiation E0 < 1 and the black-body curve e = 1. However, the value for the gray-body radiation E can also be > 1. By varying the characteristic temperatures TI, T2, the shape of the summation curve is approximated to that of a black-body spectral specific emissivity curve calculated using the Planck equation for a black-body with reference temperature TO and reference emissivity E0SO until the deviation of the black-body curve from the summation curve is sufficiently small and, in particular, exhibits a minimum.
[0014] The individual light sources can be electrically conductive bodies. These bodies can be wires or filaments through which an electric current is passed. Preferably, electrically conductive bodies are used which, when installed in the optical device forming the calibration element, establish a unique relationship between current and light source. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01 Temperature. This is the case, for example, with metal wires. For instance, one wire may have an emissivity ε1 of 0.4 and another wire an emissivity ε1 of 0.65, such that the sum of the two emissivities ε1, ε2 > 1, provided ε0 = 1 is specified. Alternatively, ε0 = 0.1 could be specified, and one wire may have an emissivity e of 0.04 and another wire an emissivity e of 0.065, such that the sum of the two emissivities ε1, ε2 > 0.1.
[0015] Various optimization methods can be used to fit the summation curve to the blackbody curve. For example, the sum of squares of deviations between the summation curve and the blackbody curve can be determined. This involves relating values at selected wavelengths X of the summation curve to the blackbody curve, for example, by calculating their difference. An alternative is to minimize an integral over the square of the differences.
[0016] However, after appropriate initial dimensioning of the light sources, the fitting of the combined spectral curve to the blackbody curve can also be done experimentally. For this purpose, both filaments are heated successively to their nominal temperature T0, which can be observed using a spectrometer or bicolor pyrometer. The emissivity of each filament can then be determined. Preferably, the temperature of the filament with the higher emissivity is lowered in a further step; a reduction in the blue component is now observed in the spectrum. This is reduced or compensated for by raising the temperature of the second filament. These two steps are repeated until the emissivity of both filaments corresponds to the emissivity ε0 and the spectral distribution corresponds as closely as possible to the blackbody curve. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0017] In the subsequent operation of such a reference light source, it may be possible to adjust the temperature of both filaments to stabilize the reference light output and ensure similarity to the blackbody curve, for example, by means of a second aperture of an integrating sphere. A spectrometer can be used for this purpose. In its simplest form, a two-color pyrometer is also considered a spectrometer with the lowest possible spectral resolution. Using a computer, the measured intensity distribution can be compared with the blackbody curve, and the temperatures of both filaments can be determined, or the temperature-current characteristics of the filaments can be calculated. With these values, the previously described calculation for determining the optimal filament operating temperatures and currents can be performed.Fine adjustments to the filament temperatures can also be made during subsequent operation, for example, by iterating the experimental tuning procedure described above. It is also possible that, for a given pyrometer, a more accurate actual temperature Tx is used instead of the initially approximated temperature T0, which corresponds to the temperature of the blackbody curve targeted during the approximation. This more accurate temperature is determined by the computer system for the specific pyrometer being calibrated, based on the spectrometer measurement results. This approach takes into account the spectral sensitivity and measurement principle of the pyrometer.It is also possible to store predefined profiles of pyrometers to be calibrated, so that after selecting the appropriate profile, the computing device can either optimize the filaments so that the support points of the Planck curve approximation are precisely aligned with the operating points of the pyrometer to be calibrated, or at least output a temperature Tx. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0018] It is specifically intended that the emission spectrum of the filament be determined at different temperatures using a second spectrometer, for example, a two-color pyrometer. This is particularly advantageous if the filament or filaments are not gray-body radiators, where the emissivity is independent of the reference wavelength, but rather radiators where the emissivity is wavelength-dependent. The cumulative emission curve can then be calculated using experimentally determined values, where the temperature parameter can be the value at which a spectrum was experimentally determined. Spectra can be determined at several different temperatures. Spectra for temperatures that lie between experimentally used temperatures can be interpolated.
[0019] This cumulative curve can be approximated by varying the temperature parameters of a gray-body or blackbody curve. This gray-body or blackbody curve can also be experimentally determined, for example, by measuring the emission spectrum of a susceptor surface. The temperature of a susceptor in a CVD reactor can then be determined using a pyrometer calibrated in this way. Brief description of the drawings
[0020] Exemplary embodiments of the invention are explained below with reference to the accompanying drawings. These show: Fig. 1 shows the curves of the spectral specific emissivities of the radiating surfaces of two light sources 1, 2 (I₁, I₂) calculated with the Planck equation, a sum curve S of the two spectral specific emissivities I₁, I₂ and the curve of a blackbody curve S. 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 Fig. 2 schematically shows a calibration element 3 of a first embodiment in the form of an integrating sphere in conjunction with a pyrometer 6. Fig. 3 shows a first step of an iterative approximation method for determining temperature parameters, wherein two filaments are operated at a temperature TO and the sum of the emissivities is > 1, in particular 1.06, Fig. 4 shows a representation according to Figure 3 in a further iteration step, wherein the temperature of the strength light source blue component (B) is reduced disproportionately compared to the red component (R), Fig. 5 shows a subsequent representation according to Figure 3 after increasing the temperature of the weaker light source, whereby the blue component (B) has been increased so that the curve is flatter, Fig. 6 shows a representation according to Figure 3 after a repeated reduction of the temperature of the stronger light source, whereby the blue component (B) has again been reduced disproportionately compared to the red component (A), Fig. 7 shows the state after repeated increases in the temperature of the weaker light source, where the curve now approximately flattens out again. The curve now approximately corresponds to the shape of a blackbody curve, with a noticeable residual ripple remaining. The total intensity is 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 now, however, close to the intensity of the blackbody curve at TO and So = 1, Fig. 8 schematically shows a device for calibrating a pyrometer 6, wherein a spectrometer 9, for example a two-color pyrometer, is used to determine a real spectrum of the individual light sources 1, 2. Fig. 9 shows a representation similar to Figure 7 to illustrate the use of the pyrometer 6, which is a dyeing pyrometer operating at a wavelength of 1.5 μm. Description of the embodiments
[0021] The calibration element shown in Figure 2 consists of a cavity within an integrating sphere 3, which has an opening 4. The inner wall of the cavity is non-reflective but has a surface with a high degree of reflectivity. Two light sources 1, 2 in the form of filaments, for example, metal wires, through which an electric current can pass, are located within the cavity. The light sources are not directly visible through the opening 4. The opening 4 forms an emission zone 5, which lies in an optical path 7 of a pyrometer 6 that is to be calibrated using the calibration element 3.
[0022] Light sources 1 and 2 have emissivities e 1(e2, which are < e0. The sum of the two emissivity levels e 1( e2 should be greater than e0. ε1+ ε2> ε0(1) 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0023] The two light sources 1, 2 are operated at different temperatures Ti, T2. The following applies to the temperatures: r , < < T2(2) where To is the reference temperature of a blackbody. The spectral specific radiance of a blackbody is calculated using the Planck equation (with = 1) as follows: I(λ, T₀) = (2hc² / λ⁵) · ε0(3) l s (e AkT oi)
[0024] The spectral specific emissivities of the two light sources 1, 2 are calculated using the Planck equation as follows: I(λ, T₁) = (2hc² / λ⁵) · ε1(4) I(λ, T₂) = (2hc² / λ⁵) · ε2(5) / 5 (e AfcT 2-i)
[0025] Figure 1 shows an example of the course of these two emission values Ii, I2. It is evident that the two curves have different courses. These two emission values I (2, T) can be summed: = / 1(A, T1) + / 2(A, T2) (6) 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0026] Figure 1 shows the sum curve S and a blackbody curve B, which was determined according to equation 3, where Eo = 1.
[0027] An optimization calculation was used to approximate the shape of the cumulative curve S(X, Ti, T2) to the blackbody curve B by varying the temperature parameters Ti and T2. This can be achieved, for example, by minimizing the following relationship: ∫(S(λ, T1, T2) − I0(λ, T0)) 2 dλ = Minimum (7)
[0028] Alternatively, the following relationship can also be used to minimize the distance between the two curves: Σ i (S(λ i , T1, T2) − I0(λ i , T0)) 2 = Minimum (8)
[0029] The optimization then takes place at selected wavelengths X that are relevant for the operation of the pyrometer 6.
[0030] Optimizing the operating temperatures of the individual light sources can also be done experimentally, as explained in Figures 3 to 7. For this purpose, it is advantageous if the sum of the emissivities of the light sources is larger but close to 1, for example, 1.06 (Figure 3). While it is advantageous for the emissivities of the two light sources to differ, this is not strictly necessary. For example, the individual emissivities could be 0.64 and 0.42, or 0.53 and 0.53.
[0031] In a first step, the operating current is determined separately for each light source using a spectrometer or a two-color pyrometer, so 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01 that the light source temperature exactly corresponds to TO. Additionally, at this operating current, the emissivity can be determined separately or collectively for each light source by comparing the temperature determined with a spectrometer or bicolor pyrometer with another temperature determined with a monocolor pyrometer. For the subsequent procedure, it is considered advantageous, but not strictly necessary, to select the filament with the higher emissivity as the first filament.
[0032] In a second step, the operating current of a first light source (possibly with the higher emissivity) is reduced, e.g., by reducing the electrical power of the light source by one percent. The spectrometer now observes a disproportionate reduction in the blue component of the spectral distribution of the mixed light (Fig. 4). In a third step, the operating current of a second light source, or the electrical power of the second light source, is increased until the mixed light exhibits the same or at least similar intensity at at least two different wavelengths (Fig. 5).
[0033] If the emissivity of both wavelengths is still higher than 1, then in a further step 2.1 (Fig. 6) the electrical power of the first filament is further reduced, and in a subsequent further step 3.1 (Fig. 7) the electrical power of the second filament is further increased, so that mixed light that is as gray as possible is produced again. This procedure is repeated until the intensity of the mixed light is as close as possible to an emissivity of 1 and is as gray as possible. Gray is defined here as equal intensity at two different wavelengths or averaged over two different wavelength intervals. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0034] According to another embodiment, more than three light sources can be used. In this case, the following relationship applies to the individual emissivities of the light sources:
[0035] The cumulative curve is then calculated as follows: S (λ, T1, T2, ..., T n ) = I1(λ, T1) + I2(λ, T2) + ··· + I n (λ, T n ) (9)
[0036] In an arrangement with many light sources, it is possible for the individual light sources to have different emissivities. It is also possible to select individual light sources and group them into two or more groups. This offers the advantage of being able to influence not only the light source temperature but also, to a certain extent, the emissivity. This can be achieved by measuring the emissivity, analogous to the first step of the previous embodiment, to identify a subset of light sources with a target emissivity of, for example, 0.51, i.e., just slightly greater than half of 1, as precisely as possible. A further group with an emissivity of 0.51 is then selected from the remaining light sources. The closer the total emissivity approaches 1, the more precisely the mixed light corresponds to blackbody radiation T0.
[0037] In another embodiment, shown in Figure 8, a spectrometer 9 is used, which interacts with a beam path that passes through a second opening 13 of the integrating sphere. With this spectrometer 9, which can be a two-color pyrometer, the following can be determined at different temperatures of the individual light sources 1, 2: 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01 actual spectra are recorded. With the spectrometer 9, a family of radiation curves of the individual light sources 1, 2 at different temperatures T can thus be recorded. These spectra can be stored in a computing unit 8.
[0038] The spectrometer 9 can be used to examine the light from each individual light source 1, 2, for example, a filament, sequentially. It can also be used to directly examine the mixed light from the two individual light sources 1, 2.
[0039] Additionally, the computing unit 8 can also control the current flow to the individual light sources 1, 2, for example, the filaments. By varying the filament currents, the current-temperature characteristic or the emissivity can then be recorded for each light source individually. These measurements can be used to optimize the filament temperatures for subsequent operation.
[0040] Spectral profiles are determined and stored in the processing unit's memory. Each spectral profile has a value for at least one wavelength. However, it can also have a value for multiple wavelengths.
[0041] Figure 9 illustrates how the temperature can be measured using a pyrometer 6, which is sensitive at a wavelength of 1.5μm.
[0042] This allows the mixed light to be analyzed specifically for the pyrometer being calibrated, even during later operation, and, for example, a precise calibration temperature Tx to be determined. The individual light source temperatures can also be optimized, particularly with regard to... 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 considered wavelengths or wavelength intervals achieve a particularly good approximation of the blackbody curve.
[0043] The device shown in Figure 8 can be used, for example, to recalibrate a pyrometer 6, which is permanently mounted on the housing of a CVD reactor, from time to time. An optical path passes through a housing wall of the CVD reactor and, if necessary, through an opening in the process chamber ceiling into the process chamber. The temperature of a susceptor located in the process chamber can be measured via this optical path. A mirror or other deflecting device can be used to direct the optical path to a calibration device, such as the one shown in Figure 9.
[0044] Since the sum of the emissivities of the individual light sources is greater than the reference emissivity, this has the following advantages. This feature ensures that the Planck curve can be approximated as closely as possible by the sum curve. A particularly good approximation is achieved if one of the temperatures TI and T2 is lower and the other higher than the reference temperature T0.
[0045] Designing individual light sources as electrically conductive bodies, especially wires or filaments, whose characteristic temperatures can be ensured by passing a characteristic current through them, has the following advantages: electrically conductive bodies are particularly well suited for this method because they guarantee easy control of the characteristic temperatures. Furthermore, filaments are easy to manufacture and inexpensive light sources. This is based on the understanding that the sum of the temperature curves of two filaments already provides a good approximation of the temperature. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01 PLANCK curve can be achieved. This is therefore a particularly technically simple solution. The easy scalability also allows for possible adjustments at a later date.
[0046] The foregoing statements serve to explain the inventions covered by the application as a whole, which each independently further develop the prior art at least through the following combinations of features, whereby two, several or all of these combinations of features may also be combined, namely:
[0047] A method for calibrating a pyrometer 6 comprising the following steps: providing a calibration element 3 having an emission zone 5 emitting light with a spectrum, in particular a gray-body radiation, of a reference temperature T0 and reference emissivity e0, wherein the light is generated by at least two individual light sources 1, 2, wherein the radiating surfaces of the individual light sources 1, 2 have emissivities Ei, 82 and the sum of the emissivities Σ1, 82 is greater than e0, wherein a characteristic temperature TI, T2 is determined for each individual light source 1, 2, wherein a sum curve SX, Ti, T2 of the spectral specific emissivities of the radiating surfaces is determined, and temperature parameters are varied by means of an optimization calculation such that the course of the sum curve SX, Ti, T2 approximates a course of a gray-body or black-body curve of a body with the reference temperature T0 and reference emissivity e0.wherein the individual light sources 1, 2 are heated to the characteristic temperatures TI, T2 and a mixed light generated by the individual light sources 1, 2 is used for calibration.
[0048] A method for producing a calibration element 3 having an emission zone 5 which emits light with a spectrum in particular 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01 of a gray-body radiation of a reference temperature TO and a reference emissivity E0 emitted, in particular for carrying out the method according to claim 1, which is characterized by the following steps: Arranging two individual light sources 1, 2 in an optical device 1 such that the emission zone 5 emits mixed light of the individual light sources 1, 2, wherein the radiating surfaces of the individual light sources 1, 2 have emissivities Ei, E2 and the sum of the emissivities is greater than E0, wherein a characteristic temperature TI, T2 is determined for each individual light source 1, 2, wherein a sum curve of the spectral specific emissions of the radiating surfaces is determined and temperature parameters are varied by means of an optimization calculation such that the course of the sum curve SX, Ti, T2 approximates a course of a gray-body or black-body curve of a body with the reference temperature TO.
[0049] A calibration element with two individual light sources 1, 2, arranged in an optical device 3 such that an emission zone 5 emits a mixed light from the individual light sources 1, 2, wherein the radiating surfaces of the individual light sources 1, 2 have emissivities Ei, £2 and the sum of the emissivities is greater than a reference emissivity E0, wherein each individual light source 1, 2 can be heated to a characteristic temperature TI, T2, wherein the characteristic temperatures TI, T2 are selected such that the shape of a sum curve SX, Ti, T2 of the spectral specific emissivities of the radiating surfaces approximates a shape of a gray or blackbody curve of a body with a reference temperature T0.
[0050] A method or a calibration element 3 characterized in that the emissivity Ei, E2 are different from each other. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
[0051] A method or a calibration element 3, characterized in that the sum curve SX, Ti, T2 is determined using the PLANCK equation and the temperature parameter is the temperature parameter of the PLANCK equation, and the sum curve SX, Ti, T2 is approximated to a grey or blackbody curve calculated using the PLANCK equation.
[0052] A method or a calibration element 3 characterized in that the individual light sources 1, 2 are electrically conductive bodies, in particular wires or filaments, and the characteristic temperatures (TI, T2) are set or adjustable by passing a characteristic current through them.
[0053] A method or a calibration element 3 characterized in that the emission zone 5 is the opening of an integrating sphere 3.
[0054] A method characterized by minimizing the sum of squares of deviations of the cumulative curve from the blackbody curve during optimization calculations.
[0055] All disclosed features are essential to the invention (individually, but also in combination with one another). The disclosure of this application hereby incorporates in full the disclosure content of the associated / attached priority documents (copy of the earlier application), also for the purpose of including features of these documents in the claims of the present application. The dependent claims, even without the features of a referenced claim, characterize independent inventive developments of the prior art, in particular for the purpose of filing divisional applications on the basis of these claims. The features in 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 The invention specified in each claim may additionally include one or more of the features described above, in particular those provided with reference numerals and / or listed in the reference numeral list. The invention also relates to designs in which individual features mentioned in the preceding description are not realized, in particular insofar as they are recognizably unnecessary for the respective purpose or can be replaced by other technically equivalent means. 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 List of reference marks 1 Single light source E1 emissivity 2 Single light source E2 emissivity 3 Calibration element, optical device 4 Opening 5 Emission zone 6 pyrometers 7 optical path 8 Computing equipment 9 spectrometers, bicolor pyrometers 10 Spectral profile 11 Power source 12 Power source 13 Opening S summation curve Reference temperature TI characteristic temperature T2 characteristic temperature Thus reference emissivity 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01
Claims
Claims 1. Procedure for calibrating a pyrometer (6) by the following steps: Providing a calibration element (3) having an emission zone (5) which emits light with a spectrum, in particular a grey body radiation of a reference temperature (TO) and reference emissivity (e0), wherein the light is generated by at least two individual light sources (1, 2), wherein the radiating surfaces of the individual light sources (1, 2) have emissivities (Σi, Σ2) and the sum of the emissivities (Σ1, Σ2) is greater than (e0), where a characteristic temperature (TI, T2) is determined for each individual light source (1, 2), wherein a sum curve S (λ, T1, T2) of the spectral specific emissions of the radiating surfaces is determined and Temperature parameters are varied by means of an optimization calculation such that the course of the sum curve S (λ, T1, T2) approximates a course of a grey or blackbody curve of a body with the reference temperature (TO) and reference emissivity (e0), wherein the individual light sources (1, 2) are heated to the characteristic temperatures (TI, T2) and a mixed light generated by the individual light sources (1, 2) is used for calibration.
2. A method for producing a calibration element (3) having an emission zone (5) which emits light with a spectrum, in particular a gray body radiation of a reference temperature (TO) and a reference emissivity (e0), in particular for carrying out the method according to claim 1, characterized by the following steps: 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-01 Arranging two individual light sources (1, 2) in an optical device (1) such that the emission zone (5) emits mixed light from the individual light sources (1, 2), where the radiating surfaces of the individual light sources (1, 2) have emissivities (Ei, £2) and the sum of the emissivities is greater than (e0), where a characteristic temperature (TI, T2) is determined for each individual light source (1, 2), wherein a cumulative curve of the spectral specific emissions of the radiating surfaces is determined and Temperature parameters are varied using an optimization calculation such that the course of the sum curve S (λ, T1, T2) approximates a grey or blackbody curve of a body with the reference temperature (TO).
3. Calibration element with two individual light sources (1, 2) arranged in an optical device (3) such that an emission zone (5) emits a mixture of light from the individual light sources (1, 2), wherein the radiating surfaces of the individual light sources (1, 2) have emissivities (Ei, £2) and the sum of the emissivities is greater than a reference emissivity (e0), wherein each individual light source (1, 2) can be heated to a characteristic temperature (T1, T2), wherein the characteristic temperatures (T1, T2) are selected such that the course of a sum curve S (λ, T1, T2) of the spectral specific emissivities of the radiating surfaces approximates a course of a grey-body or black-body curve of a body with a reference temperature (TO). 31380PCT drg / gz 19 January 2026 Ai Ltd 2025-014. Method or calibration element (3) according to any of the preceding claims, characterized in that the emissivities (EI, £2) are different from each other.
5. Method or calibration element (3) according to one of the preceding claims, characterized in that the sum curve S (λ, T1, T2) is determined using the Planck equation and the temperature parameter is the temperature parameter of the Planck equation, and the sum curve S (λ, T1, T2) is approximated to a grey or blackbody curve calculated using the Planck equation.
6. Method or calibration element (3) according to one of the preceding claims, characterized in that the individual light sources (1, 2) are electrically conductive bodies, in particular wires or filaments, and the characteristic temperatures (TI, T2) are set or adjustable by passing a characteristic current through them.
7. Method or calibration element according to one of the preceding claims, characterized in that the emission zone (5) is the opening of an integrating sphere (3).
8. Method according to one of the preceding claims, characterized in that, in the optimization calculation, the sum of squares of deviations of the cumulative curve from the blackbody curve is minimized.
9. Device or method characterized by one or more of the characterizing features of one of the preceding claims. 31380PCT drg / gz January 19, 2026 Ai Ltd 2025-01