Method for ascertaining a property of a gas by means of a raman spectroscopy device

Abstract

The invention relates to a method for ascertaining at least one property of a gas, in particular for ascertaining at least one gas concentration, by means of a Raman spectroscopy device (30). The Raman spectroscopy device (30) comprises a laser diode (16) designed to illuminate the gas (22) in a focused manner. The Raman spectroscopy device (30) has a detector (70) for spectrally resolved detection of the Raman scattered light (34). The at least one property of the gas (22) is determined by means of an evaluation algorithm on the basis of the Raman scattered light (34) detected by the detector (70). A temperature of the laser diode (16) is selectively controlled to one of at least two target values. The method is characterised in that the evaluation algorithm is selected on the basis of the target value selected in each case.

Description

[0001] R.416718

[0002] - 1 -

[0003] Method for determining a property of a gas using a Raman spectroscopy device

[0004] Technical field

[0005] The invention relates to a method for determining at least one property of a gas, for example a gas concentration, using a Raman spectroscopy device. The Raman spectroscopy device comprises a laser diode designed for focused illumination of the gas and a detector for spectrally resolved detection of the Raman scattered light.

[0006] State of the art

[0007] A system is known from US Patent 2023 / 0010890 A1. It comprises a laser for illuminating a sample under investigation, a temperature sensor for detecting the operating temperature of the laser and for generating an output signal indicating the detected temperature, a temperature stabilization device for controlling the operating temperature of the laser, and a controller for determining a target operating temperature or temperature range for the laser based on the output of the temperature sensor and for controlling the temperature stabilization device to bring the operating temperature of the laser to the target operating temperature or target temperature range.

[0008] Description of the invention

[0009] The inventors first recognized that stabilizing the temperature of the laser diode is a necessary prerequisite for keeping the properties of its emission, such as wavelength, intensity, and bandwidth, constant. This allows the properties of the gas to be precisely determined based on the Raman scattered light resulting in the Raman spectroscopy apparatus, using a suitable detector and algorithm. Such an R.416718

[0010] - 2 -

[0011] According to the invention, stabilization is achieved by controlling the temperature of the laser diode to a setpoint (closed-loop control). In such control loops, the temperature of the laser diode can be precisely and permanently stabilized at a setpoint.

[0012] The inventors further recognized that choosing the target temperature for the laser diode is not trivial. While a relatively low temperature generally has a positive effect on the emission characteristics and lifetime of the laser diode, the choice of the target temperature, together with the given characteristics of the Raman spectroscopy system, also limits the operating temperature range in which the Raman spectroscopy system can perform meaningful measurements. If the ambient temperature is above this operating temperature range, the Raman spectroscopy system can no longer reliably lower the laser diode temperature to the aforementioned relatively low temperature.

[0013] To overcome this conflict of objectives, the invention provides that the temperature of the laser diode can be selectively controlled to one of at least two setpoints. Depending on the operating location and the actual or expected ambient temperature, the more suitable of the two setpoints can then be selected. Of course, more than two setpoints can also be provided.

[0014] It was further recognized that when the temperature of the laser diode changes, the properties of the Raman scattered light also change along with the emission properties of the laser diode. Therefore, it is also part of the present invention that an evaluation algorithm, with which the property of the gas is determined based on the Raman scattered light detected by the detector, is selected according to the respective setpoint.

[0015] The term "evaluation algorithm" should be interpreted broadly. It could be, for example, a formula or a table. It could also be a trained neural network or something similar.

[0016] The term “selecting” an evaluation algorithm is also far removed from R.416718.

[0017] - 3 - understand. For example, a separate formula or table may be stored for each target temperature, or a separate neural network may be trained and maintained with the data relating to the respective target temperature. The selection can also be made, for example, by individually choosing the parameters of a formula for each target temperature.

[0018] In a further training course, it is planned that the setpoint temperature of the laser diode will be selected based on the ambient temperature of the Raman spectroscopy system. A higher setpoint can always be selected at higher ambient temperatures than at lower ambient temperatures. The ambient temperature value can be measured by a temperature sensor of the Raman spectroscopy system. Alternatively, the ambient temperature information can also come from another source; for example, corresponding data can be received via a connectivity connection of the Raman spectroscopy system.

[0019] The Raman spectroscopy device may be designed to have a housing with an inside and an outside. This housing may be fully enclosed, protecting the interior, and in particular the Raman spectroscopy device, from contamination. All components of the Raman spectroscopy device may be located within this housing.The housing may contain, in particular: a gas measurement chamber for the gas in which the emission of the laser diode can be focused; one or more optical access points to the gas measurement chamber, for example, for coupling in the focused emission of the laser diode; one or more optical outputs from the gas measurement chamber, for example, for coupling out the Raman scattered light; a collecting optical system with at least one filter and at least one aperture for directing the Raman scattered light from the gas measurement chamber to a spectral analysis unit, which is also located in the housing. The detector is, in particular, also part of the spectral analysis unit and is, in particular, also arranged within the housing.

[0020] The housing may also contain a gas supply line for supplying gas to the gas metering room. In particular, R.416718

[0021] - 4 - it should be provided that the gas can be continuously passed through the gas measurement room during the measurement.

[0022] The temperature sensor for measuring the ambient temperature can generally be located on the laser diode or on the detector.

[0023] Additionally or alternatively, the temperature sensor for measuring the ambient temperature can be located inside the housing, for example, on the inside of the housing. The temperature measured by the temperature sensor then represents the actual influence of the ambient temperature on the laser diode.

[0024] Alternatively, the temperature sensor for measuring the ambient temperature can be located on the outside of the housing or outside the housing. The temperature measured by the temperature sensor then represents the actual ambient temperature.

[0025] Precise temperature measurements are possible, for example, if the Raman spectroscopy device includes a fan for ventilating the interior of the housing, which is, for instance, mounted on the housing of the Raman spectroscopy device, and if the temperature sensor for measuring the ambient temperature is also subjected to airflow from the fan. The ambient temperature measured by the temperature sensor then corresponds exactly to the ambient temperature.

[0026] In order to significantly increase the operating range of the Raman spectroscopy device by selecting the setpoint, it can be provided that the difference between the first setpoint of the operating temperature of the laser diode and the second setpoint of the operating temperature of the laser diode is at least 5 Kelvin.

[0027] To keep the operating temperature of the laser diode within acceptable overall limits, the difference between the first and second setpoint operating temperatures of the laser diode may be limited to a maximum of 25 Kelvin. R.416718

[0028] - 5 -

[0029] The evaluation algorithm for determining the gas's properties can incorporate a neural network. This provides a powerful tool for determining the gas's properties, capable of delivering good results even in the case of weak or noisy signals.

[0030] Regardless of the exact type of evaluation algorithm, it may be designed to explicitly or implicitly consider the dependence of the wavelength, intensity, and / or bandwidth of the light emitted by the laser diode on the operating temperature of the laser diode. In particular, it may be assumed that the corresponding property of the light emitted by the laser diode is transferred to a property of the Raman scattered light. Specifically, that a shift in the wavelength of the laser diode emission is transferred to a shift in the wavelengths of lines in the spectrum of the Raman scattered light, that the intensity of the Raman scattered light changes proportionally to the intensity of the laser diode emission, and that the bandwidth of lines in the spectrum of the Raman scattered light corresponds to or depends on the bandwidth of the laser diode emission.

[0031] As mentioned at the outset, the aim of the present invention is to enable stable measurements using the Raman spectroscopy device. This requires that the temperature of the laser diode used as the light source be kept as constant as possible (at a constant setpoint) so that wavelength drift and changes in the optical power of the emitted laser diode light are avoided. Both a changing wavelength and a changing optical power would distort the measurement result, since the gas being measured would be illuminated with these altered values ​​during the ongoing measurement, and the wavelength and optical power of the Raman scattered light would be correspondingly altered.

[0032] It is also useful to monitor the temperature of the detector that detects the Raman scattered light and to keep it as constant as possible, since otherwise the detector signal would not be fully reproducible, in particular R.416718

[0033] - 6 - high temperatures of the detector lead to so-called detector noise and thus to a distortion of the measurement result.

[0034] Therefore, in further training, it is proposed that the Raman spectroscopy device has a control and regulation device, wherein a first control loop and a second control loop are implemented in the Raman spectroscopy device, wherein the first control loop is designed to regulate the temperature of the laser diode to the respective setpoint, and wherein the second control loop is designed to regulate the temperature of the detector to a setpoint of the detector temperature.

[0035] The first control loop integrates the components for temperature management of the laser diode, such as a temperature sensor, a setpoint generator, and at least one active temperature control element. The second control loop integrates the components for temperature management of the detector, such as a temperature sensor, a setpoint generator, and at least one active temperature control element.

[0036] The first control loop is configured, in particular, to measure the actual temperature of the laser diode, and furthermore, to set a target temperature of the laser diode based on the measured actual temperature. The second control loop is configured, in particular, to measure the actual temperature of the detector, and furthermore, to set a target temperature of the detector based on the measured actual temperature. The control device according to the invention described above preferably includes a control amplifier that converts the difference signal between the respective target value and the respective actual value into a control signal that actuates the respective active temperature control element.

[0037] According to the invention, the setpoint temperature of the laser diode can be between +10° and +50°, in particular between +24° and +26°, and most preferably +25°. Furthermore, the setpoint temperature of the detector can be between -35° and +7°, in particular between -9° and -11°, and most preferably -10°. The first of these is R.416718.

[0038] - 7 -

[0039] The first setpoint is preferably higher than the second setpoint. Therefore, it is generally preferred that the detector operates at a cooler temperature than the laser diode, or that the first setpoint is higher than the second setpoint.

[0040] Furthermore, it can be advantageous to thermally connect the laser diode and the detector. Cooling of the laser diode is possible through a temperature gradient between the laser diode and the detector. This is known as cascade cooling between the laser diode and the detector.

[0041] In particular, it can be advantageously provided that the laser diode and the detector are thermally connected to each other by means of passive temperature control elements, in particular by means of rod conductors, wherein the rod conductors are made of a material with high thermal conductivity, for example aluminum, copper, gold or silver; diamond, boron nitride, silicon carbide, graphite or aluminum oxide.

[0042] Rod conductors are, in particular, solid materials extending in a longitudinal direction with a cross-sectional area that is, for example, round or polygonal, e.g. rectangular, and extends perpendicular to the longitudinal direction.

[0043] Preferably, the number of rod(s) is 1 to 100, the length of the rod(s) is between 1 and 200 mm and / or the cross-section of the rod(s) is between 0.1 and 1000 mm. 2 The rod conductors can have a length greater than the square root of their cross-section, for example, greater than four times the square root of their cross-section.

[0044] It can be provided that the first control loop has at least one temperature measuring element for measuring the temperature of the laser diode and at least one temperature control element for temperature control of the laser diode, and that the second control loop has at least one temperature measuring element for measuring the temperature of the detector and at least one temperature control element for temperature control of the detector. Furthermore, it is preferred that the at least one temperature measuring element and the at least one temperature control element of the first control loop are separate from the at least one R.416718

[0045] - 8 -

[0046] The temperature measuring element and at least one temperature control element of the second control loop are combined. This is advantageous because both the sensors for detecting the temperature, i.e., the key variable of the control loop, and the active temperature control elements can be optimally positioned on the laser diode and the detector, respectively.

[0047] As a rule, "tempering" refers to cooling, but in exceptional cases the term tempering can also include at least temporary heating, e.g. when operating in very cold environments.

[0048] It is possible that the temperature control elements are designed as Peltier elements, wherein in particular one to four Peltier elements may be provided per temperature control element, wherein the Peltier elements may have a square or rectangular shape, wherein the cross-sectional area of ​​the individual rectangular Peltier elements varies from 15mm x 15mm to 50mm x 50mm, wherein the power per Peltier element is between 20W and 70W, and wherein the Peltier elements may be formed from a single layer or from several layers of thermoelectric material.

[0049] A Peltier element is a thermoelectric device used for cooling or heating. A distinction is made between "single-stage" and "multi-stage" Peltier elements. These terms refer to the number of thermoelectric layers used in a Peltier element. A single-stage Peltier element consists of a single layer of thermoelectric material. It can generate a limited temperature difference between the two sides of the element and is typically used for applications with lower cooling capacity. A multi-stage Peltier element consists of several layers of thermoelectric material connected in series. This allows for a larger temperature difference between the two sides of the element and higher cooling capacity. Multi-stage Peltier elements are used in applications requiring greater cooling capacity.

[0050] It is also highly advantageous to have a thermal connection between the laser diode and the detector using passive heat conduction structures. This allows for reduced energy consumption and optimized dynamics of both control loops, enabling the laser diode to be mounted on a single R.416718 during spectrometer operation.

[0051] - 9 - higher target temperature (e.g. Set Point: 25°C) and to keep the detector at a lower operating temperature (e.g. Set Point: -10°C).

[0052] In a further development of the invention, the passive heat conduction structures can be formed from heat pipes, which transport the heat from the laser diode to the detector. Heat pipes are defined as rod-shaped conductors with an interior that is either closed or open. It is also conceivable that the interior is filled with a medium. The heat pipes can be made of solid material, coated material, or, for example, as hollow tubes, i.e., capillaries, e.g., with closed ends and filled with a fluid refrigerant.

[0053] In this process, the refrigerant may evaporate at the warm end and condense in a cyclical process at the cooler end of the heat pipe. The heat pipe or heat conduction tubes' mounting points, i.e., the base points for attaching the passive conductive elements to the laser diode or detector, can also be made of metallic materials or non-metallic materials with high thermal conductivity coefficients.

[0054] It may be advantageous to provide that the heat conduction tubes are made of a metallic material, in particular of Al [235 W / mK], Au [310 W / mK] Cu [400 W / mK], Ag [430 W / mK] or of alloys of these metals.

[0055] Alternatively, the heat conduction tubes may be made of a non-metallic material, in particular tool diamond [2000 W / mK], boron nitride [anisotropic up to 500 W / mK], silicon carbide [270 W / mK], graphite [anisotropic up to 200 W / mK] or aluminum oxide or corundum [30 W / mK].

[0056] Furthermore, it is possible to thermally insulate the heat pipes on their outer surface, thus creating an improved temperature gradient along their length from heat input to heat output while simultaneously reducing the influence of the ambient temperature. This insulation can be achieved through a coating, for example made of plastic, or through a casing, also for example made of plastic. R.416718

[0057] - 10 -

[0058] Using the materials described above in the manner described above is advantageous because it ensures high thermal conductivity, good processability, high ductility, good sealing properties and high corrosion resistance.

[0059] It is possible that the number, length, and cross-sectional area of ​​the heat pipes depend on the amount of heat to be dissipated and the desired temperature gradient between the laser diode and the detector, with the number of heat pipes varying from 1 to 100, the length of the heat pipes varying from 1 to 200 mm, and the cross-sectional area of ​​the heat pipes varying from 0.1 to 1000 mm². 2 This can vary. The heat pipes can have a length greater than the square root of their cross-section, for example, greater than four times the square root of their cross-section.

[0060] In a further development of the invention, it can be provided that the detector is designed as a CCD sensor or as a CMOS sensor or as a SPAD or Si photodiode array or as Si photodiodes or as InGaAs photodiodes or as a multi-pixel photon counter or as an N MOS sensor or as avalanche photodiodes or as a phototube detector.

[0061] The Peltier elements mentioned above can be controlled, for example, by means of pulse width modulation.

[0062] Brief description of the drawing

[0063] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0064] They show:

[0065] Figure 1 shows a Raman spectroscopy apparatus for carrying out the method according to the invention, R.416718

[0066] - 11 -

[0067] Figure 2 shows a three-dimensional representation of a Raman spectroscopy device for carrying out the method according to the invention.

[0068] Figure 3 shows a schematic representation of a Raman spectroscopy device for carrying out the method according to the invention.

[0069] Figure 4 shows an embodiment of the method according to the invention.

[0070] Embodiments of the invention

[0071] Fig. 1 schematically shows the setup of a Raman spectroscopy device 30. This device comprises a high-power laser 14, here a laser diode 16, as the radiation source 12. This laser is operated within the visible spectral range, particularly within the blue spectral range. A focusing optic 18, shown only schematically here, is connected downstream of the radiation source 12 as depicted in Fig. 1. This optic focuses the laser radiation generated by the at least one laser diode 16 onto a portion of a gas measurement chamber 20. The gas measurement chamber 20 contains a gas 22 or a gas mixture 24. The gas measurement chamber 20 can be part of a conduit or bypass line 26 through which a gas flow 66 passes.

[0072] The gas measurement room 20 includes at least one optical access 28 and at least one optical output 29 for the laser radiation generated by the at least one laser diode 16.

[0073] The illustration in Fig. 1 further shows that laser radiation exiting from the at least one optical output 29 enters a radiation absorber 32 to avoid scattered light influences.

[0074] From the gas measurement room 20, Raman scattered light 34 enters a Raman scattering intensity-enhancing optic 36, which is part of a spectral analysis unit 38. This unit comprises a spectrograph with at least one dispersing R.416718

[0075] - 12 -

[0076] The element comprises, for example, a grating and at least one prism. Multiple gratings and prisms, as well as combinations of gratings and prisms, are also possible. The spectral analysis unit 38 also includes a light detector 48, for example, in the form of a CCD camera 40 or a CMOS component, and / or a number of receiver diodes. Furthermore, receiver diodes can be arranged within the light detector 48 at the Raman wavelengths of the gas(es) to be analyzed. By appropriately designing the bypass 26 or by using optical windows in the gas measurement chamber 20, gases 22 or gas mixtures 24 can thus be measured in different pressure and temperature ranges.

[0077] In the Raman spectroscopy device 30 shown in Fig. 1, the gas 22 to be measured is illuminated by the laser diode 16, preferably in the visible blue spectral range, through a focusing optic 18. The Raman scattering light 34 is captured by the Raman scattering intensity-enhancing optic 36 and supplied to the spectral analysis unit 38.

[0078] The components of the Raman spectroscopy device are, for example, fully integrated in a housing 100, which is symbolically represented in Figure 1 and which has an inner side 10Oi and an outer side 100a.

[0079] The Raman spectroscopy device 30 further comprises a temperature sensor 50 for measuring the ambient temperature. In the example shown in Figure 1, it is arranged on the inside 10Oi of the housing 100.

[0080] Fig. 2 shows an example of a Raman spectroscopy device 30 according to the invention, in which the spectral analysis unit 38 has a detector 70 for spectrally resolved detection of the Raman scattered light.

[0081] Furthermore, Fig. 2 shows that both the laser diode 16 and the detector 70 are thermally connected to each other by means of passive temperature control elements 76 and also both by means of individually assigned active R.416718

[0082] - 13 -

[0083] Temperature control elements 71 are temperature controlled.

[0084] Figure 3 shows that the Raman spectroscopy device 30 has a control and regulation device 72 and that the Raman spectroscopy device 30 has a first control loop 73 and a second control loop.

[0085] 74 is realized, wherein the first control loop 73 is designed to control the temperature of the laser diode 16 to a first setpoint, wherein the second control loop 74 is designed to control the temperature of the detector 70 to a second setpoint.

[0086] Figure 3 further shows that the first control loop 73 has a temperature measuring element 75 for measuring the temperature of the laser diode 16 and a temperature control element 71 for temperature control of the laser diode 16. Figure 3 also shows that the second control loop 74 has a temperature measuring element 75 for measuring the temperature of the detector 70 and a temperature control element 71 for temperature control of the detector 70, and that the temperature measuring element 75 and the temperature control element 71 of the first control loop 73 are independent, i.e., separate, from the temperature measuring element 75 of the first control loop 73.

[0087] 75 and the temperature control element 71 of the second control loop 74 are formed.

[0088] As shown in both Fig. 2 and Fig. 3, the thermal connection between the laser diode 16 and the detector 70 is established by means of passive heat conduction structures 76. In the example shown, the passive heat conduction structures 76 are formed by heat pipes, which generally transport heat from the laser diode 16 to the detector 70. The four heat pipes shown in Fig. 2 are merely an example. For instance, only a single heat pipe, perhaps with a rectangular cross-section, may be used. The cross-sectional area of ​​this heat pipe can be relatively large, for example, 10–400 mm². 2 or even 10 - 1000 mm 2 .

[0089] An exemplary embodiment of the method according to the invention, using the Raman spectroscopy apparatus described above, is schematically illustrated in Figure 4. R.416718

[0090] - 14 -

[0091] In the preceding process step 80, the Raman spectroscopy device 30 described above is integrated into a gas line in such a way that a gas 22 continuously flows through the gas measurement room 20.

[0092] In the subsequent process step 81, the temperature sensor 50 detects that the ambient temperature is, for example, 20 °C and the corresponding information is transmitted to the control and regulating device 72.

[0093] In the subsequent process step 82, a first setpoint for the temperature of the laser diode 16 is selected based on the ambient temperature, for example 25 °C. The temperature of the laser diode 16 is then regulated to this value.

[0094] In the subsequent process step 83, Raman scattered light 34 is detected with spectral resolution using detector 70. The corresponding data are transmitted, for example, to the control unit 72.

[0095] In the subsequent process step 84, a first evaluation algorithm is selected that corresponds to the first setpoint value of the temperature of the laser diode 16. It can, for example, comprise a neural network that has been trained with suitable training data.

[0096] In the subsequent process step 85, the composition of the gas 22 is determined by the first evaluation algorithm and based on the data representing the spectrally resolved Raman scattered light 34.

[0097] At a later point in time, in process step 86, the temperature sensor 50 detects that the ambient temperature has risen to, for example, 70 °C.

[0098] In the subsequent process step 87, a second setpoint for the temperature of laser diode 16 is selected based on the increased ambient temperature, for example, 40 °C. The temperature of laser diode 16 is set to R.416718

[0099] - 15 - this value is regulated. The background is, for example, that the devices of the Raman spectroscopy device 30 are unable to cool the laser diode 16 down to a temperature of 25 °C at the high ambient temperature.

[0100] In the subsequent process step 88, Raman scattered light 34 is detected with spectral resolution using detector 70. The corresponding data are then transmitted, for example, to the control unit 72. Due to the increase in the temperature of the laser diode 16 from 25 °C to 40 °C, the properties of the light emitted by the laser diode 16 have changed. For example, the wavelength is shifted, the intensity is reduced, and the bandwidth is increased. Even if the measurements are performed on identical gases 22, this also changes the spectrum of the Raman scattered light 34. Therefore, its evaluation with the first evaluation algorithm is not feasible.

[0101] Instead, in the subsequent process step 89, a second evaluation algorithm is selected which is assigned to the second setpoint of the temperature of the laser diode 16 and which differs from the first evaluation algorithm.

[0102] In the subsequent process step 90, the composition of the gas 22 is determined by the second evaluation algorithm and based on the data representing the spectrally resolved Raman scattered light.

[0103] In the case where the measurements were carried out at different ambient temperatures on identical gases 22, the method according to the invention determines the same composition of the gas 22 in both cases, although the properties of the light emitted by the laser diode 16 and the spectrum of the Raman scattered light 34 differ between the two cases.

Claims

R.416718 - 16 - Claims 1. Method for determining at least one property of a gas (22), in particular for determining at least one gas concentration, using a Raman spectroscopy device (30), wherein the Raman spectroscopy device (30) comprises a laser diode (16) designed for focused illumination of the gas (22), wherein the Raman spectroscopy device (30) has a detector (70) for spectrally resolved detection of the Raman scattered light (34), wherein the at least one property of the gas (22) is determined by means of an evaluation algorithm based on the Raman scattered light (34) detected by the detector (70), wherein a temperature of the laser diode (16) is selectively controlled to one of at least two setpoints, characterized in that the evaluation algorithm is selected based on the respective selected setpoint.

2. Method according to claim 1, characterized in that the Raman spectroscopy device (30) has a temperature sensor (50) for measuring the ambient temperature, and that the at least two setpoints are selected depending on the ambient temperature, wherein a higher setpoint is always selected at a higher ambient temperature than at a lower ambient temperature.

3. A method according to claim 1 or 2, characterized in that the Raman spectroscopy device (30) has a housing (100) with an inner surface (100i) and an outer surface (100a), wherein the following is arranged in the housing (100): a gas measurement chamber (20) for the gas (22) and one or more optical inlets (28) to the gas measurement chamber (20) and one or more optical outlets (29) from the gas measurement chamber (20) and a collecting optical system (26) with at least one filter and at least one aperture for supplying Raman scattered light (34) from the gas measurement chamber (20) to a spectral analysis unit (38), which is also located in the housing R.416718 - 17 - (100) is arranged and includes the detector (70).

4. Method according to claim 3, characterized in that a gas supply line for supplying the gas (22) into the gas measurement room (20) is further arranged in the housing (100).

5. Method according to one of claims 3 or 4, characterized in that the temperature sensor (50) is arranged on the laser diode (16) or on the detector (70).

6. Method according to claim 3 or 4, characterized in that the temperature sensor (50) is arranged on the inside (100i) of the housing (100) or on the outside (100a) of the housing (100) or outside the housing (100).

7. Method according to one of claims 3 to 6, characterized in that the Raman spectroscopy device (30) has at least one fan for ventilating the interior of the housing (100) and that the temperature sensor (50) for measuring the ambient temperature is blown on by the at least one fan.

8. Method according to one of the preceding claims, characterized in that the difference between the first setpoint of the operating temperature of the laser diode (16) and the second setpoint of the operating temperature of the laser diode (16) is at least 5 Kelvin and in particular at most 25 Kelvin.

9. Method according to one of the preceding claims, characterized in that the evaluation algorithm for determining the property of a gas (22) comprises a neural network.

10. Method according to one of the preceding claims, characterized in that the evaluation algorithm for determining the property of a gas (22) depends on the wavelength of the light emitted by the laser diode (16) and / or the intensity of the light emitted by the laser diode (16) and / or the bandwidth of the light emitted by the R.416718 - 18 - The light emitted by the laser diode (16) is taken into account depending on the operating temperature of the laser diode (16).

11. Method according to one of the preceding claims, characterized in that the Raman spectroscopy device (30) has a control and regulation device (72), wherein a first control loop (73) and a second control loop (74) are implemented in the Raman spectroscopy device (30), wherein the first control loop (73) is configured to control the temperature of the laser diode (16) to the respective selected setpoint, and that the second control loop (74) is configured to control the temperature of the detector (70) to a setpoint of the detector temperature.

12. Method according to claim 11, wherein the setpoint of the detector temperature is always lower than the respective selected setpoint of the temperature of the laser diode (16).

13. Method according to one of the preceding claims, characterized in that the laser diode (16) and the detector (70) are thermally connected by means of at least one passive heat conduction structure (76).

14. Method according to claim 13, characterized in that the passive heat conduction structure (76) is formed from one or more rod conductors or from one or more heat conduction tubes.

15. Method according to claim 14, characterized in that the rod(s) or heat conducting tube(s) consists of a material with high thermal conductivity, for example aluminum, copper, gold or silver; diamond, boron nitride, silicon carbide, graphite or aluminum oxide.

16. Method according to claim 13, 14 or 15, characterized in that the rod(s) or heat conducting tube(s) have one or all of the following features: Quantity: 1 to 100; Length: 1 mm to 200 mm; Total cross-sectional area: 0.1 R.416718 - 19 - mm 2 up to 1000mm 2 .

17. Raman spectroscopy apparatus (30) which is configured to perform the method according to one of the preceding claims.

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