DE-102024210754-A1 - Raman spectroscopy device for measuring the concentration of a gas using Raman spectroscopy

Abstract

The invention relates to a Raman spectroscopy device (30) for measuring the concentration of a gas. The core of the invention is 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 a first setpoint, and wherein the second control loop (74) is configured to control the temperature of the detector (70) to a second setpoint.

Inventors

• Sebastian Russ
• Johannes Weber
• Alexander Stratmann
• Theodoros Garavelis
• Michael Urhahn
• Jens Schneider

Assignees

• Robert Bosch Gesellschaft mit beschränkter Haftung

Dates

Publication Date

20260513

Application Date

20241108

Claims (14)

1. Raman spectroscopy device (30) for measuring the concentration of a gas (22) comprising a gas measurement chamber (20) for the gas (22), which has one or more optical inlets (28) and one or more optical outlets, with a gas supply line for supplying the gas (22) into the gas measurement chamber (20) during the concentration measurement, wherein the Raman spectroscopy device (30) comprises a laser diode (16) configured for focused illumination of the gas (22) in the gas measurement chamber (20), wherein the Raman spectroscopy device (30) comprises a collecting optical system (36) with at least one filter and at least one aperture and a spectral analysis unit (38), and wherein the Raman spectroscopy device (30) directs Raman scattered light (34) through the collecting optical system (36) with at least one filter and at least one aperture of the spectral analysis unit. (38) supplies, wherein the spectral analysis unit (38) has a detector (70) for spectrally resolved detection of the Raman scattered light (34), 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 a first setpoint, and wherein the second control loop (74) is configured to control the temperature of the detector (70) to a second setpoint.
2. Raman spectroscopy device according to Claim 1 , characterized in that the first setpoint is between +10° and +50°, in particular between +24° and +26°, most preferably +25°.
3. Raman spectroscopy device according to Claim 1 or 2 , characterized in that the second setpoint is between -35° and +7°, in particular between -9° and -11°, most preferably -10°.
4. Raman spectroscopy device according to Claim 1 , 2 or 3 , characterized in that the first control loop (73) has at least one temperature measuring element (75) for measuring the temperature of the laser diode (16) and at least one temperature control element (71) for temperature control of the laser diode (16), that the second control loop (74) has at least one temperature measuring element (75) for measuring the temperature of the detector (70) and at least one temperature control element (71) for temperature control of the detector (70), and that the at least one temperature measuring element (75) and the at least one temperature control element (71) of the first control loop (73) are designed separately from the at least one temperature measuring element (75) and the at least one temperature control element (71) of the second control loop (74).
5. Raman spectroscopy device according to Claim 4 , characterized in that the temperature control elements (71) are designed as Peltier elements, wherein one to four Peltier elements are provided per temperature control element (71), wherein the Peltier elements have a square or rectangular shape, wherein the cross-sectional area of the individual rectangular Peltier elements is between 15mm x 15mm and 50mm x 50mm, wherein in particular the power per Peltier element is between 20W and 70W and wherein the Peltier elements are formed from a single layer or from several layers of thermoelectric material.
6. Raman spectroscopy device according to one of the preceding claims, characterized in that the laser diode (16) and the detector (70) are thermally connected to each other.
7. Raman spectroscopy device according to Claim 6 , 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).
8. Raman spectroscopy device according to Claim 7 , characterized in that the passive heat conduction structure (76) is formed from one or more rod conductors, wherein the rod conductor(s) preferably consists of a material with high thermal conductivity, for example aluminium, copper, gold or silver; diamond, boron nitride, silicon carbide, graphite or aluminium oxide.
9. Raman spectroscopy device according to Claim 8 , characterized in that the number of rod lines is 1 to 100, that the length of the rod lines is between 1 and 200 mm and that the cross-section of the rod lines is between 0.1 and 1000 mm² .
10. Raman spectroscopy device according to Claim 7 , characterized in that the passive heat conduction structure (76) is formed from one or more heat conduction tubes.
11. Raman spectroscopy device according to Claim 10 , characterized in that the heat conducting tubes consist of a metallic material, in particular of aluminium, gold, copper or silver, or of an alloy which in particular contains a proportion of aluminium, gold, copper or silver.
12. Raman spectroscopy device according to Claim 10 , characterized in that the heat conduction tubes consist of a non-metallic material, in particular tool diamond, boron nitride, silicon carbide, graphite or aluminum oxide.
13. Raman spectroscopy device according to Claim 11 or 12 , characterized in that the number of heat-conducting tubes is 1 to 100, that the length of the heat-conducting tubes is between 1 and 200 mm and that the cross-sectional area of the heat-conducting tubes is between 0.1 and 1000 mm² .
14. Raman spectroscopy device according to one of the preceding claims, characterized in that the detector (70) is configured 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 NMOS sensor or as avalanche photodiodes or as a phototube detector (70).

Description

Technical field The invention relates to a Raman spectroscopy device for concentration measurement and/or quantitative concentration evaluation of a gas or a gas mixture by means of Raman spectroscopy, with at least one gas measurement chamber for the gas or the gas mixture. State of the art From the state of the art " A. Stratmann and G. Schweiger, Fluid Phase Equilibria of Ethanol and Carbon Dioxide Mixtures with Concentration Measurements by Raman Spectroscopy, Appl. Spectrosc. 56 (6) 2002, 783-788 It is known that the particle concentration (N/V) and thus the gas density ρ can be determined locally at the Raman measurement volume V using Raman spectroscopy. A prerequisite for measurement using Raman spectroscopy is a powerful, compact light source that illuminates the gas being measured and thus excites it. For this purpose, a high-power light source, e.g., with a wavelength of 440 nm in the form of a diode laser, can be used. From the DE 10 2021 107 229 A1 , the DE 10 2009 026 744 A1 and the EP 3 748 339 A2 Measuring devices for measuring the concentration of a gas are known in which powerful diode lasers are used to excite the gas to be measured. Description of the invention The inventors recognized that stable measurements with a Raman spectroscopy device are only possible if the temperature of the laser diode used as a light source is kept as constant as possible, thus preventing wavelength drift and changes in the optical power of the emitted laser diode light. Both changing wavelengths and changing optical power would distort the measurement result, as the gas being measured would be illuminated with these altered values during the measurement, and the wavelength and optical power of the Raman scattered light would be correspondingly affected. The inventors further recognized that it is equally necessary to monitor and keep as constant as possible the temperature of the detector, which detects the Raman scattered light or the Stokes response, as otherwise the detector signal would not be fully reproducible. For example, high detector temperatures would lead to so-called detector noise and thus to a distortion of the measurement result. The proposed solution ensures stable operation of the laser diode and the detector, thereby enabling the Raman spectroscopy device to produce the most accurate measurement results possible. The invention relates to a Raman spectroscopy device for measuring the concentration of a gas, comprising a gas measurement chamber for the gas, which has one or more optical inlets and one or more optical outlets, and a gas supply line for supplying the gas to the gas measurement chamber during the concentration measurement, wherein the Raman spectroscopy device includes a laser diode configured for focused illumination of the gas in the gas measurement chamber, wherein the Raman spectroscopy device comprises a collecting optical system with at least one filter and at least one aperture and a spectral analysis unit, and wherein the Raman spectroscopy device supplies Raman scattered light through the collecting optical system with at least one filter and at least one aperture to the spectral analysis unit, wherein the spectral analysis unit comprises a detector for spectrally resolved detection of the Raman scattered light. The core of the invention is 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 a first setpoint, and wherein the second control loop is designed to regulate the temperature of the detector to a second setpoint. The first control loop integrates components for the 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 components for the temperature management of the detector, such as a temperature sensor, a setpoint generator, and at least one active temperature control element. The first control loop is specifically designed 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 specifically designed to measure the actual temperature of the The detector is configured, wherein the second control loop is further configured, in particular, for setting a setpoint temperature of the detector based on the measured actual temperature value of the detector. The control device according to the invention described above preferably includes a control amplifier that converts the difference signal from the setpoint and the actual value into a control signal that actuates the respective active temperature control element. According to the invention, the setpoint temperature of the laser diode can be bet