NOVEL SENSOR FOR RAMAN SPECTROSCOPY

Description

Field of invention

[0001] The invention relates to a system for measurement in Raman spectroscopy. Background of the invention

[0002] Raman spectroscopy is ideally suited for process control in the chemical and pharmaceutical industries, in medical technology (e.g., for measuring conditions in the human body), for environmental monitoring, in the food industry, and for researching process engineering procedures. The major disadvantage of existing spectroscopy instruments is the need for powerful lasers, which poses a cost and, above all, a safety concern. This is also the reason for the limited adoption of Raman spectroscopy systems to date.

[0003] Monitoring processes in industrial environments using Raman spectroscopy is difficult or even impossible with existing equipment, as commercially available systems are designed for laser powers on the order of several hundred milliwatts (typically 500 mW for an excitation wavelength of 785 nm). In contrast, European explosion protection regulations (ATEX), for example, only permit a maximum of 35 mW in atmospheres that are constantly, frequently, or for long periods potentially ignitable.

[0004] Optical applications in the field of Raman spectroscopy are typically based on measuring transmission because this results in a particularly high amount of light reaching the detector. Remission is generally 100 to 1000 times lower than transmission and is therefore not as common. Fluorescence is approximately 100 times weaker than remission again and is considered the "gold standard" in detection technology. Fluorescence is already at the limit of detection resolution in many molecular mixtures, making unambiguously selective measurements an extraordinary challenge for experts.

[0005] Raman spectroscopy, however, is approximately 100 times weaker than the aforementioned fluorescence, resulting in considerable practical difficulties. To increase the detection resolution and to be able to perform Raman spectroscopic measurements at all despite these difficulties, the state of the art uses very powerful lasers, which, however, have two disadvantages: Firstly, their application in the widespread "Ex area" (which includes the aforementioned areas with permanently, frequently, or long-term ignitable atmospheres) of chemical and pharmaceutical production is ultimately not feasible.

[0006] Secondly, animal and / or human tissue can be damaged by the high light exposure. Therefore, even from a safety perspective, the use of existing Raman spectroscopy systems is not justifiable.

[0007] Moreover, the initial costs for currently available Raman spectrometer systems are very high. The investment costs for a process installation are typically disproportionately high if only individual parameters are to be monitored. Many applications do not justify these costs. For these reasons, Raman analyzers are currently practically non-existent in production for process monitoring, even though inventors can demonstrate in the laboratory that reaction control is indeed possible.

[0008] The invention described here presupposes this state of the art and instead deals with an energy-saving system that can be operated with low laser power, thus enabling its use in a wide variety of environments, including sensitive ones.

[0009] The article by Christian Mohr et al., "Inexpensive Raman Spectrometer for Undergraduate and Graduate Experiments and Research," JOURNAL OF CHEMICAL EDUCATION, Vol. 87, No. 3, 1. 2010, pp. 326-330, discloses a cost-effective Raman spectrometer with an excitation light source of less than 4 mW output power, the radiation of which is focused onto a sample by a lens. The Raman backscatter from the sample is recorded by the same lens with a wide aperture. To couple the excitation light into the lens without preventing Raman backscatter, a minimal portion of a transparent disk is coated with a reflective aluminum film. General description of the invention

[0010] The invention described herein presents a system that allows the laser power to be reduced by means of a novel optic to such an extent that the existing disadvantages of Raman spectroscopy are eliminated. The invention thus enables the wider dissemination and application of Raman technology in previously inaccessible areas. The invention is defined by the subject matter of claim 1.

[0011] The aim of the present invention is, for example, to enable the monitoring of chemical processes in the broadest sense, which offers significant potential for increasing quality, yield, and / or throughput. The present invention thus moves in the same direction as, for example, the nationwide initiative for the introduction of the next generation of intelligent process monitoring (Industry 4.0), which in turn can lead to concerted actions by industry associations. Therefore, commercial application of this invention is also expected.

[0012] A systematic industry survey was conducted beforehand, resulting in a list of 70 application areas for which the present invention can be used. From this list, the following potential initial applications, with a high number of potential installations, are listed from the fields of chemistry / petrochemistry, biotechnology, food, healthcare, and medical technology. Chemistry: Quantification of individual components in binary organic solvent mixtures, in particular the quantification of residual water, e.g. in ethanol; Biotechnology: Quantification of glucose and / or lactates in bioreactors; Petrochemicals / Energy: Monitoring and control of gas purification via amine scrubbing; Healthcare and medical technology: Tissue analysis including transcutaneous measurements (Raman and fluorescence); Food industry: Quantification of end-product yield-determining parameters such as casein in raw milk.

[0013] The dangerously high laser power required by existing Raman spectroscopy systems, approximately 500 mW, is reduced by the inventive design to the range of "laser class 1," i.e., a maximum of 7 mW, or below the power level specified in the "ATEX Directive," i.e., a maximum of 35 mW. This significantly simplifies applications in the medical (technology) and food, biotechnology, and process industries. Compared to existing Raman spectroscopy systems, the measuring device based on the present invention offers a considerably lower price and easier handling for selected applications.

[0014] The technological basis could be a newly developed Raman photometer, which, through single-photon detection, is approximately ten times more sensitive than the world's best Raman spectrometers. In addition to the already achieved higher sensitivity, the inventors anticipate that the newly developed Raman photometer will be only one-tenth the size of conventional instruments. Furthermore, due to the components used, it is expected to have a tenfold longer lifespan and thus be suitable for long-term continuous operation.

[0015] The 10 to 100-fold reduction in laser power found according to the invention allows for both broad use in large-scale, food and petrochemical industries, as well as simplified handling of the device in the laboratory sector for medical technology and biological work.

[0016] It is advantageous to design each individual device for one to a maximum of four substances to be measured, thus making it more specific. However, it is not excluded that the Raman photometer according to the invention could be designed to be less selective while maintaining the same or better detection sensitivity, i.e., that more than four substances to be measured could be resolved simultaneously, for example, six or more substances or eight or more substances.

[0017] Compared to spectrometers currently on the market, the Raman photometer, with lower excitation power, achieves a detection sensitivity of photocurrents of 10 atomic amperes (0.01 femtoamperes), which is approximately 10 times more sensitive and can detect wavelengths from UV to well into the mid-infrared range (120 nm - 25 µm), which is of great importance for biological samples.

[0018] The principle of Raman spectroscopy means that virtual molecular states are excited in molecules, typically via laser light, even though the molecule does not possess a transition state at the applied quantum energy. This results in extremely short lifetimes of the excited molecules and a return to the electronic ground state, but potentially also a change in the vibrational and rotational quantum numbers. This translates to a wavelength shift of the light towards longer wavelengths (Stokes shift) or shorter wavelengths (anti-Stokes shift), and a very precisely defined wavelength offset. This is associated with extremely narrow emission Raman bands, which contribute to the unparalleled selectivity of Raman spectroscopy. This could make cancer detection possible using an optical method.Similar molecular selectivities could, with a simplified application of Raman spectroscopy compared to the state of the art, also help to create improved diagnostic possibilities in many other medical and chemical / pharmaceutical application areas.

[0019] Explosion-hazardous areas comprise approximately 70% of process and technical environments in the chemical, pharmaceutical, and petrochemical industries, as well as all related "satellite industries," such as the paint industry, formulation plants, mixing plants, bioprocesses (e.g., digesters and biogas plants), wastewater control, and many others. Restrictions in explosion-hazardous areas are differentiated according to the frequency of the hazard. Zone 0 is generally located inside the reactor. Zone 1 is located in the immediate vicinity of the reactor (production hall), and Zone 2 is located in adjacent rooms that do not themselves pose an explosion hazard. According to this zone classification, which can also be supplemented with regard to dust explosion hazard zones, the safety regulations for the corresponding equipment must be observed. A key safety regulation in this context is the limited light output per unit area for all optical devices.This results in the current lack of Raman systems on the market for use in potentially explosive atmospheres, or only those approved with extremely high costs. Raman spectroscopy, with its current detection strategies, requires very high light power. Lasers with several hundred milliwatts of optical power (typically 500 mW) are used. This makes this spectroscopic technique and direct process monitoring in hazardous areas mutually exclusive.

[0020] Against this background, the present invention aims to provide a system and a sensor setup with which it is possible to carry out spectroscopic measurements using Raman spectroscopy, particularly in specially protected areas.

[0021] The invention is able to overcome the disadvantages mentioned in the description in relation to known systems for Raman spectroscopy.

[0022] Raman spectroscopy is a non-destructive measurement technique, but in biomedical applications, it is only suitable for sufficiently low laser energies. It delivers measurement results in real time, requires no reagents or labels such as synthetic fluorophores, and, unlike near- or mid-infrared spectroscopy, exhibits virtually no interfering water bands. It can be used to detect the fundamental vibration of molecules using fiber-optic probes. This enables in-line reaction monitoring of, for example, chemical or biological processes. In contrast to optical measurement methods in the infrared or visible range, Raman spectroscopy does not measure the absorption of the radiation used upon sample contact, but rather the radiation scattered by the molecules. To achieve this, a laser is typically used as the light source. The monochromatic light from the light source is inelastically scattered or re-emitted by the molecules. This is known as the Raman effect.

[0023] Three types of scattering are generally distinguished: Rayleigh, Stokes, and anti-Stokes scattering. Rayleigh scattering is elastic, while Stokes scattering is inelastic. The frequency of the elastic scattered radiation corresponds to the frequency of the light source. An extremely narrowband filter (notch filter), placed between the scattering sample and the detector, removes the Rayleigh scattered radiation along with the excitation from the spectrum. In contrast to Rayleigh scattering, Stokes and anti-Stokes scattering occur to a significantly lesser extent. Therefore, a high-quality notch filter is advantageous. Stokes scattering has lower energy, and anti-Stokes scattering has higher energy, than the excitation radiation. Stokes scattering is preferentially detected and analyzed because it has a higher intensity than anti-Stokes scattering.

[0024] The energy shift to a higher or lower wavenumber is called a Raman shift. The Raman shift contains information about the molecules being detected. The unit of the Raman shift is cm⁻¹. For these scatterings to occur, the molecule must change its polarizability during vibration. Therefore, polarizable compounds are particularly suitable for investigation using Raman spectroscopy. The polarizability of a molecule indicates the degree to which its electron cloud can be "deformed." The excitation wavelength has a significant influence on the obtained spectra. The shorter the wavelength, i.e., the higher the wavenumber, the more Raman signal can be detected. This results in higher signal bands. However, a short excitation wavelength can sometimes promote the occurrence of fluorescence and potentially mask the Raman signal.

[0025] The extremely low photon yield of Raman spectroscopy systems and sensor setups presents a major challenge. Traditionally, this has been addressed by requiring high laser power, resulting in extremely high instrument costs exceeding 100 TEU. Additional costs include the probe, ex-housing, installation, system modification planning, cable routing, and other related expenses. Consequently, the use of Raman spectrometers is limited to research institutions, hospitals, or expensive applications in the chemical and pharmaceutical industries. Furthermore, the high laser power of currently available instruments severely restricts their applicability in medicine, biotechnology, and medical technology.

[0026] According to the invention, the ubiquitous advantages of Raman spectroscopy were retained, and a widely applicable, inexpensive, and compact device was developed. This was achieved in particular by means of the concept of a Raman photometer, optionally with the extension to include the ability to measure multiple wavelengths.

[0027] A further advantage in intensity arises from the achievable geometry. In conventional spectrometers, the detection area for a wavelength is defined by splitting all detected wavelengths using a grating spectrometer. The spectrometer's input slit is ultimately mapped onto pixels ranging in size from 25 µm to a maximum of 2000 µm. This area thus constitutes the detection area.

[0028] The photometer omits the dispersive element of the spectrometer. Instead, it functions as an interferometer. The interferometer consists of a large-area filter that is transparent only to the desired wavelength. The size of the light-sensitive area of ​​the avalanche diode is 1 mm², which increases the detection area by a factor of 20 compared to the spectrometer. This light gain is intended to be distributed between the reduced laser power and the increased detection sensitivity of molecules. The additional increase in area-specific detection sensitivity through single-photon detection results in a further factor of 5 compared to the world's best CCD sensors. Theoretically, a factor of 100 is calculated as the limit for optimizing the overall sensitivity. Therefore, an improvement in sensitivity of at least a factor of 10 can already be seen based on the outlined technical possibilities and is well within the scope of the invention.

[0029] For a substance to be detected, a sharp Raman detection band can be obtained for the direct detection of the analyte, as well as a broader fluorescence band, which typically occurs simultaneously with the Raman peak and can be detected by a broadband detector. This allows for a clear correlation of the measurement signal with the analyte concentration over a maximum of three wavelengths. Only one of these wavelengths needs to be detected by an avalanche diode.

[0030] The measuring points used for evaluating the fluorescence can advantageously be implemented with a broadband bandwidth. Since this allows more light to reach the detection side, inexpensive, highly sensitive PIN diodes can also be used as detectors. A possible schematic diagram for the simultaneous measurement of Raman and fluorescence signals is shown in Fig. 8 given.

[0031] The fluorescence light, which typically arrives almost simultaneously, can significantly overpower the actual Raman intensity by up to a factor of 100. Therefore, when performing a reference measurement and subsequent mathematical analysis of the two signals, for example by calculating the difference, it is essential to ensure that both signals are measured under identical boundary conditions. For this purpose, simultaneous measurement, i.e., a coincident measurement, is particularly advantageous.

[0032] This simultaneity of measurement can be achieved in a "photometer variant," for example, using the following measuring setup: The light beam coming from a probe, parallelized via suitable optics, is confocally focused. The rays near the axis are directed relatively perpendicularly onto the bandpass interference filter, which is only or only substantially transparent to Raman light. After the bandpass interference filter, the measurement signal, corresponding to the Raman wavelengths, is "blocked" by a suitable optical arrangement and directed to one or more Raman detectors (avalanche photodiodes). In this example, the aforementioned blocking can be achieved via fiber optics or by a small deflection mirror, e.g., 1 mm, inserted into the beam path. This allows for better spatial separation of the fluorescence and Raman detectors, thus preventing steric interference within the measuring instrument.The off-axis rays pass by the bandpass filter and the output coupling optics and strike a detector for fluorescence detection in a highly focused beam at an oblique angle.

[0033] The simultaneous measurement of the Raman and fluorescence signals achieved in this way enables the measurement of slightly inhomogeneous or temporally inconsistent objects. For example, consider chemical reactions with slight but always present concentration differences, which appear as schlieren in a stirred reactor or a pumped line. The schlieren may exhibit only a small concentration difference, e.g., 1%, which is directly reflected in the difference between the two signals. If, for example, the Raman signal is 1% of the fluorescence signal and the total intensity fluctuates by 1%, a 100% measurement error of the Raman signal will occur if the reference and the signal plus reference are recorded at different times.

[0034] High detection sensitivities can be achieved, for example, with APDs, MPPCs, or CPMs. The use of the Raman photometry principle in combination with the inventive sensor geometries leads to increased detection sensitivities and a measuring device that is significantly superior to known measuring devices on the market. The combination with the probe head according to the invention provides, for the first time, a simple, small, and relatively inexpensive Raman photometer available for widespread application. Brief description of the characters They show:

[0035] Fig. 1 A first embodiment of the sensor system with probe head, Fig. 2 A further embodiment with improved details of the sensor system, Fig. 3a Details of a first optical interface, Fig. 3b Details of a second optical interface, Fig. 3c Details of a 9-fiber probe, Fig. 4 Design features for the optical interface, Fig. 5 A further embodiment of the sensor system, Fig. 6 An example of a 7-fiber probe for use in the sensor system, Fig. 7 Raytrace model of a wide-aperture probe, Fig. 8 Example of the improved setup for simultaneous measurement of Raman and fluorescence light, Fig. 9 A further embodiment of the sensor system, Fig. 10 A photographic representation of a pre-production version of an embodiment of the sensor system according to Fig. 9 . Detailed description of the invention

[0036] Referring to Fig. 1A sensor system 30 according to the invention is shown. The sensor system 30 comprises a monochromatic light source 2, in this example a comparatively weak laser, with a power of about 1 mW. In other cases of the sensor system 30 according to the invention, however, light sources 2 with a power of up to 7 mW or up to 30 mW can also be included. Preferably, the light source 2 of the sensor system 30 has a significantly lower power than the currently conventional light sources, which typically have a power of at least 300 mW, i.e., that the light source 2 has a power of less than 300 mW.

[0037] The one with reference to Fig. 1 The setup 30 shown comprises an optical arrangement 4, 5, 6, 6a, which allows the incident Raman light 3 to interact with the sample 7 to be examined.

[0038] In Fig. 2It has been shown that the sensor system 30 can comprise a detector system 14, 15a, 15b, 16 which advantageously has the highest possible detection sensitivity and, depending on the application, can in particular consist of a plurality of detectors.

[0039] The essential optical components and functions of the apparatus 30 are described below. Particular attention is paid to a special probe head, which makes the present inventive apparatus 30 particularly convenient and easy to operate, and which is illustrated in one embodiment in Fig. 1 .

[0040] The laser light 3 is in Fig. 1The laser light 3 is guided laterally into the probe head via a laser 2, for example, directly coupled in a free beam. Coupling can also be achieved via an optical waveguide 32 (multimode or single-mode fiber), provided this does not entail any other disadvantages. The laser light 3 thus penetrates as a beam, in one embodiment as a beam 3 that is as thin as possible, onto a mirror arrangement 4. The mirror arrangement 4 comprises, for example, an optical interface in the form of a flat disk, i.e., an optically flat medium such as a glass disk, in particular made of borosilicate, quartz, or sapphire, or of another optically transparent material that has a higher refractive index than air.

[0041] The surface of this mirror arrangement 4 is, in the example shown, the Fig. 1only partially provided with a reflective layer. In other words, the mirror arrangement 4 is a partially transparent flat panel. The partial transparency of the mirror arrangement 4 preferably refers to a partial area of ​​the surface, such that, for example, a first partial area 5 of the surface of the mirror arrangement 4 is slightly transparent and a second partial area 51 of the surface of the mirror arrangement is fully transparent.

[0042] Partial transparency can be achieved, for example, by partially or regionally removing the reflective layer from a reflective flat disk through etching or other processes, while the reflective layer remains in other locations. In this embodiment, a reflective area—i.e., a partially transparent area—remains approximately centrally (or at another location within the mirror) at position 5. Here, the laser light is reflected, for example, as shown in Fig. 1The light is directed at 90° or another advantageous angle and is thus guided through a lens system into the process chamber 9. Advantageously, in the invention, the light is not further focused; it remains unfocused. Therefore, the lenses 6 and 6a can be pierced in the middle or at another advantageous position, or their refractive properties can be removed by another suitable method, so that this light beam passes through unhindered.

[0043] In other words, lenses 6 and 6a each have a borehole 61, 62 in which lenses 6 and 6a have no refractive properties. A flat disk made of sapphire or diamond, or another suitable material, can preferably be inserted into the borehole. This disk, with its specific Raman signal, ensures continuous monitoring of the laser power (which is directly proportional to the Raman signal) and serves as an internal standard / reference.

[0044] The excitation light 3 entering process chamber 9 encounters a product introduced into process chamber 9, resulting in scattering effects of fluids, particles, and / or gases, depending on the product used. These scattering effects include, in particular, Raman scattering 10 and fluorescence emission. Both Raman scattering radiation 10 and fluorescence emission typically propagate isotropically into all solid angles. Raman scattering produces the light 10. The scattering location 7 is shown in the example of... Fig. 1The light is collected via the lens arrangement 6a and 6, i.e., an arrangement of two lenses, where the arrangement can consist of, for example, one to six lenses, and detected further along the beam path with a large solid angle, also known as aperture. The large solid angle made possible by the setup 30 allows for a significant increase in light yield. This increase in light yield, in turn, results in the advantage of high detection sensitivities, which contribute to the possibility of reducing the laser power.

[0045] Light 10 can then be in the Fig. 1In the embodiment shown, the Raman light 10 passes through the mirror system 4 as approximately parallel light (or in another geometrically favorable arrangement). In other words, the Raman light 10 penetrates the low-reflectivity regions 5a of the optical interface 4 from the first side 41 to the second side 42. The low-reflectivity or transmissive regions 51 of the optical interface 4 are preferably fully or almost fully transparent, so that only a small or no fraction of the Raman light 10 is deflected in another direction, but rather the full or almost full fraction of the Raman light 10 reaches the detection point 13.

[0046] In the further beam path, the Raman light 10 is directed from the optical interface 4 onto a converging lens 12 and to the detection point 13. In the Fig. 1Not shown, filter systems can be integrated at suitable locations in the optical beam path to appropriately suppress the proportion of direct scattering and other sources of elastic radiation; see, for example, [reference to relevant source]. Figs. 9 and 10 .

[0047] At the in Fig. 1 At the location designated as position 13, i.e., the detection point 13, a fiber optic or plastic fiber arrangement 33 or another optically conductive arrangement – ​​possibly also in a free beam – can be arranged and guide the Raman light 10 to a detector 14. It is, of course, also possible to arrange the detector 14 directly at position 13 in another embodiment.

[0048] With the in Fig. 1In the illustrated arrangement 30, the product 9 can be detected with high sensitivity by means of optically transparent surfaces 8, for example, discs 8, particularly those made of glass. The extremely simple design, especially with the individually adjustable mirror 4, can be implemented in a particularly cost-effective manner. Cost reduction is achieved, firstly, through the use of simple and few optical components, and secondly, through a cost-efficient detection solution. Cost reductions in the detection area result, in particular, from the fact that the setup 30 is designed such that a low detection sensitivity of the detector 14 is sufficient, while still achieving a comparable detection resolution, thus enabling the detector 14 to be manufactured more cheaply.

[0049] In one embodiment, which is related to the in Fig. 1Since the setup shown in 30 is feasible, the depth of field at the event location 7 can be reduced to obtain local resolution in the beam direction. This can be advantageous, for example, for observing processes or mixing in fluid layers.

[0050] One advantage of the with Fig. 1The advantage of the mirror arrangement shown, compared to, for example, semi-transparent mirrors, is that with semi-transparent mirrors, half of the light is deflected in the wrong direction – both on the outward and return paths – and is therefore lost for detection. Compared to dichroic mirrors, the simplicity of the design and the applicability to any wavelength are compelling, whereas with dichroic mirrors, the wavelength limit is fixed. This makes this element suitable for all common wavelengths / wavelength ranges of fluorescence excitation in the fields of fluorescence spectroscopy / fluorescence photometry as well as Raman spectroscopy / Raman photometry.

[0051] The high efficiency of the setup 30 is further enhanced by the fact that the light from a large solid angle, i.e., from a large aperture angle, is captured by the lens arrangement 6 and 6a – and possibly by additional lenses. The scattered light, on the other hand, which is emitted parallel to or near the optical axis of incidence, is blocked by the mirror 5. This allows for a particularly shallow depth of field. A different arrangement of the mirrors 4 and the position 5 can also be advantageous; it can even be beneficial to allow only defined angular ranges to pass through the mirror if these angular ranges or scattering angles, calculated, for example, in particle measurement technology, allow for a statement about the size of the particles or similar properties, e.g., via Mie theory. In such an arrangement, for example, further or different sub-areas 51 would be provided in the optical interface 4, which would be partially or fully transparent.

[0052] This order 30 according to Fig. 1 can be supplemented and has a particularly beneficial effect through additive elements, such as those in particular those in Fig. 1 Elastic scattering 32 is introduced at the point of incidence 2; thus, slightly offset from the incident laser, the light scattered by the processor 7 and directed to position 2 or 3 via mirrors 5 can be measured separately. This provides a reference signal from the Raman scattering setup 30, whereby absolute fluctuations of the laser 2, which could potentially be reflected proportionally or otherwise in the result, can be controlled by means of the reference signal, and any fluctuations that may occur can be factored out of the effect. In other words, the light incident on the highly reflective area 5 of the optical interface 4 – i.e., in particular scattered light – reaches a scattered light detector 32 and is evaluated as a reference signal to improve the signal quality.

[0053] Similar effects, and others as well, result in an embodiment according to Fig. 2 , if in addition to the in Fig. 2 In the disk 8 shown on the right, a second disk 8 is arranged on a side facing away from the sample, and the light converging at focus 9a then exits the apparatus. In such a setup 30, it can be performed according to Fig. 2 A collecting mirror 14a is attached, which reflects the light back into the focal point 9a and directs it towards the detector system. In other words, by means of an additional reflector 14a, a portion of the Raman light 10 can be directed back to the process chamber 9 and to the focal point 9a, so that this portion of the Raman light 10 also reaches the detector 14 (see Fig. 1 ) can be conducted. This roughly doubles the signal-to-noise ratio and thus the detection sensitivity.

[0054] The in Fig. 2The arrangement 15a shown measures the transmitted light again with a simple detector 14b. Furthermore, an arrangement 15b is integrated, which functions as a beam catcher / light trap 15b. In other words, the (nearly) axis-parallel light is captured in this embodiment and not reflected back to the focal point 9.

[0055] In a particularly advantageous way, the in Figs. 1 and 2In the system 30 shown, the incident laser beam 2 is not focused. Therefore, a setup 30 can be implemented in explosion-proof areas and in medical technology (e.g., transcutaneous fluorescence spectrometry / fluorescence photometry as well as Raman spectrometry / Raman photometry) to perform measurements. The arrangement is particularly advantageous in that it can even use weak lasers such as those in laser class 1, i.e., lasers used in common laser pointers. Thus, approval for these lasers and the securing of the irradiated area to protect the human eye are no longer necessary.

[0056] The special arrangement of the separate illumination 2 and detection position 13 prevents the fluorescence caused by the glasses from entering the measuring channel. This is further improved because the glasses 8 only fluoresce at the point where the light beam 2 and the Raman light 10 pass through, but where no detection takes place. In other words, the Raman signal 10 to be measured is partially or completely separated from an interfering signal, such as a fluorescence signal, by means of the glasses 8. This allows a reduction in beam power because interfering signals are eliminated or reduced. At position 16 in the embodiment in Fig. 2A secondary detector 16 is arranged for detecting interfering influences that cause contamination (turbidity) of the medium being measured. Extremely high collection efficiency can be achieved by arranging a special type of cascaded Fresnel lens or another optical arrangement with a similar effect. The flat design of the Fresnel lens allows two or more to be connected in series, thus further increasing the aperture. It is quite possible to obtain 30 apertures better than f / 0.8 with this special setup, which is not achievable with conventional, even good, lenses.

[0057] For the detection of the Raman signal 10, grating spectrometers, spectrophotometers, Fabry-Perot interferometers, or photometers can be used, for example. An arrangement using AOTF selectors, i.e., acousto-optic modulators or micro-opto-electro-mechanical systems (MEMS), proves particularly advantageous, as these can transmute the set wavelength over a large area. This offers advantages, for example, for applications where the measurement location 9 consists not of a fluid but of a scattering object. The incident laser 2, LED, or filtered broadband light source is scattered into the immediate vicinity of the focus 9a or the scattering object and generates Raman light 10 at location 9, i.e., in the process space 9 or at the focus 9a. It may also generate fluorescent light, which is likewise directed in the detection direction by the surroundings of the scattering medium.This makes the measurement spot 9a to be detected – i.e., the focus 9a – larger than the point 3 illuminated by the laser 2. A large-area detection arrangement has particular advantages here over a spatially resolved grating spectral apparatus, since, according to the Helmholtz-Lagrange relationship, the object size and the image size are linked via a maximum aperture angle. This results in only a small area of ​​the object being imaged onto a narrow entrance point or entrance slit of a spectrometer.

[0058] However, when using an area-based detection system 14, this can be improved, for example, as follows. In a preferred arrangement, the detector 14 is a combination of an AOTF detector with a large-area customized channel photomultiplier (CPM). Instead of the CPM, for example, an avalanche photodiode (APD), a multi-pixel photon counter (MPPC), image intensifiers, CCD and / or CMOS detectors, as well as "normal" photodiodes, can also be used. With all the aforementioned embodiments of a detector 14, a significant increase in detection sensitivity can be achieved with a suitable combination, which is reflected in the reduction of the excitation power required, e.g., in the form of a laser, and / or a lower detection limit of the analyte under investigation.

[0059] In the example of the Fig. 1In other words, monochromatic light 3 from a laser 2, which can be operated, for example, in pulsed or continuous mode, is coupled into a fiber or directly into a probe head 34. The Raman light 10 reflected or remitted by the object reaches the detection unit 14 either via an optical fiber 33 or a corresponding free-space optic. The corresponding measurement method is described in Fig. 5 sketched. Fig. 5 This shows an example of a Raman photometer measurement.

[0060] Fig. 3 shows details of various optical interfaces 4. In Fig. 3a An optical interface 4 is shown, which has a reflective area 5 in the interior and a transmissive area 51 concentrically around the reflective area. Fig. 3bshows an optical interface 4 which also has a reflective region 5 in the interior and a transmissive region 51 concentrically around the reflective region; The interior region 5 of the embodiment of Fig. 3b However, it is smaller, and the transmissive area 51 is ring-shaped. A further reflective area 52 surrounds the transmissive area 51. The embodiment of the Fig. 3b This is advantageous in that it can correct for laser intensity fluctuations in elastically scattered light. In inelastically scattered light, it enables the detection of deposit formation and / or its use as an internal reference.

[0061] Fig. 3cFigure 1 shows a top view of an example of a fiber optic bundle 43 in the form of a 9-fiber probe 43 with 8 image lines 43d and 1 laser light line 43a in the center. An excitation light fiber 43a carries the light from the light source 2 to the object 9, and eight Raman light fibers 43b carry the Raman light 10 to the detector. Further description of a multi-fiber probe 43, in which the fiber 43a for transporting the laser light 2 differs from the fibers 43b for transporting the Raman signal 10, is based on the description of the 7-fiber probe 43 with reference to [reference to relevant section]. Fig. 6 to be taken.

[0062] Fig. 4Figure 1 shows a selection of eight different embodiments 4a to 4h for the design of the optical interface 4. These embodiments relate to examples of geometries for the deflecting mirror coating 5 and for the arrangement of the reflective 5 and non-reflective areas 51 of the optical interface 4. Each embodiment 4a to 4h enables specific selective suppression of solid angle components of the inelastically scattered light 10, thus potentially increasing measurement effects or suppressing interference. The embodiment 4a of the optical interface 4 corresponds to the one described in Figure 1. Fig. 1The discussed arrangement consists of a reflective core region 5 located in the central region of the optical interface 4a, and a transmissive region 51 arranged around the core region 5. Interface 4b shows a square core region 5 around which the transmissive region 51 is arranged. Interface 4c shows a rectangular core region 5 around which the transmissive region 51 is arranged. Finally, interface 4d shows a core region 5 comprising three adjacent circular regions surrounded by the transmissive region 51.

[0063] The interface 4e is equipped with a round reflective region 5, resembling a "spot," and has a similarly round transmissive region 51 concentrically surrounding the reflective region 5. The outer region 52 is also reflective. Interface 4e thus allows only a comparatively small fraction of the solid angle to pass through. Interface 4f has an enlarged round reflective region 5.

[0064] Interface 4g is structured in reverse to interface 4e, such that a transmissive region 53 is arranged in the center, a reflective region 5 is concentrically located thereto, and another transmissive region 51 is arranged on the outside. Interface 4g is advantageous in that radiation close to the optical axis is transmitted through the optical interface 4. Depending on the arrangement, interface 4g can, for example, be used in a detector 14 that is positioned opposite the radiation source. Finally, interface 4h has a reflective region 5 that is not arranged centrally, but rather offset to the side. This allows, for example, the offset installation of the radiation source 2.

[0065] Referring to Fig. 5Figure 1 shows a schematic setup of a device 30 with a probe head 34. The excitation light 3 is coupled into the probe head 34 by a fiber 35 from the laser 2, which has a converging lens. The laser light 3 strikes a beam splitter 1, after which a portion of the excitation light 3 couples into fibers 40, 49 to excite the sample 9. In this embodiment, the single fiber 40, acting as the coupling fiber 49, transmits both the excitation light 3 and – with a time delay – the Raman light 10, which is emitted by the sample 9 after excitation by the excitation light 3. The Raman light 10 is directed onto the beam splitter 1, whereby a portion of the Raman light 10 again passes through the beam splitter 1 and is directed onto an output coupling fiber 55. The output coupling fiber 55 carries the Raman light 10 to the detector 14 (see Figure 1). Fig. 1 ).

[0066] Instead of the in Fig. 5The single fiber 40 used, which is employed for both excitation and detection in combination with a beam splitter 1 (semi-transparent mirror 1), can also be, for example, equipped with Fig. 6 The 7-fiber probe 43 shown is used. The setup 30, which is in Fig. 6 As partially shown, it is particularly suitable for highly scattering media 9. The optical paths for excitation and detection only partially overlap here. It is clear to those skilled in the art that the improvements shown, e.g., with single fiber 40 or 7-fiber probe 43, can also be used in combination with the optical interface 4, and in particular, embodiments 4a to 4h of the optical interface can be usefully combined with the 7-fiber probe 43 to obtain an optimal signal-to-noise ratio of the Raman light 10.

[0067] Referring to Fig. 6The 7-fiber probe 43 is shown with structural details of how it can be implemented in one embodiment. An excitation light fiber 43a carries the light from the light source 2 to the object 9, and six Raman light fibers 43b carry the Raman light 10 to the detector. A nitinol cannula 45 has a first 45a and a second adhesive joint 45b. Optionally, a third adhesive joint 45c is also present for extending the nitinol cannula 45. A distributor 46 is arranged at the second adhesive joint 45b, which divides the 7 individual fibers of the 7-fiber probe 43 into the excitation 47 and detection 48 branches. In this embodiment, the ends of the excitation and detection branches 47 and 48 are provided with SMA couplings.

[0068] Another promising embodiment is described with Fig. 7This was demonstrated with the integration of a wide-aperture probe. This enables a significant increase in the Raman signal yield by increasing the solid angle for capturing the light. Fresnel lenses 6b are used for this purpose, which exhibit a high numerical aperture at a comparatively short focal length. Unlike spherical, plano-convex lenses with high numerical aperture, the Fresnel lenses also allow for shorter focal lengths, thus reducing the probe's overall length to a practical level. Fig. 7 The corresponding beam path illustrates a comparison of the optical setup 30 with plano-convex lenses with a setup 30 with a Fresnel lens in front.

[0069] Fig. 7This is illustrated by an optical ray tracing simulation, demonstrating how significantly more light can be captured and directed to the detection side when a Fresnel lens is used upstream. The simulation results in an approximately threefold increase in collection efficiency. The detection unit shown contains a notch filter with high attenuation in a narrow wavelength range, which is positioned upstream of the detector and blocks the excitation wavelength. This is followed by another filter (bandpass interference filter) that transmits the wavelength to be detected, which was precisely defined in preliminary tests.

[0070] The required bandpass filters in the necessary performance class (narrow bandwidth with high transmittance in the measurement range and extremely low transmittance in the stopband) are not currently available on the market for every wavelength. To nevertheless be able to detect at the measurement wavelength required for Raman measurements and thus remain flexible with regard to the material systems, especially during the experimental phase, the fact that the transmitted wavelength range depends on the angle of incidence of the light on the interference filter is exploited.

[0071] Regarding the detectors 14 to be used, it has been noted within the scope of the invention that photomultipliers, for example, exhibit lower dark noise compared to avalanche diodes. In contrast, avalanche diodes offer the advantage of high detection sensitivity in the red and near-infrared spectral range up to 1500 nm using indium gallium arsenide (InGaAs) avalanche diodes.

[0072] The high dark pulse rate, which is responsible for dark noise, can be compensated for or reduced by using pulsed light sources. In typical, moderately cooled systems built at reasonable costs, the dark pulse rate is on the order of 300 counts per second. If the laser is pulsed, for example, for 1 ms and then switched off for a further 99 ms, and data acquisition takes place only during this "bright" millisecond, the detector's dark noise is reduced by a factor of 100 to approximately 3 counts per second. The detection limit is also reduced. The maximum count rate (upper limit of the measurement range) will be around 10 million pulses per second. A further intensity advantage results from the achievable geometry. The detection area of ​​a wavelength in conventional spectrometers is defined by splitting all detected wavelengths using a grating spectrometer.The spectrometer's input slit is ultimately mapped onto pixels ranging in size from approximately 25 µm to a maximum of 2000 µm; for example, the pixels have a size of 25 µm by 2000 µm. This area is therefore the detection area.

[0073] Unlike a spectrometer with a dispersive element, this photometer functions as an interferometer. The interferometer consists of a large-area filter that is selectively transparent to the desired wavelength. The size of the light-sensitive area of ​​the avalanche diode, for example, is (1 x 1) mm². The detection area can therefore be increased 20-fold compared to a spectrometer. It has proven advantageous to combine the light gain between a reduction in laser power on the one hand and an increased detection sensitivity for molecules on the other. Due to the increased area-specific detection sensitivity through single-photon detection, this improves by approximately a factor of 5 compared to CCD sensors.

[0074] Within the scope of the invention, it has been shown that in many cases, a sharp Raman detection band for the direct detection of the analyte, as well as a broader fluorescence band, can be obtained for a substance to be detected. The fluorescence band typically occurs simultaneously with the Raman peak and can be detected, for example, using a broadband detector. This allows, for example, a clear correlation of the measurement signal with the analyte concentration being sought over up to three wavelengths. It has been shown that it may be sufficient if only one of the wavelengths is detected by an avalanche diode. The measuring points or detectors used for evaluating the fluorescence can be broadband. Since this allows more light to reach the detection side, inexpensive, highly sensitive PIN diodes can also be used as detectors. A possible schematic diagram for the simultaneous measurement of the Raman and fluorescence signals is shown in Fig. 8Given. A detector 14 measures the Raman light 10, which is directed through the optical interface 4 onto the detector 14; A secondary detector 16 measures the fluorescence signal 11, which is directed past the optical interface 4 by the lens 6 or, depending on the embodiment of the optical interface 4, hits transmissive areas 51 of the optical interface and passes through the optical interface 4.

[0075] Process analysis technology plays a crucial role in the chemical industry, both during the process for monitoring critical process steps and for subsequent quality control. Optical measurement methods occupy a special place, as they typically offer the possibility of monitoring process parameters online or inline. For complex processes, measurement methods in the NIR and MIR spectral ranges have proven particularly effective. Especially in the mid-infrared spectral range, conclusions can be drawn about the state of the process and the composition of the reactants. Since optical fibers absorb mid-infrared radiation, spectrometers must be positioned close to the process. To circumvent this, NIR spectroscopy is often preferred. While the information content in the near-infrared spectral range is lower, the use of optical fibers is possible here as well.

[0076] Raman spectroscopy combines the advantages of MIR and NIR spectroscopy.

[0077] In fiber-coupled systems, an optical waveguide is connected to the entrance slit. To increase efficiency and light throughput, a cross-sectional converter or an aperture can be used at the entrance slit. Radiation emerges from this, for example, in a cone shape. The opening of the cone is described by the numerical aperture, the exit angle.

[0078] Since beam paths are reversible, the maximum angle of incidence also corresponds to the maximum angle of exit of the electromagnetic waves from an optical waveguide. The radiation strikes a first concave mirror—which can be replaced by an optical lens—and is reflected and collimated. The collimated light rays then strike a grating, which diffracts the light rays at different angles depending on their wavelength. The light rays diffracted at different wavelengths then strike a second mirror. This focuses the electromagnetic waves onto a detector in a spectrometer or onto an exit slit in a monochromator. By rotating the grating, it is possible to image the desired spectral range onto the detector.

[0079] A blaze grating is most commonly used as an optical grating. Its surface consists of step-like grooves. Rays are diffracted differently at these grooves depending on their wavelength. Elementary waves appear in adjacent steps, exhibiting a path difference that is an integer multiple of the wavelength, resulting in positive interference. Theta_e describes the angle of incidence relative to the normal on the substrate, and Theta the angle of reflection. Alpha indicates the difference between the normal on the substrate and the normal on the grooves, and G or B the width of the grooves. The structure of the blaze grating ensures that the majority of the radiation is refracted at the first order. Zeroth order diffraction represents direct reflection without any spectral splitting of the radiation and is therefore unusable. From first-order reflection onward, the radiation is spectrally split.

[0080] In an exemplary setup 30, the Raman signal is excited with a laser at 785 nm. A silicon charge-coupled device (Si-CCD) array serves as the detector in the reference spectrometer. A CCD array is a semiconductor, usually made of silicon. Silicon CCD arrays have their maximum sensitivity at approximately 600 nm and can be used up to approximately 1100 nm. The array consists of several consecutive pixels. Each pixel has a junction between an n- and a p-doped semiconductor. When photons are introduced into a pixel, electrons are excited from the valence band to the conduction band. This causes an electric current to flow between the n- and p-doped semiconductors. The current is proportional to the intensity of the incident electromagnetic radiation. Since a CCD detector consists of many pixels, several wavelengths can be detected simultaneously.

[0081] Spectrophotometers can be used because they combine the advantages of a spectrometer (recording a complete spectrum) with those of a photometer (higher detection sensitivity). Spectrophotometers almost exclusively use prisms to split the electromagnetic radiation; these act as monochromators with an aperture. In industrial applications, one or more optical filters can replace the prism. Replacing the prism has the advantage that no moving parts are required in the construction of the photometer. This significantly increases the robustness of the instruments, as they are no longer susceptible to vibrations. Another advantage is the ability to design a much smaller photometer.

[0082] The setup of a photometer with optical filters consists, for example, of a light source, two lenses for parallelizing and subsequently focusing them onto a detector, and the optical filter itself. Unlike a UV / VIS photometer, a Raman photometer does not use a broadband light source, but rather a monochromatic light source, such as a laser. Furthermore, it measures Raman scattering, not absorption. For this reason, it is advantageous to place the bandpass filter between the sample and the detector in a Raman photometer—unlike in a UV / VIS photometer, where it is located in front of the sample.

[0083] To measure Raman signals, a highly sensitive detector is required. This can be achieved with an avalanche diode. An avalanche diode consists of several semiconductor layers across which a voltage, the so-called accelerating voltage, is applied. The incoming photon passes through the first p-doped semiconductor layer to the intrinsic layer, where it creates an electron-hole pair. The applied accelerating voltage separates the pair, accelerating it towards the anode and cathode, respectively. If the applied voltage is sufficiently high, the electrons can generate further electron-hole pairs through collisions in the subsequent p-doped semiconductor layer. This results in the so-called avalanche breakdown. The avalanche triggered by this breakdown is proportional to the number of photons striking the detector and can be detected by an external counting unit. Avalanche diodes are very robust in their design and relatively stable against external influences.Another application of avalanche diodes is in multi-pixel photon counters (MPPCs). These offer the additional advantage of significantly increasing the active area compared to single avalanche diodes. Furthermore, avalanche diodes, along with photomultipliers, are among the most light-sensitive detectors and are suitable for single-photon detection. The use of photomultipliers or PIN photodiodes is also possible.

[0084] The following describes a simple setup of a Raman photometer 30 usable with the invention, as it can be constructed with Fig. 9 shown.

[0085] For the optical design of the Raman photometer 30, a modular system was developed as the preferred further training in order to ensure the greatest possible flexibility in the event of changing requirements.

[0086] The measurement signal input can be implemented, for example, via an SMA connector on the photometer, and the light beam can be collimated using a plano-convex lens. The light then passes through the tunable bandpass filter, which filters out the desired wavelengths. The advantage of this filter, compared to conventional bandpass filters, lies in its ability to be angled up to 60 degrees relative to the optical axis without incurring any significant transmission loss. The bandpass filters used here are tunable between approximately 760 nm and 900 nm, corresponding to a Raman shift of 0 to approximately 1630 1 / cm. After the bandpass filters, the measurement signal passes through a beam splitter. This splits the radiation between 700 and 1100 nm in a 50:50 ratio. This splitter allows the measurement results of the avalanche diodes to be compared and verified with a reference Raman spectrometer.In setup 30, this can be placed in front of the bandpass filters to enable simultaneous fluorescence measurement. Finally, the measurement signal is focused onto an SMA connector for an avalanche diode and the reference spectrometer, using a plano-convex lens.

[0087] In other words, referring to Fig. 9 A setup 30 is shown with an input 37 through which Raman light 10 enters either from a probe head 34 or from the sample 9. A lens 6 and two filters 18, in this example tunable filters 18, are arranged in the beam path after the input 37. An optical interface 4 is connected to the tunable filters 18, which directs the Raman light – focused by each lens 6 – to a respective output (avalanche diode or reference output).

[0088] To be highlighted in this with Fig. 9The embodiment of the Raman photometer design shown uses avalanche photodiodes as detectors.

[0089] To reduce distracting reflections, for example from shiny aluminum, one option is to treat the surface with a matte black paint and / or charcoal dust. The matte black paint can be sprayed directly onto the roughened aluminum surface. While still wet, the charcoal, ground into dust or fine particles, is then applied to the paint. This creates a rough surface. The rough surface diffuses the light. Diffusely scattered light is scattered in all directions, so that only a smaller proportion reaches the detector, and therefore it is of lower intensity.

[0090] Referring to Fig. 10 Finally, an already realized embodiment is shown, which is based on the embodiment of the Fig. 9The figure is based on a pre-production model and shows a finished device for carrying out the invention. Identical items are labeled with the same reference numerals.

[0091] It is evident to the person skilled in the art that the embodiments described above are to be understood as examples and that the invention is not limited to these, but can be varied in many ways without leaving the scope of protection of the claims.

[0092] In all figures, the same reference symbols represent the same objects, so that descriptions of objects that may only be mentioned in one figure, or at least not with regard to all figures, can also be applied to those figures for which the object is not explicitly described. Reference symbol list:

[0093] 2 Light source, laser 3 Excitation light, laser light, thin beam of excitation light 4 Optical interface or mirror arrangement or glass plate 4a to 4h Examples of an optical interface 4 5 Reflective part of the optical interface 6 Lens 6a Lens 6b Fresnel lens 7 Scattering location or event location 8 Optically transparent surface or plate 9 Process space or product as process space fd Raman scattering 9a Focal point 10 Raman light 11 Fluorescent light 12 Converging lens 13 Detection location 14 Detector 14a Mirror 14b Detector 15a Arrangement, photodiode for contamination detection 15b Beam catcher or light trap 16 Secondary detector 18 Filter 30 Sensor system or setup 32 Optical waveguide or elastic scattering 33 Fiber optic or plastic fiber arrangement 34 Probe head 35 Fiber 36 Probe head housing 37 Input 40 Single fiber 41 First side of the optical interface 42 Second side of the optical interface 43 Multi-fiber probe orFiber optic bundle 43a Excitation light fiber 43b Single fiber of the multi-fiber probe, Raman light fiber 45a First splice 45b Second splice 45c Third splice 45 Nitinol cannula 46 Distributor 47 Excitation branch 48 Detection branch 49 Input fiber 51 Transmissive part of the optical interface 52 Further reflective part of the optical interface 55 Output fiber 61 Borehole 62 Borehole.

Claims

1. Raman measurement system (30) adapted for low light intensity (3), comprising: a light source (2) for providing coherent unfocused light as excitation light for Raman scattered radiation (10) backscattered from a sample (9), a Raman detector (14) for detecting the intensity of Raman scattered radiation (10) backscattered from a sample (9) an optical interface (1, 4), wherein the optical interface is partially transparent or wherein the optical interface has a reflective area (5) and a transmissive area (51), wherein the optical interface is adapted and arranged to receive the coherent, unfocused light from the light source on a first side (41) of the optical interface and to direct it in the further beam path from the optical interface onto the sample to generate the scattered radiation, and further to receive the Raman scattered radiation on the same side of the optical interface and then to guide it to the detector (14) in the further path of the beam, wherein the light source (2) for providing coherent unfocused light has an output power of less than 35 mW, and, further comprising a wide-aperture pick-up with at least one Fresnel lens (6b) for enlarging the pick-up angle of the Raman measurement system (30) for the Raman scattered radiation (10).

2. Raman measuring system (30) according to the preceding claim, characterised in that the light source (2) for providing coherent light has an output power of less than 7 mW and, in particular, less than 3 mW.

3. Raman measuring system (30) according to any of the preceding claims, further comprising a probe head (34), wherein the optical interface (1, 4) is arranged in the probe head.

4. Raman measuring system (30) according to any of the preceding claims, wherein the optical interface (1, 4) is partially transparent in such a way that, for Raman scattered radiation (10) backscattered from the sample (9), a first sub-region (5) of the optical interface is substantially opaque, and a second sub-region (51) of the optical interface is substantially transparent, wherein, in particular, the first sub-region is arranged centrally, and the second sub-region is arranged concentrically around the first partial region.

5. Raman measuring system (30) according to any of the preceding claims, wherein the coherent light (3) of the light source (2) is initially directed from the light source onto a first side (41) of the optical interface (1, 4) facing the sample (9), and is guided from the optical interface in the direction of the sample, wherein the scattered radiation (10) strikes the first side of the optical interface facing the sample and penetrates the optical interface from the first side to a second side (42).

6. Raman measuring system (30) according to claims 4 and 5, wherein the coherent light (3) of the light source (2) is directed towards the first sub-region (41) of the optical interface (1, 4), and wherein the first sub-region is reflective or substantially reflective, so that the coherent light of the light source is deflected from the optical interface, and wherein the Raman scattered radiation (10) coming from the sample (9) is directed substantially towards the second sub-region (51) of the optical interface and, wherein, the second sub-region is transmissive or substantially transparent, so that the scattered radiation passes through the optical interface.

7. Raman measuring system (30) according to any of the preceding claims, further comprising a multi-fibre probe (43) with at least one excitation light fibre (43a) and one Raman light fibre (43b), so that the excitation light (3) is guided to the sample (9) separately from the Raman light (10).

8. Raman measuring system (30) according to any of the preceding claims, further comprising at least one optically transparent surface (8) arranged between the sample and the optical interface (1, 4) for attenuating scattered radiation, wherein the optically transparent surface comprises a disc, a face plate or a glass pane.

9. Raman measuring system (30) according to any of the preceding claims, further comprising at least one second optically transparent surface (8) arranged on a side facing away from the sample and a collecting mirror (14a) arranged behind the second optically transparent surface for increasing the light yield of the Raman scattered radiation (10).

10. Raman measuring system (30) according to the preceding claim, furthermore, with a beam catcher (15) for catching the excitation light (3), which is parallel to the axis in particular.

11. Raman measurement system (30) according to any one of claims 3 to 10, wherein the coherent light from the light source (2) strikes the optical interface (1, 4) as a free beam.

12. Raman measuring system (30) according to any of the preceding claims, further comprising a lens arrangement (6, 6a, 6b), wherein the lens arrangement is partially or regionally free of refractive properties for transmitting the monochromatic light (3) from the light source (2).

13. Raman measuring system (30) according to the preceding claim, wherein the lens arrangement (6, 6a, 6b) comprises a drilled hole (61, 62) for passing the monochromatic light (3) of the light source (2).

14. A Raman measurement system (30) comprising a probe head (34) according to any one of claims 3 to 13, wherein the probe head (34) further comprises a lens arrangement (6, 6a, 6b), wherein the lens arrangement is partially or regionally free of refractive properties for transmitting the monochromatic light (3) from the light source (2).

15. Raman measuring system (30) with a probe head (34) according to the preceding claim, wherein the lens arrangement (6, 6a, 6b) has a borehole (61, 62) for the passage of the monochromatic light (3) of the light source (2).

16. A Raman measurement system (30) comprising a probe head (34) according to any one of claims 3 to 15, wherein the probe head (34) further comprises a variable filter (18) in the beam path after the optical interface (1, 4) and before the detector (14).

17. A Raman measurement system (30) comprising a probe head (34) according to any one of claims 3 to 16, wherein the probe head (34) further comprises a light-tight probe head housing (36) adapted to hold the components of the probe head, and to manually align the probe head in relation to the sample (9) and / or the detector (14).