DEVICE AND METHOD FOR MEASURING STRANGE LIGHT AND USE, FOR EXAMPLE, IN WASTEWATER TREATMENT PLANTS

Description

Field of invention

[0001] The invention relates to a device and a method for measuring scattered light, in particular Raman-scattered, fluorescent and / or phosphorescent light, especially applicable to both turbid and clear fluid media and transparent or slightly turbid solids, as well as its use for monitoring the discharge at sewage treatment plants or other wastewater. Background of the invention

[0002] The Raman effect, compared to other optical analysis methods, is characterized by small cross-sections and inelastically scattered photons. Therefore, Raman spectroscopy in particular struggles with a comparatively weak measurement effect and correspondingly low photon fluxes. This also applies to fluorescence and phosphorescence effects.

[0003] In well-known Raman spectroscopy, the wavelength resolution required for molecular selectivity typically corresponds to a spatial resolution when using conventional dispersive optical elements. For example, conventional monochromators can be employed. A larger entrance slit leads to a lower wavelength resolution but, conversely, to increased light intensity at the detector. Furthermore, it follows from the imaging equations known to those skilled in the art that only small objects can be imaged onto small areas. These relationships are described in general terms by the Helmholtz-Lagrange equation and are known to those skilled in the art, thus requiring no further explanation. Therefore, these principles typically allow only small objects to be spectroscopically measured or detected with high wavelength resolution.The pixel sizes, which actually indicate the presence of the detecting CCD / CMOS elements, are defined by a width of, for example, 20 µm or 25 µm – often even less – and a pixel height of 500 µm, sometimes slightly more. Nevertheless, the area to be detected cannot be significantly larger than the area of ​​the pixels.

[0004] Some commercially available systems described in the literature utilize cross-sectional transducers with a circular entrance aperture on the probe side. Light enters a spectrometer and is shaped into a slit precisely matching these dimensions (e.g., 25 x 500 µm). Thus, circular entrance apertures of approximately 100 µm or 200 µm correspond to 600 µm in diameter. In the largest versions, with pixel sizes up to 2.5 mm high (often achieved through horizontal binning), this results in circular entrance apertures of only 600 µm. Consequently, with a fixed aperture angle, which in typical technical designs is only slightly variable, only objects with a diameter of approximately 0.6 mm can be imaged. Furthermore, conventional measuring probes typically image only a specific volume element directly in front of the sensor tip along the beam path.

[0005] In Raman spectroscopy, on average only one photon per approximately 10⁸ to 10¹¹ injected photons in a sample will experience the Raman effect. This limits the typical applications of Raman spectroscopy and Raman photometry to relatively high concentration ranges, and / or conventional Raman spectrometers are equipped with very powerful laser light sources. Laser power of up to 500 mW or more is typically used. For detection, highly sensitive line detectors or area detectors (CCD, EMCCD, CMOS, sCMOS), e.g., from the scientific and astronomical fields, are frequently employed, as well as detectors for time-resolved spectroscopy. These are generally cooled in one or more stages using Peltier elements or liquid nitrogen to reduce thermal noise.

[0006] Such systems are usually complex and expensive in order to achieve sufficient detection sensitivities.

[0007] The concentrations currently detectable with Raman spectroscopy typically start at 0.1% by volume or mass and extend up to 100% by volume or mass. Applications are found in laboratories, the chemical industry, etc.

[0008] One application area for the invention, one not currently served by existing devices, is measurement and control technology in wastewater treatment plants. In Germany alone, there are approximately 10,000 public wastewater treatment plants. These plants treat about 10 billion cubic meters of wastewater (consisting of roughly 5 billion cubic meters of sewage and approximately 5 billion cubic meters of extraneous and stormwater) and discharge it into surface waters. The annual revenue in the wastewater treatment sector in Germany amounts to several billion euros. Nevertheless, further growth and investment are expected. This will involve both capacity expansion and quality improvements through the development of measurement and control technology.

[0009] The application of Raman spectroscopy in the analysis of water and the detection of microorganisms is described, for example, in "Identification of water pathogens by Raman microspectroscopy" in Water Research, 48 (2014), 179-189 and "The application of Raman spectroscopy for the detection and identification of microorganisms" in Journal of Raman Spectroscopy, 2016, 47, 89-109. Further fundamentals and examples of light sources are described, for example, in ChemPhysChem 2003, 4, 14-30.

[0010] A wastewater treatment plant is a highly complex system consisting of mechanical (pre-treatment), biological, and abiotic-chemical stages. In the mechanical stages, approximately 20 to 30% of the undissolved floating and suspended solids are eliminated. The second stage employs biological processes that utilize microbiological degradation – with the aim of mineralizing biodegradable organic substances as completely as possible. This means that the substances are broken down aerobically into the end products: water, carbon dioxide, nitrate, phosphate, and sulfate.

[0011] Through an anaerobic process, carbon compounds are converted into acids, methane, and carbon dioxide. Organically bound nitrogen and ammonium are converted through bacterial nitrification and denitrification stages, drastically reducing the nitrogen content. The biological stage is very sensitive to inhibitors. In poorly buffered water, these can lead to a change in pH and, in the worst case, halt the degradation process.

[0012] In the downstream abiotic-chemical stage, phosphorus is mainly removed by precipitation reactions (phosphorus elimination) to avoid eutrophication (enrichment with nutrients) of the receiving water body.

[0013] To monitor the complex and challenging conditions in wastewater treatment plants, significant measurement efforts are employed, particularly in the field of water and wastewater analysis. Most publications focus on measurement techniques in these areas. Turbidity measurement technology: UV / VIS, NIR, fluorescence and Raman spectroscopy.

[0014] However, with molecule-selective Raman technology, even the smallest detection limits can be achieved, which until now have typically only been possible with Raman-SERS techniques, i.e., surface-enhanced Raman. This technique, however, is only of limited or no process robustness for use in wastewater treatment plants.

[0015] It is particularly common for samples to be measured using Raman to be almost water-clear. In this case, most of the light simply passes through the sample volume. This results in, for example, 99.999999% of the light being lost, further reducing the detection possibilities.

[0016] From WO 2010 / 111508 A1, a system with linear arrangements, each with a plurality of optical fibers and an ND:YAG laser for fluorescence spectroscopy, is known.

[0017] From EP 2 602 611 A2, a high-pressure fluorescence flow cell arrangement, a fluorescence detector, and a supercritical fluid chromatograph (SFC) are disclosed. SFCs use UV-VIS absorption detectors, ELSDs, and mass spectrometers, and the flow cell must withstand a pressure of 10 MPa or higher.

[0018] From WO 2012 / 019102 A2, a portable diagnostic system with a tunable laser for the clinical diagnosis of, for example, malignant tumors or arteriosclerosis is known. An LCTF or AOTF is used, for example, for glucose measurement.

[0019] US 2006 / 01764478 A1 describes Raman spectroscopy with stabilized multimode lasers for the chemical analysis of organic components in a sample chamber.

[0020] Utility model DE 20 2004 007 868 U1 describes a measuring probe with a liquid-tight housing and a detector for detecting a fluorescence spectrum.

[0021] US patent 9,513,225 B2 relates to a method and a system for improving the resolution of a spectrometer with an optical medium having a predetermined tunable spectral transmission curve. General description of the invention

[0022] It is therefore an object of the present invention to provide a device and a method for measuring scattered light, in particular Raman-scattered, fluorescent and / or phosphorescent light, which has a high sensitivity or detection efficiency and is particularly suitable for measurement in turbid and in clear or transparent fluid and solid media.

[0023] Another aspect of the task is to provide a device and a method for measuring scattered light, in particular Raman-scattered, fluorescent and / or phosphorescent light, which is suitable for measurement on low-concentration fluid or solid media.

[0024] Another aspect of the task is to provide a device and a method for measuring scattered light, in particular Raman-scattered, fluorescent and / or phosphorescent light, which is process-robust and suitable for measurement and control technology in wastewater treatment.

[0025] According to one aspect of the present invention, a device for measuring secondary light scattered, in particular in turbid or clear fluid or turbid or transparent solid media, is provided according to claim 1. Fluid media can be liquid or gaseous. Turbid media can be, for example, dispersions. Gaseous turbid media can be present as aerosols, i.e., as fog or smoke. Turbid liquid media can be present as a suspension, for example. The device comprises a light source that generates a collimated, preferably parallel, primary light beam which is directed into the medium under investigation, wherein the primary light beam defines a beam axis in the medium under investigation, which is preferably fluid (i.e., liquid or gaseous) or solid.In other words, the primary light beam passes through the medium along the beam axis and excites light scattering in the medium, in particular Raman scattering, fluorescence and / or phosphorescence, so that the medium emits secondary light with a secondary light spectrum due to the light scattering along the beam axis.

[0026] Furthermore, the device comprises a probe arrangement for receiving and transmitting the secondary light emitted along the beam axis. The probe arrangement, in turn, comprises a plurality of optical fibers, each with a light entry tip and a defined light entry area. These light entry tips, i.e., the sample-side end of the optical fibers where the secondary light enters the optical fiber, extend transversely to the beam axis of the primary light beam and are arranged side by side in at least one row along the beam axis. In other words, the plurality or plurality of optical fibers form a series arrangement or "battery" of optical fibers, with each individual optical fiber extending transversely to the beam axis and the series arrangement of all the optical fibers extending along the beam axis, comparable to the arrangement of the cylinders of an inline engine with respect to its crankshaft."Perpendicular to the beam axis" in this context can mean that the individual optical fibers run perpendicular to the beam axis or at an acute angle to a plane extending perpendicular to the beam axis. Thus, the optical fibers can receive secondary light, such as Raman-scattered light, emitted perpendicular to the beam axis, not just at a single point at a single light entry tip, but over a certain distance along the beam axis. The series of optical fibers therefore receives the secondary light over an extended detection length along the beam axis of the primary light beam, a detection length considerably greater than the diameter of a single optical fiber.The length of the probe area formed by all the optical fibers corresponds to the detection length, which is approximately the product of the optical fiber diameter (2*r L ) and the number of optical fibers (n L ), where r L is the diameter of a single optical fiber and n L is the number of optical fibers arranged side by side. Therefore, this is also referred to as a multi-optical fiber lateral probe. The total light-entry area or total probe area of ​​the series of optical fibers thus has an elongated extent with a long extension (2*r L * n L ) along the beam axis and a short extension (2*r L ) perpendicular to the beam axis. For a series of optical fibers, the short extension corresponds to the diameter (2*r L ) of a single optical fiber, and the long extension corresponds to the detection length, i.e., the product of the optical fiber diameter and the number of optical fibers (2*r L * n L ). The total probe area AG of the row arrangement is therefore AG = π*r L 2< *n L .With such a series arrangement, light can therefore be received and collected along the long extent of the probe surface, i.e., along the detection length. It should not be ruled out that some (a few) optical fibers in the series are used for special purposes, such as turbidity measurement.

[0027] The light received across the elongated surface of the probe is collected and directed to a detector for detection. The device includes a detector for detecting the secondary light emitted perpendicular to the primary light beam, collected by the majority of the optical fibers, and directed to the detector.

[0028] Advantageously, this allows a significantly greater amount of secondary light, particularly Raman-scattered light, to be received, collected, and detected along the beam axis than would be possible with a fiber optic cable or conventional probes, thus considerably increasing detection efficiency. This advantageously enables the investigation of low concentrations in the medium, a reduction in laser power, or both.

[0029] The optical fibers are designed as plastic fibers or waveguides and / or each has an optical fiber diameter of at least 100 µm, preferably at least 200 µm, and even more preferably at least 500 µm. This allows, on the one hand, a cost-effective series arrangement of a large number of optical fibers to be formed, and on the other hand, a large total probe area (AG) to be achieved.

[0030] Preferably at least 5, preferably at least 10, preferably at least 25, preferably at least 40 light guides are arranged side by side in a row along the beam axis, so that the total probe area can be multiplied compared to a single light guide or a few light guides.

[0031] The total probe area or the total cross-sectional area of ​​all optical fibers is at least 10 mm², preferably at least 20 mm², preferably at least 40 mm².

[0032] The device comprises a cross-sectional converter that transforms the total light-entry area of ​​the light-entry tips, which extends linearly along the beam axis (i.e., the total probe area AG = π*r L 2< *n L), into a two-dimensional area with a greater width and shorter length than the linearly elongated total light-entry area. For example, the transformation occurs into a square or circular, or at least not elongated, cross-section. This is achieved, for instance, by having the optical fibers form the cross-sectional converter and transforming their total cross-sectional area from an elongated shape with a length of approximately 2*r L * n L to a more square or circular shape. Simply put, an elongated cross-sectional shape similar to 2r L * 2n L r L is transformed into a compact cross-sectional shape similar to {2sqrt(n L )r L} 2< .

[0033] The device preferably comprises a cuvette with a fluid inlet and a fluid outlet, so that the fluid medium to be examined can be passed through the cuvette. The primary light beam is directed along the beam axis through the preferably elongated cuvette, so that the medium passing through the cuvette is illuminated by the primary light beam during flow-through operation.

[0034] For this purpose, the cuvette can include a primary light beam entry window at a first end and / or a primary light beam exit window at a second end opposite the first end, through which the primary light beam can enter and / or exit the cuvette, which extends longitudinally along or around the beam axis. This advantageously allows a fluid, e.g., liquid, medium to be analyzed in a flow-through manner.

[0035] Several embodiments for extracting the secondary light are possible, as follows: The cuvette can have a side wall or a window extending along the beam axis, made of a transparent or translucent material, so that the secondary light can exit the cuvette through the side wall or window. The probe arrangement can be positioned externally on the cuvette to capture the secondary light exiting through the side wall or window outside the cuvette.

[0036] The cuvette can also have a lateral opening through which the optical fibers protrude into the interior, so that the light entry tips of the optical fibers are located directly in the fluid medium in order to capture the secondary light generated in the fluid medium directly within the cuvette or within the fluid medium itself. Preferably, the opening around the optical fibers is sealed to form a fluid-tight cuvette-probe assembly.

[0037] Furthermore, the multi-light guide lateral probe can be configured as an immersion or submersible probe, or as a gas-phase Raman probe. In this embodiment, a submersible vessel containing the fluid medium is included, and the immersion or submersible probe is immersed in the fluid medium so that the light entry tips within the submersible vessel are immersed in the fluid medium to directly capture the secondary light generated in the fluid medium.

[0038] The light output of the multi-light guide lateral probe can be further increased by including a cylindrical concave mirror which is arranged along the cuvette and focuses the secondary light emerging from the cuvette in various radial directions onto the light entrance tips of the light guides, or by partially (internally) mirroring the cuvette to focus the light emitted in various radial directions onto the light entrance tips.

[0039] Preferably, the cylindrical concave mirror or the mirrored cuvette can have an elliptical cross-section perpendicular to the beam axis. If the beam axis and / or the light entry tips of the optical fibers are arranged at the focal points of the ellipse, the light emitted in various radial directions around the beam axis is collected particularly effectively.

[0040] According to a preferred embodiment, even several rows, e.g., 2, 3, 4 or more rows, each with a plurality of light guides, can be arranged along and around the beam axis. This allows the total probe area to be further increased. Multiplexing operation is also possible, in which the individual rows can detect sequentially.

[0041] According to a further preferred embodiment, some (a few) of the optical fibers, which are then arranged intermittently in series along the longitudinal axis, can be used for absorption measurement and / or intensity measurement and for signal correction. This advantageously allows a turbidity measurement or concentration measurement of a dispersed medium (dust, droplets, particles, etc.) to be carried out simultaneously with the Raman measurement along the beam axis, e.g., to normalize the Raman signals from the optical fibers to each other.

[0042] It comprises a wavelength-selective element that disperses the secondary light spectrum, allowing the secondary light to be detected wavelength-selectively by the detector device in order to image and, if necessary, graphically represent at least a portion of the secondary light spectrum. Therefore, it does not only measure one wavelength and preferably not only one intensity of all wavelengths, but analyzes at least a portion of the secondary light spectrum, thus making the device a spectrometer or Raman spectrometer.

[0043] The wavelength-selective element is designed as a tunable filter to detect at least part of the secondary light spectrum with the detector device. With a tunable filter, the spectral resolution of the secondary light spectrum is temporal.

[0044] A particularly advantageous feature in the context of the invention is a detection method that covers an entire area.

[0045] A tunable filter, in particular an acousto-optically tunable filter, i.e., a so-called AOTF, or another tunable filter, is suitable. Advantageously, an AOTF has a large active area that can spectrally select the secondary light from the multitude of optical fibers. In this regard and with respect to possible applications, reference is made to application DE 10 2018 106 819.0 dated March 22, 2018, which is hereby incorporated by reference into the present disclosure. Optionally, a focusing optic can be provided between the output of the cross-sectional converter and the tunable filter to focus the secondary light exiting the cross-sectional converter with its large output area onto the tunable filter and / or the detector device, or to direct the incoming light to angles of incidence favorable to the filter used.

[0046] The detector assembly comprises at least one single-photon detector. The single-photon detector has a detection area with a diameter greater than or equal to 3 mm, preferably greater than or equal to 5 mm, and more preferably greater than or equal to 10 mm. This advantageously allows for high detection efficiency.

[0047] The single-photon detector can be, for example, a secondary electron multiplier, also known as a photomultiplier, and in particular a customized photomultiplier (CPM). Avalanche photodiodes, multipixel photon counters, or other detector systems can also be used.

[0048] Preferably, the primary light beam is emitted through the medium as a collimated beam or parallel beam, i.e., with a small aperture angle, and thus not focused to a single point. This allows the secondary light to be collected in the same way along the entire beam axis using the multi-light guide lateral probe and directed to the wavelength-selective element or detector device.

[0049] The light source is preferably at least narrowband and easily alignable. A laser possesses both of these properties. Therefore, a laser is typically used as the light source to generate the primary light beam. However, one or more LEDs could also be used.

[0050] When using a laser, a particular advantage arises if its power output is below the ATEX limit for explosion-proof areas. In this case, the system can be approved for use in such areas. This means that, provided the laser beam is not focused on or within the medium, the device can even be used in explosion-proof areas or obtain EX approval. For this purpose, it is particularly advantageous if the laser has a maximum luminous power of 1 milliwatt. This offers advantages in terms of EX approval, as well as protection against the harmful effects of laser radiation on people.

[0051] The device further includes an evaluation unit which is designed to generate, evaluate, calculate, store and, if necessary, display on a monitor a Raman spectrum, fluorescence spectrum and / or phosphorescence spectrum of the secondary light.

[0052] The invention also relates to a method for detecting Raman-scattered, fluorescent and / or phosphorescent secondary light according to claim 14, wherein the method comprises the following steps: Providing a Raman-active, fluorescent and / or phosphorescent clear or turbid medium, optionally with a concentration of less than 0.01% by weight of Raman-active, fluorescent and phosphorescent material; shining a light beam, in particular a parallel, essentially unfocused laser beam, into the Raman-active, fluorescent and / or phosphorescent clear or turbid medium along a beam axis; detecting secondary light emitted transversely, in particular perpendicularly, to the beam axis along an extended measuring distance along the beam axis, wherein the length of the measuring distance is considerably greater than the diameter of the light beam and / or the diameter of an optical fiber of the probe. The length of the measuring distance is, for example, at least several millimeters, e.g., at least 5 mm or at least 10 mm, preferably at least 20 mm or at least 40 mm.

[0053] The invention also relates to its use for monitoring a flow in the area of ​​a wastewater treatment plant, e.g. monitoring the outlet or another flow into, to or from a wastewater treatment plant, in particular for the simultaneous monitoring of nitrate, ammonium, phosphate, sulfate and / or organic components in a partial flow of the wastewater treatment plant or other wastewater.

[0054] Further applications for the invention can be found, for example, in the following areas: Automotive: Oil in water, scale inhibitors, detection of ammonium ions, nitrate, sulfate, and phosphate ions; Wastewater: Turbidity, concentration; Beverage industry: Turbidity, yeast count, concentration, color; Biotechnology: Protein content, biomass, glucose concentration, monitoring, control, and endpoint determination in fermentation processes; Chemistry: Concentration determination, monitoring and control of reaction processes, physical data such as density, viscosity, and color (APHA, HAZEN); Pharmaceuticals: Quality assurance, identification of active ingredients; Petrochemicals: Water content, octane number, color (ASTM); Food: Fat content in meat, CIP monitoring, color; Textiles: Color, particle concentration, phase separation; Drinking water: Chlorine dioxide, ozone, turbidity, detection of ammonium ions, nitrate, sulfate, and phosphate ions

[0055] The invention will now be explained in more detail with reference to exemplary embodiments and the figures, whereby identical and similar elements are partially provided with the same reference numerals and the features of the different exemplary embodiments can be combined with one another. Brief description of the characters

[0056] They show: Fig. 1 a schematic side view of a cuvette with a multi-light guide lateral probe of a device according to an exemplary embodiment of the invention, Fig. 2 a schematic representation of an AOTF and a detector device of a device according to an exemplary embodiment of the invention, Fig. 3 a schematic sectional view of a submersible probe of a device according to a further exemplary embodiment of the invention, Fig. 4 a schematic cross-sectional view of an exemplary modification of the embodiment from Fig. 3, Fig. 5 a schematic representation of an exemplary embodiment of the device according to the invention, Figs. 6-14 schematic cross-sectional representations of exemplary arrangements of light guides and mirrors around the cuvette or mirror coatings of the cuvette. Detailed description of the invention

[0057] Referring to Fig. 1A fluid, in particular liquid or gaseous, medium 10 is fed via a medium supply line 12 into a cuvette 14, in this example a cuvette made of a transparent material, e.g. glass. The fluid medium 10, e.g. a liquid or gas with Raman-active components, e.g. in the form of water from a wastewater treatment plant sample, flows through the longitudinally extending cuvette 14 and exits the system again at a medium outlet 16, so that the medium 10 can be examined in flow-through operation through the cuvette 14. In this example, the cuvette 14 has a (circular) cross-section and extends longitudinally along a beam axis 18. The cuvette 14 has a light entry window 32 at a first end face 22, through which a primary light beam 42 is directed into the cuvette 14 and thus into the medium 10 in the cuvette 14.In this example, the primary light beam 42 is generated by a laser as a light source 44, and the laser beam 42 is not focused but is emitted as a parallel beam along the beam axis 18 through the cuvette 14. The parallel primary light beam, or parallel laser beam 42, thus generates secondary light scattered along its path along the longitudinal axis 18 over an extended measuring distance 46 in the medium 10 within the cuvette 14, e.g., by Raman scattering. The Raman-scattered secondary light is therefore emitted along the extended measuring distance 46 along the beam axis 18 at every point along the measuring distance 46 in all spatial directions.

[0058] The primary light beam 42 exits the cuvette 14 through an exit window 34 at a second end 24 opposite the first end 22 and can be absorbed in a light trap 36, which in this example is arranged coaxially to the primary light beam 42. The primary light beam 42 thus radiates through the cuvette 14 from the entrance window 22 to the exit window 24 and generates secondary light along the longitudinally extended measuring section 46, e.g., by Raman scattering. This secondary light is emitted at every point along the beam axis 18 within the cuvette with a specific angular characteristic into all solid angles. A probe arrangement 50 in the form of a multi-light guide lateral probe is attached laterally to the cuvette 14, which in this example is formed by a transparent tube.The multi-light guide lateral probe 50 comprises a plurality of light guides 52, in this example 51 light guides 52, which are arranged in a row along the cuvette 14 or along the beam axis 18. The individual light guides 52 extend transversely, in this example perpendicularly, to the beam axis 18 in the region of the probe head 51, and, arranged side by side, form an elongated battery or row arrangement 56, the row or row arrangement 56 as a whole extending longitudinally along the cuvette 14 or along the beam axis 18. In other words, the probe head 51 comprises an arrangement 56 of adjacent, in particular large-area, light guides 52, e.g., optical fibers.

[0059] Each light guide 52 comprises a light entry tip 54 at the sensor head or probe head 51, which is in contact with, or in close proximity to, the transparent side wall 15 in the form of an annular wall of the cuvette 14 in order to receive that portion of the secondary light from the cuvette 14 which is emitted from the medium 10 perpendicular to the beam axis 18. Due to the large number of light guides 52 arranged in series 56 along the measuring path 46, a relatively large amount of secondary light can be received by the multi-light guide lateral probe 50. In the present example, the light guides 52 are designed as commercially available optical fibers, e.g., plastic fibers with a diameter of approximately 1 mm.

[0060] In other words, the invention presented here employs a special multi-light guide arrangement consisting of parallel light guides 52, namely in the form of a series arrangement 56, for receiving and collecting the secondary light in order to achieve higher detection sensitivity compared to the use of only one or a few optical fibers that detect only a small, essentially point-like sample volume. The fluid medium 10, as a sample or other component of a product, is pumped or passed through the cuvette 14, which is an elongated sample vessel. The sample volume detectable by the probe arrangement or probe 50 according to the invention therefore extends along the longitudinally extended measuring section 46 along the beam axis 18.

[0061] In the Fig. 1In the example shown, the cuvette 14 has transparent walls; however, it is also conceivable to slit the cuvette laterally and integrate and seal the row arrangement 56 of light guides 52 into the side wall or ring wall 15 of the cuvette, so that the light entry tips 54 are located directly in the medium 10 in the cuvette 14 (see also Figs. 10-14 ).

[0062] If, as proposed above, a laser beam is used as the primary light beam 42, which is guided through the medium 10, it can be directed into the medium 10 parallel, i.e., with a small aperture angle, according to the usual properties of laser beams. Even simple laser pointers can thus be projected almost parallel over relatively long distances and can be suitable as a primary light source for the parallel, especially unfocused, primary light beam 42. As already explained, Raman radiation is generated along the entire optical path of the laser beam 42 by the volume unit in the cuvette 14 or in the container filled with the medium 10, or, in this example, through which the light flows. Previously known measuring probes typically detect only a specific small volume element directly in front of a probe tip.In the embodiment according to the present invention, the series arrangement 56 of a plurality of light guides 52 is positioned laterally, e.g. at 90°, or at another suitable angle, so that the plurality of light guides 52 together form a large-area probe arrangement in the form of a multi-light guide lateral probe 50, such that the primary light beam shines past the light entry surface of the multi-light guide lateral probe 50, which extends longitudinally along the beam axis 18 over the measuring section 46. Thus, the scattered secondary light, e.g. Raman light, which is scattered into all solid angles along the longitudinally extended measuring section 46, penetrates all light guides 52.

[0063] Thus, with the presented large-area or large-volume fiber probe 50 from the series arrangement 56 of a multitude of light guides 52, the amount of light of the collected secondary light to be detected, e.g. Raman light, can be multiplied by means of the multitude of light guides 52 used.

[0064] Top right in Fig. 1A schematic representation of a cross-sectional converter 60 is shown. The cross-sectional converter 60 consists of the optical fibers 52, which form the elongated row arrangement 56 of the probe head 51 at their probe-side light entry tips 54. Along the cross-sectional converter 60, the optical fibers 52 are transformed from the elongated row arrangement 56 into a compact, in this example essentially circular, bundle arrangement 62 by rearranging the optical fibers 52. The cross-sectional converter 60 therefore consists of a fiber arrangement of optical fibers 52. It should be noted that the representation of the cross-sectional converter 60 is schematic and does not show nearly as many optical fibers 52 as are actually present in the diagram at the top right. Fig. 1as also shown. With the cross-sectional converter 60, the relatively large cross-sectional area of ​​all optical fibers 52 can now be transformed from the elongated row arrangement 56 to a more compact, e.g., circular, bundle arrangement 62 in order to be fed to the detector device. In other words, the cross-sectional converter 60 is formed by the bundle of optical fibers 52, whereby the bundle is transformed from a probe-side row arrangement 56 to a more compact detector-side bundle arrangement 62.

[0065] Referring to Fig. 2The secondary light collected by the probe or probe arrangement 50 is coupled out of the light guides 52 at detector-side light exit ends 64 and directed onto a large-area tunable filter 68, in this example an acousto-optical tunable filter (AOTF) 68. Between the cross-sectional converter 60 and the AOTF 68, one or more beam-shaping elements, e.g., a lens 66 for focusing, are arranged. The tunable filter 68 then disperses the secondary light, so that the secondary light spectrum can be recorded by a detector 72 of a detector assembly 70 by tuning the filter 68. In this example, the detector 72 is a so-called customized photomultiplier (CPM), which detects a first-order beam 82 from the AOTF 68. The zero-order beam 84 can be detected by a detector 74 and the other first-order beam 86 by a detector 76, but this is optional.Furthermore, additional optical elements, such as refractive elements or blocking filters, can be incorporated if this is useful or desired, for example, for primary light suppression.

[0066] Advantageously, a large-area detection detector 72 can be used, which is not limited by the small entrance apertures of spectrometers. In the present example, the optical fibers 52 of the probe 50, positioned in the series arrangement 56, are arranged along the extended measuring path 46 and are directed at the detector-side end 64 in a compact bundle arrangement 62, e.g., circular or oval, onto the tunable filter 68, e.g., an AOTF or another tunable filter, in order to be detected on the large detection area of ​​the customized photomultiplier 72, thereby increasing the detection sensitivity. It is possible to use plastic fibers as optical fibers 52, e.g., with a diameter on the order of up to 1 mm or more. Such commercially available plastic fibers can be positioned in the described series arrangement 56, e.g.,As shown here, 51 pieces or more or less. This creates a probe head 51 with a probe entry surface approximately 51 mm long and approximately 1 mm wide, neglecting the spaces between the circular fibers for the sake of simplicity. This series arrangement 56 of, for example, 51 fibers is then formed into a bundle 62, for example, a circular or oval bundle, and the light exiting the detector-side light exit surface of the cross-sectional transducer 60 is parallelized by the lens 66 and subsequently passes through the AOTF 68.

[0067] The AOTF 68 is therefore preferably illuminated in parallel due to the steepness of the filtering edges, thus achieving high selectivity. The AOTF 68 selects the individual Raman wavelengths from the collected secondary light. The customized photomultiplier 72 is positioned downstream, which, as a single-photon detector with extremely high detection sensitivity, detects the spectrally resolved secondary light.

[0068] This arrangement allows a cross-sectional area of ​​approximately 40 mm² for the probe 50 or the sum of the optical fibers 52 in the given example. However, smaller or larger cross-sectional areas, e.g., up to 70 mm², 100 mm², or even more, can be achieved by adjusting the number of optical fibers 52 or their diameter.

[0069] In summary, the detector device 70 detects the secondary light with high sensitivity. Since virtually each individual optical fiber 52 functions like its own detection system, using a large number of n L optical fibers 52 (in this case n L = 51) increases the amount of light by a factor of n L. In some cases, this can result in an n L-fold increase in detection sensitivity, or an even higher detection sensitivity with an even larger number n L of optical fibers or even larger diameters of optical fibers 52. In other cases, for example, when fluorescence is also present, the actual increases in the detection limits can be calculated via error propagation. This effect is based on the low absorption of the light beam, especially in clear media, in the field of Raman spectroscopy.This enables, as in this case, very long optical paths and thus a very long measuring distance 46. This advantage is particularly evident when, as here, a large-area tunable filter 68, e.g., an AOTF, is used and a large-area, highly sensitive detector is available, such as a customized photomultiplier 72 in the present example. While the use of a large-area AOTF 68 and a customized photomultiplier 72 is particularly advantageous in the present embodiment, it is optional within the scope of the invention in its general form. Suitable photomultipliers include, for example, MPPC modules of the C13366 series, the H12775 photon counter head, or photon counter heads of the H7421 series from Hamamatsu (see www.hamamatsu.com), or customized photon multiplier module heads of the PV-HM 9XZ / 13XZ / 19XZ series.

[0070] Referring to Figs. 3 and 4The probe 50 can also be configured as an immersion or submersible probe. In this case, the medium 10 is located in an open vessel 114, and the probe 50, or rather the probe head 51, is immersed in the medium 10 with its light entry tips 54. In this example, the primary light beam 42 is emitted from the laser 44 into the medium 10 and reflected onto the beam axis 18 by an entry mirror 122. The portion of the primary light beam 42 that passes through the medium 10 also traverses an extended measuring path 46, which in this example is several centimeters long. This probe 50, also configured as a submersible probe, features a series 56 of numerous optical fibers 52, of which 15 are shown schematically here.It is apparent to those skilled in the art that there can also be a larger or smaller number of light guides 52 arranged side by side in a series arrangement 56 at the probe head 51. The primary light beam 42 is reflected upwards again via an exit mirror 124 to be absorbed in the light trap 36. In this example as well, the multi-light guide lateral probe 50, with its battery or series arrangement 56 of light guides 52 extending transversely to the beam axis 18 along the extended measuring section 46 at the probe head 51, detects the secondary light emitted transversely to the beam axis 18.

[0071] Referring to Fig. 4 is a modification of the diving probe made of Fig. 3The diagram shows an array in which signal correction light guides 53 are intermittently arranged between a plurality of light guides 52. By intermittently arranging the additional signal correction light guides 53 at specific intervals along the beam axis 18, the turbidity of the medium 10, or the absorption in the medium 10, can be determined, and thus a signal correction of the Raman measurement can be performed. This is particularly advantageous for turbid media when significant absorption of the primary light beam is expected along the longitudinally extended measurement path 46. If such significant absorption of the primary light beam 42 occurs, the Raman signal also decreases along the measurement path 46, so that the light guides 52 that are further away from the light entry window 32 or the entry mirror 122 also detect a weaker Raman signal.This effect can be corrected using the signal correction optical fiber 53 in the form of signal correction.

[0072] Referring to Fig. 5 Figure 1 shows a schematic representation of the device from the probe 50 to the detector unit 70. The device 1 can contain an evaluation unit 130, e.g. in the form of a computer, which evaluates the signals detected by the detector unit 70 and, if necessary, generates Raman spectra from them and / or, if necessary, performs signal corrections or other calculations or further processing steps.

[0073] Referring to the Fig. 6-14 Further embodiments are schematically illustrated, with which the detection efficiency of the multi-light guide lateral probe 50 can be further increased. Fig. 6-14 The diagram shows schematic cross-sections through the probe 50 in conjunction with the cuvette 14. Fig. 1 .

[0074] Fig. 6shows a single row arrangement 56 of a plurality of optical fibers 52. Referring to the Figs. 7-9 However, several row arrangements 56a-56d can also be arranged around the circumference of the cuvette 14. This is shown by the Fig. 7 two row arrangements 56a, 56b, which Fig. 8 three row arrangements 56a-56c and the Fig. 9 Four series orders 56a-56d, which are arranged, for example, in a star shape around the cuvette 14. Each series order 56a, 56b, 56c and / or 56d in turn contains a plurality of optical fibers 52 arranged side by side along the measuring section 46 or along the beam axis 18, which is not shown in the schematic representation for the sake of simplicity. Fig. 9This therefore represents four row arrangements 56a-56d or batteries of light guides 52, each with, for example, 51 light guides in a star-shaped arrangement around the cuvette 14, so that a total of 204 light guides are present in the several row arrangements 56a-56d, which increases the detection efficiency compared to the arrangement in Fig. 6 quadrupled again.

[0075] The Figs. 10-14 Schematic representations of further embodiments are shown, which can further increase the detection efficiency. These examples each comprise a series arrangement 56 of a plurality of optical fibers 52, as e.g. in Fig. 1 and Fig. 6 illustrated. In the embodiments of the Figs. 10-14The cuvette 14 has an opening 132 in the form of a slit on its side wall or ring wall 15, extending longitudinally along the measuring section 46 or the beam axis 18, and the light guides 52 penetrate through the slit through the side wall or ring wall 15 into the interior 134 of the cuvette 14 and thus into the medium 10, so that the light entry tips 54 are located inside 134 of the cuvette 14 and thus directly in the medium 10.

[0076] Referring to Fig. 10 The side wall or ring wall 15 of the cuvette 14 is provided with a reflective coating 142, which reflects at least some of the secondary light emitted at various radial or azimuthal angles back onto the light entrance tips 54 of the light guides 52. This further increases the detection efficiency.

[0077] Referring to Fig. 11 The mirror coating 142 may only affect a part of the circumference of the cuvette 14.

[0078] Referring to Fig. 12 The cuvette 14 can also be surrounded by a cylindrical concave mirror 144, which, like the mirror coating 142, is recessed at the points where the light is coupled out into the light guide 52.

[0079] Referring to Fig. 13 The cuvette 14 can also be provided with an internal mirror coating 146.

[0080] Referring to Fig. 14 The mirror 148 can have an elliptical cross-section, with the beam axis of the primary light beam 42 and the light entry points 54 each located at the two focal points of the ellipse. This allows the secondary light emitted along the beam axis 18 to be focused particularly efficiently onto the light entry points 54 in order to achieve high detection efficiency.

[0081] The detection effect can therefore be further enhanced by the schematically depicted mirrors or reflectors, since secondary light, which is scattered into other azimuth angles, is additionally, possibly even largely, focused onto the light incidence peaks 54 of the light guide 52.

[0082] In addition to or as an alternative to lowering the detection limit, the primary light power can also be reduced, meaning, for example, that weaker lasers can be used. Previously, Raman applications typically used lasers with a power of, for example, 300 mW. The increase in detection efficiency according to the invention makes it possible to use a laser 44 or another primary light source with a power of, for example, one milliwatt. This leads to better user protection and easier use of the device, for example, in the medical field or in any area where people come into close proximity to the primary light or the probe 50.

[0083] An interesting application of the invention lies in the monitoring of partial flows from wastewater treatment plants. These flows contain residues of nitrate, ammonium, phosphate, and sulfate. To protect the environment, particularly rivers and streams, from malfunctions and disruptions in the treatment plant, it can be advantageous to install a device according to the invention presented here at the outlet or another point within the plant. The device can be pre-configured on the secondary light spectrum side to the Raman spectrum of the four aforementioned salts, allowing the device to distinguish each salt with its own spectral range and thus monitor it simultaneously using its respective Raman spectrum. Therefore, nitrate, ammonium, phosphate, sulfate, and organic matter can be optically measured online simultaneously, and continuous readings can be displayed. The simultaneous detection of up to eight analytes also appears possible.Contrary to expectations that optical measuring devices might be susceptible to damage in harsh wastewater treatment plant operation, continuous monitoring with, for example, only two maintenance interventions per year is conceivable.

[0084] The probe 50 can be designed according to IP67.

[0085] Comparing the device proposed here with a commercially available Raman spectrometer or Raman photometer with focusing probes or conventional backscattering probes, the latter are highly susceptible to attenuation processes in the medium and quickly lose sensitivity, only detecting very small samples with sufficient volume. A conventional probe has a detection area on the order of 0.2 mm². In the present invention, four row arrangements are used (see...). Fig. 9) with 300 optical fibers each, 52 with a diameter of 400 µm, results in a detection area of ​​approximately 150 mm². This theoretically allows for an increase in detection efficiency by a factor of approximately 800 compared to the so-called "flower probe".

[0086] The increase in detection sensitivity compared to a conventional Raman spectrometer system depends on the detector area, or, in the conventional system, on the size of the detector entrance slit. Compared to a typical conventional spectrometer with an entrance slit of, for example, 600 µm, an increase in detection efficiency by a factor of several hundred or more is also possible. Larger detector areas and the associated, even greater increases in sensitivity are technically feasible.

[0087] If necessary, the device can even be designed to be so sensitive that anti-Stokes lines can also be detected.

[0088] In summary, the advantages of the present invention are high detection sensitivity, simple design, low cost and / or low laser power, and therefore lower safety requirements. By using a large detection area, a large portion of the measurement volume can be mapped onto the detector.

[0089] Advantageously, it may even be possible to obtain EX approval for the device, particularly if the primary light beam is not additionally focused and is absorbed in the primary light trap 36. Suitable lasers include, for example, the LBN-L50 or LBD-L50 series from Tippkemper / Matrix elektronik AG (see www.tippkemper-matrix.com).

[0090] Furthermore, the detector 72 can be supplemented by additional detectors for signal acquisition of the Raman-scattered secondary light, e.g. in additional transmission or absorption measurements.

[0091] Mirrors or the use of internally mirrored waveguides as cuvette 14, as in Figs. 10-14 schematically represented, they can further contribute to increasing efficiency.

[0092] If necessary, the use of a hyperspectral filter can also allow the location information, and thus the information of an optical fiber 52, to be detected individually. Multiplexing operation can also be implemented in this case.

[0093] Furthermore, tunable lasers or RGB lasers can be used for multi-wavelength excitation. The use of multiple laser diodes as backups within a single laser, or an opposing laser serving as a backup or as an additional primary light source, is also fundamentally possible.

[0094] In summary, the embodiments presented here employ a sensor head elongated transversely to the direction of incidence as a series arrangement of optical fibers, in other words, an arrangement of fiber sensors positioned in series, particularly with a CPM. This is expected to result in higher detection sensitivity compared to previously known Raman measuring devices. A sample of the fluid to be measured is passed through a suitable sample vessel, e.g., a measuring cuvette 14, which, for example, has transparent walls 15. The probe head 51 can also be integrated into the cuvette wall 15 or designed as an immersion probe.

[0095] If a laser beam 42 is used and directed into the medium 10, it can be directed into the sample parallel, i.e., with a small aperture angle, according to the usual properties of laser beams. Even simple lasers 44 can be imaged almost parallel over long distances. If the laser beam is sent longitudinally through the medium 10 as a Raman-active sample volume, Raman radiation is generated along the entire path, which is collected and evaluated along a certain length 46 along the beam axis 18.

[0096] 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 within the scope of protection of the claims.

Claims

1. A device (1) for measuring secondary light scattered in a medium (10), in particular in a turbid or clear medium (10), comprising: a light source (44) for generating a primary light beam (42) for irradiating into the medium (10) to be examined along a beam axis (18) of the primary light beam (42), in order to excite light scattering in the medium (10) with the primary light beam (42) along the beam axis (18), in particular Raman scattering, fluorescence and / or phosphorescence, such that the medium (10) emits secondary light in a secondary light spectrum due to the light scattering along the beam axis (18); a probe arrangement (50) for receiving and forwarding the secondary light emitted along the beam axis (18); wherein the probe arrangement (50) comprises a plurality of light guides (52) which extend transversely to the beam axis (18) of the primary light beam (42) at their light entry tips (54) and which are arranged next to one another in an elongated row arrangement (56) along the beam axis (18) so as to form an overall light entry area made up of the light entry tips (54) and extending linearly along the beam axis (18); a detector device (70) for detecting the secondary light collected by the plurality of light guides (52) and supplied to the detector device (70), wherein the detector device (70) comprises at least one single-photon detector (72, 74, 76); wherein: a tunable filter (68) is comprised as a wavelength-selective element which spatially disperses the secondary light, such that, by tuning the filter, the secondary light is detectable in a wavelength-selective manner using the detector device (70) in order to map at least part of the secondary light spectrum; the light guides (52) are in the form of hollow waveguides or plastic fibers; the total cross-sectional area of all light guides (52) together is at least 10 mm2; the light guides (52) define a cross-section converter (60) as the cross-section converter (60) is reshaped along its extension by rearranging the light guides (52) from the elongated row arrangement (56) into a compact bundle arrangement (62), thereby reshaping the overall light entry area of the light entry tips (54) extending linearly along the beam axis (18) into a two-dimensional overall area having a greater width and a smaller length than the linear overall light entry area; the secondary light collected by the probe arrangement (50) is emitted from the light guides (52) at detector-side light exit ends (64) and directed onto the tunable filter (68); one or more beam-shaping elements are arranged between the cross-section converter (60) and the tunable filter (68); and the single-photon detector (72, 74, 76) has a detection area with a diameter of greater than or equal to 3 mm.

2. The device (1) according to claim 1, wherein the light guides (52) each have a light guide diameter of at least 100 µm, preferably at least 200 µm, preferably at least 500 µm.

3. The device (1) according to any one of the preceding claims, wherein at least 5, preferably at least 10, preferably at least 25 light guides (52) are arranged next to one another in a row (56) along the beam axis (18).

4. The device (1) according to any one of the preceding claims, wherein the total cross-sectional area of all light guides (52) together is at least 20 mm2, preferably at least 40 mm2.

5. The device (1) according to any one of the preceding claims, wherein the medium (10) to be examined is a fluid medium, further comprising a cuvette (14) having a fluid inlet (12) and a fluid outlet (16), such that the fluid medium (10) to be examined can be directed through the cuvette (14) and the primary light beam (42) can be radiated through the cuvette (14), such that the fluid medium (10) directed through the cuvette (14) is irradiated by the primary light beam (42) while flowing through the cuvette (14); in particular wherein the cuvette (14) comprises a primary light beam entry window (32) at a first end (22) thereof and / or a primary light beam exit window (34) at a second end (24) opposite the first end (22) thereof, through which the primary light beam (42) can enter the cuvette (14) and / or exit the cuvette (14).

6. The device (1) according to claim 5, wherein the cuvette (14) comprises a side wall (15) or a window extending along the beam axis (18) made of a transparent or translucent material, such that the secondary light can exit the cuvette (14) outward through the side wall (15) or the window, and wherein the probe arrangement (50) is arranged outside on the cuvette (14) in order to capture the secondary light exiting through said side wall (15) or window; or wherein the cuvette (14) has a lateral opening (132) and the light guides (52) protrude through said lateral opening (132) into the interior (134) of the cuvette (14), such that the light entry tips (54) of the light guides (52) are located directly in the fluid medium (10) in order to directly capture the secondary light generated in the fluid medium (10).

7. The device (1) according to any one of claims 1 - 4, wherein the medium (10) to be examined is a fluid medium, further comprising an immersion vessel (114) in which the fluid medium (10) is held, and wherein the probe arrangement (50) is in the form of an immersion probe in order to immerse the light entry tips (54) into the fluid medium (10) within the immersion vessel (114) and to directly capture the secondary light generated in the fluid medium (10).

8. The device (1) according to claim 5 or 6, wherein a cylindrical concave mirror (144, 148) is comprised, which is arranged along the cuvette (14) in order to focus the secondary light exiting from the cuvette (14) in different radial directions onto the light entry tips (54) of the light guides (52); or wherein the cuvette (14) is partially mirrored (142, 146); in particular wherein the cylindrical concave mirror (148) or the mirrored cuvette (14) has an elliptical cross section perpendicular to the beam axis and the beam axis (18) and / or the light entry tips (54) of the light guides (52) are arranged at the focal points of the ellipse.

9. The device (1) according to any one of the preceding claims, wherein the tunable filter (68) is an acousto-optic tunable filter (AOTF).

10. The device (1) according to any one of the preceding claims, wherein the detector device (70) comprises one or more secondary electron multipliers (72, 74, 76), in particular customized photomultipliers.

11. The device (1) according to any one of the preceding claims, wherein the primary light beam (42) is radiated through the medium (10) as a parallel beam.

12. The device (1) according to any one of the preceding claims, wherein the light source (44) is in the form of a laser and the laser in particular has a light output power of not more than 1 milliwatt.

13. The device (1) according to any one of the preceding claims, further comprising an evaluation device (130) which is configured to generate a Raman spectrum, fluorescence spectrum and / or phosphorescence spectrum of the secondary light.

14. A method for detecting Raman-scattered, fluorescent and / or phosphorescent secondary light, comprising the steps of: providing a Raman-active, fluorescent and / or phosphorescent medium (10); irradiating a primary light beam (42) into the Raman-active, fluorescent and / or phosphorescent medium (10) along a beam axis (18); detecting secondary light which is emitted transversely, in particular perpendicularly to the beam axis (18) along an elongated measurement path (46) along the beam axis (18) using a probe arrangement (50) and a detector device (70); wherein the probe arrangement (50) comprises a plurality of light guides (52) which extend transversely to the beam axis (18) of the primary light beam (42) at their light entry tips (54) and which are arranged next to one another in an elongated row arrangement (56) along the beam axis (18) so as to form an overall light entry area made up of the light entry tips (54) and extending linearly along the beam axis (18); wherein the light guides (52) define a cross-section converter (60) as the cross-section converter (60) is reshaped along its extension by rearranging the light guides (52) from the elongated row arrangement (56) into a compact bundle arrangement (62), thereby reshaping the overall light entry area made up of the light entry tips (54) and extending linearly along the beam axis (18) into a two-dimensional overall area having a greater width and a smaller length than the linear overall light entry area; wherein the secondary light collected by the probe arrangement (50) is emitted from the light guides (52) at detector-side light exit ends (64) and directed onto a tunable filter (68); wherein the light guides (52) are in the form of hollow waveguides or plastic fibers and the total cross-sectional area of all light guides (52) together is at least 10 mm2; wherein one or more beam-shaping elements are arranged between the cross-section converter (60) and the tunable filter (68); wherein the detector device (70) comprises at least one single-photon detector (72, 74, 76); wherein the single-photon detector (72, 74, 76) has a detection area with a diameter of greater than or equal to 3 mm; and wherein the secondary light is spatially dispersed by the tunable filter (68) as a wavelength-selective element, such that, by tuning the filter, the secondary light is detected in a wavelength-selective manner by the detector device (70) in order to map at least part of the secondary light spectrum.

15. Use of the device (1) according to any one of claims 1 - 13 and / or of the method according to claim 14 for monitoring a flow in an area of a sewage plant or of other wastewater, wherein in particular nitrate, ammonium, phosphate, sulfate and / or organic constituents are monitored in the outflow or at another location of the sewage plant.