DE19751403A1 - Process and assembly for determining absorption, fluorescence, scatter and refraction of liquids, gases and solids - Google Patents

Abstract

In the process, a light beam of defined wavelength is coupled into a multi-reflective assembly. A localized receiver is positioned immediately behind a mirror which passes a limited amount of light, measuring the incident coupled light. The light reflected by the measured volume, and in the opposite direction to the incident light, is measured by a localized receiver on the mirror. The process also measures the reflected light from the measured volume boundary layer. The absorption is derived from the reciprocal value of the transmitted coupled light. The scatter and the fluorescence are derived from a combination of the reflectance spectrometry and transmitted light. The refraction is derived from the combination of reflected and transmitted radiation.

Description

Technical field

Analytics, environmental, quality and process monitoring, spectroscopy, absorption, remission, Scattering, fluorescence, refraction.

State of the art Absorption spectroscopy

Conventional absorption methods are used to detect absorbing substances in liquids, gases and solids (measuring volume). Radiation of a defined wavelength is coupled into the measurement volume. On their way through the Meßvolu men, the coupled radiation is weakened by absorbing substances. After a defined distance, the coupling radiation is coupled out again and directed to an optoelectronic receiver which registers the weakened intensity I. The quotient of the weakened and non-weakened intensity I ₀ is the transmission T:

T = I / I ₀ = exp (-α _T x) (1).

This law by Bouguer-Beer-Lambert describes the relationship between transmission and the total absorption coefficient α _T (for the sake of simplicity, the scatter has been neglected here). The term x is the path that the coupling radiation travels in the measurement volume. [1], [2].

A special absorption method is based on the principle of evanescent wave fields or attenuated total reflection (ATR). Here radiation is in a light-conducting solid, for. B. ATR crystal or optical waveguide, coupled and decoupled again after passing through a defined distance. The optical fiber is in contact with the measuring volume to be examined. The coupling radiation is totally reflected in the optical fiber at the interface to the measurement volume, with a small part of the radiation penetrating into the measurement volume (evanescent wave) and acting with it. This weakens the coupling radiation. This weakening is measured. The classic relationship in formula (1) applies. [1]
In the case of measuring volumes with very low optical densities (e.g. gases), the distance of the injected radiation in the measuring volume is increased in order to obtain evaluable signals. Long distances can be achieved with the help of reflective elements, for example. [3] In [4] an internally mirrored spherical cell is presented, in which the coupled radiation is reflected back and forth several times and then coupled out again and directed at a receiver. A gas absorption cell is described in [5].

In [6] to [8] a method for determining the total absorption is proposed, in which not the coupling radiation weakened after traveling a defined distance is measured, but rather the interaction radiation generated by the coupling radiation (Fluorescence and scattering). The special feature is that the coupled beam tion is almost completely absorbed by the measuring volume due to long distances.

Reflectance spectroscopy

The reflectance is made up of diffuse reflectance and specular or directional Reflection together.

(a) Remission

The reflectance R is the diffuse reflection of radiation from matter (measuring volume). It is a measure of the intensity of the photons reflected against the direction of incidence. In the classic sense, these are scattered photons. The reflectance is determined by the scattering capacity (scattering coefficient β) and absorption capacity (total absorption coefficient α _T ,) of the measuring volume. For the sake of simplicity, the absorption will dominate in the following. The theory of Kubelka and Munk is used to describe the remission mathematically. In the case of an infinitely extended measurement volume (e.g. deep water), the remission is proportional to the quotient of the scattering coefficient and absorption coefficient,

R _S ∼ β / α _T (2).

If fluorescence is also generated by the radiation incident in the measurement volume, then the remission is determined in the broader sense not only by the scattering but also by the fluorescence ability, which is determined by the product of the fluorescence quantum yield Q _F and the absorption coefficient of the fluorophores α _{F of} the measurement volume (Q _F α _F ) is characterized. The fluorescence contribution to the remission of large measurement volumes is determined by the quotient

R _F ∼ Q _F α _F (λ _E ) / [α _T (λ _E ) + (α _T (λ _F )] (3)

controlled, where λ _E and λ _{F are} the wavelengths of the incident radiation and fluorescence. In many cases of transmitting measurement volumes, the absorption at the wavelength of the incident radiation is greater than the absorption at the fluorescence wavelength (e.g. in the case of eutrophicated surface waters). Then (3) merges into (4):

R _F ∼ Q _F α _F (λ _E ) / α _T (λ _E ) (4).

The formulas (2) and (4) are characterized by the same mathematical structure. The In both cases, reflectance is proportional to the scattering and fluorescence ability and on the other hand, inversely proportional to the total absorption.

For example, remission spectroscopy is fundamental for remote sensing and is used in both optically very dense as well as applied to transmitting measurement volumes. examples for The first case is remission measurements on vegetation (leaves or needles) around which determine physiological condition or measurements on soils to determine example wise moisture and structure.

The second case of the transmitting measuring volumes include atmosphere, water and Oceans. Comparatively simple relationships are given when the incident Radiation (global radiation, lidar) can run dead in the measurement volume, d. H. that in the example of Water bodies the incident radiation does not reach the water floor. [9], [10].

(b) reflection

Reflection spectroscopy is preferably used to examine solid surfaces used. The radiation that is directly reflected or directed by a surface is thereby analyzed (reflection law), which provides information about the spectral reflectivity.

When analyzing the diffuse reflectance R of transmitting solid, liquid and gas moderate measurement volume (see (a)) is the one occurring at the interface with the measurement volume specular reflection usually a disturbance variable that is masked out by suitable measuring arrangements becomes.

The specular or directional reflection R _G depends, among other things, on the refractive index n of the measurement volume. Since the measurement volume absorbs in many cases, the refractive index that is customary for reflection is determined in addition to the refractive power by the absorption capacity of the measurement volume. The refractive index consists of a real part and an imaginary part (complex number):

R _G = ((n-1) / (n + 1)) ² (5)

with n = n _real + n _imaginary . Formula (5) is a simplified representation for the air / measurement volume interface with vertical radiation. The refractive index is practically determined goniometrically or interferometrically as a real part. [1], [2]

Problem / task

In the application [11] a method is proposed, the absorption and remission based on the complete absorption of the coupling radiation in the measuring volume trimmed. Radiation of a defined wavelength is injected into the measurement volume to be examined, which is preferably transmissive. The measuring volume is there between two opposing mirrors. The mirrors are designed in such a way that a sufficiently high number of reflections the way of the coupling mirror Coupled radiation is so long that it is completely absorbed in the measuring volume can be. Complete absorption is a prerequisite for the development of remission according to the formulas given above (term here: saturated long-term remission). The  saturated long-term remission is arranged with a on the coupling mirror and on the Measuring volume aligned photoelectronic receiver in conventional reflectance measuring geome trie, i.e. backwards, measured. The measurement signal is according to formula (2) in the case of scatter and described in the case of fluorescence according to formula (4).

A second essential measuring process takes place synchronously with this. The coupling mirror (or also the counter mirror) is partially transparent, e.g. B. 5% transmission and 95% reflectivity. Consequently, after each reflection or after each revolution, part of the coupling radiation transmitted by the measuring volume passes through the coupling mirror and arrives at a second receiver arranged immediately behind the coupling mirror. If the fluorescence and scattering photons passing through the partially transparent mirror are neglected, the intensity I _{Tr of} the transmitted radiation is approximated by the following formula:

I _Tr ∼ m / α _T (6).

The term m is a constant that is characteristic and known for the permeability of the coupling mirror. The total absorption coefficient α _T can thus be determined directly from (6). Compared to classic absorption spectrometry (Lambert-Beer Exponential Law) (6) is characterized by a higher sensitivity, which leads to deeper detection limits and higher accuracy. With increasing α _T , I _Tr decreases. This is evident, since with increasing α _T the mean path length of the injected radiation decreases until it is almost completely absorbed in the measuring volume and thus the number of reflections or cycles decreases. This also reduces the intensity I _Tr of the coupling radiation passing through the partially transparent mirror. In addition, the intensity I _{Tr is} also determined by the mirror constant m. The larger m, ie the smaller the reflectivity or the greater the permeability of the coupling mirror, the higher I _Tr .

By inserting α _T in the formulas (2) and (4), the scattering and fluorescence ability β and Q _F α _{F can also} be determined indirectly. The ambiguity of classic reflectance spectroscopy is eliminated by the combination with the absorption spectroscopy presented above.

Furthermore, an apparatus for performing the method is described. This Device has basic features, which are considered industriel operations in harsh on-site conditions, a modular structure to achieve a large scope of application and a simple manufacturing technology concretized and must be qualitatively expanded. A device for this is presented below.  

solution

Claim 1 is explained. The absorption module ( 1 ) is illustrated in Fig. 1. This is formed by the coupling, measuring, light guide and connection module ( 5 ), ( 2 ), ( 3 ), ( 4 ). The absorption module is also the carrier for the modules for measuring reflectance ( 6 ) and refraction ( 7 ). The coupling module serves, on the one hand, to couple radiation into the measurement volume (coupling radiation). The coupling radiation is then reflected several times between reflecting elements, for which purpose the absorption module is opposed by a reflection module (for the various versions of the reflection module, see below). On the other hand, the coupling module serves to couple radiation back into the sensor (transmitted coupling radiation through the partially transparent mirror ( 5 a)). The coupling module consists of the coupling mirror ( 5 a) and the fiber optic block ( 5 b). The coupling mirror is preferably flat: it can also be spherical in certain applications. The coupling mirror or its mirror substrate (e.g. glass) is covered with a partially transparent layer ( 5 c) which, for example, transmits 10% radiation and reflects 90% (neglecting the absorption of the layer). This layer is applied on the inward, in the direction of the measuring module ( 2 ) side of the mirror. This has the advantage that this reflective layer is protected from the outside against environmental influences by the glass substrate, an additional protective layer is therefore not necessary. The block ( 5 b) contains several optical fibers ( 5 e), which are glued close together. The diameter of the optical waveguide is small compared to the diameter of the coupling mirror. The optical fibers are aligned parallel to the normal of the coupling mirror. The end faces of the optical fibers are on a straight line and form a common vertical plane. The end face of the block ( 5 b) also lies in this plane. This light wave conductor level lies flat from the inside against the upper area ( 5 d) of the coupling mirror. This area is not mirrored. The coupling mirror is transparent in this area for the radiation to be coupled into the measuring volume. The mirror layer and optical fiber end faces form a common vertical plane. Immediately behind the coupling mirror is a radiation-carrying volume, which, for. B. is formed as an internally mirrored conical reflector ( 8 ) which guides the coupling radiation passing through the coupling mirror to the measuring module ( 2 ) with the optoelectronic receiver attached there. The receiver registers (in addition to remission photons) the intensity of the transmitted coupling radiation, the reciprocal of which is a measure of the absorption of the measurement volume. The coupling module is followed by the fiber optic module ( 3 ), which receives the fiber optics from the fiber optic block ( 5 b) and forwards them to fixed positions in the block ( 3 a). There the optical fibers are fixed, e.g. B. by gluing in the holes provided. In ( 3 a) the flat end faces of the optical fibers lie in a common vertical plane. The end face of the connection module ( 4 ) also lies in this plane. This connection module, which is arranged downstream of the light guide module ( 3 ), has the function of providing the light guide module with radiation for its transmission. There are several light emitting diodes (LED) ( 4 b) and an optical fiber ( 4 a). The optical fiber is used to conduct radiation from an external source, the z. B. is connected via a SMA connection with the sensor ver. Spectrally selective elements can also be arranged between the sensor and the external radiation source. The end faces of the LED and that of the optical waveguide lie in a common vertical plane. The end face of the connection module ( 4 ) is also on this level. Instead of the LED, optical fibers can also be located, which are led to the outside. Because of its modular structure, the arrangement described has the advantage that it can be easily adapted to the measuring conditions on site and that it can be easily manufactured.

Different types of reflection modules can be combined with this absorption module become. The resultant arrangements result in the measurement volume being once in the multiple reflection space between the coupling mirror and the counter mirror and to the other of which can be located outside. Furthermore, the measurement volume can be in one radiation-carrying volume. But it can also be of such a volume be unaffected, d. H. the measuring volume is not in a radiation-carrying range Volume.

The end faces of the optical fibers are located directly above the mirror layer ( 5 c) (claim 2). This makes optical adjustment much easier and generates fewer losses of coupling radiation during multiple reflection in the event that the reflection module is equipped with a concave mirror ( Fig. 4).

The immediately behind the coupling mirror ( 5 a) arranged conical reflector ( 8 ) acts as a cross-sectional converter for the coupling radiation passing through the coupling mirror (claim 3). Its mirror-side diameter corresponds to the diameter of the mirrored layer on the coupling mirror and its receiver-side diameter corresponds to the light-sensitive surface of the receiver in the measuring module ( 2 ). The diameter of the cone on the mirror side is larger than its diameter on the receiver side. Thus, receivers can be used whose dimensions are sufficiently small so that they do not interfere with the positioning of the optical waveguides in the coupling-in and light-guiding module ( 5 ), ( 3 ) and in order nevertheless to be able to register the entire transmitted coupling radiation. Instead of the receiver in the measuring module, an optical waveguide can also be located, which is guided to the outside. If necessary, a scattering or diffuser plate can be arranged between the coupling mirror and the optical waveguide to reduce directional radiation.

According to claim 4, the LEDs located in the connection module ( 4 ) are flat in the direction of radiation. The original LED dome is shortened to such an extent that the distance between the emitter and the radiation surface is as small as possible. The radiation surface is polished for maximum radiation transmission.

According to claim 5, the end faces of the connection and light guide modules ( 4 ), ( 3 a) are connected flat on top of each other. The optical fibers ( 5 e) in the light guide module and the LED ( 4 b) and the one optical fiber ( 4 a) in the connection module are positioned in such a way that the light-guiding end faces in the light guide module are centrally and tightly opposed to the light-guiding end faces in the connection module. This ensures maximum radiation transmission from the connection module to the light guide module.

According to claim 6, the transmitted coupling radiation and also through the one reflectance photons entering the coupling mirror with spectrally selective elements (e.g. bandpass filter or edge filter). There are between the coupling mirror and Measuring module arranged spectrally selective elements. For example, in the case of the On coupling of white light is an advantage. The then also transmitted white coupling beam lung can be resolved spectrally (e.g. by means of a polychromator that transmits the Coupling radiation is supplied via an optical fiber).

Furthermore, a protective glass and / or a filter can be used instead of the coupling mirror be localized. The sensor then works as a classic absorption spectrometer, with the  Reflection module (see explanations below) to extend the path of the on coupling radiation is used. With optically denser measuring volumes, the sensor is without reflection module operated and in this case is a classic reflectance spectrometer.

According to claim 7 are spectrally selective elements for the coupling and measuring radiation (LED, filter, grid) adapted to the respective application and in the following way educated. On the one hand, the sensor wavelengths are in the absorption areas of the substances to be detected. On the other hand, these are outside of these absorption areas localized and, if possible, at a characteristic absorption point of the solvent arranged. In the first mode, after measuring absorption and remission di closed right on the absorbent substance. The second mode uses the fact from that to detect the absorption of the solvent with increasing the concentration of the substance is reduced. The measuring volume lightens due to this dilution effect the absorption point characteristic of the solvent. This has the advantage that substances that are completely incapable of absorption can also be detected. Advance Settlement is simply the presence of a constant and well-defined absorption site of the solvent. In addition, spectrally selective elements can be arranged that neither in the absorption area of the substance to be detected still in the absorption area of the Lö solvent.

According to claim 8, the remission module ( 6 ) is at a minimal distance from the optical fibers of the coupling module ( Fig. 2, top view). Its optical window ( 10 ) and the coupling mirror of the absorption module lie in a common plane. This ensures that the remitted radiation is not or only slightly shadowed by the dimensions of the sensor that protrude into the beam path between the remission photons and the remission receiver. The window of a silicon diode can serve as a protective window for the reflectance module. The reflectance module can also be equipped with two receivers ( 9 ), one recording the scatter and the other the fluorescence (edge filter ( 11 ) in front of the receiver). The two receivers can also be arranged in such a way that there is a defined distance between the two. This is useful if, due to the effect of an imaging mirror, the radiation specularly reflected by optical interfaces completely falls into the space between the two receivers. The receivers only register the remission of the measurement volume. Furthermore, a further receiver can be located between the two remission receivers, which registers both specularly reflected radiation and remission. Instead of the receiver, optical waveguides can also be arranged, which are guided to the outside.

On the other hand, with a remission receiver shifted backwards by a defined distance and adapted to the application, the remission effect can be enhanced by the above-mentioned shading, in particular in the case of optically denser measurement volumes, provided the effect of the distance law 1 / r ^{2 is} not too great.

For the measurement of a linear short-path remission, the remission module is equipped with a Optics geared directly to the coupling location.

According to claim 9 in the refraction module ( 7 ), for. B. with the help of an LED ( 12 ), radiation generated. The refraction module is shown in Fig. 3. The LED is on collective lenses ( 13 ), ( 14 ) on a receiver ( 18 ), for. B. on a scale of 1: 1. The radiation is reflected at the optical window ( 17 ). There are reflective elements ( 15 ), ( 16 ) (e.g. aluminum mirror) both in the beam path of the incident light beam and in the beam path of the reflected beam. Sufficiently long paths of LED radiation are achieved on the one hand, and on the other hand an oblique radiation incidence on the optical window. A long path or a sufficiently large distance between the receiver and the measurement volume is required to reduce the remission photons originating from the measurement volume and striking the receiver. The receiver thus registers specularly reflected radiation mainly at interfaces. An oblique incidence of the LED radiation on the window increases the selectivity between the reflex of interest at the window / measurement volume interface and the undesired reflex at the air / window interface. A small receiver area means that the number of remission photons hitting the receiver is even smaller. It is advantageous for a high signal-to-noise ratio that the above-mentioned 1: 1 image of a small radiating area, eg. B. to realize the emitter of an LED. The optical window of the refraction module with the coupling mirror is expediently arranged in a common plane. Instead of the radiation source and the receiver, optical waveguides can also be located, which are routed to the outside.

Fig. 4 shows a case in which the measurement volume is located between the planar coupling mirror and a concave counter mirror ( 20 ). The optical coupling of the coupling radiation is realized by the imaging concave mirror. The multiple reflection takes place between the coupling mirror and the concave mirror. The measuring volume can be of various types: classic cuvette filling, flow or free jet. According to claim 10, a concave mirror ( 20 ) is mounted in the reflection module ( 19 ), which is variable with respect to its distance from the coupling mirror and the other with regard to the tilt angle of its mirror plane with the aid of leaf springs ( 21 ), ( 22 ) via adjusting screws. The concave mirror is set with respect to its distance so that the end faces of the optical fibers are localized in the coupling module between single and double focal length. With regard to its tilt angle, the concave mirror is set so that at a mirror distance that corresponds to twice the focal length, the images of the end faces of the optical fibers (magnification 1: 1) are localized in the lower region of the coupling mirror. The lower area is the area of the coupling mirror opposite the optical fibers (ie the end faces of the optical fibers are on the top - their images below, with the images lying on the mirror layer!). Such an arrangement enables an easily performed adjustment procedure to achieve an efficient multiple reflection of the coupling radiation. In special applications, the mirror distance is equal to the focal length of the concave mirror. Applications e.g. E.g .: Transparent liquids in the mineral oil, textile, food and chemical industries.

Claim 11 is an advantageous embodiment of claim 10, for example for the cases in which the external conditions of sensor assembly and complicated sensor requirements do not allow the concave mirror to be tilted. The mirror will then replace one Tilt adjusted via a vertical shift.

Claim 12 describes an application in which the measurement volume ( 23 ) is located between a coupling and counter mirror in a radiation-carrying volume ( Fig. 5). The reflectance and refraction modules are in operation or not, depending on the application. The counter mirror ( 26 ) is a full mirror and flat. The radiation-guiding volume ( 24 ) can, for. B. an HPLC flow capillary, which leads the coupling radiation. The multiple reflection takes place between the coupling mirror and the counter mirror and the capillary. If necessary, a light-conducting cone ( 25 ) for directing the coupling radiation is arranged between the coupling module and the optical end face of the capillary facing it, the capillary-side diameter of which corresponds to that of the capillary. The counter mirror can be arranged separately or vapor-deposited on the other end face of the capillary. Instead of a rigid capillary, a flexible, hollow and liquid-carrying Lichtwellenlei ter can be arranged. Furthermore, an optoelectronic receiver ( 27 ) can be mounted in such a way that it detects the interaction photons generated at an angle of 90 ° to the radiation, such as fluorescence and scattering. Applications e.g. E.g .: transparent liquids for flow measurements, HPLC laboratory analysis.

Claim 13 deals with a special embodiment of Claim 12. Here, the end face of the coupling ( 29 ) is arranged directly in front of the coupling mirror ( 31 ) ( Fig. 6). The measuring module ( 32 ), ie the optoelectronic receiver is immediately downstream of the coupling mirror. Such a device can easily be realized from a commercially available LED ( 28 ). The electrical connections of the LED are led out to the side. This provides sufficient space for the vapor deposition of a partially transparent mirror layer ( 31 ) on the LED base. The receiver ( 32 ) is e.g. B. glued directly to the LED base. The coupling mirror can also be located at another location. To do this, the LED dome is cut off immediately in front of the LED emitter, the layer for the coupling mirror is evaporated onto the inner surface, and the two parts are reassembled. The partially transparent layer then contains a small, optically transparent opening for coupling in the emitter radiation. The counter mirror ( 30 ) is evaporated on the surface opposite the partially permeable coupling mirror. The counter mirror can be concave or flat. The multiple reflection takes place via coupling-in and counter mirrors. The LED body (dome) can serve as a radiation guide due to total reflection. The cathedral can also be mirrored from the outside. The measuring volume ( 23 ) is located in an opening between the coupling mirror and the counter mirror. The size of the opening is adapted to the optical properties of the measurement volume to be examined. Several LEDs are arranged to implement different wavelengths.

Another modification is that no mirror layers as coupling and counter apply mirror. In this case, another receiver on the emitter attached to the opposite side, then the LED is a simple absorption and draw sion spectrometer, several LEDs arranged to implement different wavelengths be net.

The arrangement of several LEDs can be linear or as a drum, for example. Here it makes sense to emit radiation towards the front (absorption) and backwards (remission) bring optical device to a receiver. In this case, the LEDs are closed controlled different times in flash mode. Another option is to use the Control LED simultaneously and map it to a diode array or one Realize CCD camera.

Fig. 7 illustrates claim 14. The measurement volume is located outside the sensor, ie the measurement volume is located outside the multiple reflection space, which is spanned by the coupling and counter mirrors. The multiple reflection takes place between the planar coupling mirror ( 5 a) of the coupling module, the counter mirror ( 34 ) and a radiation-guiding body ( 33 ) located between the two mirrors, which can be, for example, an ATR crystal. The mirror is a full mirror and flat. The coupling radiation is guided in the ATR crystal. The interaction between the coupling radiation and the measurement volume ( 23 ) located on the outside of the ATR crystal takes place via the evanescent wave fields existing in the immediate vicinity of the crystal. The ATR crystal can also be coated with a substance-selective layer. If necessary, a radiation-conducting cone can be arranged between the coupling mirror and the ATR crystal to adjust the diameter of the coupling mirror and the ATR crystal. Instead of the ATR crystal, a flexible optical waveguide can also be arranged. The refraction module is in operation and in contact with the measuring volume. The remission module is usually not in operation. By a special flange of the ATR crystal in such a way that part of the end faces of the optical fibers in the coupling module couple radiation into the measurement volume and another part radiation into the ATR crystal, the remission module can also be in operation. With this arrangement, absorption, remission and refraction can thus be determined synchronously, for example in strongly cloudy measurement volumes. Applications z. For example: industrial waste water.

According to claim 15, the measurement volume is outside the sensor ( Fig. 8). Instead of a counter mirror, which has been dealt with up to this point, an optical window ( 38 ) is located in one embodiment or a counter mirror ( 38 ) with transmitting areas on the measurement volume ( 23 ) is located in the other embodiment. The window design is first explained. A radiation-carrying volume ( 37 ) is arranged between the measurement volume or window and the coupling mirror. After the irradiation via the optical waveguide block ( 5 b) of the coupling module, there is a multiple reflection between the measurement volume, a coupling mirror ( 5 a) and the radiation-carrying volume ( 37 ). This volume can be an internally mirrored hollow body and / or a solid body guiding radiation through total reflection. The shape of the radiation-carrying volume can be different, e.g. B. cylin drisch or conical. The sensor sits on the measuring volume ( 23 ) by means of ( 35 ), ( 36 ). This contact for measuring volume contact is a solid body or block. If necessary, the reflectance and refraction modules can be in operation while sitting on the measurement volume. In this case, the reflectance and refraction modules are shifted forward in the direction of the measurement volume in comparison to FIG. 1 and even form the support for contacting the measurement volume. The window ( 38 ) in contact with the measuring volume is optically transparent. The radiation-carrying volume between the coupling mirror and the window can also be a flexible optical waveguide. Depending on the application, this can be arranged in a bundle with additional optical waveguides of the reflectance and refraction modules. The sensor can also be designed without a window, for example on solid surfaces. If the radiation-carrying volume ( 37 ) is a solid carrying radiation through total reflection, then its surface on the measurement volume side is identical to the window. Applications include measurement volumes with comparatively high remission capacities, such as milk and paper.

Furthermore, a partially transparent mirror ( 38 ) can be arranged instead of the window. The multiple reflection of the coupling radiation takes place in the radiation-guiding space ( 37 ) between the coupling mirror ( 5 a) and the counter mirror ( 38 ). The mirror layer of the counter mirror is partially transparent in such a way that non-mirrored areas exist at defined locations of the mirror, which act as optical openings. These areas transmit part of the coupling radiation into the measuring volume. The other part of the coupling radiation is reflected again in the direction of the coupling mirror. Furthermore, interaction photons from the measurement volume through the non-mirrored areas in the mirror in the sensor. The receiver located behind the coupling mirror registers an intensity that depends on the reflectivity of the measurement volume. Applications are e.g. B. Meßvo lumina with comparatively low reflectivity, such as surface water, water and landfill leachate.

According to claim 16, the window ( 38 ) mentioned in claim 15 can be covered with an indicator- or substance-selective layer which is in contact with the measurement volume. This window can also be mechanically roughened or have mechanical structures with a defined pore size. The pores act as a material-selective surface, for example for the separation of liquid substances from solid particles. Analogously, the counter mirror can be equipped at its optical openings with an indicator or substance-selective layer or surface, which interacts with the measurement volume.

Based on the LED modification presented in claim 13, claim 17 deals with a special embodiment of claims 15 and 16 ( Fig. 9). In comparison to Fig. 6, the LED dome ( 28 ) has no opening for the measuring volume. The measuring volume ( 23 ) is located outside. The surface of the LED ( 39 ) opposite the coupling mirror ( 31 ), which can either be flat or originally convex, has the function of the window or that of the counter mirror with transmitting areas. The dome serves to guide the radiation and can be mirrored if necessary .

Claim 18 describes an advantageous embodiment of claim 17 mirror layers for coupling and counter mirrors are not applied. Fig. 10 shows the coupling of two LEDs ( 28 ), one of which has a normally designed (convex to the outside) or front plan dome ( 40 ) and the other a front plan and oblique termination ( 41 ) for coupling the radiation into it Measuring volume ( 23 ). The radiation is coupled directly into the measuring volume via the LED dome. The measuring module ( 32 ) behind the LED with the flat window ( 40 ) receives both photons from the measuring volume (remission) and specularly reflected photons (refractive index and absorption) at the thorn / measuring volume interface. The measuring module ( 32 ) behind the LED with an oblique plan window ( 41 ), on the other hand, only receives photons from the measuring volume, since the specularly reflected photons are not directed towards the receiver due to the oblique surface. The coupling of the two measurement signals thus enables the absorption and remission properties of the measurement volume to be determined synchronously. In a further embodiment, the windows contacted with the measurement volume are provided with surfaces analogous to claim 16. Depending on the application, several LEDs, e.g. B. linear or as a drum. The receivers attached directly to the LED base can be replaced by an optical arrangement with a subsequent diode array or CCD camera.

Another advantageous embodiment of claim 15 is claim 19. Here, a radiation-guiding tube is mounted directly on the window or the mirror. The tube containing the measurement volume to be examined can be cylindrical and without a mirror. Its inner diameter facing the sensor is the same as that of the window or counter mirror. The tube has a refractive index that allows total reflection of coupling and remission photons located in the tube. Application examples are: a macro flow cell or an optical fiber filled with a liquid. Such an arrangement has the advantage that the distance law 1 / r ^2, which has a disturbing effect when the radiation is coupled into a large measuring volume, has little or no influence.

According to claim 20 are those described in claims 13, 17 and 18 LED modifications arranged in a common device.

In the following with the claims 21 to 23 advantageous embodiments of the one coupling and measuring modules described.

According to claim 21 ( Fig. 11 and 12), the coupling takes place via the partially transparent plane mirror ( 43 ) by means of optical fibers ( 42 ), the diameter of which is significantly smaller than the diameter of the coupling mirror. Only then are the radiation losses due to coupling out through the coupling light waveguide low. The detection or decoupling of transmitted coupling radiation from the multiple reflection space is implemented via an optical waveguide ( 44 ) which is arranged directly after the coupling mirror and which brings the radiation onto the receiver ( 45 ). The coupling mirror side diameter of the light waveguide is the same as that of the mirror layer. This optical fiber can be an optical fiber bundle. The optical waveguide has the function of the light-guiding cone ( 8 ) in Fig. 1. The optical waveguide intended for the coupling and the optical waveguide intended for the detection of the transmitted coupling radiation can also be arranged as a bundle ( 47 ) ( Fig. 12). The coupling can then at any and non-mirrored location of the coupling mirror, for. B. be realized centrally. Depending on the application, spectrally selective elements can be arranged between the radiation source ( 46 ) and the optical waveguide and between the optical waveguide and the receiver.

According to claim 22, the coupling mirror ( 48 ) is a full mirror (ie not partially transparent) and the counter mirror ( 49 ) is partially transparent ( Figs. 13 and 14). The radiation is coupled in through a small optical opening in the coupling mirror. This takes place either directly via an optical fiber ( 42 ) or an optical system ( 50 ). The receiver ( 45 ) for registering transmitted coupling radiation is arranged downstream of the partially transparent counter mirror ( 49 ). Depending on the application, spectrally selective elements can be arranged between the receiver and the counter mirror and between the radiation source and the optical waveguide / optical system.

Claim 23 documents advantageous designs in which both the coupling mirror and the counter mirror are designed as full mirrors ( Figs. 15 to 18). In Fig. 15, the radiation is coupled in through a small optical opening in the coupling mirror ( 48 ). This takes place either directly via an optical system or via an optical waveguide ( 42 ). For coupling out coupling radiation, a second optical waveguide ( 51 ) is arranged downstream of the coupling mirror, which is located at an optical opening in the coupling mirror. Fig. 16 illustrates the case in which coupling and decoupling take place via an optical fiber splitter ( 52 ). In Fig. 17, a radiation-conducting volume ( 53 ), which has an opening in its jacket, is arranged in front of the coupling mirror in order to couple out coupling radiation. Through this opening, part of the radiation can leave the radiation-guiding volume after each revolution. This opening can be followed by a light waveguide ( 54 ). This system works in the same way as the optical fiber splitter. The coupling mirror side diameter of the splitter is the same as the coupling mirror. The coupling mirror can be vapor-deposited on the branch. Fig. 18 illustrates another variant of the coupling, which consists in that the coupling mirror is preceded by a transmitting body ( 55 ) (e.g. a glass plate), which couples a small part of the coupling radiation that is dependent on the refractive index from the beam path , which is applied to the receiver ( 45 ). When using a glass plate, approximately 4.5% of the incident radiation is reflected. The reflectance of the plate is set depending on the application, z. B. on the choice of material or by designing defined interfaces between this plate and a support. Instead of a plate, a radiation-carrying volume with an oblique interface can also be arranged. In addition, the coupling mirror can be preceded by an indicator volume with defined and constant optical properties. This volume is penetrated by the coupling radiation and provides a measurable optical signal for the receiver, for example as fluorescence or scattering.

According to claim 24, the essential features of the device described are not only for light wavelengths or wavelengths of the optical spectral range, but also can be used for different wavelengths. Examples: ultrasound and nuclear radiation.

The sensor system described can, on the one hand, be used in spectroscopic spectroscopic sensors Measurement technology using the electronics contained therein can be installed or installed. To the the sensors can be equipped with a separate, highly integrated electronic control and Evaluation unit are coupled. The electronics enable both cw operation and also the flash mode. In the flash mode, the dark signal is measured after each flash possible. A special feature is (claim 25) that depending on the optical Properties of the measurement volume to be examined, the sensitivity of the measurement elec is set tronically. On the one hand, the LED current can be varied, which is immediate Has an effect on the emitted LED intensity. On the other hand is the final wi The state of the optoelectronic receivers can be varied, which has an immediate impact has the electrical signal present at the receiver.  

Reference list Fig. 1

1

Absorption module

2nd

Measuring module

3rd

Light guide module

3rd

a block for optical fibers

4th

Connection module

4th

a Optical fiber for external connection

4th

b LED

5

Coupling module

5

a coupling mirror

5

b Block for optical fibers

5

c semi-transparent mirror layer

5

d uncoated area

5

e optical fiber

6

Remission module

7

Refractive index

8th

conical reflector

Fig. 2

6

Remission module

9

receiver

10th

window

11

spectrally selective element

Fig. 3

7

Refractive index

12th

Radiation source

13

imaging optics

14

imaging optics

15

reflector

16

reflector

17th

window

18th

receiver

Fig. 4

1

Absorption module

19th

Reflection module

20th

Mirror

21

Leaf spring for variation of the mirror distance

22

Leaf spring for variation of the angle of the mirror plane

23

Measuring volume

Fig. 5

1

Absorption module

23

Measuring volume

24th

radiation-carrying volume (e.g. capillary)

25th

radiating cone

26

Mirror

27

Receiver (90 °)

Fig. 6

23

Measuring volume

28

Light emitting diode (LED)

29

Emitter

30th

Mirror layer (counter mirror)

31

Mirror layer (partially permeable coupling mirror)

32

receiver

Fig. 7

1

Absorption module

23

Measuring volume

33

radiation-carrying volume (e.g. ATR crystal)

34

Mirror layer (counter mirror)

Fig. 8

1

Absorption module

23

Measuring volume

35

Support for measuring volume contact

36

Support for measuring volume contact

37

radiation-carrying volume

38

Window or mirror with transmitting areas

Fig. 9

23

Measuring volume

28

LED

29

Emitter

31

Mirror layer (partially permeable coupling mirror)

32

receiver

39

Exit window or evaporated counter mirror with transmitting areas

Fig. 10

23

Measuring volume

28

LED

29

Emitter

32

receiver

40

Window (plan)

41

Window (oblique)

Fig. 11

42

Optical fiber for coupling

43

semipermeable coupling mirror

44

Optical fiber / bundle for guiding the transmitted coupling radiation

45

receiver

46

Radiation source

Fig. 12

42

Optical fiber for coupling

43

semipermeable coupling mirror

45

receiver

46

Radiation source

47

Optical fiber bundle for coupling and decoupling

Fig. 13

42

Optical fiber for coupling

45

receiver

46

Radiation source

48

Coupling mirror (full mirror) with optical opening

49

semi-transparent mirror

Fig. 14

45

receiver

46

Radiation source

48

Coupling mirror (full mirror) with optical opening

49

semi-transparent mirror

50

imaging optical system for coupling

Fig. 15

42

Optical fiber for coupling

45

receiver

46

Radiation source

48

Coupling mirror (full mirror) with optical opening

51

Optical fiber for coupling out coupling radiation

Fig. 16

45

receiver

46

Radiation source

48

Coupling mirror (full mirror) with optical opening

52

Optical fiber splitter

Fig. 17

42

Optical fiber for coupling

45

receiver

46

Radiation source

48

Coupling mirror (full mirror) with optical opening

53

radiation-carrying volume (e.g. fiber optic cable)

54

Optical fiber for coupling out coupling radiation

Fig. 18

42

Optical fiber for coupling

45

receiver

46

Radiation source

48

Coupling mirror (full mirror) with optical opening

55

Transmitting body (e.g. glass plate) for coupling out coupling radiation.

literature

[1] BERGMANN and SCHAEFER: Textbook of experimental physics. Optics. Berlin - New York, Walter de Gruyter, 1993.
[2] SCHMIDT, W .: Optical Spectroscopy. Weinheim-New York-Basel-Cambridge-Tokyo, VCH publishing company, 1994.
[3] BAUMBACH, G .: Air pollution control. Berlin-Heidelberg-New York, Springer Verlag, 1992.
[4] DE 41 04 316 A1.
[5] DE 41 24 545 A1.
[6] DD 3 01 863 A7.
[7] MITTENZWEY, K.-H., J. RAUCHFUß, G. SINN, H.-D. KRONFELDT: A new fluo rescence technique to measure the total absorption coefficient in fluids. Fres. J. Anal. Chem., 354 (1996) 159-162.
[8] DE 43 37 227 A1.
[9] KORTÜM, G .: Reflection spectroscopy. Berlin-Heidelberg-New York, Springer Verlag, 1969.
[10] COLWELL, RN: Manual of remote sensing. Falls Church, The Sheridan Press, 1983.
[11] Patent application 1 96 47 222.9-52, November 15, 1996. Optosens GmbH.

Claims (26)

1.Device for the synchronous determination of the absorption, scattering, fluorescence and refraction of liquids, gases and solids (measuring volume) by coupling radiation of a defined wavelength into a multiple reflection device with coupling and counter mirrors via the coupling mirror, this coupling radiation due to long distances in the Measurement volume is almost completely absorbed, with a receiver located directly behind one of the two mirrors, which is partially transparent, the transmitted coupling radiation and with a receiver aligned with the measurement volume and located at the coupling mirror, the remission directed against the direction of incidence (saturated long-term remission) is measured are determined, the absorption capacity from the reciprocal of the transmitted coupling radiation and the scattering and fluorescence capacity indirectly from the combination of saturated long-term remission and transmitted coupling radiation rden, characterized by
that an absorption module made up of coupling, measuring, light guide and connection module and designed as a carrier for the reflectance and refraction module, wherein
Several optical fibers are arranged in the coupling module and are aligned parallel to the normal of the coupling mirror, the end faces of which form a common straight line and a common vertical plane, the coupling mirror is mirrored on the back with a partially transparent layer and there is an area not mirrored between the edge of the mirror and the mirror layer the end faces of the optical fibers lie flat and form a common vertical plane with the mirror layer, and
a conical radiation-guiding volume is arranged between the receiver located in the measuring module and coupling mirror, and
The coupling module is followed by a light guide module in which the optical waveguides are guided along a defined path and their end faces are positioned in a common vertical plane, and
a connection module is arranged downstream of the light guide module, in which the end faces of a plurality of light emitting diodes (LED) and an optical waveguide are positioned in a common vertical plane, and
with the absorption module, different types of reflection modules can be coupled in such a way that the measurement volume is located on the one hand in the multiple reflection space between a coupling and counter mirror or on the other hand thereof, the measurement volume being in a radiation-carrying volume or not. 2. Device according to claim 1, characterized in that that the localized optical fiber in the coupling module in the immediate vicinity of the game Gel layer are arranged. 3. Device according to claim 1, characterized in that that the radiation-guiding localized between the measuring module and coupling mirror Volume acts as a cross-sectional converter, with its coupling mirror-side diameter the size of the reflecting layer of the coupling mirror and its receiver-side passage are adapted to the size of the photosensitive surface of the receiver and the diameter on the coupling mirror side is larger than the diameter on the receiver side. 4. The device according to claim 1, characterized in that that the end faces of the LED arranged in the connection module are flat and in immediate close to the LED emitter.   5. Device according to claims 1 and 4, characterized in that that light guide and connection module are connected in such a way that the end faces of the Optical fiber in the light guide module and the end faces of the LED and one light the waveguide in the connection module lie flat against each other and centrally opposite each other stand. 6. The device according to claim 1, characterized in that that between the coupling mirror and the measuring module is a spectrally selective element and / or instead of the coupling mirror, a protective glass and / or a spectrally selective element are ordered. 7. The device according to claim 1, characterized in that that spectrally selective elements once in the absorption area of the substances to be detected and on the other hand in the absorption area of the solvent but outside the absorption area of the substances to be detected are arranged. 8. The device according to claim 1, characterized in that that the remission module in the immediate vicinity of the optical fiber of the coupling module is arranged and its optical window and the coupling mirror in a common Level. 9. The device according to claim 1, characterized in that that the optical window of the refraction module and the coupling mirror in one same level and the radiation generated in the refraction module obliquely on the optical Window meets and from this along a sufficiently long path to a recipient is reflected longer, each with a reflecting element in the beam path of the incident the light beam and the reflected light beam are arranged. 10. The device according to claim 1, characterized in that that the measurement volume is located between the coupling mirror and reflection module, the Multiple reflections via the concave mirror in the reflection module and the on coupling mirror takes place, the concave mirror via adjustment elements with respect to mirrors stood and tilt of the concave mirror plane is set in such a way that the end faces the optical fiber of the coupling module between single and double focal length of the Concave mirror and the images of the end faces after the first reflection of the coupling radiation at the concave mirror at a mirror distance of twice the focal length on the plan coupling mirrors are localized. 11. The device according to claim 10, characterized in that that an adjustment element with respect to a vertical displacement in the reflection module is ordered. 12. The apparatus according to claim 1, characterized in that that the measurement volume between the coupling mirror and reflection module in a radiation leading volume is localized, the multiple reflection over that in the reflection module located mirror, the radiation-carrying volume and the coupling mirror takes place, wherein between the coupling module and the end face of the coupling module facing the radiation-carrying volume a radiation-carrying body is arranged, the one coupling-side diameter that of the coupling mirror and its diameter the opposite overlying area corresponds to that of the end face of the radiation-carrying volume.   13. The apparatus according to claim 12, characterized in that that the radiation-carrying body supports the coupling mirror, measuring module, mirror and Is the end face of the coupling between the coupling mirror and the counter mirror, immediately in front of the coupling mirror, or immediately behind the coupling mirror net, in which case the coupling mirror is an optical opening for the input has coupling radiation, the radiation-guiding body on the coupling mirror opposite side for realizing the counter mirror is coated from the outside and closes with a protective layer and the measuring volume in an opening inside between Coupling and counter mirror is localized in the radiation-carrying body. 14. The apparatus according to claim 1, characterized in that that the measuring volume outside the sensor both at the optical window of the refraction modules as well as localized on a radiation-guiding body, the multiple reflection about the mirror in the reflection module, the coupling mirror and the one in between lying radiating body takes place on which the interaction via evaneszen te waves occur. 15. The apparatus according to claim 1, characterized in that that the measuring volume outside the sensor at an optically transparent window or a multiple mirror is localized with optically transparent areas, the multiple reflection via the coupling mirror, a radiation-carrying volume and the window or the Counter mirror with the localized measurement volume takes place there, the radiation leading Volume is arranged between the coupling mirror and window or counter mirror and the optical window of the reflectance and refraction module in contact with the measuring volume or these two modules are replaced by support blocks for measuring volume contacting. 16. The apparatus according to claim 15, characterized in that that an indicator- or substance-selective layer or a roughening with defined pores size on the window or on the permeable areas in the counter mirror is applied on both sides. 17. The device according to claims 13, 15 and 16, characterized in that that the radiation-carrying body carrier for coupling mirror, measuring module, window or Counter mirror is, as well as the surface opposite the coupling mirror either as Window or as a mirror with optically transparent areas is formed, which measurement volume located outside the sensor is in contact with this surface. 18. The apparatus according to claim 17, characterized in that that the radiation-guiding body has no additional mirror layers, at least two radiation-guiding bodies are coupled, one at the site of the interaction with the measuring volume a convex or flat surface and the other one there has inclined plane surface, so that the optoelectronic receiver of a radiation leading body with remission photons from the measuring volume as well as with the Interface to the measuring volume specularly reflected photons and the receiver of the other body preferably with remission photons from the measurement volume become. 19. The apparatus according to claim 15, characterized in that that the measurement volume on the window or on the counter mirror is in a radiation path  the volume is localized. 20. Device according to claims 13, 17 and 18, characterized in that that the radiation-carrying body, in which the measuring volume in an opening between one coupling and counter mirror is localized and the radiation-carrying body, in which the Measurement volume is located outside, are designed as coupled together. 21. The apparatus according to claim 1, characterized in that that for the detection of those transmitted through the partially transparent coupling mirror Radiation an optical fiber or fiber optic bundle directly the coupling mirror is subordinate and its coupling mirror diameter with that of the mirror layer is the same, the optical waveguide or the optical waveguide bundle either separately or with the light waveguide relevant for the coupling of the radiation into the measuring volume ter is arranged as a bundle. 22. The apparatus according to claim 1, characterized in that that the coupling mirror as a full mirror and the counter mirror as a partially transparent mirror are formed, the coupling mirror a non-mirrored area for the coupling the radiation contains, via an optical fiber or an imaging optical system is transported to the coupling mirror and the partially transparent mirror is a receiver is subordinate to the registration of transmitted radiation. 23. The device according to claim 1, characterized in that that coupling and counter mirrors are designed as full mirrors, and on the one hand coupling mirror for coupling and decoupling radiation optically transparent, non-mirrored Contains areas in which separate optical fibers or for coupling in and out Coupling and decoupling a common optical fiber branch are arranged, or on the other hand, the coupling mirror for radiation coupling optically transparent, non-ver contains mirrored areas and for coupling out coupling radiation the coupling mirror a radiation-conducting volume is arranged in front, which is designed as a light wave splitter or the coupling mirror is preceded by a transmitting element that is part of the Coupling radiation reflected in the direction of the receiver or that part of the coupling beam brings as fluorescence and scattering in the direction of the receiver. 24. The device according to claim 1, characterized in that that in the absorption, remission, refraction and reflection module that in the optical spec elements suitable for the generation, forwarding, Coupling, reflection and registration of waves outside the optical spec tral range are arranged. 25. The device according to claim 1, characterized in that to investigate that for the optimal setting of the measuring sensitivity depending on the measuring volume on the one hand the current at the LED and on the other hand the terminating resistor are variable on the optoelectronic receivers.