Abstract:
The invention relates to a device for measuring light-activated fluorescence of at least one coating that contains a fluorescent material, and its use for measuring fluid materials which cause fluorescence-quenching in at least one of the fluorescent coatings. To activate the fluorescence, at least one first light wave-guide is directed onto at least one coating applied to a support and the fluorescent light is directed at a detector by means of at least one-second light wave-guide, in order to determine the intensity of the fluorescent light. The end faces of the different fluorescent light wave guides are then arranged to have overlapping entry and/or exit cones and/or be of a shape substantially identical to the at least one coating containing a fluorescent material, in such a way that an accurate measurement of the fluorescence intensity can be attained, and that the light source(s), light wave guides and the detector(s) are lodged in a measuring head.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit, under 35 USC § 119(e)(1), of U.S. Provisional application Ser. No. 11/052,399; filed Feb. 7, 2005, which application is incorporated herein by reference in its entirety. Application Ser. No. 11/052,399 is co-pending as of the date of the present application. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The invention relates to a device for measuring fluorescence excited by light in at least one layer containing a fluorescing material, and to the use thereof for measuring fluid materials which effect fluorescence quenching in at least one of the fluorescing layers.  
         [0004]     Measuring methods and measuring devices customarily used to date have the disadvantage that the ratio of fluorescent light to the light required to excite the fluorescence is very low, with the result that a separation is required and, consequently, a miniaturization, which is necessary for many applications, has so far been ruled out.  
         [0005]     Further known solutions do not achieve satisfactory separation between the exciting light and the fluorescent light.  
         [0006]     To counter this, use has so far been made of an expensive, complicated optical design which requires many optical elements, which are also cost intensive, the result being, in particular, the appearance of problems with the miniaturization and process integration.  
         [0007]     The known solutions also have the disadvantage that the detection of the measuring signal has proceeded relatively slowly and that furthermore, errors have occurred due to coupling drift (temperature fluctuation, mismatching, or due to modem coupling), and could be taken into account only with difficulty.  
         [0008]     2. Description of the Related Art  
         [0009]     DD 106 086 describes a measuring probe in which fluorescence is excited in a layer, the exciting light being directed onto the layer by a single optical fiber which surrounds, in the shape of a ring, at least one further optical fiber for fluorescent light. The fluorescent light can be measured with a detector, and the measured value thereof can be used as a measure of the content or the concentration of a material, as a consequence of fluorescence quenching. Use is made for a reference measurement of a second optical fiber which directs fluorescent light of a layer region, which is screened from the measurement medium, onto a second detector.  
         [0010]     However, it is not possible with this solution to ensure a concrete and accurate local assignment of the detectable fluorescence intensity over the excited layer surface, something which is, however, also necessary for accurate measurements because of an imprecisely defined local excitation or a non-defined, inhomogeneous arrangement of the fluorescing material in the layer. Moreover, an absolute optical separation is necessary for a simultaneous reference measurement or further measurements for other materials.  
         [0011]     In addition, GB 2265711 A1 describes an optical fiber sensor in which two optical fibers inclined at a specific angle to one another are to be used. In this case, one of the optical fibers serves the purpose of sending light, and the other optical fiber serves the purpose of receiving reflected light and directing it onto a suitable detector. The alignment of the two optical fibers at an angle to one another is proposed there in order to achieve enlargement of the possible detection range of reflected light, since it is possible to achieve an enlarged overlap of the light exit cone with the light entrance cone of the two optical fibers.  
         [0012]     U.S. Pat. No. 3,992,631 describes a system and a method for carrying out fluorescence immune tests in which, inter alia, reference is made to the possibility of using different optical fibers in a bundle arrangement.  
         [0013]     It is therefore the object of the invention to propose a device which can be of miniaturized construction and therefore be adapted flexibly to different applications and achieves a satisfactory measuring accuracy.  
       SUMMARY OF THE INVENTION  
       [0014]     According to the invention, this object is achieved by means of the features of Patent Claim  1 . Advantageous embodiments and developments of the invention follow in the case of the use of the features named in the dependent claims.  
         [0015]     The device according to the invention for measuring fluorescence excited by light at least one layer containing a fluorescing material essentially comprises a measuring head in which at least one light source which emits light of wavelength(s) exciting fluorescence(s) in the layer or layers, and at least one detector which measures the intensity of the fluorescent light, are held. The light directed onto the layer(s) in order to excite the fluorescence is directed onto the fluorescing layer via at least one optical conductor. In this case, the same optical conductor can also direct the fluorescent light onto the detector. A plurality of fluorescing layers can be arranged next to one another in a fashion separated from one another locally or, if appropriate, partially overlapping, and be irradiated in each case with exciting light.  
         [0016]     It is important for the end faces of the optical conductors of the fluorescent light at the measuring face of the measuring head to be arranged and/or aligned taking account of the numerical apertures of all the optical conductors, in order to achieve an accurate measurement of each area of the fluorescence being measured. This is necessary for an accurate local assignment of values. In doing this, it is important that the numerical apertures of the optical fibers be chosen so that the entry and/or exit cones of each optical fiber overlap with the entry and/or exit cones of the adjacent optical fibers. If this overlap is not present, some of the fluorescent and/or reflected light will not be captured, and an accurate measurement will not be obtained. A further possibility for achieving this aim consists in aligning these optical conductors with reference to one or more layer(s) containing fluorescing material(s).  
         [0017]     For the measurement, the fluorescing layer(s) is/are arranged on the end or ends of the optical conductors or on a suitable support or a body, or make contact therewith.  
         [0018]     Optical fibers are preferably used as the optical conductors.  
         [0019]     There is thus, in principle, the possibility of arranging a plurality of different fluorescing layers, and using them with one or more different light sources which in each case emit light with wavelengths which excite fluorescence(s). It is thereby possible, with the aid of only one measurement using a single measuring head having at least one fluorescing optical fiber for each of said plurality of different fluorescing layers, to detect a plurality of different fluid materials, which effect fluorescence quenching in the different layers.  
         [0020]     However, the invention can also be developed for the use of a plurality of optical fibers, which direct different types of light to different detectors arranged separately from one another.  
         [0021]     Thus, for example, the light of a light source can be directed onto a fluorescing layer by a first optical fiber, from there the fluorescent light can be directed by a second optical fiber onto a detector arranged in the measuring head, and, for the purpose of obtaining a reference signal, exciting light reflected in the layer can be directed onto a second detector by a third optical fiber. For each additional type of fluorescing material present, for example, a second fluorescing dye, an additional fluorescing optical fiber, may be provided.  
         [0022]     In this case, the fluorescing layer or a plurality of fluorescing layers which are preferably applied to a substrate serving as support can simply be plugged onto the measuring head using a cap or an exchangeable support, thus rendering a simple exchange possible. In this case, it is particularly advantageous when a coupling medium is present between the substrate, to which the fluorescing layer(s) is/are applied, and the ends of the optical fibers, in order to reduce light losses.  
         [0023]     It is favorable for various applications when at least a part of the measuring head, and in this case at least the part which holds the optical fibers, which is directed in the direction of the fluorescing layer(s), is of flexible construction, or the upper part of the measuring head is at least partially bent.  
         [0024]     In order to improve the optical properties of the device according to the invention, it is advantageous for a filter and/or a launching optical system to be arranged between the light source or sources and the respectively assigned optical fibers, in order, on the one hand, to avoid light losses and, on the other hand, to delimit the wavelength region of the light which is directed onto the respective fluorescing layer, so that the measuring errors can be further reduced. It is particularly favorable that the filters can be exchanged for others which are suitable for other wavelengths, that is to say other fluorescing materials, and consequently also other materials to be detected.  
         [0025]     A corresponding arrangement of coupling-out optical systems and/or filters upstream of the various detectors acts in the same way.  
         [0026]     In the device according to the invention, however, it is also possible to make use of a bundle of a plurality of optical fibers, it being possible to arrange the individual optical fibers in the bundle differently in order to be able to detect optimum measuring signals of fluorescent light, and reflected light of the light source(s) moreover measuring errors can be minimized. The arrangement of the individual optical fibers in the bundle can be performed in this case in the shape of a ring, in one variant, and in the shape of concentric rings in a second variant.  
         [0027]     In the case of an arrangement in the shape of a ring, it is possible to arrange next to one another in an alternating fashion, in an outer ring, optical fibers which, on the one hand, direct exciting light onto the fluorescing layer and, on the other hand, direct light reflected there as reference signal onto a detector. It is then possible to arrange internal thereto optical fibers which direct fluorescent light onto at least one detector in the measuring head. An additional optical fiber which likewise directs exciting light onto the fluorescing layer can then be arranged at the centre of the ring.  
         [0028]     In another arrangement of the individual optical fibers, it is favorable to arrange an optical fiber through which exciting light is directed onto the fluorescing layer, and to arrange next to one another, in an alternating arrangement, optical fibers with which reference light and fluorescent light are directed onto detectors.  
         [0029]     The arrangement of the respective optical fibers for the various types of light can, however, also be selected taking account of the arrangement of different fluorescing layers, it being possible, for example, to select an arrangement of the optical fibers in the shape of a circular arc when the fluorescing layers are constructed as circular arcs.  
         [0030]     In another embodiment of the device according to the invention, the individual optical fibers are not, however, arranged in parallel but, at least in their end regions, that is to say in the direction of the fluorescing layer(s), are inclined at specific angles to one another, so that, for example, fluorescence-exciting light is directed at a specific angle, which is not equal to 90°, onto the fluorescing layer, and there is aligned at a second correspondingly aligned angle at least one optical fiber by which the reflected reference light can enter and be directed onto a detector. A third optical fiber can then preferably be arranged orthogonally relative to the fluorescing layer through which the fluorescent light reaches the corresponding detector.  
         [0031]     In all these cases, however, it is favorable to arrange and/or align the optical fibers such that for the purpose of launching and coupling out exciting and fluorescent light their end faces are arranged, taking account of their numerical apertures, so that the entry and or exit cones of the optical fibers overlap.  
         [0032]     It is favorable for specific applications of the device according to the invention when, at least in the upper measuring head region, a heater is present which can prevent condensation of, for example, water on the fluorescing layer(s). Moreover, it is favorable to use at least one temperature sensor and a corresponding controller or regulator to manipulate the heater in accordance with the ambient conditions, that is to say the ambient temperature and the atmospheric humidity, and thereby to be able to set different prescribable temperatures in the region of the fluorescing layer(s) and/or in the upper measuring head region. The heater can in this case be arranged in the upper measuring head region, but it is also possible to arrange appropriate heating elements in the immediate vicinity of the fluorescing layer(s). One possibility for this is to fit the heater on the substrate to which the fluorescing layer(s) is/are applied.  
         [0033]     The device according to the invention can further be improved when the lower region of the measuring head is constructed in a thermally insulated fashion with respect to the upper heated measuring head region.  
         [0034]     It can be favorable for various applications to construct the upper measuring head region not only in a flexible fashion but also in a tapering fashion, solely or in conjunction with a flexible design, it being possible to taper virtually to the diameter of the optical fibers.  
         [0035]     Depending on the actual design of a measuring device according to the invention, it is possible to detect at least one fluid material which affects a specific quantifiable measure of fluorescence quenching in the fluorescing layer. It is also possible to detect different materials with different fluorescing layers which are arranged next to one another. However, it is also possible, in principle, to detect a plurality of materials by directing light of different wavelengths onto only one fluorescing layer and carrying out the detection in terms of wavelength resolution.  
         [0036]     Despite an at least partially integrated electronic evaluation system, the device according to the invention must be of small and flexible construction so that the most varied applications are possible. In particular, the slim and, if appropriate, flexible construction of the upper measuring head region has the positive effect that alignment relative to the measuring location or to the fluorescing layer(s) is possible in a simple way.  
         [0037]     A further advantage consists in that the optical fibers can be used without rigid connections, such as optical connectors, with the result that an exchange is possible although the optical fibers are held fixed and therefore can no longer be moved, it thereby being possible to avoid modal noise.  
         [0038]     If a plurality of optical fibers are used as a bundle, varied arrangements at the end of the measuring head in the direction of the fluorescing layer(s) can ensure optimum measuring conditions and reduce the component of scattered light as well as greatly minimize cross talking of exciting light, and it is also possible in this case to detect a reference signal.  
         [0039]     The spatial separation and additional thermal insulation of the upper measuring head region can optimize the temperature control in the region of the fluorescing layer(s) with reference to energy consumption, and unnecessary heating of the lower region of the measuring head is prevented.  
         [0040]     Further advantages of the invention are the better and more effective illumination of the fluorescing layer(s), and less influence from extraneous and scattered light.  
         [0041]     The invention can take account of a plurality of material concentrations by means of different fluorescent dyes and/or reference signals. It is possible for such layers to be selectively excited and correspondingly detected.  
         [0042]     The temperature control or heating can be carried out only in the immediate vicinity of the layers.  
         [0043]     There is no need for any external optical connectors which could lead to coupling problems.  
         [0044]     Miniaturization, a lower mass and, in addition, flexible access to the measuring medium are possible by optical separation of measuring tip and the detection and evaluation of measured values.  
         [0045]     The device according to the invention is not only capable of flexible construction, but is also cost-effective to produce and operate, since some parts can also be replaced cost-effectively by being exchanged.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0046]     The invention is to be described in more detail below using exemplary embodiments.  
         [0047]      FIG. 1  shows the diagrammatic design of a first example of a device according to the invention.  
         [0048]      FIGS. 2, 2   a  and  2   b  show various arrangements of optical fiber bundles on the upper measuring head.  
         [0049]      FIGS. 3, 3   a  and  3   b  show three examples of a measuring head according to the invention.  
         [0050]      FIG. 3   c  shows a modification of the measuring head shown in the upper representation of  FIG. 3 , wherein each pair of optical conductors is associated with its own light source which is not seen by the other light source, and may emit a different light.  
         [0051]      FIG. 4  shows a first example of a support which can be mounted on a measuring head, in two views.  
         [0052]      FIG. 5  shows a second example of a support which can be mounted on a measuring head, in two views.  
         [0053]      FIG. 6  shows a third example of a support which can be mounted on a measuring head, in two views.  
         [0054]      FIG. 7  shows a fourth example of a support which can be mounted on a measuring head, in two views.  
         [0055]      FIG. 8  shows a fifth example of a support which can be mounted on a measuring head, in two views.  
         [0056]      FIG. 9  shows a support with a symmetrically constructed planar optical conductor.  
         [0057]      FIG. 10  shows two symmetrically arranged supports.  
         [0058]      FIG. 11  shows examples for launching light into, and coupling it out of end faces of, supports which can be mounted on a measuring head.  
         [0059]      FIG. 12  shows a sixth example of a support which can be mounted on a measuring head, in two views.  
         [0060]      FIG. 13  shows a seventh example of a support which can be mounted on a measuring head, in two views.  
         [0061]      FIG. 14  shows an eighth example of a support which can be mounted on a measuring head, in two views.  
         [0062]      FIG. 15  shows a ninth example of a support which can be mounted on a measuring head, in two views.  
         [0063]      FIG. 16  shows a body which can be mounted on a measuring head.  
         [0064]      FIG. 17  shows a body which can be mounted on a measuring head.  
         [0065]      FIG. 18  shows a body which can be mounted on a measuring head.  
         [0066]      FIG. 19  shows a first holder for fluorescent layers, in three views.  
         [0067]      FIG. 20  shows a second holder for fluorescent layers in three views.  
         [0068]      FIG. 21  shows a measuring head for measuring with wavelength resolution.  
         [0069]      FIG. 22  shows a further measuring head in three views. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0070]     The diagrammatic design of a first exemplary embodiment of a device according to the invention is represented in  FIG. 1 . There is shown a measuring head  1 , having a face  1 B on a metal tip  14  to which a fluorescing layer  11  is applied. The fluorescing layer  111  may also be applied to a support  30  ( FIGS. 4-15 ) which is in contact with the face  1 B, thus placing the fluorescing layer  11  in optical contact with the face  1 B.  
         [0071]     In this case, there is held in the closed measuring head  1  at least one light source  2  from which exciting light is directed onto a fluorescing layer  11  via a filter  6 , which is preferably also an exchangeable bandpass filter, by the first optical fiber  3 , which is guided through the upper measuring head region  17 . Fluorescent light from the fluorescing layer  11  passes through a second optical fiber  15  via an edge filter  7 , possibly likewise exchangeable, onto a detector  4  with which the intensity of the fluorescent light can be measured, and the detector  4  is connected to an electronic evaluation system  9 .  
         [0072]     Reflected light then passes as a reference signal through a third optical fiber  16 , likewise via a filter  8 , which can, again, be exchangeable, onto a second detector  5 , which is connected to a second electronic system  10 .  
         [0073]     In this case, the exchange of the filters  6 ,  8  is advantageously possible from outside via openings with a lock. Thus, when the measuring head  1  is finished measuring one type of fluorescence, and is to be used in another application, the filters  6 , 8  can be removed from measuring head  1 , and replaced with whatever filters are needed for the new application, all with a minimum of downtime and expense.  
         [0074]     A heater  12 , which may be mounted in a metal tip  14  in order to improve the thermal conduction, is provided in the uppermost region of the upper measuring head region  17 . Likewise held in the metal tip for the purpose of controlling or regulating the heater  12  is a temperature sensor  13  whose measuring signal is led to an electronic control system which then influences the heat output.  
         [0075]     Two lines at the lower part of the measuring head  1  indicate connections to an electronic evaluation system which can further process the preprocessed signals from the electronic systems  9  and  10 , and  5  display and output them.  
         [0076]     Of course, the number of the light sources  2  of the detectors  4  and  5  can be appropriately increased.  
         [0077]     Different variants for possible arrangements of different optical fibers are then represented in  FIGS. 2, 2   a  and  2   b . Referring first to  FIG. 2 , the upper representation in  FIG. 2  shows a bundle of different optical fibers, the excitation optical fibers  20  directing light of the light source  2  onto the fluorescing layer. The reflected light optical fibers  21  direct the light reflected at the fluorescing layer as a reference signal onto the detector  5 , and the fluorescing light optical fibers  22  direct fluorescent light from the fluorescing layer or layers onto one or more detector(s)  4 .  
         [0078]     Shown in the lower left hand representation of  FIG. 2  is face  1 B of measuring head  1  at the upper measuring head region  17 . In this arrangement of optical fibers, an excitation optical fiber  20  is centrally located with its&#39; longitudinal axis orthogonal to the face  1 B. Laterally aligned with excitation fiber  20  are a pair of reflected light fibers  21 , one on each side of the excitation fiber  20 . Arranged orthogonally to the axis of the reflected light fibers  21 , with respect to the face  1 B, are a pair of fluorescing light optical fibers  22 . In this arrangement at least the reflected light fibers are bent at their ends near the face  1 B, Thus, the axis of the reflected light fibers at the face  1 B are not parallel to the axis of the excitation light fiber  20 .  
         [0079]     In the lower middle representation of  FIG. 2  is shown an arrangement of fibers where the axis of both the excitation light fiber  20 , and the reflected light fiber  21 , are not parallel to the axis of the fluorescing light fiber  22 .  
         [0080]     In the lower right representation of  FIG. 2  is shown an arrangement of fibers where the axis of both the excitation light fiber  21  and the fluorescing light fiber  22 , are not parallel to the axis of the excitation light fiber  20 .  
         [0081]     In all the representations of  FIG. 2 , the numbers of the excitation light fiber  20 , the reflected light fiber  21 , and the fluorescing light fiber  22  can be increased at will.  
         [0082]     In the lower representations of  FIG. 2 , furthermore, the arrangement of the different optical fibers  20 ,  21  and  22  in the upper measuring head region  17  is represented in preferred form. In this case, different optical fibers, arranged in the outer region, in particular, are constructed in an angled fashion so that it is possible to achieve an improved illumination of the fluorescing layer, and a reduction in the influence of extraneous light and scattered light.  
         [0083]     The examples represented in  FIG. 2  are not, however, limited to a design of a measuring head, according to the invention, in which only one fluorescing layer is used. When a plurality of different fluorescing layers are used on the measuring head according to the invention, an arrangement of the different optical fibers required for the measurement of the multiple fluorescing layers can be performed in a simple way, with the result that optimum conditions can be obtained in each case for the various fluorescence and reference signals.  
         [0084]     Referring to the upper left representation of  FIG. 2   b , in some applications it is preferred to have a respectively very large single fluorescing light fiber  22  surrounded by a ring of alternating exciting light fibers  20  and reflected light fibers  21 .  
         [0085]     Referring to the upper right representation of  FIG. 2   b , there is shown an arrangement of fibers, which is useful when two different types of fluorescing materials, such as two fluorescing dyes, are being measured. Since two different types of fluorescing materials are being measured, two separate and different fluorescing fibers are needed. In this arrangement, a relatively large first fluorescing fiber  22  is centrally located. First fluorescing fiber  22  is surrounded by a ring of alternating exciting light fibers  20  and second fluorescing light fibers  23 .  
         [0086]     In each case, the optical fibers  22  can, however, be arranged and/or aligned such that, even taking account of their own numerical apertures and those of the optical fibers  20  for exciting light, locally defined regions can be detected in the layer or layers. Arrangements are possible with one detector having two light sources, or one light source having two detectors, depending on the application.  
         [0087]     It is also preferable to have arrangements which are adapted to measure two or more separate areas or channels of the fluorescing layer or layers. In this case, it is necessary to have either a single light source with separate bundles of fibers arranged in pairs, or multiple light sources, isolated from each other, but each associated with specific pairs of bundles of fibers. Such arrangements are useful to take into account bleaching of the fluorescing layer, use of different dyes, or dyes having different sensitivities.  
         [0088]     Referring now to  FIG. 3 , a second example of a measuring head  1  according to the invention is shown wherein measuring head  1  is shown having a smaller width in relation to its length, and therefore, in particular, offers more favorable preconditions for measurement in flowing media than is the case with, for example, circular or square shapes, since the flow conditions, and consequently also the measurement result, can be negatively influenced by, for example, turbulence which is produced, higher flow rates or pressure rises.  
         [0089]     Exchangeable supports, of which a few examples are represented in FIGS.  4  to  15  still to be described below, can then be mounted on such a measuring head  1 .  
         [0090]     As is also to be seen in  FIG. 3 , optical fibers  15  and  16  can be arranged in row arrangements opposite one another in pairs, the rows being aligned parallel to the longitudinal axis of such a measuring head. Referring to the top or plan view of the measuring head  1 , shown at the top right of  FIG. 3 , a first pair of rows of optical fibers ( 15 , 16 ) is shown proximate the left end of the measuring head  1 , and a second pair of rows of optical fibers ( 15 , 16 ) is shown proximate the right end of the measuring head  1 .  
         [0091]     It is also possible in this case to arrange in one row exclusively optical fibers  3  for exciting light, and in the opposite row exclusively optical fibers  15 ,  16  for fluorescent light, or at least in one row an alternating arrangement of optical fibers  3  for exciting light and optical fibers  15 ,  16  for fluorescent light.  
         [0092]     Accommodated once again in the measuring head  1  are the light sources  2 , preferably exchangeable filters  6  and  8 , launching and coupling-out optical systems  25 , detectors  4  and the corresponding electronic evaluation and control system  9 .  
         [0093]     Also represented in  FIG. 3  are temperature sensors  13  and heating elements  12  which project from the upper socket of the measuring head  1  in the form of a pin or in another suitable form, so that they can be positioned and fixed in a self-closed fashion in connection with correspondingly constructed holding bores in the supports  30  or bodies  40  (still to be described).  
         [0094]     The supports  30  or bodies  40  can be mounted on the otherwise planar surface of the socket by means of an optical cement.  
         [0095]     Referring now to  FIG. 3A , measuring head  1  with a mounted body  40  in accordance with  FIG. 16  is shown. Similarly to that shown in  FIG. 3 , and referring to the top or plan view of the measuring head  1 , shown at the top right of  FIG. 3A , a first pair of rows of optical fibers ( 15 , 16 ) is again shown proximate the left end of the measuring head  1 , and a second pair of rows of optical fibers ( 15 , 16 ) is shown proximate the right end of the measuring head  1 .  
         [0096]      FIG. 3   b  shows an example of a measuring head  1  on which, again, a support  30  or body  40  can be mounted. The single or a plurality of heating element(s)  12  can be surrounded by a material  12 . 1  having good thermal conduction. If desired, a first pair of rows of optical fibers ( 15 , 16 ) may be arranged proximate the left end of the measuring head  1 , and a second pair of rows of optical fibers ( 15 , 16 ) may be arranged proximate the right end of the measuring head  1 . Those skilled in the art will appreciate that a wide variety of arrangements of optical fibers ( 3 , 15 , 16 ) supports  30  or bodies  40  can be used, and are well within the scope of the present invention.  
         [0097]     With reference to  FIG. 3   c , there is shown an arrangement wherein two channels or areas of a fluorescing layer can be easily measured. There is shown two light sources  3 , each of which cannot be seen by the other, and each of which has rows of second optical fibers  15 , and third optical fibers  16  arranged opposite each other in pairs. It can be understood that there could be three, or more, such arrangements on a single measuring head  1  because of the miniaturization achieved by the present invention. Each arrangement would measure a different area of a fluorescing layer to permit accurate local assignment of value to the fluorescing layer.  
         [0098]     Represented in two different views in  FIG. 4  is a first example of a support  30  which, as represented in  FIG. 3 , can be mounted on a measuring head  1 , and is made from an optically transparent material.  
         [0099]     It is to be noted here that, as also holds for the following pictorial representations in FIGS.  5  to  13 , the proportions do not correspond to the actual ones, rather, to simplify and improve comprehension, the width is represented to be substantially larger than is the case in a practical design, and in that for use in flowing fluid media the width of such a support  30  is substantially smaller in relation to its length, with the result that the flow resistance is kept correspondingly low.  
         [0100]     The support  30  in accordance with  FIG. 4  comprises two limbs  30 ′,  30 ″ which are optically separated from one another at least partially by an interposed, preferably reflecting layer  36 .  
         [0101]     In this example, layers  32  containing fluorescing materials are applied to both outer sides of the support  30 , and the remaining outer surfaces  37  are likewise constructed or coated to be reflective.  
         [0102]     The exciting light is now irradiated via optical fibers  3  into at least one of the two end faces of the limbs  30 ′,  30 ″ into the transparent support  30 , and the fluorescence is excited there in the layers  32  by multiple reflection. A portion of the fluorescent light is irradiated again onto the support  30  and, by reflection at the outer surfaces of the support  30 , directed onto optical fibers  15 ,  16  for fluorescent light by the lower end faces of one or both limbs  30 ′,  30 ″, and the intensity of the fluorescent light is detected by detectors  4  and, consequently, the material concentration can be measured as a consequence of fluorescence quenching.  
         [0103]     Also to be seen in the left-hand representation of  FIG. 4  is the fact that the upper bounding surfaces of the support  30  are constructed inclined at an angle to one another, the angle being selected such that optimum reflection conditions can be achieved in accordance with the wavelengths used.  
         [0104]     Represented in the right-hand representation of  FIG. 4  is a view orthogonal to the longitudinal axis of such a support  30 , from which it may be seen that a plurality of regions can be separated optically from one another (also possible in the following examples) by, for example, reflecting layers  36 , and different layers  32 . 1 ,  32 . 2  and  32 . 3  are applied or constructed in the regions. Given these different layers  32 . 1  to  32 . 3 , it is possible to use a measuring head  1  according to the invention to determine a plurality of material concentrations simultaneously and/or to carry out at least one reference measurement in one of these regions. The same reference numerals are used for identical elements in the following figures.  
         [0105]     A further variant of a support  30  is represented in  FIG. 5 , this variant differing from those previously described only in the outer contour.  
         [0106]     The example, represented in  FIG. 6  likewise in two views, of a support  30  which can be mounted on a measuring head  1  according to the invention corresponds essentially to parts of the support  30  already mentioned in the description of  FIG. 4 .  
         [0107]     The only point is that a cavity reaching over the entire length of the support  30 , or one or more cutouts, whose surfaces are also provided with a reflecting coating  36  is/are constructed between the limbs  30 ′ and  30 ″.  
         [0108]     A self-closing fastening on the measuring head  1  can be achieved with this cavity or the cutout(s).  
         [0109]     Constructed for this purpose on the surface of the measuring head  1  is an appropriate longitudinal web which can engage in a self-closed fashion in the cavity constructed in the support  30 , and can hold it correspondingly.  
         [0110]     If one or more cutouts are constructed in the support  30 , the correspondingly shaped and contoured heating elements  12  and temperature sensors  13 , or other, for example, pin-shaped elements without a further function, can, constructed exclusively for fastening such a support  30  on the measuring head  1 , be inserted into the cutouts or cavities in a self-closed fashion and be held there fastened appropriately.  
         [0111]     The support  30  likewise represented in two views in  FIG. 7  differs from the support  30  shown in  FIG. 6  once again only in the web-like flattening in the upper region.  
         [0112]     In the support  30  represented in  FIG. 8 , the layers  32  containing fluorescing materials are applied in the inclined upper region, with the result that they are not aligned parallel to one another, but are inclined relative to one another.  
         [0113]     A particular design has been selected in the example of a support  30  represented in  FIG. 9 . Use is made in this case only of a support  30  to which layer(s)  32 . 1  to  32 . 3  containing one or more fluorescing materials are applied, and, at a spacing therefrom, an otherwise symmetrically constructed planar optical conductor  35  which both have, above the layer(s)  32  containing fluorescing materials, a surface which is inclined at an angle and at which both the exciting light and the fluorescent light are reflected. In this example, exciting light is launched exclusively into the lower end face of the support  30  and reflected therein, so that fluorescence is excited in the layer(s)  32 . Since the opposite surfaces of the support  30  and of the planar optical conductor  35  are constructed or coated in a reflecting fashion only in the lower part, at least a portion of the fluorescent light can pass by reflection at the inclined surface of the support  30  into the planar optical conductor  35  and be directed from the lower end face thereof via the appropriately arranged optical fibers onto the detectors for the purpose of measuring the fluorescence intensity. However, instead of the reflecting layers  36 , it is also possible to introduce a less strongly refracting medium into the interspace in a fashion producing the same effect, this state of affairs also being valid for the examples according to FIGS.  6  to  8 .  
         [0114]     Moreover, instead of the planar optical  35  conductor  35 , it is also possible to use a second support  30 , so that a symmetrical arrangement can be achieved, in which case it is then also possible thereby to apply different layers  32 .  
         [0115]     In the example represented in  FIG. 10 , by contrast, for example in accordance with  FIG. 9 , the layers  32  containing fluorescing materials are constructed or applied in the upper, inclined region of the supports  30 .  
         [0116]     In the supports  30  represented in  FIG. 4  to  FIG. 15 , the layers  32  containing fluorescing materials can be applied directly to the corresponding surfaces of the supports  30 . In another variant, however, the layers  32  containing fluorescing materials can be applied in advance to a preferably plate-shaped transparent substrate and be fastened subsequently thereto on the respective support  30  at the respective location, it being possible for this purpose to make use of mechanically acting self-closed and/or force-closed connections alone or in conjunction with an optically suitable binding agent, or of such a binding agent alone.  
         [0117]      FIG. 11  represents possible variants of the construction of end faces of the supports  30  or of the planar optical conductors  35  into which or from which the exciting light or the fluorescent light can respectively be launched or coupled out, these end faces being correspondingly inclined in all these examples such that the reflection in the limbs  30 ′,  30 ″ of the supports  30  can be optimized, on the one hand, for the excitation of the fluorescence and, on the other hand, for the alignment of the fluorescent light to be measured.  
         [0118]     In these cases, the upper part of the measuring head  1 , on which such a support  30  is to be mounted, must be of complementary shape in order to avoid optical losses. The same also applies to the supports  30  of the examples according to  FIGS. 14 and 15 .  
         [0119]      FIGS. 12 and 13  show further possibilities of how a support  30  can be constructed, only slightly modified U shapes having been represented here by way example.  
         [0120]      FIGS. 14 and 15  show rotationally symmetrical supports  30  whose upper part is of conical construction, and in which the layers  32 . 1  and  32 . 2  containing fluorescing materials are arranged or constructed in the shape of a circular ring around the outer lateral surface of the support  30 , if appropriate on an additional, appropriately constructed support, or directly on the surface.  
         [0121]     The two examples of  FIGS. 14 and 15  differ 10 only in the construction of the reflecting coating  36 . In “both examples, the light is launched into and coupled out of the support  30  through conically recessed end faces.  
         [0122]     Represented in  FIG. 16  is a body  40  made from 15 an optically scattering material such as, for example, a polyester filled with titanium oxide, aluminum oxide or zirconium oxide, to which, in turn, layers  32 . 1  and  32 . 2  containing fluorescing materials are applied directly or on a flat substrate.  
         [0123]     Such a body  40 , which can also be designated as a diffuser plate, can have cutouts or cavities  42  which are dimensioned and arranged such that the body  40  can be mounted on a measuring head  1  as represented, for example, in  FIG. 3 . In this case, the exciting light is radiated into the body  40  by the optical fiber  3  and distributed there diffusely, as a result of which a uniform excitation of fluorescence is achieved in the layers  32  and at least a portion of the fluorescent light is redirected into the body  40 , and directed from there into the optical fibers  16  and  15  onto the detectors  4  for the purpose of measuring the fluorescence intensity.  
         [0124]     It is also possible that the fluorescent light can be launched into the optical fibers  15 ,  16  from an end face of the layer(s)  32 , and can thereby be directed onto the detector(s)  4 ,  5 .  
         [0125]     Such a body  40  can, however, also consist of an optically transparent material which is provided on the exposed surfaces with a reflecting coating, and the surface of the body  40  is constructed in an optically scattering fashion in the region of the layers  32  containing fluorescing materials.  
         [0126]     A cap  41  with a body  40 , which can be 5 constructed, in turn, as already set forth in the description of  FIG. 16 , is shown in  FIG. 17 , and on the body  40 , in turn, at least one layer  32  containing a fluorescing material is arranged or constructed there. As was represented, for example, in  FIG. 1 , the cap  41  can then be mounted on a measuring head  1 , and in this case the arrangement and alignment of the optical fibers  15  and  16  for the fluorescent light should be performed to correspond with those of the respective layers  32 . 1  or  32 . 3 .  
         [0127]     A further example of a body  40  which can already be constructed, as mentioned above, is represented in  FIG. 18 .  
         [0128]     Such a body  40 , can, in turn, easily be made available in a simple way as an exchangeable part, as is also the case for the cap  41  in accordance with  FIG. 17  and the body  40  in accordance with  FIG. 16 .  
         [0129]     If, as also represented in  FIG. 3   a , the body  40  according to  FIG. 18  is mounted on a measuring head  1 , the light of the light source  2  passes relatively accurately into the middle of the body  40  and is scattered there diffusely and fluorescence is excited in the layers  32 . 1  and  32 . 3  virtually simultaneously. The fluorescent light retro reflected into the body  40  passes via the limbs  40 ′ and  40 ″ of the body  40  and the optical fibers  15  via an optical system  25  onto a photo detector  4 , it being possible for an optical filter  8  to be arranged upstream of the latter, and the evaluation of the measuring signals being carried out with the electronic system  9  integrated in the measuring head  1 .  
         [0130]      FIGS. 19 and 20  represent two examples of holders  43  on which it is possible to fasten layers  32 . 1  and  32 . 2  containing fluorescing materials. These layers  32 . 1  and  32 . 2  are preferably applied to a plane, flat, transparent substrate which can be fastened on the holder  43  in a self-closed fashion and/or with a binding agent.  
         [0131]     A holder  43  thus prepared can then readily be 5 mounted and fastened on, for example, a body  40  which can, if appropriate, be a permanent component of a measuring head  1 , as is represented in  FIG. 3   a.    
         [0132]     Represented in  FIG. 21  is a further example of a measuring head  1  according to the invention, on whose upper tip there is arranged, in turn, a layer  11  in which at least one fluorescing material is contained. Arranged, in turn, below this layer  11  is a temperature sensor  13  and a heating element  12 , the aim being, if required, to prevent the formation of condensate on the layer  11 .  
         [0133]     The exciting light is once again launched into an optical fiber  3  starting from the light source  2  via an optical system  53  and an exchangeable filter  6 , and directed onto the layer  11 . The excited fluorescent light passes via the optical fiber  15 , the optical systems  52  and the exchangeable filter  8  into a spectrometer  50 , for the purpose of wavelength-resolved measurement, to different detectors  54 ′ and  54 ″ via an optocoupler  51 .  
         [0134]     A further example of a measuring head  1  according to the invention is represented in  FIG. 22 , in two views. In this case, the exciting light of the light source  2  is launched only on one side into a limb  30 ′ or  30 ″ of a support  30  such as is represented in FIGS.  4  to  15 , and coupled out again from the respective other limb  30 ′ or  30 ″ or both limbs  30 ′ and  30 ″, and directed onto detectors  4  in order to determine the fluorescence intensity.