EP0938658A1 - Procede et dispositif de spectroscopie combinee par absorption et par reflectance - Google Patents

Procede et dispositif de spectroscopie combinee par absorption et par reflectance

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Publication number
EP0938658A1
EP0938658A1 EP97951785A EP97951785A EP0938658A1 EP 0938658 A1 EP0938658 A1 EP 0938658A1 EP 97951785 A EP97951785 A EP 97951785A EP 97951785 A EP97951785 A EP 97951785A EP 0938658 A1 EP0938658 A1 EP 0938658A1
Authority
EP
European Patent Office
Prior art keywords
coupling
radiation
mirror
volume
remission
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97951785A
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German (de)
English (en)
Inventor
Klaus-Henrik Mittenzwey
Gert Sinn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Optosens Optische spektrokopie und Sensortechnik GmbH
Original Assignee
Optosens Optische spektrokopie und Sensortechnik GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from DE1996147222 external-priority patent/DE19647222C1/de
Priority claimed from DE19730826A external-priority patent/DE19730826A1/de
Priority claimed from DE1997133253 external-priority patent/DE19733253A1/de
Application filed by Optosens Optische spektrokopie und Sensortechnik GmbH filed Critical Optosens Optische spektrokopie und Sensortechnik GmbH
Publication of EP0938658A1 publication Critical patent/EP0938658A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/645—Specially adapted constructive features of fluorimeters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/031—Multipass arrangements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/59—Transmissivity
    • G01N21/5907—Densitometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/645—Specially adapted constructive features of fluorimeters
    • G01N2021/6484—Optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N2021/6491—Measuring fluorescence and transmission; Correcting inner filter effect
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/02—Mechanical
    • G01N2201/024—Modular construction

Definitions

  • a special absorption method is based on the principle of the evanescent wave fields or the attenuated total reflection (ATR).
  • radiation is coupled into a highly conductive solid, e.g. ATR crystal or optical waveguide, and decoupled again after passing through a defined distance.
  • the optical waveguide stands with the one to be examined Measuring volume in contact
  • the coupling radiation is totally reflected in the optical fiber at the interface to the measuring volume, whereby a small part of the radiation penetrates into the measuring volume (evanescent wave) and interacts with it.
  • the coupling radiation is weakened. This attenuation is measured. hang in formula (1). (BERGMANN and SCHAEFER: Textbook of Experimental Physics. Optics. Berlin - New York, Walter de Gruyter, 1993)
  • DE 4104316A1 presents an internally mirrored spherical cell in which the coupled radiation is reflected back and forth several times and then coupled out again and directed to a receiver .
  • DE 4124545A1 describes a gas absorption cell.
  • the reflectance is composed of the diffuse reflectance and the specular or directional reflection.
  • 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 ß) and absorption capacity (total absorption coefficient ⁇ ⁇ ,) of the measuring volume. For the sake of simplicity, the absorption will dominate in the following.
  • the theory of Kubelka and Munk is used for the mathematical description of the remission. In the case of an infinitely extended measuring volume (e.g. deep water), the remission is proportional to the quotient of the scattering coefficient and absorption coefficient,
  • the remission in the broader sense is determined 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 ⁇ F of the measurement volume (Q FF ) is characterized.
  • the fluorescence contribution to the remission of large measurement volumes is determined by the quotient
  • the formulas (2) and (4) are characterized by the same mathematical structure. In both cases, the reflectance is proportional to the scattering or fluorescent ability and inversely proportional to the total absorption.
  • reflectance spectroscopy is fundamental for remote sensing and is used for both optically very dense and transmitting measurement volumes.
  • Examples of the first case are remission measurements on vegetation (leaves or needles) to determine the physiological state or measurements on soils to determine, for example, moisture and structure.
  • the second case of the transmitting measuring volumes includes atmosphere, bodies of water and oceans. Comparatively simple conditions exist when the incident radiation (global radiation, lidar) can run dead in the measurement volume, i.e. that in the example of the water the incident radiation does not reach the water floor.
  • Reflection spectroscopy is preferably used to examine solid surfaces.
  • the radiation directly reflected or directed by a surface is analyzed (law of reflection), which provides information about the spectral reflectivity.
  • the specular reflection occurring at the interface with the measurement volume is usually a disturbance variable which is masked out by suitable measuring arrangements.
  • 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 relevant for the reflection is determined not only by the refractive power but also by the absorption capacity of the measurement volume.
  • the refractive index consists of a real part and an imaginary part (complex number):
  • 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.
  • BERGMANN and SCHAEFER Textbook of Experimental Physics. Optics. Berlin - New York, Walter de Gruyter, 1993 and SCHMIDT, W .: Optical Spectroscopy. Weinheim-New York-Basel-Cambridge-Tokyo, VCH Publishing Company, 1994
  • a major advantage of classic absorption spectrometry compared to fluorescence and scattering is that the coupled radiation falls directly on the receiver, which means that considerably more photons are available for the measurement.
  • a major advantage of remission spectroscopy is that the relationship between the total absorption coefficient and the remission is inversely proportional (see formulas (2) - (4)). This makes the remission more sensitive than classic absorption spectrometry. Furthermore, the reflectance contains information about the scattering and fluorescent ability of the measurement volume.
  • a disadvantage of reflectance spectroscopy is that the relationship between R and ⁇ ⁇ , ß, Q F ⁇ F is ambiguous. This means that an exact separation of the scattering, fluorescence and absorption ability is difficult and in many cases not possible.
  • the use of remission for a sensitive determination of the absorption capacity of transmitting measurement volumes is linked to extended measurement volumes, since the radiation only runs dead in the measurement volume after longer distances (eg 10 - 230cm with absorption coefficients of 1 - 23m "1 typical for surface waters) This is not possible for samples with smaller layer thicknesses (eg classic cuvettes), and if light beams with a finite cross section are irradiated into the extended measuring volume (eg Lidar), the photometric distance law has a disruptive effect on the signal-to-noise ratio.
  • reflection spectroscopy An advantage of reflection spectroscopy is that the intensity of the radiation specularly reflected at the interface with the measurement volume provides information about the refractive power, which is substance-specific.
  • the refractive power can also be used to characterize substances that are completely incapable of absorption. It is disadvantageous, however, that the specular reflection also depends on the absorption capacity of the measuring volume and is therefore ambiguous.
  • absorption and reflectance spectroscopy should be combined in such a way that all their advantages are combined and their disadvantages are eliminated.
  • Absorption, scattering, fluorescence and refraction should be able to be determined synchronously and in a single measurement process.
  • a method and a device for carrying out the method are to be developed. solution
  • Measurement volumes are considered that are localized in the multiple reflection space spanned by the coupling-in and counter mirrors and that are located outside of them, usually. located directly on the edge or in the vicinity of the multiple reflection room.
  • the explanations should first be made using the example of transmitting measurement volumes. Radiation of a defined wavelength is injected into the measurement volume to be examined. The measuring volume is located between two opposing mirrors. The mirrors are designed in such a way that, due to a sufficiently high number of reflections, the path of the radiation coupled in via the coupling mirror is so long that it can be completely absorbed in the measurement volume.
  • the coupling mirror (or also the counter mirror) is partially transparent, for example 10% transmission and 90% reflectivity. Consequently, after each reflection or after each revolution, part of the coupling radiation transmitted by the measurement volume passes through the coupling mirror and arrives at a second receiver arranged directly 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:
  • m is a constant that is characteristic and known for the permeability of the coupling mirror.
  • the total absorption coefficient ⁇ ⁇ 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 lower detection limits and higher accuracies. With increasing ⁇ ⁇ , I Tr decreases. This makes sense, since with increasing ⁇ ⁇ the mean path length of the injected radiation decreases until it is almost completely absorbed in the measuring volume and the number of reflections or revolutions 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 greater m, ie the smaller the reflectivity or the greater the transmittance of the coupling mirror, the higher I Tr .
  • the scattering and fluorescence capability ⁇ and Q F ⁇ F can thus also be determined indirectly, taking into account claim 2 (see below).
  • the ambiguity of classic reflectance spectroscopy is eliminated by the combination with the absorption spectroscopy presented above.
  • the remission measurement can be omitted, which leads to a lower expenditure on equipment. The same applies vice versa if only the scatter and fluorescence ability is asked and the determination of the absorption ability is therefore not necessary.
  • Specular reflection takes place at the optical interface to the measuring volume if the adjoining media have different refractive indices.
  • Such an interface can e.g. Be glass / water, the glass serving as an optical window for the entry of the coupling radiation into the measuring volume.
  • the intensity of the reflected radiation is registered with a receiver. This intensity provides information about the refractive index of the measuring volume (formula (5)). Since this refractive index is fundamentally complex, that is, in addition to the actual refractive power of the measuring volume also depends on its absorption force, a correction is carried out.
  • the refractive index determined from the reflected intensity is combined with the absorption coefficient determined from the transmitted radiation in such a way that a refractive index (real part in formula (5)) finally results which is independent of the absorption of the measurement volume.
  • the ambiguity of reflection spectroscopy is eliminated by this combination.
  • the remission is measured integrally, i.e. a receiver without spectrally selective elements (e.g. filter) is aligned to the measuring volume.
  • spectrally selective elements e.g. filter
  • scattering and fluorescence are measured with two optoelectronic receivers and filters for suppressing the scattered or fluorescent radiation are arranged in front of the receiver aligned with the measurement volume in order to selectively determine the scatter and fluorescence component of the remission.
  • the claim 3 solves a problem that occurs with scattering or fluorescent measurement volumes when determining the Abso ⁇ tions sheep using I Tr (formula (6)).
  • the receiver located immediately behind the coupling mirror registers not only the coupling radiation transmitted by the measuring volume, but also scattering and fluorescent photons of the measuring volume. The overall signal is therefore larger. Consequently, smaller total absorption coefficients are simulated according to formula (6). A correction is therefore necessary.
  • an intensity is subtracted from the total intensity of the photons transmitted through the partially transparent mirror (direct coupling radiation plus scattering or fluorescence), which is proportional to the saturated long-path remission (scattering or fluorescence).
  • the proportionality factor is, among other things, a function of the reflectivity and thus the transmission of the partially transparent mirror.
  • the scattering and fluorescence ability of the measurement volume can also be determined directly.
  • the remission is measured that comes from the part of the measuring volume that is immediately behind the coupling point (term here: linear short-path remission).
  • the coupled radiation can therefore only travel a short distance. This means that a complete absorption of the coupling radiation does not occur in this part of the measuring volume.
  • the relationship between remission and scattering and fluorescence ability is linear and independent of the total absorption coefficient. Scattering and fluorescence capability can thus be determined directly with the aid of the linear short path remission.
  • the saturated long-path remission and the linear short-path remission are measured in a time-resolved manner, for example when coupling in very short pulses of small Ins. Their latitudes are determined. The reciprocal of the difference in latitude is a measure of the ability to absorb.
  • This method has the advantage that different device-specific properties such as radiation intensity, filter transmission, aperture, radiation and receiver area have no disruptive effect. The direct comparison between the saturated long-term remission and the linear short-term remission is possible without extensive correction.
  • the content of claim 6 is that the remission is time-integrally registered in a short time window (measurement of the linear short-path remission) and on the other hand in a long time window (measurement of the saturated long-path remission).
  • Short distances in the measurement volume to be examined are covered by the coupled radiation in short times and long distances in long times. That short times are typical for linear short-path remission and long times for saturated long-path remission.
  • the quotient of the short time window and long time window is a measure of the absorption capacity of the measurement volume. This has the advantage that both remissions can be measured electronically without great effort, which leads to a robust construction and easy handling.
  • the widths of the time windows to be set depend on the measurement volume to be examined. With optically denser measuring volumes, the time windows are set shorter than with optically thinner measuring volumes. This leads to the correct measurement of saturated long-path remissions and linear short-path remissions as well as to optimization of the signal / noise ratios.
  • spectrally selective elements for the coupling and measuring radiation are adapted to the respective application and selected as follows.
  • wavelengths are used which lie in the absorption ranges of the substances to be detected.
  • the wavelengths are as far as possible outside of these absorption ranges and are localized at a characteristic absorption point of the solvent.
  • the absorbent substance is determined directly after the measurement of absorption and remission.
  • the second mode takes advantage of the fact that the absorption of the solvent is reduced as the concentration of the substance to be detected increases. As a result of this dilution effect, the measuring volume brightens up at the absorption point which is characteristic of the solvent.
  • Claim 8 has a favorable effect on optically thin measurement volumes in which no saturated long-term remissions can be generated because the path lengths necessary for an almost complete absorption of the coupling radiation cannot be generated with the aid of simple multiple reflection devices.
  • the reflectance generated with optically thin measurement volumes is characterized by a linear relationship to the scattering and fluorescence ability and is independent of the total absorption coefficient. dependent (term here: linear long-term remission).
  • the scatter and fluorescence ability can thus be determined directly from the linear long-term remission.
  • the absorption capacity or the total absorption coefficient is determined by decoupling the radiation coupled into the measurement volume after a defined number of reflections or cycles from the multiple reflection device and directing it onto a receiver. The ability to absorb is therefore not determined according to formula (6), but in the classic way according to the Lambert-Beer law (formula (1)).
  • Claim 9 relates to optically thin measurement volumes, which also do not have a sufficiently high minimum absorption, so that no saturated long-term remission can be generated as a result of multiple reflection. It is proposed to determine the absorption capacity only via the coupling radiation transmitted through the partially transparent coupling mirror. This means that changes (removal of mirrors, implementation of the coupling-out of the coupling radiation after passing through a defined distance) no longer need to be made.
  • artificial absorbers are used in the multiple reflection device or in the multiple reflection space (claim 10). This leads to a defined shortening of the path of the injected radiation up to its complete absorption.
  • the reciprocal of the smallest possible total absorption coefficient of the measuring volume serves as a measure of the path length to be set.
  • gray filters can be used as artificial absorbers.
  • the transmitting coupling mirror itself can also act as an artificial absorber. The greater the permeability of this semitransparent mirror, the shorter the mean path length of the injected radiation until it is completely absorbed in the measuring volume. The mean path length is thus influenced in a defined manner by the permeability.
  • the mean path length of the injected radiation in the measurement volume is inversely proportional to the total absorption coefficient
  • the greatest possible mean path length can be estimated from knowledge of the smallest possible absorption coefficient of the measurement volumes to be examined, and the permeability of the partially transparent layer of the coupling mirror can be adjusted on this basis.
  • the claim 11 represents a solution that is used in optically denser (but still transmitting) measurement volumes.
  • the number of cycles to complete absorption of the incident radiation is small with denser measuring volumes.
  • the determination of the absorption capability with high sensitivity via the coupling radiation passing through the coupling mirror and transmitted by the measuring volume would only be possible to a limited extent according to formula (6). It is therefore proposed to determine the absorption capacity using the classic method, either by placing a receiver instead of the counter mirror for direct measurement of the coupling radiation weakened by the measurement volume, or by removing the coupling mirror and using the receiver located directly behind it to measure the weakened coupling intensity.
  • the scattering and fluorescence capability is determined from the linear short-path remission.
  • Claim 12 is intended to solve a problem which arises when, in the case of fluorescence, the absorption at the measurement or fluorescence wavelength can no longer be neglected (formula (3)).
  • the (fluorescence) reflectance is then dependent on the absorption at the wavelength of the coupling radiation and the fluorescence wavelength.
  • the solution is that in addition to measuring the (fluorescence) reflectance, the fluorescence is also measured at an angle of 90 ° to the coupling radiation. If the multiple reflection cell is designed accordingly, the 90 ° fluorescence is not dependent on the absorption at the fluorescence wavelength.
  • the combination of (fluorescence) reflectance, 90 ° fluorescence and transmitted coupling radiation on the one hand provides the correct fluorescence capability of the measurement volume and on the other hand also the absorption at the measurement or fluorescence wavelength.
  • the coupling radiation transmitted through the semitransparent coupling mirror and the reflectance of the measurement volume are also measured in such wavelength ranges where, due to the reflectivities of the semitransparent coupling mirror being too low, the coupling radiation is no longer almost completely absorbed by the measurement volume alone.
  • the course of the intensity of the coupling radiation on its way through the multiple reflection cell is also essentially determined by the specular reflectivity. The smaller the specular reflectivity, the more the intensity of the coupling radiation decreases along its path.
  • the state of saturation is, based on its above Definition, reached when the intensity of the coupling radiation on its way in the multiple reflection cell has dropped to almost zero. This drop is now caused here by the absorption of the measuring volume and by the mirror reflectivity of ⁇ 1, which acts as a loss component.
  • the mathematical relationship between the intensity of the transmitted coupling radiation and the absorption capacity of the measuring volume is of a somewhat more complex structure compared to formula (6), since device-related variables, such as mirror reflectivity, also have a noticeable influence on the measuring signals. Basically, this relationship is still characterized by the fact that is a function of the reciprocal of the intensity of the transmitted coupling radiation, i.e. the intensity of the transmitted coupling radiation decreases with increasing absorption of the measurement volume. The connection is clear. Consequently, the absorption capacity of the measurement volume can be determined from the transmitted coupling radiation.
  • the measured reflectance is also determined by the specular reflectivity, the absorption of the measurement volume and the scattering and fluorescence ability of the measurement volume. In the case of the state of saturation, the saturated long-term remission occurs.
  • the reflectivity is indirectly determined by coupling the measured intensity of the transmitted coupling radiation with the reflectance signals.
  • Claim 14 concretizes the method for measurement volumes that have a sufficiently high minimum absorption, so that a saturated long-term remission due to multiple reflection is always generated solely by the effect of the measurement volume. This means that the saturated long-term remission is generated even with high specular reflectivities (that is, with little influence of the mirrors on the intensity of the coupling radiation).
  • the spectral reflectivity of the semitransparent mirror is matched to the spectral absorption behavior of the measuring volume. In other words, knowing the expected spectral profile of the absorption of the measurement volume to be examined, a mirror is used whose wavelength ranges of high reflectivities coincide with the ranges of low subsections of the measurement volume.
  • the spectral reflectivity of the partially transparent coupling mirror to the spectral Abso ⁇ tion optically thin measurement volume to be adjusted so that the wavelength ranges of high specular reflectivity coincide with the wavelength ranges of comparatively high Abso ⁇ tion of the measurement volume. It is thereby achieved that the specular reflectivity has a comparatively small influence on the intensity profile of the coupling radiation and thus a sufficiently high measuring sensitivity can nevertheless be achieved. It is clear that the wavelength ranges of low specular reflectivities in the case of optically thin measurement volumes are not very suitable for sensitive measurement of the absorption of the measurement volume. This means that the usable wavelength range is smaller for optically thin measurement volumes than for measurement volumes which, as above, have a sufficiently high minimum absorption.
  • Claim 16 explains a method that can be applied to optically dense measurement volumes in which the saturated long-path remission is generated in the measurement volume after very short distances of the coupling radiation. If the measurement volume is located in the multiple reflection space between the coupling mirror and the counter mirror, then the coupling radiation no longer reaches the counter mirror, which consequently is no longer required for the measuring process.
  • the counter mirror designed as a full mirror is therefore replaced by an optically transparent protective window, the measurement volume being located outside the multiple reflection space on the outside of the window.
  • the radiation coupled into the measurement volume produces a remission typical of the measurement volume, which is controlled by the scattering and absorption coefficients.
  • the radiation remitted by the measuring volume falls on the partially transparent coupling mirror.
  • the remission transmitted through the semi-transparent coupling mirror and / or the remission that hits the remission receiver is measured.
  • This measurement process differs significantly from classic remission spectroscopy, in which the remitted Radiation without multiple reflection is measured immediately after the first back reflection from the measurement volume.
  • the advantage of the remission measurement proposed here is that the interaction between photons and the measurement volume is significantly increased by coupling the remitted radiation several times, which leads to an increase in sensitivity.
  • the multiple reflection can also be carried out between a window provided with a material-selective surface and the coupling mirror. The surface is on the outside, the measuring volume being brought into contact with this surface.
  • a partially transparent mirror can be used instead of the window.
  • the mirror layer of this 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 get into the sensor through the non-mirrored areas in the counter mirror. The receiver located behind the coupling mirror registers an intensity that depends on the reflectivity of the measurement volume.
  • the increase in sensitivity in the case of window measurement is particularly noticeable in the case of measurement volumes with reflectance of, for example, greater than 0.4.
  • Remittent are e.g. light powder (pharmaceutical industry) and paper (pulp paper industry). This effect becomes smaller with smaller remissions.
  • surface waters are usually characterized by comparatively low remissions of around 0.05 - 0.1.
  • a light-conducting solid body eg a modified ATR crystal
  • the radiation coupled into the fixed body via the coupling mirror travels long distances there due to the multiple reflection and is almost completely absorbed.
  • the measuring volume to be examined is brought into contact with the solid body (of course not at the coupling and decoupling surfaces), so that the coupling radiation propagating in the solid body at the solid / measuring volume interface interacts with the measuring volume via evanescent radiation and is absorbed by it.
  • the transmitted radiation is registered via the receiver located behind the partially transparent coupling mirror.
  • Claims 20-22. specify the measurement of the radiation specularly reflected at the interface to the measurement volume and the determination of the refractive power of the measurement volume.
  • photons from a radiation source are directed obliquely (that is, at an angle different from the perpendicular) onto the interface.
  • the interface can be an optical window to a liquid, for example.
  • the radiation source preferably has small dimensions (eg point source). The radiation hits the optical window. A part is reflected both at the air / window interface and at the window / measurement volume interface of interest. The rest of the radiation penetrates into the measuring volume.
  • the radiation source is imaged on a receiver located in the reflection angle via a lens.
  • a lens can be arranged both in the incident and in the reflected beam.
  • Two images of the radiation source are created in the imaging plane: (a) that over the air / window interface and (b) that over the window / measurement volume interface.
  • the receiver is set to the figure above (b), since only this contains the information on the refractive power of the measuring volume.
  • the two images can be separated well if oblique angles of incidence and sufficiently thick windows are used. Since 1. a specular reflection takes place at the interface, 2. the optical imaging is adjusted to the level of this interface and 3. photons from the measuring volume run in all spatial directions and for which the distance law 1 / r 2 applies, the proportion is off the measured volume and the photons hitting the receiver are small compared to the specularly reflected ones. If necessary, a correction with regard to this disturbing remitted portion can be carried out by means of the other receivers which are aimed directly at the measurement volume.
  • the combination of refraction at the interface and remission from the measurement volume can also be advantageous when examining solid, non-transmitting surfaces, one of which is the properties of the solid phase (type, structure) and the other the properties of the liquid or gaseous phases are to be detected.
  • An example of this is the examination of masonry (moisture and condition).
  • Claim 23 deals with measurement volumes whose refractive index changes only slightly or not at all. This is e.g. in the case of solvents with substances in the mg / 1 range and below.
  • a very common solvent is water (surface water, waste water, etc.). If water comes into contact with the optical window of a sensor, it can accumulate (e.g. lime, algae, bacteria). As a result, the remission let through the window and the transmitted coupling radiation can be changed. The result is incorrect statements about the measuring volume to be examined.
  • the deposits at the window / water interface lead to a change in the intensity of the radiation reflected at the specular interface, which is used as a measure of the disturbing change in the optical properties of the window. This measure serves to correct the diffuse reflectance and the transmitted radiation.
  • the refraction must also be taken into account in the case of multiple reflection, since specularly reflected coupling-in radiation occurs at the optical interfaces. If possible, these reflexes should not hit the remission recipient. Therefore, the reflectance receivers are arranged outside the direction of reflection.
  • the specular reflected Coupling radiation strikes a light trap to completely eliminate it. Since the specularly reflected coupling radiation contains information about the refractive power of the measurement volume, on the other hand, an additional receiver can be used instead of the light trap, which measures the specularly reflected intensity.
  • the refraction of the measurement volume is determined using an evaluation algorithm. This evaluation algorithm eliminates device-specific properties and combines the specularly reflected intensity with the intensity of the coupling radiation transmitted through the semitransparent mirror in order to determine the real part from the complex refractive index.
  • Claims 25-33 describe a method in which the flow velocity is determined from the reflectance of moving measurement volumes. Two different remissions are determined with regard to the time.
  • an integral remission is determined within a fixed, comparatively large time interval, which depends both on the inherent absorption, scattering and fluorescence ability and refractive power as well as on the flow rate of the measurement volume.
  • a differential remission is determined within comparatively small time intervals, which depends exclusively on the inherent absorption, scattering and fluorescence ability and refractive power of the measurement volume. The time independence of the differential remission is generated by determining the remission in a very short time interval. This leads to the fact that the measuring volume column flowing past the receiver practically rests at the moment of the measured value acquisition.
  • the combination of integral and differential remission results in a parameter that only depends on the speed.
  • the speed is determined in detail as follows.
  • the number of all remission pulses detected with an optoelectronic receiver in a defined time interval is determined. These impulses come from the particles or structures of the measuring volume.
  • the sum of the pulses (integral remission) is proportional to the number of particles flowing past the receiver. This particle number depends on the particle concentration (particle distance) and the flow rate.
  • the particle concentration is determined from the inherent absorption, scattering and fluorescence capability as well as the refractive power of the measurement volume via the time-independent differential reflectance. This results in a clear connection to the flow rate: the more particles flow past the receiver within a defined time, the greater their speed must be.
  • Another method is to determine the integral reflectance of individual particles during their dwell time in the active zone under consideration and seen by the receiver. During this time, the remission on the particle is "integrated". This reflectance depends on the reflectivity of the measuring volume or the particles and on the particle speed. The reflectivity is determined from the inherent absorption, scattering, fluorescence and refractive power, again using the time-independent differential reflectance. This results in a clear connection to the flow rate: the greater the remission integrated on the particle, the longer the particle must remain in the active zone.
  • the dwell time is inverse to the particle speed. This dwell time can also be determined as follows.
  • the particle pulse is measured in a time-resolved manner and its mean width is used as a direct measure of the residence time of the particle in the active zone (the extent of which is also known).
  • the pulse width is rn.aW. the remission integral normalized to the reflectivity of the particle.
  • a special case is moving measuring volumes with rotating elements. So one can form rapidly moving liquid whirlpool.
  • the speed of rotation of the strudel greatly influences the strudel cross section and its position in the liquid column (meander). Assuming known hydraulic conditions (eg constant and known input), the speed of rotation is determined by optoelectronic observation (camera) and determination of the vortex position.
  • Figure 1 shows the absorption module (1). This is formed by the coupling, measuring, light guide and connection module (5), (2), (3), (4).
  • the Abso ⁇ tionsmodul is also the carrier for the modules for measuring the 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 (5a)).
  • the coupling module consists of the coupling mirror (5a) and the optical fiber block (5b).
  • the coupling mirror is preferably flat; can also be spherical in certain applications.
  • the coupling mirror or its mirror substrate eg glass
  • a partially transparent layer 5c
  • 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 (5b) contains several optical fibers (5e) 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 (5b) also lies in this plane.
  • This optical waveguide level lies flat against the upper area (5d) of the coupling mirror from the inside. This area is not mirrored.
  • the coupling mirror is transparent to the radiation to be coupled into the measuring volume.
  • the mirror layer and optical fiber end faces form a common vertical plane.
  • a radiation-carrying volume which is designed, for example, 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.
  • Downstream of the coupling module is the light guide module (3), which receives the optical fibers from the optical fiber block (5b) and forwards them to fixed positions in block (3a).
  • the optical fibers are fixed there, for example by gluing in the holes provided.
  • (3a) 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 forwarding.
  • LED light emitting diodes
  • the optical fiber is used to conduct radiation from an external source, which is connected to the sensor via an SMA connection, for example. is bound. 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) also lies in this plane.
  • 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.
  • the measurement volume can be localized in the multiple reflection space between the coupling mirror and the counter mirror and on the other hand outside. Furthermore, the measurement volume can be in a radiation-carrying volume. However, it can also be unaffected by such a volume, i.e. the measuring volume is not in a radiation-carrying volume.
  • the end faces of the optical fibers are located directly above the mirror layer (5c). 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 conical reflector (8) arranged directly behind the coupling mirror (5a) acts as a cross-sectional converter for the coupling radiation passing through the coupling mirror (claim 36).
  • 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 that on the receiver side. It is thus possible to use receivers 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 to be able to register the entire transmitted coupling radiation.
  • an optical waveguide can also be located, which is guided to the outside. If necessary, a diffusion plate is arranged between the coupling mirror and the optical waveguide to reduce directional radiation.
  • 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 the purpose of maximum radiation transmission.
  • connection and light guide modules (4), (3a) are connected flat on top of each other.
  • the optical fibers (5e) in the light guide module and the LED (4b) and the one optical fiber (4a) 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.
  • the transmitted coupling radiation and also the reflectance photons passing through the coupling mirror are influenced in a defined manner with spectrally selective elements (eg bandpass filter or edge filter).
  • spectrally selective elements eg bandpass filter or edge filter.
  • the then also transmitted coupling radiation can then be spectrally resolved (for example by means of a polychromator, which receives the transmitted coupling radiation via an optical waveguide).
  • a protective glass and / or a filter can be localized instead of the coupling mirror.
  • the sensor then works as a classic absorption spectrometer, with the reflection module (see explanations below) serving to extend the path of the coupling radiation. In the case of optically denser measuring volumes, the sensor is operated without a reflection module and in this case is a classic reflectance spectrometer.
  • spectrally selective elements for the coupling and measuring radiation are adapted to the respective application and designed in the following manner.
  • the sensor wavelengths are in the absorption ranges of the substances to be detected.
  • these are located outside of these absorption areas and, if possible, are arranged at a characteristic absorption point of the solvent.
  • the absorbent substance is determined directly after the measurement of absorption and remission.
  • the second mode takes advantage of the fact that the absorption of the solvent is reduced as the concentration of the substance to be detected increases. As a result of this dilution effect, the measuring volume brightens up at the absorption point which is characteristic of the solvent.
  • the reflectance module (6) is at a minimal distance from the optical fibers of the coupling module ( Figure 2, top view). Its optical window (10) and the coupling mirror of the absorption module are 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 the receiver can already serve as a protective window for the remission 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.
  • optical waveguides can also be arranged, which are guided to the outside.
  • 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.
  • the remission module is equipped with a Optics geared directly to the coupling location.
  • FIG. 42 in the refraction module (7), e.g. with the help of an LED (12), radiation is generated.
  • Figure 3 shows the refraction module.
  • the LED is connected to a receiver (18), e.g. 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 the LED radiation are achieved on the one hand, and on the other hand an oblique incidence of light rays 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 1: 1 image of a small radiating area, e.g. 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.
  • Figure 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.
  • a concave mirror (20) is mounted in the reflection module (19), which can be varied with adjusting screws on the one hand with regard to its distance to the coupling mirror and on the other hand with regard to the tilt angle of its mirror plane with the aid of leaf springs (21), (22).
  • the distance of the concave mirror is adjusted so that the end faces of the optical fibers in the coupling module are located between single and double focal lengths.
  • 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 (scale 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 (i.e. the end faces of the optical fibers are on the top - their pictures below, with the pictures lying on the mirror layer!).
  • the mirror distance is equal to the focal length of the concave mirror. Applications e.g. transparent liquids in the mineral oil, textile, food and chemical industries.
  • Claim 44 is an advantageous embodiment of claim 43. for example in the cases in which the external conditions of the sensor assembly and complicated sensor requirements do not allow the concave mirror to be tilted. The mirror is then adjusted via a vertical shift instead of a tilt.
  • Claim 45 describes an application in which the measurement volume (23) between the coupling mirror and the counter mirror is located in a radiation-carrying volume ( Figure 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-carrying volume (24) can be, for example, an HPLC flow-through capillary which guides the coupling radiation. The multiple reflection takes place between the coupling mirror and the counter mirror and the capillary.
  • 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.
  • a flexible, hollow and liquid-carrying optical waveguide can also be arranged.
  • an optoelectronic receiver (27) can be mounted in such a way that it registers the interaction photons, such as fluorescence and scattering, generated at an angle of 90 ° to the radiation.
  • Applications eg: transparent liquids for flow measurements, HPLC - laboratory analysis.
  • Claim 46 deals with a special embodiment of Claim 45.
  • the end face of the coupling (29) is arranged directly in front of the coupling mirror (31) ( Figure 6).
  • the measuring module (32), i.e. 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 laterally outwards. 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. glued directly onto the LED base.
  • the coupling mirror can also be located at another location.
  • 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 both parts are put together again.
  • the partially transparent layer then contains a small, optically transparent opening for coupling the emitter radiation.
  • the counter mirror (30) is vapor-deposited on the surface opposite the partially transparent 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 be used to guide the radiation as a result of 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.
  • LEDs are arranged to implement different wavelengths.
  • a further modification consists in not applying mirror layers as coupling-in and counter mirrors. If in this case a further receiver is attached to the side opposite the emitter, the LED is a simple absorption and remission spectrometer, with several LEDs being arranged to implement different wavelengths.
  • the arrangement of several LEDs can be linear or as a drum, for example. In this case, it makes sense to bring the radiation to the front (absorption) and back (remission) via an optical device to a receiver. In this case, the LEDs are controlled at different times in flash mode. Another possibility is to control the LED at the same time and to implement the imaging on a diode array or a CCD camera.
  • FIG. 7 illustrates claim 47.
  • the measuring volume is located here outside the sensor, ie the measuring volume is located outside the multiple reflection space, which is spanned by the coupling mirror and the counter mirror.
  • the multiple reflection takes place between the planar coupling mirror (5 a) of the coupling module, the counter mirror (34) and a radiation-carrying 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.
  • a radiation-guiding cone can be arranged between the coupling mirror and the ATR crystal to adjust the diameter of the coupling mirror and the ATR crystal.
  • a flexible optical waveguide can also be arranged instead of the ATR crystal.
  • the refraction module is in operation and in contact with the measuring volume.
  • the remission module is usually not in operation. Due to a special flanging 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 measuring volume and another part radiation into the ATR crystal, the reflectance module can also be in operation. With this arrangement, absorption, remission and refraction can thus be determined synchronously, for example in heavily clouded measurement volumes. Applications eg: industrial wastewater.
  • the measuring volume is outside the sensor ( Figure 8).
  • an optical window (38) is located in one embodiment or a counter mirror (38) with transmitting areas on the measurement volume (23) 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 irradiation via the optical waveguide block (5b) of the coupling module, there is multiple reflection between the measurement volume, coupling mirror (5a) and the radiation-carrying volume (37).
  • This volume can be an internally mirrored hollow body and / or a solid body that carries radiation through total reflection.
  • the shape of the radiation-carrying volume can be different, e.g. cylindrical or conical.
  • the sensor sits on the measuring volume (23) by means of (35), (36).
  • This support for measuring volume contacting is a fixed body or block.
  • the reflectance and refraction modules can be in operation while sitting on the measurement volume. In this case, the reflectance and refraction modules are arranged shifted forward in the direction of the measurement volume in comparison to FIG.
  • 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 fibers 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 body that emits radiation through total reflection, its surface on the measurement volume side is identical to the window.
  • Applications include Measuring volumes with comparatively high reflectivity, such as milk and paper.
  • 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 (5a) and the counter mirror (38).
  • the mirror layer of the counter mirror is partially transparent in such a way that non-mirrored at defined locations of the mirror Areas exist that 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 get into the sensor through the non-mirrored areas in the counter mirror.
  • the receiver located behind the coupling mirror registers an intensity that depends on the reflectivity of the measurement volume. Applications include measuring volumes with comparatively low reflectivity, such as surface water, waste water and landfill leachate.
  • the window (38) mentioned in claim 48. 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.
  • 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.
  • claim 50 deals with a special embodiment of claims 48 and 49 (Figure 9).
  • 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 51 describes an advantageous embodiment of claim 50.
  • Mirror layers for coupling and counter mirrors are not applied.
  • Figure 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 one of the flat and oblique termination (41) for coupling the radiation into the measurement 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 dome / measuring volume interface.
  • the coupling of the two measurement signals thus enables the absorption and remission properties of the measurement volume to be determined synchronously.
  • the windows contacted with the measurement volume are provided with surfaces analogous to claim 49.
  • several LEDs e.g. 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.
  • a further advantageous embodiment of claim 48 is claim 52.
  • a radiation-carrying tube is mounted directly on the window or the counter 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 such a refractive index that a total reflection of im Coupling and remission photons located in the tube are allowed.
  • 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.
  • the coupling takes place via the partially transparent plane mirror (43) by means of optical fibers (42), the diameter of which is substantially 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 diameter of the optical waveguide on the coupling mirror side 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-conducting cone (8) in Figure 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) ( Figure 12).
  • the coupling can then be at any arbitrary and non-mirrored location of the coupling mirror, e.g. central, can be realized.
  • spectrally selective elements can be arranged between the radiation source (46) and the optical waveguide and between the optical waveguide and the receiver.
  • the coupling mirror (48) is a full mirror (ie not partially transparent) and the counter mirror (49) is partially transparent ( Figures 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 mirror (49).
  • 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 56 documents advantageous versions in which both the coupling mirror and the counter mirror are designed as full mirrors ( Figures 15 to 18).
  • 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).
  • Figure 16 illustrates the case in which coupling and decoupling take place via an optical fiber splitter (52).
  • a radiation-conducting volume (53) which has an opening in its jacket, is arranged in front of the coupling mirror in order to couple coupling radiation. Through this opening, part of the radiation can leave the radiation-guiding volume after each revolution.
  • This opening can be a light Be waveguide (54) downstream.
  • This system works in the same way as the optical fiber splitter.
  • the diameter of the branching mirror on the coupling mirror is the same as that of the coupling mirror.
  • the coupling mirror can be vapor-deposited on the branch.
  • Figure 18 illustrates another variant of the coupling-out, which consists in that the coupling-in mirror is preceded by a transmitting body (55) (e.g. a glass plate), which couples a small part of the coupling-in radiation dependent on the refractive index from the beam path, with which the receiver ( 45) is applied. When using a glass plate, approximately 4.5% of the incident radiation is reflected.
  • a transmitting body e.g. a glass plate
  • the reflectance of the plate is adjusted depending on the application, for example via the choice of material or by designing defined interfaces between this plate and a support.
  • a radiation-carrying volume with an oblique interface can also be arranged.
  • 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 an optical signal that can be measured by the receiver, for example as fluorescence or scattering.
  • the essential features of the described device can be used not only for light wavelengths or wavelengths of the optical spectral range, but also for wavelengths different therefrom. Examples: ultrasound and nuclear radiation.
  • the sensor system described can be installed on the one hand in the spectroscopic measurement technology available on the market using the electronics contained therein.
  • the sensor system can be coupled to a separate, highly integrated electronic control and evaluation unit.
  • the electronics enable both cw mode and flash mode. In flash mode, the dark signal can be measured after each flash.
  • flash mode the dark signal can be measured after each flash.
  • a special feature is that the sensitivity of the measurement is set electronically depending on the optical properties of the measurement volume to be examined.
  • the LED current can be varied, which has a direct effect on the emitted LED intensity.
  • the terminating resistor on the optoelectronic receivers can also be varied, which has a direct impact on the electrical signal applied to the receiver.

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Abstract

L'invention concerne la détermination simultanée de l'absorption, de la fluorescence, de la dispersion et de la réfraction de liquides, de gaz et de solides (volume de mesure) avec une grande sensibilité. Un rayonnement d'une longueur d'onde définie est injecté dans un dispositif à réfraction multiple. On mesure le rayonnement d'entrée transmis avec un récepteur semi-réfléchissant implanté juste derrière un miroir, et on mesure la réflexion spectrale de sens opposé à la direction d'incidence ainsi que le rayonnement se réfléchissant de façon spéculaire à la surface du volume à mesurer avec un récepteur orienté vers le volume de mesure et implanté au niveau du miroir d'injection. La capacité d'absorption est calculée à partir de la valeur inverse du rayonnement transmis. La capacité de dispersion et celle de fluorescence sont calculées indirectement à partir de la combinaison de la réflexion spectrale et du rayonnement transmis. Enfin la réfraction est calculée à partir de la combinaison du rayonnement réfléchi de façon spéculaire et du rayonnement transmis. L'invention concerne un procédé et un dispositif simple, solide et modulaire ayant comme domaines d'application l'analyse, le contrôle qualité et la surveillance dans l'industrie, l'environnement et la médecine.
EP97951785A 1996-11-15 1997-11-14 Procede et dispositif de spectroscopie combinee par absorption et par reflectance Withdrawn EP0938658A1 (fr)

Applications Claiming Priority (7)

Application Number Priority Date Filing Date Title
DE19647222 1996-11-15
DE1996147222 DE19647222C1 (de) 1996-11-15 1996-11-15 Verfahren und Vorrichtung zur kombinierten Absorptions- und Remissionsspektroskopie für die Ermittlung der Absorptions-, Streu- und Fluoreszenzfähigkeit transmittierender Flüssigkeiten, Gase und Festkörper
DE19730826A DE19730826A1 (de) 1996-11-15 1997-07-18 Kombinierte Absorptions- und Reflektanzspektroskopie zur synchronen Ermittlung der Absorption, Fluoreszenz, Streuung und Brechung transmittierender Flüssigkeiten, Gase und Festkörper
DE19730826 1997-07-18
DE19733253 1997-08-01
DE1997133253 DE19733253A1 (de) 1996-11-15 1997-08-01 Kombinierte Absorptions- und Reflektanzspektroskopie zur synchronen Ermittlung der Absorption, Fluoreszenz, Streuung und Brechung von Flüssigkeiten, Gasen und Festkörpern
PCT/DE1997/002718 WO1998022802A1 (fr) 1996-11-15 1997-11-14 Procede et dispositif de spectroscopie combinee par absorption et par reflectance

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SE9903423D0 (sv) * 1999-09-22 1999-09-22 Astra Ab New measuring technique
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