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
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/55—Specular reflectivity
  • G01N21/552—Attenuated total 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
  • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
  • G01N21/43—Refractivity; Phase-affecting properties, e.g. optical path length by measuring critical angle
  • G01N2021/434—Dipping block in contact with sample, e.g. prism
• • 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
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/85—Investigating moving fluids or granular solids
  • G01N21/8507—Probe photometers, i.e. with optical measuring part dipped into fluid sample
• • 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
  • G01N2201/08—Optical fibres; light guides

Definitions

• the present invention relates to an ATR probe for detecting an optical property of a medium comprising a monolithic ATR body having at least one surface portion to be acted upon by the medium, and a transmission light guide for irradiating non-collimated light into the ATR body; and a receiving optical fiber array for receiving the irradiated light after passing through the ATR body.
• Such an ATR probe is disclosed, for example, in the published patent application DE 10 2006 036 409 A1.
• This probe relies on a single dead-fly reflection at the media-contacting interface of an ATR body and has a very simple construction. However, the sensitivity of this probe can be improved.
• US2001 / 0030288 A1 discloses ATR probes with Zyiinderiinsen between transmitter and ATR body and between the ATR body and a diode line detector.
• US 5 991 029 A discloses an ATR probe with multiple reflections on media-contacting surfaces of an ATR body, the facet having the smallest reflection angle! is mirrored to avoid a coupling of the light there.
• US 5 773 825 A discloses an ATR probe with a prism for coupling in the light and, in addition, a thin optical disk.
• US 5,703,366 A similarly discloses a multi-part ATR body having a first crystal body and a crystal disk and an optically transmissive interface therebetween.
• US 4 826 313 A discloses an ATR probe with optical lenses for the collimation of divergent beams.
• EP 0 206 433 A2 discloses an ATR probe with at least two media-contacting surfaces.
• the probes mentioned are visually or constructively very complex to implement and thus lead to increased production costs, especially when the probe is to be integrated into a cylindrical probe shaft with a small diameter.
• the object of the present invention to provide an ATR probe, in particular for process applications, which overcomes the disadvantages of the prior art, in particular has an improved signal to noise ratio, and is suitable for simple mass production.
• the probe is chemically resistant to solvents, bases and acids as well as abrasive media.
• the ATR probe according to the invention for detecting an optical property of a medium comprises: a monolithic ATR body which has at least one surface portion which can be acted upon by the medium; a transmission picker assembly for injecting non-collimated light into the ATR body; a receiving optical fiber arrangement for receiving the irradiated light after passage through the ATR body, wherein the passage of the light through the ATR body comprises at least two total reflections at a media-contacting surface of the ATR body; characterized in that the effective area of the receiver stirrer assembly for receiving the light emerging from the ATR body is a factor F greater than the effective area of the transmission optical fiber array for irradiating the light into the ATR body, where F is at least 1 at least 4/3 and more preferably at least 3/2 and more preferably at least 2, and wherein the transmitting light conductor arrangement comprises at least two transmitting optical fibers and the receiving optical fiber arrangement comprises at least three Empfangsüchtleiter.
• the ATR body comprises at least one section with a conical or frustoconical surface, and the frusto-conical surface is at least partially acted upon by the medium.
• the section with the conical or frustoconical surface for example, a half opening angle! of not less than 40 ° and not more than 50 °, preferably not less than 43 ° and not more than 47 °, especially 45 °.
• Half the opening angle denotes the angle between the axis of symmetry of the cone and the lateral surface of the cone.
• the ATR body may comprise a cylindrical portion which adjoins the base of the conical or frustoconical portion.
• the cylindrical portion may have a height that is not more than 1/2, preferably not more than 1/3, more preferably not more than 1/4 of the radius of the base of the conical or frusto-conical portion.
• the ATR body has a rounded tip, which adjoins the kegeistumpfförmigen section.
• the rounded tip may have a radius that is not more than 1/6, preferably not more than 1/7, more preferably not more than 1/8, of the radius of the base of the frusto-conical portion.
• the ATR probe further comprises a Feruile, by means of which the SendÜtleiter and the receiving light guides are positioned, and a spacer body is clamped between the Ferulle and the ATR body, wherein the spacer body may comprise, for example, a coupling ring.
• the transmitting light conductor arrangement comprises a plurality of transmitting light guides whose end face centers are arranged on a circular arc according to an embodiment of the invention, wherein the circular arc preferably has the cone axis as the center.
• the end faces of the transmission optical fibers can be arranged immediately adjacent to each other according to an embodiment of the invention. By this it is meant that there are no receiving front ends between the immediately adjacent transmitting optical fiber end faces. However, this does not exclude that the transmitting and receiving light guides are taken in Ferullen and thus the optical fibers including their faces by Ferullenmaterial separated or spaced from each other.
• the Empfangslächtieiteran extract comprises a plurality of Empfangsiichtieiter whose end faces are arranged in a region whose shortest closed boundary line encloses an image of the end faces of the transmitting light conductor, which is formed by a rotation of the end faces of the transmitting light guide about the cone axis by an angle of 180 °.
• the end faces of the receiving light emitters can cover, for example, at least 20%, preferably at least 35% and particularly preferably at least 50% of the area of the area whose shortest closed bounding line encloses an image of the end faces of the transmission light conductors, which differs by rotation
• End faces of the transmitting light conductor around the cone axis by an angle of 180 ° arises.
• the receiving optical fiber assembly a plurality of receiving optical fibers include their end faces are arranged in a region whose shortest closed boundary line encloses a simulated image of the end faces of the Sendelichtieiter, which through the beam path of the irradiated by the transmitting light conductors in the ATR body light Assumption of a numerical aperture in air of not less than 0.1 and not more than 0.3 after two total reflections at the conical surface of the ATR body and exit from the ATR body in the plane of the end face of the receiving optical fiber is formed.
• the simulated image can be made, for example assuming a numerical aperture in air of not more than 0.15, wherein the end faces of the receiving light guide, for example, at least 20%, preferably at least 35% and more preferably at least 50% of the area of the area cover its shortest closed Begrenzungslinäe the said simulated image of the end faces of the transmission optical conductor encloses.
• the ATR probe comprises a ferrule, by means of which the transmitting optical fibers and the receiving optical fibers are positioned, wherein the optical axis of the transmitting optical fiber or the receiving optical fiber in the ferrule extends substantially parallel to the axis of the conical or kegeistumpfförmigen portion.
• the ATR probe comprises a ferrule, by means of which the transmitting optical fibers and the Empfangslichtieiter are positioned, wherein the optical axes of the Sendelichtieiter or the Empfangsandersammlungr in the Ferulle each with respect to the axis of the cone or keirustumpfförmigen section to the axis of the cone are tilted so that the k vector of the light irradiated along the optical axis of a transmission optical fiber in the ATR body has a radially inwardly directed component and the k vector of light received along the optical axis of a receiving optical fiber in the ATR body having a radially outwardly directed component.
• the end faces of the fibers are preferably perpendicular to the optical axis of the fiber.
• Section and the intersection of the optical axis of the respective light guide is defined with the end face, is twisted, so that the k-
• Vector of along the optical axis of the transmission optical fiber irradiated light in the ATR body has a tangential component or the k vector of the light received along the optical axis of a received light guide in the ATR body has a tangential component
• the area centroid or the area of maximum intensity of the light reflected twice by the ATR body, which emanates from a transmission light guide can firstly be displaced radially inwards in the plane of the end faces of the light guides. Secondly, the area centroid or the area of maximum intensity of the light reflected twice by the ATR body, which emanates from a transmitting optical waveguide, is also twisted in the plane of the end faces of the optical waveguides with respect to a point reflection of the receiving fiber on the cone axis.
• the discussed displacement and twisting of this point enables the position to remain free with respect to one transmit light guide for another transmit light guide.
• even-numbered symmetries of transmission fiber arrays are possible, in particular quadrivalent or hexagonal symmetries, with hexagonal symmetries allowing the largest packing density of optical fibers.
• end faces of receiving light guides may be arranged between the end faces of transmitting light conductors. This means that the connecting line between points of two adjacent transmitting optical fiber end faces intersects a receiving optical fiber end face.
• the end faces of the transmitting light conductors lie on a circle, wherein the centers of the faces of at least 50% ailer Empfanglichtleiter, preferably at least 75% of all Empfangslichtielaborer, in particular all received light guide within this circle.
• the transmission optical fiber assembly comprises at least one transmission optical fiber, wherein the light emitted by a transmission optical fiber is detected after passing through the ATR body of two or more receiving optical fibers.
• the transmitting light guides and the receiving light guides each have an end face at the distance to the ATR body at least ⁇ o / 2 in air, for example 5 microns preferably at least 100 microns and more preferably at least 200 microns.
• the value ⁇ 0 denotes the largest wavelength that is taken into account in the evaluation of the ATR signal.
• This distance prevents pressure- or temperature-dependent interference in the air gap between the optical fibers (in particular optical fibers) and the ATR body from leading to intensity modulations of the ATR signal.
• a Fabry-Perot effect is thus largely eliminated.
• the ATR probe comprises a ferrule, by means of which the transmitting optical fibers and the receiving optical fibers are positioned, and a housing having a mediate-side opening and a sealing ring, which is arranged around the medial-side opening, wherein the ATR body to the Sealing ring rests and is axially elastically clamped between the sealing ring and the ferrule.
• the elasticity can be given in particular by an elastic sealing ring, or by an elastic body, which is arranged in the clamping path, ie the sequence of components via which the clamping forces are transmitted to the rear side facing away from the ATR body of the Ferulle at any position.
• the transmitting optical fiber array and the receiving optical fiber array are preferably positioned and aligned so that light impinging on surface portions of the ATR body against which the sealing ring abuts is less than 5%, preferably less than 2%, and more preferably less than 1%, to the signal ATR probe contributes.
• the ATR body may in principle comprise any materials which are transparent in the required spectral range and have a sufficiently high refractive index in order to enable total reflection at interfaces with the media to be investigated, in particular aqueous media. Furthermore, chemical and abrasive resistance of
• the transmitting optical fibers or the receiving optical fibers may preferably comprise optical fibers which preferably comprise silver halide, quartz, a polymer or chalcogenide which has sufficient transmission in the wavelength range of the light used.
• any immersion media is used like oils or glue dispensed.
• immersion media are dispensed with in the entire beam path of the probe, ie even when coupling a source or a receiver to the light guides.
• the transmission fibers and the receiving optical fibers may comprise optical waveguides having an inner coating containing, for example, silver halide or Au.
• Fig. 1 A schematic diagram of an ATR probe according to the invention with a conical ATR body
• FIG. 2 a sectional view of a probe head of an ATR probe according to the invention with conical ATR body;
• FIG. 3 shows a sectional drawing through a conical ATR body for the beam calculation of an ATR probe with conical ATR body
• FIG. 4 shows a plan view of an end face of a fiber reticulum for positioning under a conical ATR body according to an embodiment of the invention
• Fig. 5 A projection of the end faces of paraxial
• Fig. 6 A recorded with an ATR probe according to the invention spectrum of iso-propanol.
• FIG. 7 a a projection of the end faces of transmitting light guides inclined and twisted with respect to the cone axis according to another embodiment of the invention onto the end face of the fiber web with a half opening angle of the 1 ° light fluence emitted by the light guides in the material of the ATR body;
• Fig. 7b A projection of the end faces of tilted and twisted with respect to the cone axis transmitting optical fibers according to another embodiment of the invention on the end face of the Faserferülie with half an opening angle emitted by the light guides Eiskegeis of 6 ° in the material of the ATR body.
• Fig. 7c A resulting from the projections positioning of
• FIG. 1 shows the principle of an ATR probe according to the invention.
• Light is irradiated via a transmitting optical fiber bundle 1, here a transmitting fiber bundle, into a conical ATR body 2 at its base and after two total refiexionen on the lateral surface of the cone at the base of the ATR body 2 by means of a receiving optical fiber bundle, here a receive fiber bundle 3 decoupled.
• the irradiation of light via optical fibers which supply the light from spatially separated sources, and decoupling of the light via optical fibers to remote receivers on the one hand allows the construction of a compact probe head and on the other hand, requirements for the explosion protection can be well met.
• FIG. 1 The construction of a probe head of an ATR probe according to the invention is shown in longitudinal section in FIG.
• ATR body 2 a substantially conical ZnSe crystal with a cylindrical projection on the base 22 of the cone is provided, which is axially supported by means of an elastic O-ring 4 on a circumferential sealing surface 51 about an end opening 52 in a cylindrical probe housing 5 is.
• O-ring 4 can in principle have any medium-resistant and temperature-resistant materials with a sufficient, currently Kalrez is preferred.
• a fiber bead 6 is disposed on the side of the base of the conical ATR body with which the optical fibers are positioned.
• the fibers are not shown in the drawing to preserve the clarity of the drawing.
• the end surface 64 of the ferrule 6 may abut directly against the base of the ATR body, however, it should be understood that the end faces of the fibers should preferably be spaced sufficiently apart from the ATR body to avoid intensity variations due to Fabry-Perot interference ,
• either the end faces of the fibers with respect to the end face 64 of the ferrule 6 may be reset, or between the ferrule 6 and the ATR body is still a spacer provided when the end faces 64 of the fibers are substantially aligned with the end face of the Ferulle.
• the ferrule 6 is supported on the rear by means of a threaded ring 54 in the probe housing 5, wherein the threaded ring 54 engages in a thread in the wall of the probe housing 6 and on a second axial stop 67, which is formed as a radial projection on the lateral surface of the Feruile 6, is applied.
• the ferrule also has a rear-side central bore 68, through which the light guides are guided to the respective bores 61, 63 for positioning the light guides.
• the Ferulle can in principle have any sufficiently stable materials that are compatible with the material of the optical fiber or optical
• Fibers are compatible, with PEEK currently being preferred since it has a enables simple and accurate production, is inexpensive and has sufficient mechanical stability even at high temperatures.
• FIG. 3 shows a representation for determining the positions of the transmission fibers and the optical fibers in the optical design.
• the light distribution at the receiving fibers is calculated in each case with a predetermined position of the light source fibers or transmit density director by means of a 2-dimensional ray calculation. It is numerically estimated how the light passes through the ATR body and how the Uchtquellmaschinen or Sendelambatieiter and detector fibers or Empfangsiichtleiter should be organized spatially in the Faserferulie, so that a possible high light output and thus signal can be achieved at the detector.
• Uchtquellmaschinen or Sendelambaiter and detector fibers or Empfangsiichtleiter should be organized spatially in the Faserferulie, so that a possible high light output and thus signal can be achieved at the detector.
• d L Q a large radial distance d L Q between the cone axis of the ATR body and the axis of the light source fiber, starting from the non-negligible numerical aperture NA of the beam, would cause the cone of light to enter through the long light path in the ATR body upon arrival in the plane of the base of the ATR body for decoupling into the receiving fibers would be distributed over a too large area. In this case, it would be necessary to work with many of the expensive receiving fibers. In that regard, it is preferred for cost reasons to keep d L ⁇ minimum.
• the conical ATR body has a small radius at its cone tip during manufacture, for example not more than 0.5 mm.
• no light hits the area of the rounded cone tip, because this light is otherwise lost for the ATR effect.
• NA numerical aperture
• d t ⁇ between, for example, 0.210 and 0.245 base radii preferably between 0.220 and 0.235 Basisradäen, wherein the base radius by the intersection of the conical surface with the plane of the base of the entire ATR body, ie including the cylindrical part is defined.
• the value for dua is 0.227 base radii.
• the monolithic conical ATR body has a diameter of 9 mm and has a 1 mm high cylinder portion as the base to which a conical section with 4.5 mm height and 90 ° Konuswinke! or half an opening angle of 45 °, the base radius is therefore 5.5 mm.
• This optical component is made of ZnSe.
• Fig. 2 now shows a simulation with the entrance of the light at the bottom left at the base of the ATR body. The light rays are reflected at the top left of the cone, reach the right upper edge of the cone and are reflected down to the right in the spatial area in which the receiving fibers are to be positioned to detect the light.
• the light beams of a light guide are drawn in Figure 3 as thin lines.
• a 2D histogram is first calculated for the light rays arriving at the base of the ATR body (bottom right in FIG. 3).
• the 2D histogram is represented by the solid thick line. It shows the number of rays striking the base per unit length.
• the envelope of this distribution corresponds approximately to a uniform rectangle distribution.
• the skew-shaped deviation of the curve from a rectangular distribution is due to the limited number of rays from the light source which were taken into account in the calculation.
• the dotted curve represents the distribution of the beams incident on the base per unit area in a simplified 3D model.
• the number of beams is taken from the 2D model and divided by the ring surface elements, so that this distribution is concentrated to the center.
• the receiving light guides are to be positioned so that they capture the light incident on the base as effectively as possible.
• Fig. 4 shows an arrangement of transmitting and receiving light guides, which takes into account the result of the above calculations.
• six transmission optical fibers 11 are positioned with their center on a radius of 0.227 base radii about the cone axis.
• the reception optical fibers define an area in which a sufficiently large proportion of the light incident on the base is detected.
• FIG. 5 Another simulation result of the light distribution is shown in FIG. 5. It first shows the positions of the six transmission light guides of FIG. 4.
• the outer edge of the area is shown in which the light from the light cones, which are radiated by the parallax-oriented transmit optical fibers, after two occurring at the Kegeimantei feelings total reflections hits the base.
• a half opening angle of 6 ° was assumed for the light cone. The result essentially confirms that the positioning of the receiving light guides according to FIG. 4 makes sense and detects a sufficiently large proportion of the reflected light.
• Fig. 6 finally shows an absorption spectrum of an aqueous solution of 0.5% by weight of iso-propanoi, which was taken up by means of the ATR probe.
• the signal-to-noise ratio is excellent, for a commercial ATR probe.
• FIGS. 7a to c show simulation data for another embodiment of an ATR probe according to the invention with a conical ATR body, in which the end faces of six transmitters in hexagonal symmetry are arranged on a circular arc.
• the axes of the transmission light guide are inclined radially inwardly.
• the k-vector of the light irradiated along the radiator axes has a radially inward and a tangential component.
• the transmission optical axes are aligned in the case such that the inclination of the axis of irradiated light in the ATR body is about 6 ° and the rotation about 40 ° relative to the axial plane, then the respective center of the light from an optical fiber on the base surface of the reflected light are shifted so that the centers of the light to be coupled out with the end faces of the Send light guides in a first approximation form a hexagonal pattern, the centers fall on gaps between the end faces of the transmission light guide.
• a half opening angle of 1 ° was set in the ATR body for the irradiated light cone.
• the resulting positions 24 are shown in Fig. 7a together with the end faces 14 of the transmission light guide.
• FIG. 7b shows the distribution of the light 26 to be coupled out assuming a half opening angle of 6 ° in the ATR body for the incident light cone.
• a seventh addressee feed occupies the gap in the center of the light guide assembly.
• a receive light guide is positioned so that the angular range of maximum intensity about the axis of the irradiated light is detected by this one receiving light guide.
• the receiving light guides are hexagonal, that is arranged in the densest possible package, which also the outside of the core region of a reflected light beam occurring light is optimally detected by adjacent receiving light guides.

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Citations (9)

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• 2007
  • 2007-12-04 DE DE102007058611A patent/DE102007058611A1/de not_active Withdrawn
• 2008
  • 2008-12-02 CN CN2008801191579A patent/CN101889195B/zh not_active Expired - Fee Related
  • 2008-12-02 US US12/734,845 patent/US20100303413A1/en not_active Abandoned
  • 2008-12-02 EP EP08856785A patent/EP2217912A2/de not_active Withdrawn
  • 2008-12-02 WO PCT/EP2008/066656 patent/WO2009071557A2/de active Application Filing

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