Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
  • G01J3/0218—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using optical fibers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/12—Generating the spectrum; Monochromators
  • G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/44—Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
  • G01J3/4406—Fluorescence spectrometry
• • 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
  • G01N21/6402—Atomic fluorescence; Laser induced fluorescence

Definitions

• the present invention relates to the field of tools for determining the chemical composition of a sample.
• the present invention relates more particularly to an improvement in the detection of chemical elements in a sample by laser-induced fluorescence emission (LIF: Laser Induced
• a very large number of analyzes are based on gas chromatography coupled with known techniques of mass spectroscopy or plasma emission spectroscopy. Despite the effectiveness of these analysis tools in terms of detection threshold, they are on the one hand very expensive and on the other hand not portable. They are installed in analytical laboratories, require very careful preparation of the sample, and a highly qualified staff to perform the measurements and interpret the spectra. An analysis thus requires an average duration of three days between taking samples and the result of its composition.
• LIBS Laser Induced Breakdown Spectroscopy
• a material whether in solid, liquid or gaseous form, can, after excitation by a laser, be transformed into plasma (mixture of free electrons, ions, atoms and molecules) resulting from the ionization caused for example by multi-photon absorptions or the tunnel effect.
• plasma mixture of free electrons, ions, atoms and molecules
• other well-known physical phenomena come into play such as cascading ionizations and collisions between free electrons. These effects increase the temperature of the plasma produced.
• the braking radiation of electrons in motion (inverse Bremsstrahlung effect) then gives a white light emitted by the plasma.
• the conventional laser sources used in this type of application are laser sources of nanoscale YAG type at the wavelength 1064 nm delivering energy pulses of the order of a few tens of millijoules.
• the focusing of the laser beam is done using a lens generally protected by an interchangeable protective window.
• the detection and the collection of the fluorescence are carried out according to the prior art with an optical fiber placed at the level of the pen of the plasma.
• the light transmitted by the fiber is sent into a spectrometer for detection by a CCD or ICCD camera accompanied by a scale network or more generally a monochromator.
• a CCD or ICCD camera accompanied by a scale network or more generally a monochromator.
• Such a system includes a waveguide within which Bragg gratings have been arranged to redirect light from the waveguide out of the guide.
• Such a system can function as a spectrophotometer, spectrofluorometer, or other means to analyze the light components after a sample pass.
• the fact that the Bragg gratings are directly integrated with the optical fiber prevents tuning the wavelengths of detection of these networks because the angle of incidence on the Bragg grating of the guided light is fixed.
• the networks registered in the fibers therefore have many practical limitations.
• An object of the present invention is also to provide a detection system that is wavelength tunable.
• the present invention also intends to overcome the drawbacks of the prior art by proposing an element detection system to obtain a compact system, while maintaining a good resolution and high brightness.
• the present invention is remarkable, in its broadest sense, as it relates to a system for the detection of a chemical element in a material comprising at least one laser emission means for ionizing a part of said material to create a fluorescence, at least one transmission type Bragg grating for filtering the wavelength corresponding to the de-energizing wavelength of said element and at least one photodiode for detecting the corresponding line at said filtering wavelength, characterized in that said at least one Bragg grating is movable so as to vary said filtering wavelength.
• FIG. 1 represents the collection and detection system in single sensor mode, according to the invention
• FIG. 2 illustrates a second embodiment of the invention
• FIG. 3 represents the collection and detection system in multi-sensor mode, according to the invention
• FIG. 4 represents a multi-sensor embodiment with a Bragg grating in which a plurality of diffraction gratings are etched in FIG. inside of it.
• the system comprises an optical fiber (1) for transporting light from the plasma.
• This embodiment is then used with a material placed at the beginning of the optical fiber (1a).
• the laser emission at the material creating the plasma at one end of the optical fiber may damage it by projections. Therefore, a quartz plate may be used to protect the end of the optical fiber (1).
• the fluorescence is then transmitted to the final end (Ib) of the optical fiber (1).
• the end of the optical fiber (Ib) is placed at the focus of an off-axis parabolic mirror (2).
• the light is thus reflected and collimated as shown in Figure 1.
• the Bragg grating (3) is a Bragg grating in volume transmission.
• These networks may be of the type described in the reference already cited US 6,673,497, more precisely used in wavelength selector as in Figure 11a of the patent cited. For example, they are made of a Photo Thermo Refractive (PTR) material and are etched using UV laser irradiation and thermal development.
• PTR Photo Thermo Refractive
• a known property of these networks is that they deviate only one wavelength with a very high efficiency, for example greater than 95%, whereas the other wavelengths are transmitted without diffraction.
• the wavelength is then sent to sensors (4) for the detection of lines corresponding to the desired element.
• the network has a characteristic dimension of 2.5 cm, for a beam of about 2 cm aperture.
• the parabolic mirror has a characteristic dimension of about 5 cm, and the exit end of the fiber is placed at the focus of the dish.
• the optical fibers have a core size of about 100 ⁇ m.
• the networks are adapted in terms of pitch, blaze, and profile of the index gradient as a function of the desired wavelength, the acceptable resolution and the element considered. Such developments are known to those skilled in the field of diffraction gratings.
• the wave is diffracted by the Bragg grating, it is focused by a lens and detected by a diode.
• the type of diode used in the present invention is particularly suitable for fluorescence emission, for example in LIBS techniques. Indeed, as was mentioned above, the fluorescence emission is accompanied by the emission of a white light emitted by the plasma and produced by different phenomena, including the inverse Bremsstrahlung effect. However, the atomic lines having a much longer life span than the continuum of white light, a delayed detection of the spectrum makes it possible to isolate the atomic lines of the spectrum to go back to the composition.
• the photodiodes used are, for example, avalanche photodiodes that can be synchronized with respect to laser firing. Thus the triggering of the photodiodes can be delayed so as not to capture the continuum of white light.
• the typical size of the detectors is about 1 mm 2 .
• FIG. 2 The laser (6) is focused on the material (5) containing the elements to be detected by means of a lens (7) through a hole (8) made in the dish ( 2) Fluorescence collection.
• the optical fiber (2) is no longer necessary.
• the detection principles are then the same as in the first embodiment.
• the brightness of the system can even be increased by minimizing the optical path.
• the system can also include an association of several networks to detect several atomic lines.
• the rotation of a network with respect to an incident ray allows the transmission of a variable wavelength over a certain range of wavelengths.
• an incident ray (10) arrives on a first network (3a).
• the wavelength corresponding to the Bragg length ⁇ 0 of the grating is then deflected along the radius (10a) while the other wavelengths continue their path along the radius (10b).
• the possible stacking of several networks (3a), (3b) and (3c) then allows the detection of several lines according to the wavelengths selected by the networks.
• the lines are detected by the photodiodes (4a), (4b), (4c).
• the detection of a particular line is also facilitated by the rotation of a network.
• a rotation of the network modifies the angle of incidence of the radius and therefore the length of the wavelength. transmitted wave ( ⁇ 0 depending on the angle of incidence).
• a sufficiently wide lens is then used to focus the diffracted light on the detector.
• the system may also include a Bragg grating in which a plurality of diffraction gratings are etched therein. In this case, the different lengths of chosen waves are diffracted in different directions towards the photodiodes f 4a 4b, 4c. This allows to have a spectrometer equivalent to that of Figure 3 more compact.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

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• 2004
  • 2004-10-01 FR FR0452235A patent/FR2876185B1/fr not_active Expired - Fee Related
• 2005
  • 2005-09-30 EP EP05807791A patent/EP1794648A1/de not_active Withdrawn
  • 2005-09-30 US US11/664,432 patent/US7609379B2/en not_active Expired - Fee Related
  • 2005-09-30 WO PCT/FR2005/002419 patent/WO2006037879A1/fr active Application Filing
  • 2005-09-30 JP JP2007534050A patent/JP2008514944A/ja active Pending

Non-Patent Citations (1)

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