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
  • G01N21/65—Raman scattering
• • 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
  • G01J3/10—Arrangements of light sources specially adapted for spectrometry or colorimetry
• • 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
• • 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
  • G01J2003/4424—Fluorescence correction for Raman 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
  • G01N21/65—Raman scattering
  • G01N2021/653—Coherent methods [CARS]
  • G01N2021/656—Raman microprobe

Definitions

• the invention relates to a method and a device having the features mentioned in the preambles of claims 1 (method) and 19 (device).
• Raman spectroscopy has recently become an established method in materials science, chemical engineering, pharmacy, environmental technology, analytics, and process monitoring, not least due to the development of lower cost semiconductor lasers.
• probes are used that are usually coupled with a spectrometer.
• the Fixed Pattern is a fixed interfering structure that overlays the images of CCD cameras or CCD scanners.
• the fixed pattern masks the weak Raman signals (when using CCD-based receivers) and limits the achievable sensitivity.
• Conventional methods correct this with dark or empty spectra. However, such a correction often does not sufficiently eliminate the fixed pattern since it is measured in a different intensity range and thus does not sufficiently take into account the physical nature of the fixed pattern.
• Spectroscopy 1992, 46, 707 known that by the use of two laser wavelengths which are shifted from each other, a background correction to eliminate the fluorescence can be realized possible.
• the light source is described by Shreve et al. a Ti: sapphire laser is used, which is shifted by means of a diffractive element to two wavelengths in frequency. A disadvantage of this arrangement can be seen above all in the complex structure.
• the main disadvantage of the prior art is that the aforementioned methods and apparatus for generating and detecting Raman spectra require sufficient equipment to achieve sufficient sensitivity.
• the object of the present invention is to provide a method and a device for generating and detecting a Raman spectrum of a medium to be examined, with which the Raman spectrum of a medium to be examined can be determined with a high sensitivity with relatively little expenditure on equipment.
• the use of multiple excitation light sources should be avoided.
• the method should enable temporally high-resolution in-situ measurements.
• the method according to the invention for generating and detecting a Raman spectrum of a medium to be investigated has the following method steps:
• the one laser diode for generating excitation radiation of at least two different wavelengths is driven with at least two different excitation conditions and from the scattered radiation for the different excitation wavelengths at least two frequency-shifted Raman spectra are detected and from the at least two detected Raman spectra the Raman spectrum of and the two different excitation conditions for the laser diode are adjusted by the electric current applied to the laser diode.
• a particular advantage of the method according to the invention is that only one laser diode is used, it being possible by the (preferably alternating) control of the laser diode with different excitation conditions (ie driving the laser diode with different current strengths) that the laser diode at two different wavelengths ( preferably alternately) emitted, so that in each case a Raman spectrum can be detected for these two different (excitation) wavelengths and from the at least two Raman spectra obtained a Raman spectrum for the medium to be examined can be calculated, wherein the fluorescence component by the detection of at least two frequency-shifted Raman spectra can be excluded. Furthermore, it is possible to eliminate the fixed pattern and a device-specific spectral background (filter characteristic) when using CCD elements in the spectral optical system.
• a high detection sensitivity is obtained with comparatively low outlay on equipment, in particular only one laser diode is required as the excitation light source.
• a laser diode with internal frequency-selective element preferably grating, etalon or Mach-Zehnder interferometer
• Another advantage of the invention is that the control of the laser diode via the current intensity of the laser diode takes place. Therefore, it is possible to rapidly switch back and forth between the different conditions of excitation, so that processes which change rapidly by means of Raman spectroscopy, despite a low outlay on equipment, have a high sensitivity can be monitored.
• the control of the laser diode on the current is advantageously much faster than the control of the laser diode over the temperature. Furthermore, the apparatus of the apparatus is reduced, since the device preferably has no means for variation and / or control of the temperature of the laser diode.
• the line width (FWHM) of the laser diode is preferably less than 30 GHz, particularly preferably less than 3 GHz, particularly preferably less than 100 MHz, particularly preferably less than 10 MHz.
• the laser diode used is preferably monolithic and tunable narrowband for a given wavelength range.
• the laser diode with a frequency greater than 0.1 Hz (more preferably greater than 1 Hz) between the two current levels (or other excitation conditions) switched back and forth.
• a non-periodic excitation is possible.
• the only prerequisite is that the laser diode within a (preferably small) time interval with at least two different excitation conditions is controlled such that it emits at least two wavelengths with a sufficient wavelength spacing (preferably 0.5 nm).
• the time interval is preferably 60 s, more preferably 10 s, particularly preferably 1 i, particularly preferably 0.1 s, and is thus selected.
• a CCD line is preferably used.
• a spectral-optical system a spectrograph with CCD line is preferably used.
• the laser diode by means of a To drive excitation source (preferably current source), wherein the output power of the excitation source is modulated.
• a function generator more preferably a rectangular generator, is preferably used.
• the spectral optical system with a data processing device for evaluating the measurement data obtained from the spectral optical system.
• the excitation source for driving the laser diode but also the spectral optical system or connected to the spectral optical system data processing device to gates.
• the excitation source and the spectral optical system and the data processing device with the means for driving the laser diode (modulator) are connected.
• the device for generating and detecting a Raman spectrum comprises an excitation light source, a spectral optical system and a data processing device, wherein the spectral optical system is connected to the data processing device, wherein the device further comprises means for coupling the excitation radiation in the having investigating medium and means for coupling the scattered radiation from the medium to be examined in the spectral optical system, wherein the excitation light source is a laser diode having an internal frequency-selective element, the Laser diode for generating different excitation wavelengths is connected via a modulator to a power source, wherein the spectral optical system and / or the data processing device is connected to the modulator.
• the laser diode can emit very narrowband at two wavelengths (preferably alternating, in accordance with the drive), without requiring a prior calibration of the individual wavelengths or of the laser diode.
• Raman spectra can be determined with high sensitivity (with elimination of fixed pattern and fluorescence component), wherein the device according to the invention has a comparatively simple structure (only one excitation light source, no external cavity).
• the device according to the invention additionally comprises optical filters, for example for the elimination of the Rayleigh line.
• the spectral optical system and / or the data processing device is connected to the means for driving the laser diode (eg modulator), as this excitation with different wavelengths and the detection of the scattered light can be done synchronously.
• the laser diode with respect to their excitation conditions with significantly higher frequencies, for example, greater than 10 Hz (more preferably greater than 30 Hz) can be controlled.
• the modulator is preferably a function generator, particularly preferably a square-wave generator.
• the means for coupling the excitation radiation into the medium to be examined and the means for coupling the backscattered radiation from the medium to be examined into the spectral-optical system preferably has an optical fiber.
• FIG. 1 shows a device for generating and detecting a Raman spectrum according to the present invention in a schematic representation
• FIG. 3 shows the difference spectrum of the two Raman spectra from FIG. 2, FIG.
• FIG. 4 shows a reconstruction of the difference spectrum from FIG. 3 and FIG. 4
• Fig. 5 is a reference spectrum of phenanthrene.
• the laser diode 1 shows a device according to the invention for the generation and detection of a Raman spectrum with a high sensitivity with a comparatively low outlay on equipment.
• the laser diode 1 is connected to the same Current source 3 is connected, wherein the DC power source 3 is connected to a square-wave generator 4, which generates rectangular pulses at a frequency of 0.1 Hz. With these rectangular pulses of the rectangular generator 4, the output power of the DC power source 3 is modulated.
• the laser diode 1 is driven alternately with two different electrical currents (currents).
• the laser diode 1 emits narrowband at two different wavelengths, whereby according to the invention the use of multiple excitation light sources can be avoided.
• the laser diode 1 is driven with currents of 150 rtiA and 250 rtiA alternating with a frequency of 0.1 Hz.
• the medium 8 to be examined is preferably arranged such that no interfering light impairing the measurement enters the Raman measuring head 7.
• the excitation radiation is now partly scattered by the medium 8 to be examined, and the scattered radiation of the medium 8 to be examined is transmitted via the Raman measuring head 7 and the optical fiber 9 into the spectral-optical system 10 consisting of the spectrograph 14 and the CCD. Line 13, coupled.
• the CCD line 13 of the spectral optical system 10 and the data processing device 11 are (in addition to the laser diode 1) also connected (via the line 5) with the square-wave generator 4.
• the control of the laser diode 1 and the detection of the Raman spectra 16, 17 can thus take place synchronously.
• the data processing device 11 for the two different excitation wavelengths ⁇ i and X 2 can receive Raman spectra 16, 17 and thereby easily calculate a Raman spectrum in which the background (fixed pattern, fluorescence background) is computationally eliminated.
• first of all the difference spectrum 18 is determined from the Raman spectra 16, 17 (see FIG. 2), from which fixed patterns and background signals have already been removed.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Life Sciences & Earth Sciences (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)
• Spectrometry And Color Measurement (AREA)

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• 2005
  • 2005-06-14 DE DE102005028268A patent/DE102005028268B4/de not_active Expired - Fee Related
• 2006
  • 2006-06-13 US US11/916,997 patent/US7864311B2/en active Active
  • 2006-06-13 JP JP2008516301A patent/JP2008544238A/ja active Pending
  • 2006-06-13 EP EP06763667.0A patent/EP1891408B1/de active Active
  • 2006-06-13 WO PCT/EP2006/063141 patent/WO2006134103A1/de not_active Ceased

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