WO2007101092A2 - Spectrograph calibration using known light source and raman scattering - Google Patents
Spectrograph calibration using known light source and raman scattering Download PDFInfo
- Publication number
- WO2007101092A2 WO2007101092A2 PCT/US2007/062665 US2007062665W WO2007101092A2 WO 2007101092 A2 WO2007101092 A2 WO 2007101092A2 US 2007062665 W US2007062665 W US 2007062665W WO 2007101092 A2 WO2007101092 A2 WO 2007101092A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- chemical
- light source
- dispersion curve
- raman
- line peak
- Prior art date
Links
- 238000001069 Raman spectroscopy Methods 0.000 title claims abstract description 75
- 238000001228 spectrum Methods 0.000 claims abstract description 53
- 239000006185 dispersion Substances 0.000 claims abstract description 52
- 239000000126 substance Substances 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 36
- 238000001514 detection method Methods 0.000 claims abstract description 8
- 238000004458 analytical method Methods 0.000 claims abstract description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 47
- 230000003595 spectral effect Effects 0.000 claims description 34
- 229910052757 nitrogen Inorganic materials 0.000 claims description 25
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 17
- 239000001301 oxygen Substances 0.000 claims description 17
- 229910052760 oxygen Inorganic materials 0.000 claims description 17
- 239000013074 reference sample Substances 0.000 claims description 10
- 230000003213 activating effect Effects 0.000 claims description 8
- 239000007789 gas Substances 0.000 claims description 4
- 239000007788 liquid Substances 0.000 claims description 4
- 238000012544 monitoring process Methods 0.000 claims description 4
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- 230000004913 activation Effects 0.000 claims description 2
- 241000269627 Amphiuma means Species 0.000 claims 1
- 238000013507 mapping Methods 0.000 description 6
- 238000005259 measurement Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000000523 sample Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- -1 e.g. Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000001237 Raman spectrum Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000013307 optical fiber Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000010183 spectrum analysis Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
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
- G01J3/28—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
-
- 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
- G01J3/2803—Investigating the spectrum using photoelectric array detector
-
- 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
- G01J2003/2866—Markers; Calibrating of scan
Definitions
- the present invention relates to spectrometers, and more particularly to a technique for spectrograph calibration.
- Spectrometer devices are useful in monitoring for the presence of certain types of chemicals.
- a spectrometer device may use principles of Raman scattering to analyze a liquid, solid or gas material for certain chemicals.
- a light dispersing element also referred to as a spectrograph or diffraction grating
- a detector such as a charge-coupled camera device. Pixels on the detector are activated depending on the nature of the dispersed light and data representing the spectrum produced by the detector is analyzed to determine the presence of one or more chemicals.
- the performance of a spectrometer depends on the mechanical alignment of its components, on temperature and pressure conditions in and around the device, and in particular on the light dispersing element. To ensure accuracy of the measurements and analysis made by a spectrometer, it is necessary to adjust or calibrate for such variations.
- a method for calibrating a spectrometer device used for Raman scattering analysis.
- a predetermined dispersion curve for a diffraction grating or spectrograph of the spectrometer device is modified based on spectrum data associated with detected dispersed light from a calibration light source to produce a modified dispersion curve.
- the wavelength of a Raman light source on a light detection device is determined.
- Calibration data for the spectrometer device is computed from the Raman line peak positions for the first chemical, the wavelength on the detection device of the Raman light source and the modified dispersion curve.
- FIG. 1 is a block diagram of a spectrometer device having calibration capability according to an embodiment of the invention.
- FIG. 2 is a generalized flow diagram depicting two basic computations performed during calibration according to an embodiment of the invention.
- FIG. 3 is a flow chart depicting in more detail the calibration procedure according to an embodiment of the invention.
- FIG. 4 is a plot showing an example of a spectral line produced from a calibration light source according to an embodiment of the invention.
- FIG. 5 is a diagram showing how the dispersion curve for the light dispersing element is modified based on the spectrum obtained by activation of the calibration light source according to an embodiment of the invention.
- FIG. 6 is a plot showing an example of the peak spectral line for oxygen in a spectrum produced when the light source is activated and the light is dispersed onto the detector according to an embodiment of the invention.
- FIG. 7 is a plot showing an example of the peak spectral line for nitrogen in a spectrum produced when the light source is activated and the light is dispersed onto the detector according to an embodiment of the invention.
- FIG. 8 is a plot showing calibration data in wavenumbers space produced from the modified dispersion curve and shifted spectral lines for nitrogen and oxygen according to an exemplary embodiment of the invention.
- a spectrometer system or device according to an embodiment of the present invention is generally shown at reference numeral 10.
- the spectrometer system 10 comprises a calibration light source 20 and a Raman light source 30.
- a light collection system 40 collects light and is coupled to a spectrograph 60 which serves as the light dispersing element.
- the light collection system 40 may comprise an auto-focused telescope and an optical fiber 50 that couples the light collected by the telescope to the spectrograph 60.
- An intensified charge-coupled device (ICCD) camera 70 is optically coupled to the spectrograph 60 and is in turn coupled to a signal processor (processor) 80.
- ICCD intensified charge-coupled device
- the processor 80 executes a calibration algorithm 100 (described hereinafter) and a spectral analysis algorithm 200, such as a Raman scattering algorithm.
- the processor 80 may be more generally referred to as a control unit since it may also perform other control functions of the spectrometer 10.
- the desired Raman scattering effect is measured when the Raman light source 30 is activated and the spectrometer 10 is in a measurement mode.
- the Raman light source 30 can be any narrow band light source used for Raman excitation.
- the light source 30 is an ultraviolet (UV) excimer laser.
- the calibration light source 20 may be any stable wavelength source and may include an undetermined number of spectral lines within the spectral region of interest.
- the calibration light source 20 is a mercury (Hg) lamp.
- the calibration light source 20 may be an Argon (Ag) lamp or any fixed wavelength light source (laser) having a desired and known spectrum.
- a diffraction grating such as the spectrograph 60
- a diffraction grating has a theoretical curve of dispersion vs. wavelength number expressed in terms of ICCD pixels and can be approximated as a polynomial curve, in an exemplary embodiment it is a cubic polynomial curve.
- the manufacturer of the grating typically provides data describing this curve.
- the dispersion curve function is previously determined either by measurement or theory.
- the calibration algorithm 100 calibrates the dispersion curve of the spectrograph 60.
- This calibration algorithm 100 may be invoked at any time to verify proper operation of the spectrometer and may be used with a calibration source that is built into the spectrographic system 10 or with a calibration light source that is external to the system 10. Moreover, this technique can be used for in-field measurements or bench-top measurements (under controlled or test conditions).
- the pixels are a certain width across, but the wavelength to pixel mapping is non-linear as a result of the light dispersing function of the spectrograph 60 that spreads out the wavelengths at different angles. This is a basic aspect of a spectrograph. Because the light dispersing function is non-linear, it is necessary to have knowledge about how that dispersion works, through calibration. Calibration for the spectrograph 60 involves determining the mapping of wavelengths to pixel numbers on the ICCD camera 70.
- Wavenumber space is in units (I/cm) and is the difference in wavenumbers between the Raman light source 30 and the Raman shifted light.
- Factors that can change the wavelength calibration include temperature, pressure and small mechanical changes in the alignment.
- the wavelength to wavenumber calibration can also be changed by a shift in the Raman light source wavelength.
- the calibration algorithm 100 is generally described.
- the calibration algorithm 100 may be viewed as a two stage process comprising obtaining the calibration spectrum at 102 and then obtaining the Raman air spectrum at 104.
- the starting point is the predetermined dispersion curve for the spectrograph.
- the (onboard or external) calibration light source 20 is activated and the resulting spectrum is obtained.
- the peak position of the calibration light source lines in the captured spectrum and known expected wavelengths of these lines are used to modify the dispersion curve for the spectrograph 60 to best fit the calibration light source lines.
- the dispersion curve is shifted along with contracting or expanding it, along the wavelength axis, which has the effect of changing the coefficients of the terms in the dispersion curve.
- the calibration light source line center positions are determined by fitting the spectral peaks near their peaks, and avoiding effects such as side mode structure at the bases of the peaks.
- the calibration light source 20 allows for a mapping of the spectrograph wavelengths to the ICCD pixels based on the dispersion curve and known line peak positions for the calibration light source 20.
- the spectrum is obtained for air by activating the Raman light source 30 and collecting the Raman scattered light associated with air.
- Peak pixel positions for first and second chemicals in the reference sample spectrum data are determined.
- the first chemical is nitrogen (N 2 ) and the second chemical is oxygen (O 2 ) and their fractional peak pixel locations are determined by a fit to a Lorentzian lineshape function.
- O 2 and N 2 peak pixel positions in the reference sample (e.g., air) spectrum data known Raman wavenumber shift of O 2 and N 2 , together with the modified dispersion curve and relationship between wavelengths and wavenumbers, the best fit for the Raman light source wavelength is determined. This in turn provides spectrographic calibration information in wavenumber space.
- the reference sample used may be a liquid, solid or gas. Air is only an example of a reference or calibration sample for the Raman light source that may be convenient for certain applications according to one embodiment.
- the nitrogen and oxygen peak line positions and the modified dispersion curve allow one to determine the wavelength of the Raman light source 30 and to do a mapping in wavenumber space.
- the position of the nitrogen and oxygen lines on the ICCD 's pixel array depend on the wavelength of the Raman light source, but the wavelength calibration light source peak line positions on the ICCD's pixel array do not depend on that wavelength.
- the line peak positions for calibration light source 20 provide a mapping of the wavelengths to the pixels.
- the nitrogen and oxygen peak position lines provide information about any shift in the Raman light source 30.
- the nitrogen and oxygen peak line positions are always the same number of wavenumbers away from that of the Raman light source 30.
- FIG. 3 is a plot showing an example of a spectral line produced from a calibration light source according to an embodiment of the invention.
- the processor 80 modifies the dispersion curve for the spectrograph 60 based on the pixel spectrum data for the calibration light source 20 to produce a calibrated or modified dispersion curve in wavelength space. Modification of the dispersion curve is shown in FIG 5 according to one embodiment, where the dispersion curve from the spectrograph is shifted and expanded or contracted based on the spectrum data generated when the calibration light source 20 is activated.
- the Raman light source 30 is activated into a reference sample, e.g., air, and the Raman shifted (scattered) light is collected and coupled to the spectrograph 60.
- the ICCD camera 70 detects dispersed light from the spectrograph 60 and produces spectrum data for the reference sample, e.g., air.
- FIG. 6 is a plot showing an example of the peak spectral line for oxygen derived from the air spectrum produced when the Raman light source is activated and the Raman scattered light is coupled into the spectrograph 60, dispersed, and detected with the ICCD camera 70 according to one embodiment.
- FIG. 6 is a plot showing an example of the peak spectral line for oxygen derived from the air spectrum produced when the Raman light source is activated and the Raman scattered light is coupled into the spectrograph 60, dispersed, and detected with the ICCD camera 70 according to one embodiment.
- FIG. 7 is a plot showing an example of the peak spectral line for nitrogen in the air spectrum produced when the Raman light source 30 is activated and the Raman scattered light is coupled into the spectrograph 60, dispersed, and detected with an ICCD camera 70 according to one embodiment.
- FIG. 8 is a plot showing exemplary calibration data in wavenumbers space produced from the modified dispersion curve and Raman shifted spectral lines for nitrogen and oxygen and the fitted Raman light source wavelength according to one embodiment.
- the Raman light source wavenumber value is zero.
- the calibration technique described above may be used in the field to verify proper operation of the spectrometer. For example, during a test session, air spectrum data is obtained by activating the Raman light source into the air and collecting the Raman air spectrum. If the line peak positions for nitrogen and oxygen are acceptable, then it may not be necessary to activate the onboard calibration light source and execute the calibration algorithm 100. However, if the nitrogen and oxygen line peak positions are not acceptable, then the algorithm 100 is invoked using the onboard calibration light source and performing the curve fitting procedure using the measurements described above.
- the calibration algorithm 100 in the embodiments described herein is very precise. However, it requires time to perform.
- the spectrometer can monitor a real-time data stream (containing spectrum data) for the location of the nitrogen peak and automatically adjusts the calibration data (shift the data pixel number) so as to always keep the nitrogen peak in the data stream within a certain number of pixels (e.g., one pixel) of the position of the nitrogen spectral peak pixel number in the (previously computed) calibration data. This achieves fast recalibration albeit with less accuracy then the complete calibration algorithm 100. If the nitrogen peak drifts too far (greater than a predetermined threshold in pixels) from the calibration nitrogen peak pixel number over time, the processor may generate an alert (audible and/or visual) to the user so the user can initiate the more precise calibration algorithm 100.
- an alert audible and/or visual
- the spectrometer may constantly monitor the spectrum and initiate this "fast" calibration in real-time when appropriate and decide when the complete calibration algorithm 100 is needed and invoked.
- many of the target chemicals and sample surfaces may have features that overlap the oxygen line, potentially confusing real-time monitoring.
- due to the physics of Raman spectra i.e. the energy of chemical vibrational bonds
- any spectral lamp with emission lines in the wavelength region of interest may be used as the calibration light source.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2008556556A JP5153656B2 (en) | 2006-02-23 | 2007-02-23 | Spectrograph calibration using a known light source and Raman scattering |
AU2007220811A AU2007220811B2 (en) | 2006-02-23 | 2007-02-23 | Spectrograph calibration using known light source and raman scattering |
EP07757390A EP1991843A4 (en) | 2006-02-23 | 2007-02-23 | Spectrograph calibration using known light source and raman scattering |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US77579706P | 2006-02-23 | 2006-02-23 | |
US60/775,797 | 2006-02-23 | ||
US11/418,107 US7583378B2 (en) | 2006-02-23 | 2006-05-05 | Spectrograph calibration using known light source and Raman scattering |
US11/418,107 | 2006-05-05 |
Publications (2)
Publication Number | Publication Date |
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WO2007101092A2 true WO2007101092A2 (en) | 2007-09-07 |
WO2007101092A3 WO2007101092A3 (en) | 2008-04-10 |
Family
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2007/062665 WO2007101092A2 (en) | 2006-02-23 | 2007-02-23 | Spectrograph calibration using known light source and raman scattering |
Country Status (3)
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EP (1) | EP1991843A4 (en) |
AU (1) | AU2007220811B2 (en) |
WO (1) | WO2007101092A2 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN101852734A (en) * | 2010-06-01 | 2010-10-06 | 中国人民解放军第二军医大学 | Fake medicine discrimination and analysis device, system and method |
AU2010200109B2 (en) * | 2009-01-26 | 2011-06-02 | Harris It Services Corporation | Data quality and ancillary data checking for raman sensor |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20220205840A1 (en) * | 2019-06-03 | 2022-06-30 | University Of Central Florida Research Foundation, Inc. | Method for fabricating an optical source for calibrating an optical system |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5341206A (en) * | 1992-12-03 | 1994-08-23 | Hewlett-Packard Company | Method for calibrating a spectrograph for gaseous samples |
US5452084A (en) * | 1993-03-29 | 1995-09-19 | Albion Instruments, Inc. | Method and apparatus for zero-calibration of a raman spectroscopy system |
US5850623A (en) * | 1997-03-14 | 1998-12-15 | Eastman Chemical Company | Method for standardizing raman spectrometers to obtain stable and transferable calibrations |
US6608677B1 (en) * | 1998-11-09 | 2003-08-19 | Brookhaven Science Associates Llc | Mini-lidar sensor for the remote stand-off sensing of chemical/biological substances and method for sensing same |
-
2007
- 2007-02-23 EP EP07757390A patent/EP1991843A4/en not_active Ceased
- 2007-02-23 AU AU2007220811A patent/AU2007220811B2/en not_active Ceased
- 2007-02-23 WO PCT/US2007/062665 patent/WO2007101092A2/en active Application Filing
Non-Patent Citations (1)
Title |
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See references of EP1991843A4 * |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
AU2010200109B2 (en) * | 2009-01-26 | 2011-06-02 | Harris It Services Corporation | Data quality and ancillary data checking for raman sensor |
US8306780B2 (en) | 2009-01-26 | 2012-11-06 | Exelis Inc. | Data quality and ancillary data checking for Raman sensor |
CN101852734A (en) * | 2010-06-01 | 2010-10-06 | 中国人民解放军第二军医大学 | Fake medicine discrimination and analysis device, system and method |
Also Published As
Publication number | Publication date |
---|---|
AU2007220811A1 (en) | 2007-09-07 |
AU2007220811B2 (en) | 2010-09-30 |
EP1991843A2 (en) | 2008-11-19 |
WO2007101092A3 (en) | 2008-04-10 |
EP1991843A4 (en) | 2012-07-25 |
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