Systems and methods using active FTIR spectroscopy for detection of chemical targets

11867,618

17/606568

April 17, 2020

Active FTIR spectroscopy systems and methods for quantitative measurements of concentrations of chemical targets, such as gas, liquid and solid chemical targets, in an open-path measuring arrangement and a method of extracting an effective illumination spectrum of IR light illuminating chemical targets arranged in an open-path measuring arrangement.

Heriot-Watt University (Edinburgh, GB)

Heriot-Watt University (Edinburgh, GB)

1. An active FTIR spectroscopy system for quantitative measurements of concentrations of chemical targets in an open-path measuring arrangement, the system comprising: an illumination source comprising an optical parametric oscillator configured to generate broadband IR light, a calibration source configured to generate calibration light, a scanning interferometer arranged to synchronously receive each of the broadband IR light and the calibration light, and then modulate each of the received broadband IR light and calibration light over a scanning period, with the received calibration light being configured to deduce optical path differences introduced by the scanning interferometer over the scanning period for each of the modulated broadband IR light and the modulated calibration light, a launch system for illuminating the chemical targets with the modulated broadband IR light, a collector system for receiving broadband IR light spectrally-modulated by the chemical targets, wherein the launch system is configured so that an optical axis of a launching path is substantially co-aligned with an optical axis of the collector system, a detector system for detecting and then recording interference fringes generated by the spectrally-modulated broadband IR light and by the modulated calibration light, a computer processor, and a non-transitory computer readable medium encoded with a computer program, wherein the computer program comprises instructions stored therein for causing the computer processor to perform a plurality of functions to simultaneously compute concentrations of each of the chemical targets from spectra of the recorded interference fringes generated by the spectrally-modulated broadband IR light and by the modulated calibration light; wherein the computer processor is configured to extract an effective illumination spectrum of infrared light illuminating the chemical targets and using the effective illumination spectrum to simultaneously compute the concentrations of each of the chemical targets.

2. The system of claim 1 , wherein the optical parametric oscillator comprises a nonlinear crystal tunable to generate broadband IR light with wavelengths from 1 μm to 16 μm, or from 2.5 μm to 4.5 μm, or from 2.8 μm to 3.9 μm, or from 3.1 μm to 3.5 μm.

3. The system of claim 1 , wherein the optical parametric oscillator is configured to generate broadband IR light with an average output power of at least 10 mW, or at least 50 mW, or at least 250 mW, or least 500 mW; or wherein the optical parametric oscillator is configured to generate broadband IR light with a repetition rate from 1 MHz to 20 GHz, or from 10 MHz to 10 GHz, or from 70 MHz to 1 GHz, or from 90 MHz to 500 MHz.

4. The system of claim 1 , wherein the calibration source comprises any one of a wavelength stabilized laser source or a narrow-line diode laser source.

5. The system of claim 1 , wherein the scanning interferometer is configured to modulate the received broadband IR light with a resolution of less than 0.5 cm −1 , or less than 0.1 cm −1 , or less than 0.07 cm −1 , or less than 0.05 cm −1 ; or wherein the scanning interferometer is configured to modulate the received broadband IR light at scanning rates from 0.1 Hz to 1000 Hz, or from 0.5 Hz to 100 Hz, or from 0.7 Hz to 10 Hz; or wherein the scanning interferometer is configured to modulate the received broadband IR light with an average power of at least 1 mW, or at least 20 mW, or at least 70 mW, or at least 100 mW.

6. The system of claim 1 , wherein the scanning interferometer comprises at least one moving retroreflector, the moving retroreflector being arranged to increase the optical paths introduced by the scanning interferometer over the scanning period for each of the modulated broadband IR light and the modulated calibration light.

7. The system of claim 1 , wherein the launch system comprises a steering arrangement, the steering arrangement comprising a steering minor or a steering prism, wherein the steering mirror is arranged at 45° with respect to the optical axis of the launching path.

8. The system of claim 1 , wherein the collector system comprises a telescope, and wherein the telescope comprises a reflecting telescope or a refracting telescope.

9. The system of claim 8 , wherein the collector system further comprises an optical relay arrangement, the optical relay arrangement comprising one or more of a minor, a lens or a prism, or a combination thereof, for relaying the received spectrally-modulated broadband IR light onto the detector system.

10. The system of claim 9 , wherein the steering arrangement of the launch system is configured to be arranged adjacent the optical relay arrangement of the collector system such that the optical axis of the launching path is co-aligned with the optical axis of the collector system.

11. The system of claim 1 , wherein the detector system comprises a combination of an IR detector for detecting spectra of interference fringes generated by the spectrally-modulated broadband IR light and a photodiode or a phototransistor for detecting spectra of interference fringes generated by the modulated calibration light.

12. The system of claim 1 , wherein the detector system further comprises a digital signal acquisition system configured to record at least one spectrum of interference fringes generated by the spectrally-modulated broadband IR light in synchronism with at least one spectrum of interference fringes generated by the modulated calibration light such that the interference fringes of the modulated calibration light are configured to provide an accurate timebase calibration for the interference fringes of the spectrally-modulated broadband IR light to enable calculating an accurate wavelength scale for the at least one spectrum of interference fringes generated by the spectrally-modulated broadband IR light.

13. The system of claim 1 , wherein the broadband IR light spectrally-modulated by the chemical targets comprises spectral-modulation by backscattering or absorption or diffuse reflectance of the broadband IR light.

14. The system of claim 1 , wherein the plurality of functions comprises simultaneously computing concentrations of each of the chemical targets by performing calibration and Fourier transformation of the recorded spectra of interference fringes generated by the spectrally-modulated broadband IR light and by the modulated calibration light to produce at least one absorption spectrum for the chemical targets, fitting library absorption spectra for each of the chemical targets and the extracted effective illumination spectrum of the generated broadband IR light to the at least one absorption spectrum, and then calculating concentrations of each of the chemical targets from said produced and said fitted spectrum.

15. The system of claim 1 , wherein the non-transitory computer readable medium is configured to store i) spectra I of interference fringes generated by spectrally-modulated broadband IR light upon illumination of the chemical targets, and ii) library absorption spectra for at least one known concentration of each of the chemical targets, and wherein the non-transitory computer readable medium is encoded with a computer program comprising instructions stored therein for causing the computer processor to perform an algorithm which allows the effective illumination spectrum Io to be modelled as an interpolation function and to become a free parameter when fitting the library absorption spectra for each of the chemical targets to the spectra I of interference fringes generated by spectrally-modulated broadband IR light upon illumination of the chemical targets.

16. The system of claim 1 , wherein the open-path of the open-path measuring arrangement is at least 0.1 meters long, or at least 10 meters long, or at least 30 meters long, or at least 70 meters long.

17. The system of claim 1 , further comprising a scattering aid having a convex or a plane surface, wherein the scattering aid comprises a pane of paper, concrete, laminate, wood, brick, stone, painted surface, metal or plastic.

18. The system of claim 17 , wherein the chemical targets are configured to be arranged in the open-path measuring arrangement between the launch system and the scattering aid such that an optical axis of the scattering aid is co-aligned with the optical axis of the launching path.

19. The system of claim 1 , wherein the system is configured for quantitative measurements of concentrations of IR-absorbing gaseous, liquid, aerosol or powder chemical targets in an open-path measuring arrangement.

20. A method for quantitative measurements of concentrations of chemical targets in an open-path measuring arrangement, the method comprising: providing an active FTIR spectroscopy system according to claim 1 .

21. A method for quantitative measurements of concentrations of chemical targets in an open-path measuring arrangement, the method comprising: generating broadband IR light, generating calibration light, synchronously receiving and then modulating, by means of a scanning interferometer, the generated broadband IR light and the generated calibration light, providing a launch system for illuminating the chemical targets with the modulated broadband IR light and a collector system for receiving the modulated broadband IR light spectrally-modulated by the chemical targets such that an optical axis of a launching path of the launch system is substantially co-aligned with an optical axis of the collector system, providing a detector system for detecting and then recording spectra of interference fringes generated by the spectrally-modulated broadband IR light and by the modulated calibration light, providing a computer processor, providing a non-transitory computer readable medium encoded with a computer program, wherein the computer program comprises instructions stored therein for causing a computer processor to perform a plurality of functions to simultaneously compute concentrations of each of the chemical targets from spectra of the recorded interference fringes generated by the spectrally-modulated broadband IR light and by the modulated calibration light; and extracting an effective illumination spectrum of infrared light illuminating the chemical targets and using the effective illumination spectrum to simultaneously compute the concentrations of each of the chemical targets.

22. The method of claim 21 , wherein the determining by the plurality of functions comprises simultaneously computing concentrations of each of the chemical targets by performing calibration and Fourier transformation of the recorded spectra of interference fringes generated by the spectrally-modulated broadband IR light and by the modulated calibration light to produce at least one absorption spectrum for the chemical targets, fitting library absorption spectra for each of the chemical targets and the extracted illumination spectrum of the generated broadband IR light to the at least one absorption spectrum, and then calculating concentrations of each of the chemical targets from said produced and said fitted spectrum.

23. The method of claim 21 , further comprising providing a scattering aid having a convex or a plane surface, wherein the chemical targets are configured to be arranged in the open-path measuring arrangement between the launch system and the scattering aid such that an optical axis of the scattering aid is co-aligned with the optical axis of the launching path; and wherein the method is configured for quantitative measurements of concentrations of IR-absorbing gaseous, liquid, aerosol or powder chemical targets in an open-path measuring arrangement.

24. A method of extracting, using a non-transitory computer readable medium encoded with a computer program, an effective illumination spectrum I o of a broadband IR light generated by an optical parametric oscillator in order to illuminate chemical targets arranged in an open-path measuring arrangement for the purpose of computing concentrations of each of the chemical targets, the method comprising the steps of: storing to the non-transitory computer readable medium spectra I of interference fringes generated by spectrally-modulated broadband IR light upon illumination of the chemical targets, storing on the non-transitory computer readable medium library absorption spectra for at least one known concentration of each of the chemical targets, and encoding the medium with a computer program comprising instructions stored therein for causing a computer processor to perform an algorithm which allows the effective illumination spectrum I o to be modelled as a many-point spline function and to become a free parameter when fitting the library absorption spectra for each of the chemical targets to the spectra I of interference fringes generated by spectrally-modulated broadband IR light upon illumination of the chemical targets.

5373160 December 1994 Taylor
5982486 November 1999 Wang
7342664 March 2008 Radziszewski
8358420 January 2013 Dewitt
199209877 June 1992
WO-9209877 June 1992
2018213212 November 2018
2020217046 October 2020

Sandridge et al., “Using beam-steering mirrors and long-distance sources to extend coverage of long-path FTIRs”, SPIE Proceedings, vol. 2366, pp. 194-202. (Year: 1955). cited by examiner
Combined Search and Examination Report dated Oct. 29, 2019, issued in corresponding United Kingdom Application No. GB 1905848.6, filed Apr. 26, 2019, 9 pages. cited by applicant
International Search Report and Written Opinion dated Sep. 16, 2020, issued in corresponding International Application No. PCT/GB2020/050969, filed Apr. 17, 2020, 22 pages. cited by applicant
Schütze, C., et al. “Ground-based remote sensing with open-path Fourier-transform infrared (OP-FTIR) spectroscopy for large-scale monitoring of greenhouse gases.” Energy Procedia 37 (2013): 4276-4282. cited by applicant
Smith, T. E. L., et al. “Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO 2, CH 4 and CO over concentrations representative of“clean air” and“polluted plumes”.” Atmospheric Measurement Techniques 4.1 (2011): 97-116. cited by applicant
Cossel, Kevin C., et al. “Gas-phase broadband spectroscopy using active sources: progress, status, and applications.” JOSA B 34.1 (2017): 104-129. cited by applicant
Rieker, Gregory B., et al. “Frequency-comb-based remote sensing of greenhouse gases over kilometer air paths.” Optica 1.5 (2014): 290-298. cited by applicant
Nugent-Glandorf, Lora, Fabrizio R. Giorgetta, and Scott A. Diddams. “Open-air, broad-bandwidth trace gas sensing with a mid-infrared optical frequency comb.” Applied Physics B 119.2 (2015): 327-338. cited by applicant
Gurton, Kristan P., David Ligon, and Rachid Dahmani. “Measured infrared optical cross sections for a variety of chemical and biological aerosol simulants.” Applied optics 43.23 (2004): 4564-4570. cited by applicant
Neuberger, Sabine, and Christian Neusüß. “Determination of counterfeit medicines by Raman spectroscopy: Systematic study based on a large set of model tablets.” Journal of pharmaceutical and biomedical analysis 112 (2015): 70-78. cited by applicant
Su, Wen-Hao, and Da-Wen Sun. “Fourier transform infrared and Raman and hyperspectral imaging techniques for quality determinations of powdery foods: A review.” Comprehensive Reviews in Food Science and Food Safety 17.1 (2018): 104-122. cited by applicant
Kazarian, Sergei G., and KL Andrew Chan. “Micro-and macro-attenuated total reflection Fourier transform infrared spectroscopic imaging.” Applied spectroscopy 64.5 (2010): 135A-152A. cited by applicant
“HazMatID™ Elite,” Technical Information, Smiths Detection, 2019, [Retrieved Oct. 25, 2021], 2 pages. cited by applicant
Grdadolnik, Jo{hacek over (z)}e. “ATR-FTIR spectroscopy: Its advantage and limitations.” Acta Chimica Slovenica 49.3 (2002): 631-642. cited by applicant
Deisingh, Anil K. “Pharmaceutical counterfeiting.” Analyst 130.3 (2005): 271-279. cited by applicant
Sharpe, Steven W., et al. “Gas-phase databases for quantitative infrared spectroscopy.” Applied spectroscopy 58.12 (2004): 1452-1461. cited by applicant
E. J. Dlugokencky, ESRL GMD Data Set, National Science Foundation, description creation time: Jul. 7, 2016. cited by applicant
Rothman, Laurence S., et al. “The HITRAN2012 molecular spectroscopic database.” Journal of Quantitative Spectroscopy and Radiative Transfer 130 (2013): 4-50. cited by applicant
George M. Russwurm, and Jeffrey W. Childers, “FT-IR Open-path Monitoring Guidance Document,” U.S. Environmental Protection Agency, Human Exposure and Atmospheric Sciences Division, National Exposure Research Laboratory, 1999. cited by applicant
“D-fenceline™ and OPS,” Bruker, Atmosfir, 2019, [Retrieved Oct. 21, 2021], 8 pages. cited by applicant
Kara, Oguzhan, et al. “Dual-comb spectroscopy in the spectral fingerprint region using OPGaP optical parametric oscillators.” Optics Express 25.26 (2017): 32713-32721. cited by applicant
Maidment, Luke, Peter G. Schunemann, and Derryck T. Reid. “White powder identification using broadband coherent light in the molecular fingerprint region.” Optics express 26.19 (2018): 25364-25369. cited by applicant
Marshall, Timothy L., et al. “An introduction to open-path FT-IR atmospheric monitoring.” Environmental science & technology 28.5 (1994): 224A-231A. cited by applicant
Zhang, Zhaowei, et al. “Stand-off spectroscopy and chemical sensing using a femtosecond optical parametric oscillator.” CLEO: Laser Science to Photonic Applications, Optical Society of America, 2014. cited by applicant
Kelly, James F., et al. “Applications of wideband FM spectroscopy to environmental and industrial process monitoring.” Proceedings of SPIE vol. 3127. Oct. 31, 1997, pp. 64-102. cited by applicant
Reid, Derryck T., Zhaowei Zhang, and Christopher R. Howle. “Active FTIR-based standoff detection in the 3-4 micron region using broadband femtosecond optical parametric oscillators.” Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XV. Proceedings of SPIE vol. 9073. 907302. May 2014. cited by applicant
Maidment, Luke, et al. “Stand-off detection of aerosols using mid-infrared backscattering Fourier transform spectroscopy.” Optics and Photonics for Counterterrorism, Crime Fighting, and Defence XII. vol. 9995. International Society for Optics and Photonics, 2016. cited by applicant
Zhang, Zhaowei, et al. “Active FTIR-based stand-off spectroscopy using a femtosecond optical parametric oscillator.” Optics letters 39.20 (2014): 6005-6008. cited by applicant
Maidment, Luke, et al. “Stand-off identification of aerosols using mid-infrared backscattering Fourier-transform spectroscopy.” Optical Society of America, 2016. cited by applicant
Kara, Oguzhan, et al. “Open-path remote sensing for multi-species gas detection using a broadband optical parametric oscillator.” Real-time Measurements, Rogue Phenomena, and Single-Shot Applications V. Proceedings of SPIE vol. 11265. 112650Q. Mar. 2020. cited by applicant
Examination Report dated Nov. 2, 2023, issued in corresponding European Application No. 20729138.6, filed Apr. 17, 2020, 10 pages. cited by applicant
Luis H. Espinoza et al., “Generation of Synthetic Background Spectra by Filtering the Sample Interferogram in FT-IR”, Society for Applied Spectroscopy, 1998, pp. 375-379, vol. 52, No. 3. cited by applicant
Peter G. Zemek et al., “Portable open-path optical remote sensing (ORS) Fourier transform infrared (FTIR) instrumentation miniaturization and software for point and click real-time analysis”, Next-Generation Spectroscopic Technologies III, 2010, pp. 1-12, vol. 7680, 2010 SPIE—CCC code: 0277-786X/10/$18—doi: 10.1117/12.845995. cited by applicant
Esteban Garcia-Cuesta et al., “Application of Neural Networks to Atmospheric Pollutants Remote Sensing”, LIR—Laboratorio de Sensores y Teledeteccion IR, Departamento de Fisica, Universidad Carlos III de Madrid Departamento de Ciencias, Universidad Europea de Madrid, 2007, pp. 589-598, Springer-Verlag Berlin Heidelberg. cited by applicant
Daewoong Hong et al., “Improved Methods for Performing Multivariate Analysis and Deriving Background Spectra in Atmosphere OpenPath FT-IR Monitoring”, Society for Applied Spectroscopy, 2003, pp. 299-308, vol. 57, No. 3. cited by applicant

edspgr.11867618