Abstract

Optical gas imaging is critical for many applications, but its use is currently limited by complexity and cost. Here we experimentally demonstrate a low cost solution based on an alternating bispectral IR filter. This filter is based on liquid crystal having absorption lines, which overlap those of hydrocarbon gases, and depend on the orientation of the liquid crystal molecules. An alternating voltage modulates the orientation and thus the transmittance in the absorption bands, giving rise to different on-to-off intensity ratios for gases, and any clutter emission. Our demonstration of refrigerant gas R134a detection shows a high gas to clutter contrast and opens the way for using this method in many low cost applications.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Full Article  |  PDF Article
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References

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  1. J. Hodgkinson and R. P. Tatam, “Optical gas sensing: a review,” Meas. Sci. Technol. 24(1), 012004 (2013).
    [Crossref]
  2. X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
    [Crossref] [PubMed]
  3. R. Bogue, “Detecting gases with light: a review of optical gas sensor technologies,” Sens. Rev. 35(2), 133–140 (2015).
    [Crossref]
  4. J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
    [Crossref]
  5. E. Hirsch and E. Agassi, “Detection of gaseous plumes in IR hyperspectral images using hierarchical clustering,” Appl. Opt. 46(25), 6368–6374 (2007).
    [Crossref] [PubMed]
  6. J.-M. Thériault, E. Puckrin, F. Bouffard, and B. Déry, “Passive remote monitoring of chemical vapors by differential Fourier-transform infrared radiometry: results at a range of 1.5 km,” Appl. Opt. 43(6), 1425–1434 (2004).
    [Crossref] [PubMed]
  7. P. W. Yuen and M. Richardson, “An introduction to hyperspectral imaging and its application for security, surveillance and target acquisition,” Imaging Sci. J. 58(5), 241–253 (2010).
    [Crossref]
  8. R. Harig and G. Matz, “Toxic cloud imaging by infrared spectrometry: A scanning FTIR system for identification and visualization,” Field Anal. Chem. Technol. 5(1-2), 75–90 (2001).
    [Crossref]
  9. M. Kastek, T. Piątkowski, and P. Trzaskawka, “Infrared Imaging Fourier Transform Spectrometer as the Stand-Off Gas Detection System,” Metrol. Meas. Syst. 18(4), 161–172 (2011).
    [Crossref]
  10. J. Y. Wong and R. L. Anderson, Non-Dispersive Infrared Gas Measurement (International Frequency Sensor Assosiation, 2012).
  11. P.-S. Murvay and I. Silea, “A survey on gas leak detection and localization techniques,” J. Loss Prev. Process Ind. 25(6), 966–973 (2012).
    [Crossref]
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    [Crossref]
  13. I.-C. Khoo and S.-T. Wu, Optics and Nonlinear Optics of Liquid Crystals (World Scientific, 1993), Vol. 1.
  14. A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
    [Crossref]
  15. N. I. S. T. Chemistry Webbook, http://webbook.nist.gov/chemistry/ .
  16. Vapor phase IR spectral library, https://secure2.pnl.gov/nsd/nsd.nsf , https://secure2.pnl.gov/nsd/nsd.nsf/Welcome
  17. M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
    [Crossref]
  18. W.-T. Tsai, “An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs),” Chemosphere 61(11), 1539–1547 (2005).
    [Crossref] [PubMed]
  19. H. W. Icenogle, B. C. Platt, and W. L. Wolfe, “Refractive indexes and temperature coefficients of germanium and silicon,” Appl. Opt. 15(10), 2348–2351 (1976).
    [Crossref] [PubMed]
  20. S.-T. Wu and D.-K. Yang, Fundamentals of Liquid Crystal Devices (John Wiley & Sons, 2006).
  21. M. W. Geis, T. M. Lyszczarz, R. M. Osgood, and B. R. Kimball, “30 to 50 ns liquid-crystal optical switches,” Opt. Express 18(18), 18886–18893 (2010).
    [Crossref] [PubMed]
  22. Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
    [Crossref]

2015 (1)

R. Bogue, “Detecting gases with light: a review of optical gas sensor technologies,” Sens. Rev. 35(2), 133–140 (2015).
[Crossref]

2013 (1)

J. Hodgkinson and R. P. Tatam, “Optical gas sensing: a review,” Meas. Sci. Technol. 24(1), 012004 (2013).
[Crossref]

2012 (2)

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

P.-S. Murvay and I. Silea, “A survey on gas leak detection and localization techniques,” J. Loss Prev. Process Ind. 25(6), 966–973 (2012).
[Crossref]

2011 (3)

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

M. Kastek, T. Piątkowski, and P. Trzaskawka, “Infrared Imaging Fourier Transform Spectrometer as the Stand-Off Gas Detection System,” Metrol. Meas. Syst. 18(4), 161–172 (2011).
[Crossref]

2010 (2)

M. W. Geis, T. M. Lyszczarz, R. M. Osgood, and B. R. Kimball, “30 to 50 ns liquid-crystal optical switches,” Opt. Express 18(18), 18886–18893 (2010).
[Crossref] [PubMed]

P. W. Yuen and M. Richardson, “An introduction to hyperspectral imaging and its application for security, surveillance and target acquisition,” Imaging Sci. J. 58(5), 241–253 (2010).
[Crossref]

2009 (1)

M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
[Crossref]

2007 (1)

2005 (1)

W.-T. Tsai, “An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs),” Chemosphere 61(11), 1539–1547 (2005).
[Crossref] [PubMed]

2004 (2)

J.-M. Thériault, E. Puckrin, F. Bouffard, and B. Déry, “Passive remote monitoring of chemical vapors by differential Fourier-transform infrared radiometry: results at a range of 1.5 km,” Appl. Opt. 43(6), 1425–1434 (2004).
[Crossref] [PubMed]

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

2001 (1)

R. Harig and G. Matz, “Toxic cloud imaging by infrared spectrometry: A scanning FTIR system for identification and visualization,” Field Anal. Chem. Technol. 5(1-2), 75–90 (2001).
[Crossref]

1984 (1)

S. Wu, U. Efron, and L. D. Hess, “Infrared birefringence of liquid crystals,” Appl. Phys. Lett. 44(11), 1033–1035 (1984).
[Crossref]

1976 (1)

Agassi, E.

Barros, M. T.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Bogue, R.

R. Bogue, “Detecting gases with light: a review of optical gas sensor technologies,” Sens. Rev. 35(2), 133–140 (2015).
[Crossref]

Bouffard, F.

Chandrasekar, P.

M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
[Crossref]

Cheng, S.

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Decker, M.

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

Déry, B.

Efron, U.

S. Wu, U. Efron, and L. D. Hess, “Infrared birefringence of liquid crystals,” Appl. Phys. Lett. 44(11), 1033–1035 (1984).
[Crossref]

Fan, Y.-H.

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

Figueirinhas, J. L.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Gauza, S.

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

Geis, M. W.

Gerlach, G.

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

Guth, U.

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

Harig, R.

R. Harig and G. Matz, “Toxic cloud imaging by infrared spectrometry: A scanning FTIR system for identification and visualization,” Field Anal. Chem. Technol. 5(1-2), 75–90 (2001).
[Crossref]

Hess, L. D.

S. Wu, U. Efron, and L. D. Hess, “Infrared birefringence of liquid crystals,” Appl. Phys. Lett. 44(11), 1033–1035 (1984).
[Crossref]

Hirsch, E.

Hodgkinson, J.

J. Hodgkinson and R. P. Tatam, “Optical gas sensing: a review,” Meas. Sci. Technol. 24(1), 012004 (2013).
[Crossref]

Hu, S.

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Icenogle, H. W.

Jayaraj, S.

M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
[Crossref]

Kastek, M.

M. Kastek, T. Piątkowski, and P. Trzaskawka, “Infrared Imaging Fourier Transform Spectrometer as the Stand-Off Gas Detection System,” Metrol. Meas. Syst. 18(4), 161–172 (2011).
[Crossref]

Kimball, B. R.

Lin, Y.-H.

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

Liu, H.

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Liu, X.

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Lyszczarz, T. M.

Maiau, A.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Matz, G.

R. Harig and G. Matz, “Toxic cloud imaging by infrared spectrometry: A scanning FTIR system for identification and visualization,” Field Anal. Chem. Technol. 5(1-2), 75–90 (2001).
[Crossref]

Mohanraj, M.

M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
[Crossref]

Mouquinho, A.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Muraleedharan, C.

M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
[Crossref]

Murvay, P.-S.

P.-S. Murvay and I. Silea, “A survey on gas leak detection and localization techniques,” J. Loss Prev. Process Ind. 25(6), 966–973 (2012).
[Crossref]

Ning, H.

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Oelßner, W.

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

Osgood, R. M.

Petrova, K.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Piatkowski, T.

M. Kastek, T. Piątkowski, and P. Trzaskawka, “Infrared Imaging Fourier Transform Spectrometer as the Stand-Off Gas Detection System,” Metrol. Meas. Syst. 18(4), 161–172 (2011).
[Crossref]

Platt, B. C.

Puckrin, E.

Ren, H.

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

Richardson, M.

P. W. Yuen and M. Richardson, “An introduction to hyperspectral imaging and its application for security, surveillance and target acquisition,” Imaging Sci. J. 58(5), 241–253 (2010).
[Crossref]

Saavedra, M.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Silea, I.

P.-S. Murvay and I. Silea, “A survey on gas leak detection and localization techniques,” J. Loss Prev. Process Ind. 25(6), 966–973 (2012).
[Crossref]

Sotomayor, J.

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Tatam, R. P.

J. Hodgkinson and R. P. Tatam, “Optical gas sensing: a review,” Meas. Sci. Technol. 24(1), 012004 (2013).
[Crossref]

Thériault, J.-M.

Trzaskawka, P.

M. Kastek, T. Piątkowski, and P. Trzaskawka, “Infrared Imaging Fourier Transform Spectrometer as the Stand-Off Gas Detection System,” Metrol. Meas. Syst. 18(4), 161–172 (2011).
[Crossref]

Tsai, W.-T.

W.-T. Tsai, “An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs),” Chemosphere 61(11), 1539–1547 (2005).
[Crossref] [PubMed]

Wolfe, W. L.

Wu, S.

S. Wu, U. Efron, and L. D. Hess, “Infrared birefringence of liquid crystals,” Appl. Phys. Lett. 44(11), 1033–1035 (1984).
[Crossref]

Wu, S.-T.

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

Yuen, P. W.

P. W. Yuen and M. Richardson, “An introduction to hyperspectral imaging and its application for security, surveillance and target acquisition,” Imaging Sci. J. 58(5), 241–253 (2010).
[Crossref]

Zhang, D.

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Zosel, J.

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

Appl. Opt. (3)

Appl. Phys. Lett. (2)

S. Wu, U. Efron, and L. D. Hess, “Infrared birefringence of liquid crystals,” Appl. Phys. Lett. 44(11), 1033–1035 (1984).
[Crossref]

Y.-H. Fan, Y.-H. Lin, H. Ren, S. Gauza, and S.-T. Wu, “Fast-response and scattering-free polymer network liquid crystals for infrared light modulators,” Appl. Phys. Lett. 84(8), 1233–1235 (2004).
[Crossref]

Chemosphere (1)

W.-T. Tsai, “An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs),” Chemosphere 61(11), 1539–1547 (2005).
[Crossref] [PubMed]

Field Anal. Chem. Technol. (1)

R. Harig and G. Matz, “Toxic cloud imaging by infrared spectrometry: A scanning FTIR system for identification and visualization,” Field Anal. Chem. Technol. 5(1-2), 75–90 (2001).
[Crossref]

Imaging Sci. J. (1)

P. W. Yuen and M. Richardson, “An introduction to hyperspectral imaging and its application for security, surveillance and target acquisition,” Imaging Sci. J. 58(5), 241–253 (2010).
[Crossref]

Int. J. Therm. Sci. (1)

M. Mohanraj, S. Jayaraj, C. Muraleedharan, and P. Chandrasekar, “Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator,” Int. J. Therm. Sci. 48(5), 1036–1042 (2009).
[Crossref]

J. Loss Prev. Process Ind. (1)

P.-S. Murvay and I. Silea, “A survey on gas leak detection and localization techniques,” J. Loss Prev. Process Ind. 25(6), 966–973 (2012).
[Crossref]

Meas. Sci. Technol. (2)

J. Hodgkinson and R. P. Tatam, “Optical gas sensing: a review,” Meas. Sci. Technol. 24(1), 012004 (2013).
[Crossref]

J. Zosel, W. Oelßner, M. Decker, G. Gerlach, and U. Guth, “The measurement of dissolved and gaseous carbon dioxide concentration,” Meas. Sci. Technol. 22(7), 072001 (2011).
[Crossref]

Metrol. Meas. Syst. (1)

M. Kastek, T. Piątkowski, and P. Trzaskawka, “Infrared Imaging Fourier Transform Spectrometer as the Stand-Off Gas Detection System,” Metrol. Meas. Syst. 18(4), 161–172 (2011).
[Crossref]

Mol. Cryst. Liq. Cryst. (Phila. Pa.) (1)

A. Mouquinho, M. Saavedra, A. Maiau, K. Petrova, M. T. Barros, J. L. Figueirinhas, and J. Sotomayor, “Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 542(1), 132–140 (2011).
[Crossref]

Opt. Express (1)

Sens. Rev. (1)

R. Bogue, “Detecting gases with light: a review of optical gas sensor technologies,” Sens. Rev. 35(2), 133–140 (2015).
[Crossref]

Sensors (Basel) (1)

X. Liu, S. Cheng, H. Liu, S. Hu, D. Zhang, and H. Ning, “A survey on Gas Sensing Technology,” Sensors (Basel) 12(7), 9635–9665 (2012).
[Crossref] [PubMed]

Other (5)

N. I. S. T. Chemistry Webbook, http://webbook.nist.gov/chemistry/ .

Vapor phase IR spectral library, https://secure2.pnl.gov/nsd/nsd.nsf , https://secure2.pnl.gov/nsd/nsd.nsf/Welcome

I.-C. Khoo and S.-T. Wu, Optics and Nonlinear Optics of Liquid Crystals (World Scientific, 1993), Vol. 1.

J. Y. Wong and R. L. Anderson, Non-Dispersive Infrared Gas Measurement (International Frequency Sensor Assosiation, 2012).

S.-T. Wu and D.-K. Yang, Fundamentals of Liquid Crystal Devices (John Wiley & Sons, 2006).

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Figures (4)

Fig. 1
Fig. 1 Simulation of two gas detection setups: (a1) Using a single BP filter, and (a2) adding a switchable NF. (b) Example of gas, clutter, and BP transmissions separately using the a1 setup. (c) Transmissions of the NF (a2 setup) at ‘on’ and ‘off’ states aligned to gas resonance. (d) Total transmission in ‘on’ and ‘off’ states for the NF a2 setup.
Fig. 2
Fig. 2 A setup consisting of a switchable NF and BP acquire gas and clutter signals (a). Spectral transmissions of the objects in the clutters and the system components (b). The 'on' to 'off' signal ratio R C L U T T E R is constant for any spectrally flat radiation, and differs for the gas, R G A S . This allows us to distinguish between gas and clutter pixels.
Fig. 3
Fig. 3 The experimental setup and results. (a) The setup for cell transmittance measurements. (b) The uniform spectral-response of an empty cell (solid blue line) compared to the E7LC mixture in the ‘on’ state (red dot-dashed line) and ‘off’ state (dashed black line). The E7 absorption lines are associated with the vibration modes of the LC [13] (see table in the figure). (c) The chemical structure of LC 5CB – the major component of the E7 mixture, adapted from [14]. Time response measurements of the E7-filled cell (d) show a fast rise time of 20milliseconds after applying the voltage (arrow-ON), and slow fall time of 10 seconds after switching off the voltage (arrow-OFF).
Fig. 4
Fig. 4 (a) Transmittance measurements of R134a gas (dotted pink) compared to E7 transmission in the ‘on’ (red dot-dashed) and ‘off’ states (dashed black). (b) Detection of R134a gas by comparing R G A S   (dashed black) to air’s R C L U T T E R (red dotted), and the contrast (blue solid) for several CWL of BP filters with FWHM = 170nm.

Equations (5)

Equations on this page are rendered with MathJax. Learn more.

S C L U T T E R = τ C L U T T E R d λ   P T ( λ ) τ B P ( λ ) S G A S = d λ P T ( λ )   τ G A S   ( λ ) τ B P ( λ )
S C L U T T E R = S G A S
S C L U T T E R O N = τ C L U T T E R d λ   P T ( λ ) τ B P ( λ ) τ N F   O N ( λ ) S C L U T T E R O F F = τ C L U T T E R d λ   P T ( λ ) τ B P ( λ ) τ N F   O F F ( λ ) S G A S O N = d λ P T ( λ )   τ G A S   ( λ ) τ B P ( λ ) τ N F   O N ( λ ) S G A S O F F = d λ P T ( λ )   τ G A S   ( λ ) τ B P ( λ ) τ N F   O F F ( λ )
R C L U T T E R = S   C L U T T E R O N   /   S   C L U T T E R O F F R G A S = S   G A S O N   /   S   G A S O F F
C O N T R A S T ( R C L U T T E R R G A S   ) / 0.5 ( R C L U T T E R + R G A S   )

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