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LASER BASED SENSOR FOR DETECTION OF TRACE GASES IN THE ENVIRONMENT

LASER BASED SENSOR FOR DETECTION OF TRACE GASES IN THE ENVIRONMENT. M. A. Gondal, I. A. Bakhtiari and Z. H. Yamani Laser Research Laboratory & Physics Department King Fahd University of Petroleum & Minerals. Gondal. Me!!. Bakhtiari. Plan. Intro.: What is photoacoustic spectroscopy

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LASER BASED SENSOR FOR DETECTION OF TRACE GASES IN THE ENVIRONMENT

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  1. LASER BASED SENSOR FOR DETECTION OF TRACE GASES IN THE ENVIRONMENT M. A. Gondal, I. A. Bakhtiari and Z. H. Yamani Laser Research Laboratory & Physics Department King Fahd University of Petroleum & Minerals Gondal Me!! Bakhtiari

  2. Plan • Intro.: What is photoacoustic spectroscopy • Modifying the PA set up • Results for Ethylene • Future work • Conclusion

  3. Conventional Spectroscopy Introduction: What is photoacoustic spectroscopy • Principal: Energy absorbed is determined by the difference (Io - I) / Io. Io I Sample Detector Light Source

  4. Photoacoustic Spectroscopy (PA) Chopper Sample • Principal: Energy absorbed by the sample produces sound waves which are detected by sensitive microphone. The name PA is due to “Light Generated Sound” • Advantages: Sample may be gaseous, liquid, solid opaque, powdered. Highly sensitive. Light Source Microphone

  5. LASER RADIATION EXCITATION (VIBRATIONAL) CHEM. REACTION EMISSION (ELECTRONIC) HEAT PHASE TRANSITION EXPANSION RADIATION SOUND WAVES

  6. vent Photoacoustic spectroscopy system using chopper for modulation

  7. Modifying the PA set up

  8. Vacuum Pump Valve Spectrum Analyzer P. Gauge Air Filter Photoacoustic cell Valve Tunable CO2 laser Lens Motor Power Meter ` Grating Beam Microphone Splitter Newport micro stepping motor grating controller CO2 Laser Modulator. Variable duty cycle (TTL) Stepping Variable Gain Low Noise Microphone Amplifier

  9. Resonant Photoacoustic Cell developed at KFUPM R = 8 mm L = 160 mm It turns out that: n0,0,1 ~ 3400 Hz Don’t worry about higher resonance frequencies, because they are beyond microphone response limit

  10. Noise level in PA cell, filled with pure nitrogen

  11. Results for Ethylene Fundamental frequencies for Ethylene (C2H4) n1 3026 cm-1 CH2 stretchn2 1623 cm-1 CC stretchn3 1342 cm-1 CH2 scissorn4 1023 cm-1 CH2 twistn5 3103 cm-1 CH2 stretchn6 1236 cm-1 CH2 rockn7 949 cm-1 CH2 wagn8 943 cm-1 CH2 wagn9 3106 cm-1 CH2 stretchn10 826 cm-1 CH2 rockn11 2989 cm-1 CH2 stretchn12 1444 cm-1 CH2 scissor Molecular weight 28.05 amuFreezing point -169 CBoiling point -104 C Use the 10 P(14) of CO2 Spectral distribution of CO2 lines Spectral distributon of CO2 laser Spectral distributon of CO2 laser Spectral distributon of CO2 laser Spectral distributon of CO2 laser Spectral distributon of CO2 laser

  12. Mechanical (chopper) Modulation 300 ppbV of ethylene under 1000 mbar of nitrogen

  13. Electronic Modulation 300 ppbV of ethylene under 1000 mbar of nitrogen

  14. Future work This is how the lab looks when we are there!!! Domestically built CO2 laser 1- SABIC funded project on detection of ozone. 2- Improve sensitivity. 3- Go out to the field

  15. Conclusion 1- The PA system is up and running with good dynamic range and sensitivity for the detection of C2H4. 2- We have a plan for future work, including detection of ozone. 3- We are open for ideas and need your support (esp. graduate students). KFUPM is gratefully acknowledged for supporting this work Thank you for your attention و السلام عليكم.. و رحمة الله و بركاته

  16. Vacuum Pump Valve Spectrum Analyzer P. Gauge Air Filter Photoacoustic cell Valve Tunable CO2 laser Lens Motor Power Meter ` Grating Beam Microphone Splitter Newport micro stepping motor grating controller CO2 Laser Modulator. Variable duty cycle (TTL) Stepping Variable Gain Low Noise Microphone Amplifier

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