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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.

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Presentation on theme: "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."— Presentation transcript:

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2 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 Bakhtiari Me!!

3 Plan 1.Intro.: What is photoacoustic spectroscopy 2.Modifying the PA set up 3.Results for Ethylene 4.Future work 5.Conclusion

4 Conventional Spectroscopy  Principal:  Principal: Energy absorbed is determined by the difference (I o - I) / I o. Detector Sample Light Source IoIo I Introduction: What is photoacoustic spectroscopy

5 Photoacoustic Spectroscopy (PA)  Principal: Energy  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 Chopper Sample Microphone

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

7 vent Photoacoustic spectroscopy system using chopper for modulation

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9 Modifying the PA set up

10 Stepping Motor P. Gauge Valve Vacuum Pump Power Meter Air Filter Valve Lens Tunable CO 2 laser Beam Splitter Photoacoustic cell Microphone Grating ` Spectrum Analyzer Newport micro stepping motor grating controller Variable Gain Low Noise Microphone Amplifier CO 2 Laser Modulator. Variable duty cycle (TTL)

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

12 Noise level in PA cell, filled with pure nitrogen

13 Results for Ethylene cm -1 CH 2 stretch cm -1 CC stretch cm -1 CH 2 scissor cm -1 CH 2 twist cm -1 CH 2 stretch cm -1 CH 2 rock cm -1 CH 2 wag cm -1 CH 2 wag cm -1 CH 2 stretch cm -1 CH 2 rock cm -1 CH 2 stretch cm -1 CH 2 scissor Fundamental frequencies for Ethylene (C 2 H 4 ) Molecular weight amu Freezing point -169 C Boiling point -104 C Spectral distributon of CO 2 laser Spectral distribution of CO 2 lines Use the 10 P(14) of CO 2

14 300 ppbV of ethylene under 1000 mbar of nitrogen Mechanical (chopper) Modulation

15 Electronic Modulation 300 ppbV of ethylene under 1000 mbar of nitrogen

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19 1- SABIC funded project on detection of ozone. 2- Improve sensitivity. 3- Go out to the field Future work This is how the lab looks when we are there!!! Domestically built CO 2 laser

20 1- The PA system is up and running with good dynamic range and sensitivity for the detection of C 2 H We have a plan for future work, including detection of ozone. 3- We are open for ideas and need your support (esp. graduate students). Conclusion KFUPM is gratefully acknowledged for supporting this work Thank you for your attention و السلام عليكم.. و رحمة الله و بركاته

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23 Stepping Motor P. Gauge Valve Vacuum Pump Power Meter Air Filter Valve Lens Tunable CO 2 laser Beam Splitter Photoacoustic cell Microphone Grating ` Spectrum Analyzer Newport micro stepping motor grating controller Variable Gain Low Noise Microphone Amplifier CO 2 Laser Modulator. Variable duty cycle (TTL)


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