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

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 1 3026 cm -1 CH 2 stretch 2 1623 cm -1 CC stretch 3 1342 cm -1 CH 2 scissor 4 1023 cm -1 CH 2 twist 5 3103 cm -1 CH 2 stretch 6 1236 cm -1 CH 2 rock 7 949 cm -1 CH 2 wag 8 943 cm -1 CH 2 wag 9 3106 cm -1 CH 2 stretch 10 826 cm -1 CH 2 rock 11 2989 cm -1 CH 2 stretch 12 1444 cm -1 CH 2 scissor Fundamental frequencies for Ethylene (C 2 H 4 ) Molecular weight 28.05 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

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 4. 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). Conclusion KFUPM is gratefully acknowledged for supporting this work Thank you for your attention و السلام عليكم.. و رحمة الله و بركاته

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)