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Some Laser Applications Research at ODU

Some Laser Applications Research at ODU. Amin Dharamsi Dept. of Electrical and Computer Engineering Old Dominion University, Norfolk, VA 23529-0246 Presented at Graduate Seminar on 31 March 2000. Graduate Students Audra Bullock (PhD) Zibiao Wei (PhD) Jim Barrington (PhD)

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Some Laser Applications Research at ODU

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  1. Some Laser Applications Research at ODU Amin Dharamsi Dept. of Electrical and Computer Engineering Old Dominion University, Norfolk, VA 23529-0246 Presented at Graduate Seminar on 31 March 2000

  2. Graduate Students Audra Bullock (PhD) Zibiao Wei (PhD) Jim Barrington (PhD) Shujun Yang (PhD) Grady Koch (PhD) Colleen Fitzgerald (MS) David Lockwood (MS) Ted Kuhn (PhD) M. Abdel Fattah (PhD) Undergraduate Students (Senior Project Team) Ed Heath Jim Fay Aubrey Haudricourt Larry Gupton All Credit Goes to Students(Only Current Students Listed)

  3. Basic Theme Measurements with Lasers are: • sensitive • non-intrusive • many different applications • exciting (fun!!) to make!

  4. Some Recent Sample Journal Publications Relating to Modulation Spectroscopy Note: Audra Bullock,Ying Lu and Patrick Shea who are co-authors in the list below were graduate students in Dr. Dharamsi’s group. A. M. Bullock and A. N. Dharamsi, "Investigation of Interference between Absorption Lines by Wavelength Modulation Spectroscopy", J. App. Phys. Vol. 84, 6929, December 1998. A. N. Dharamsi, A. M. Bullock, and P. C. Shea, "Reduction of Fabry-Perot Fringing in Wavelength Modulation Spectroscopy Experiments", Applied Phys. Letts., Vol. 72, pp. 3118-3120, June 1998. A. M. Bullock, A. N. Dharamsi, W. P. Chu and L. R. Poole, "Measurements of Absorption Line Wing Structure by Modulation Spectroscopy", App. Phys. Letts.; 70, 1195-1197, March 1997. A. N. Dharamsi and A. M. Bullock, "Measurements of Density Fluctuations by Modulation Spectroscopy," Applied Physics Letters, Vol. 69, pp. 22-24, June 1996. A. N. Dharamsi and A. M. Bullock, "Application of Wavelength Modulation Spectroscopy in Resolution of Pressure and Modulation Broadened Spectra", App. Phys. B, Lasers and Optics; 63, 283-292, November 1996. A. N. Dharamsi and Y. Lu, "Sensitive Density-Fluctuation Measurements Using Wavelength - Modulation Spectroscopy with High-Order-Harmonic Detection," Applied Physics B., Lasers and Optics, Vol. 62, pp. 273-278, February 1996. A. N. Dharamsi, "A Theory of Modulation Spectroscopy with Applications of Higher Harmonic Detection," J. Phys. D., Vol. 28, pp. 540-549, February 1996

  5. Basic Principle of Techniques • shine laser photons • monitor effects • how many photons absorbed? • what wavelength absorbed? • how much scattering occurred? • how much Doppler Shifting? • what happened to photons? • converted to phonons? what happened to phonons? • etc, etc

  6. Techniques have several variants • Emission Spectroscopy • Raman Spectroscopy • Absorption Spectroscopy • Optoacoustic Spectroscopy • etc, etc

  7. TOPIC 1 • Description of Modulation Absorption Spectroscopy Follows

  8. Key components Coherent, monochromatic light source Detector Basics of Absorption Spectroscopy I0(n) I(n) Laser Detector • Sweep the laser frequency (wavelength) across an energy transition • Detect absorption

  9. Example of a “Transition” Probed

  10. Oxygen A-band Spectrum From Hitran 96 Database From Hitran 96 Database

  11. Absorption Profile • Frequency ® molecule • Line center shift ® velocity • Signal strength ® density • Probe two transitions simultaneously • strengths ® temperature

  12. Applications • Industrial • monitoring velocity and temperature • Environmental • measurements of atmospheric pollutants from ppb to ppt • Scientific • lineshape profiles

  13. Wavelength Modulation Spectroscopy Temperature Controller Mirror 760.228 23.5oC Wavemeter Current Controller Chamber filled with O2 Detector DC + Beam Splitter Diode Laser 1 m cell External Oscillator Lock-in Amplifier 10kHz to Lock-in Amp. 10kHz

  14. Lineshape Profiles • What are they? • How do they arise? • Why should we, as ENGINEERS, bother with them?

  15. Lineshape Profiles-What are they? • Probability of absorption/emission in the interval  and  + d is Hence

  16. Lineshape Profiles-How do they arise? V.V. Old QM says discrete levels: E3 +/-  E3 E 3 E 2 E2 +/-  E2 E 1 E1 +/-  E1

  17. Lineshape Profiles (Why bother?) • Pressure • Temperature • Collision Dynamics • Etc, etc • EVERYTHING is contained in profile

  18. Lineshape profiles Gaussian Lineshape

  19. Lorentzian Lineshape

  20. Absorption Signal Profile Theory m = 4.2, r = 0.03, y = p/10, scoll = 1.7x10-15cm2 Experiment

  21. Overlapping Lines

  22. Overlapping Lines

  23. Null Measurement Technique

  24. TOPIC 2 • Description of Optoacoustic Measurements Follows

  25. Basics of Optoacoustic Measurements • Photons irradiate target • Energy converted to phonons • Phonon K E randomizes • This is heat generation • Optoacoustic signal launched • Carries info on target and light source • Signal measured and analyzed

  26. Applications • Probing of material properties • Nondestructive evaluation • In-situ real-time applications • Biomedical applications

  27. Experiment: contact detection 20MHz piezoelectric transducer Sample Laser Driver Pulsed Laser Wide-band amplifier Thin grease layer Focusing lens Trigger out Trigger in Computer for data acquisition and processing GPIB 400MHz Digital Scope Z. Wei, S. Yang, A. N. Dharamsi, B.Hargrave "Applications of wavelet transforms in biomedical optoacoustics", Photonics West, 2000. Proceedings of the Society of Photo Instrumentation Engineers (SPIE) volume 3900- Paper Number Bio 3916-03.

  28. ExperimentData Acquisition - LabVIEW

  29. ModelingContact detection – Comparison

  30. ResultsPVC sample (1+0.5mm)– diode laser (880nm) Discontinuity Grease for Back (Grease) acoustic layer coupling Front layer Pulse 1 Pulse 2 Acoustic signal Incident Pulse 3 Laser Pulse Pulse 4 Piezoelectric transducer 1.0mm 0.5mm

  31. ExperimentSetup – non contact detection Pulsed Laser Laser Driver Pump Acoustic Wave Photo Diode Probe CW Laser Sample Knife- Edge Wideband Amplifier Trigger Computer for data acquisition and processing GPIB 400MHz Digital Scope

  32. ResultsPVC sample (1.9mm)– Nd:YAG (1064nm) Probe beam size: 0.8mm

  33. 1/T Frequency Signal ProcessingEcho Separation by Fourier Transform Method

  34. Signal Processing Echo Separation by Fourier Transform Method Direct Measurement T = 6.06s Fourier Transform T = 6.130.31s

  35. Optoacoustic Applications IIPulsed OA on Tissue Sample – Experiment C1 layer on top C2 layer on top

  36. Optoacoustic Applications IIPulsed OA on Tissue Sample –  Measurement C1 layer at 337nm =2.2103 m-1 c.f. C2 layer at 337nm =5.8103 m-1

  37. TOPIC 3 • Description of Remote Sensing with LIDAR Follows

  38. Lidar for Atmospheric Studies Grady Koch, NASA Langley and ODU PhD Student Light reflected from aerosols is collected by the telescope.

  39. Selection of Wavelengths for Lidar • Size of scattering particle • - UV and visible wavelengths best for molecular scattering. • - Infrared (1.5-10 mm) best for aerosol scattering. • - Near infrared (0.7 to 1 mm) best for mixture of above. • Eyesafety • - Infrared more safe than visible or UV. • Special Applications • - Chemical detection (laser tuned to absorption features). • - Wind detection (coherent lidar must generally be eyesafe). • Modeling of atmospheric absorption is critical to preserving • range capability. • Grady Koch, NASA Langley and ODU PhD Student

  40. Sample Atmospheric LIDAR ReturnGrady Koch, NASA Langley and ODU PhD Student

  41. Zero Crossing at Line Center, used to stabilize laser C. M. Fitzgerald, G. J. Koch, A. M. Bullock, A.N. Dharamsi, "Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 mm for lidar applications", In Laser Diodes and LEDs in Industrial, Measurement, Imaging, and Sensors Applications II; Testing, Packaging, and Reliability of Semiconductor Lasers V, Burnham, He. Linden, Wang, Editors, Proceedings of SPIE Vol. 3945, pp 98-105, (2000). - Paper Number OE 3945-A14 G. J. Koch, R.E. Davis, A.N. Dharamsi, M. Petros, and J.C. McCarthy, "Differential Absorption Measurements of Atmospheric Water Vapor with a Coherent Lidar at 2050.532 nm," 10th Conference on Coherent Laser Radar, Mt. Hood, OR, 1999.

  42. 100 Hz Labview out in lock-in amplifier ref error A-B adder C D C+D PZT driver mod out multipass cell 2 torr CO2 isolator Ho:Tm:YLF laser beam for injection seed Figure 4.1: Layout of the spectroscopy and line stabilization experiments. Optical pathe drawn as thicker lines. LIDAR STABILIZATION BY WMS

  43. Frequency fluctuations with (upper trace) and without (lower trace) stabilization engaged. Fluctuations are measured by the error signal from the lock-in amplifier. Laser Line StabilizationGrady Koch, NASA LaRC and ODU PhD student G. J. Koch, A. N. Dharamsi, C. M. Fitzgerald and J. C. McCarthy, “Frequency Stabilization of a Ho:Tm:YLF Laser to an Absorption Line of Carbon Dioxide”Accepted for publication in Applied Optics

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