Some Laser Applications Research at ODU

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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
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All Credit Goes to Students(Only Current
Students Listed)

• 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

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Basic Theme

• Measurements with Lasers are
• sensitive
• non-intrusive
• many different applications
• exciting (fun!!) to make!

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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. Dharamsis 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
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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

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Techniques have several variants

• Emission Spectroscopy
• Raman Spectroscopy
• Absorption Spectroscopy
• Optoacoustic Spectroscopy
• etc, etc

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TOPIC 1

• Description of Modulation Absorption Spectroscopy
  Follows

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Basics of Absorption Spectroscopy
I(n)
I0(n)
Laser
Detector

• Sweep the laser frequency (wavelength) across an
  energy transition
• Detect absorption

• Key components
• Coherent, monochromatic light source
• Detector

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Example of a Transition Probed
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Oxygen A-band Spectrum
From Hitran 96 Database
From Hitran 96 Database
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Absorption Profile

• Frequency molecule
• Line center shift velocity
• Signal strength density
• Probe two transitions simultaneously
• strengths temperature

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Applications

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

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

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

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Lineshape Profiles-What are they?

• Probability of absorption/emission in the
  interval ? and ? d? is
• Hence

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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
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Lineshape Profiles (Why bother?)

• Pressure
• Temperature
• Collision Dynamics
• Etc, etc
• EVERYTHING is contained in profile

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Lineshape profiles
Gaussian Lineshape
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Lorentzian Lineshape
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Absorption Signal Profile
Theory
m 4.2, r 0.03, y p/10, scoll 1.7x10-15cm2
Experiment
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Overlapping Lines
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Overlapping Lines
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Null Measurement Technique
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TOPIC 2

• Description of Optoacoustic Measurements Follows

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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

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Applications

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

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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.
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Experiment Data Acquisition - LabVIEW
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Modeling Contact detection
Comparison
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Results PVC sample (10.5mm) 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
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Experiment Setup 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
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Results PVC sample (1.9mm) NdYAG (1064nm)
Probe beam size 0.8mm
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Signal Processing Echo Separation by
Fourier Transform Method
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Signal Processing Echo Separation by
Fourier Transform Method
Direct Measurement T 6.06?s
Fourier Transform T 6.13?0.31 ?s
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Optoacoustic Applications II Pulsed OA on
Tissue Sample Experiment
C1 layer on top
C2 layer on top
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Optoacoustic Applications II Pulsed 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
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TOPIC 3

• Description of Remote Sensing with LIDAR Follows

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

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Sample Atmospheric LIDAR Return Grady Koch, NASA
Langley and ODU PhD Student
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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.
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LIDAR STABILIZATION BY WMS
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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
HoTmYLF Laser to an Absorption Line of Carbon
Dioxide Accepted for publication in Applied
Optics