LIBS Detector SystemDesign & Preliminary Testing
David Hahn, Tom Moskal, Ken Iida
Department of Mechanical Engineering
University of Florida
July 9, 2001
Emissioncollection
Laser-Induced Breakdown Spectroscopy (LIBS)Laser-inducedplasma
Pulsedlaser
Sample
Detector
Fiberoptic
Spectrometer
Atomic emission linesprovide species identification
410 415 420 425 430 435 440
Wavelength (nm)
Em
issi
on I
nten
sity
LIBS spectrum of CCA-treated wood
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Em
issi
on
Int
ensi
ty
Wavelength (nm)
Calcium(422.67)
Chromium425.54427.48428.97
Weathered
LIBS detector: Tasks and status
• Acquire laser and spectrometer components
• Interface spectrometer to the computer for data acquisition with external triggering
• Optical configuration design and design of detector package
• Construct prototype detector system
• Synchronize spectrometer data acquisition with firing of laser
LIBS detector: Tasks and status (con’t)
• Interface output trigger signal with PC for firing strobe light upon CCA detection
• Design and build detector mount
• Field test instrument (4-20-01)
• Field testing and evaluation (current)
Data acquisition
Plasma emission
Fiberoptic
Laptop computer
Spectrometer
Ext. trigger from laserData acquisition
and analysis
Strobetrigger
Instrument synchronization
Time0
Laser pulse (10 ns)
Plasma emission (25 us)
Chromium emission (10 us)
Pre-trigger
Detector Delay
Identification of CCA-treated wood
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12000
14000
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Em
issi
on In
tens
ity
Wavelength (nm)
Calcium
Chromium
Peak
Base
Field calibration of detector system
• Detect CCA-treated wood by presence of chromium atomic emission
• Non-treated wood also emits light (background emission) at the same spectral region
• Select a threshold for CCA detection
Single laser shots: Untreated wood
P/B (5)
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10
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P/B (5)
LIB
S C
r S
igna
l
Laser Shot Number
Single laser shots: Treated wood
P/B (5)
0
1
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P/B (5)
LIB
S C
r S
igna
l
Laser Shot Number
Analysis of single laser shots
Treated
Lumber
Untreated
Lumber
100%
accuracy
99%
accuracy
10-shot
average
92%
accuracy
95%
accuracy
Single-shot
analysis
35.069.1 44.198.3 Cr Signal
Output signal for detection of treated wood
• Fire strobe lights when CCA is detected
• Requires firing rate of 2 Hz and TTL trigger logic
• NOVA Electronics built a custom strobe unit with four output channels