LIBS Detector System Design Preliminary Testing David Hahn

LIBS Detector System Design & Preliminary Testing David Hahn, Tom Moskal, Ken Iida Department of Mechanical Engineering University of Florida July 9, 2001

Laser-Induced Breakdown Spectroscopy (LIBS) Laser-induced plasma Atomic emission lines provide species identification Pulsed laser Fiber optic Spectrometer Emission collection Detector Emission Intensity Sample 410 415 420 425 430 Wavelength (nm) 435 440

LIBS spectrum of CCA-treated wood

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)

Detector configuration To PC Laser

Data acquisition Laptop computer Plasma emission Strobe trigger Spectrometer Data acquisition and analysis Ext. trigger from laser Fiber optic

Instrument synchronization Laser pulse (10 ns) Plasma emission (25 us) Chromium emission (10 us) Delay Pre-trigger Detector 0 Time

Identification of CCA-treated wood 14000 Calcium Emission Intensity 12000 10000 8000 Peak 6000 4000 Base Chromium 2000 0 415 420 425 Wavelength (nm) 430 435 440

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

LIBS Cr Signal Single laser shots: Untreated wood Laser Shot Number

LIBS Cr Signal Single laser shots: Treated wood Laser Shot Number

Analysis of single laser shots Untreated Lumber Treated Lumber 95% accuracy 99% accuracy 92% accuracy 100% accuracy Cr Signal Single-shot analysis 10 -shot average

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

Sarasota field test on 7 -3 -01 Threshold

Summary of LIBS work to date • Successfully detect CCA-treated wood by presence of chromium in the field • Indicator strobe enables real-time, on-line sorting with accuracy approaching 100% • Continue to assess accuracy of LIBS-based detector and to formulate system improvements