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

2. Emission collection Laser-Induced Breakdown Spectroscopy (LIBS) Laser-induced plasma Pulsed laser Sample Detector Fiber optic Spectrometer Atomic emission lines provide species identification 410415420425430435440 Wavelength (nm) Emission Intensity

3. LIBS spectrum of CCA-treated wood

4. 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

5. 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)

6. Detector configuration Laser To PC

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

8. Instrument synchronization Time0 Laser pulse (10 ns) Plasma emission (25 us) Chromium emission (10 us) Pre-trigger Detector Delay

9. Identification of CCA-treated wood 0 2000 4000 6000 8000 10000 12000 14000 410415420425430435440 Emission Intensity Wavelength (nm) Calcium Chromium Peak Base

10. 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

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

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

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

14. 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

15. Sarasota field test on 7-3-01 Threshold

16. 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