1. A Fundamental Study of Laser- Induced Breakdown Spectroscopy Using Fiber Optics for Remote Measurements of Trace Metals Scott R. Goode and S. Michael Angel Department of Chemistry and Biochemistry University of South Carolina

2. Approach –Fiber optic technology –Wavelength resolution –Time resolution Accomplishments –Two operating instruments –Examining surface morphology –Studying matrix effects Future –Solutions and slurries LIBS for Elemental Analysis

3. Laser-Induced Breakdown Spectroscopy Use laser to vaporize sample Laser electric field high enough to cause breakdown Monitor emission Fiber optics afford capability for remote analysis

4. Limiting Factor Discriminating analyte atomic emission from continuum background emission limits the analysis –Time –Wavelength

5. Time-Resolved LIBS Apparatus Pulsed Laser mirror focusing lens Spectrograph plasma collection lens intensified detector Timing Control 1064 nm

6. Pulsed laser Lens Delay generator Controller Detector Computer Laser trigger Spectrograph Lens Fiber-optic LIBS probe Fiber-Optic LIBS System Configuration

7. SampleFocusing lens Excitation Fiber Collection Fiber f/2 LensPlasma Fiber-Optic LIBS Probe Design

8. Lead in Paint Using Fiber-Optic LIBS Probe Wavelength (nm) Ti 140 0 120 0 1000 800 600 400 200 0 406.0404.0402.0400.0398.0 Pb Solder Leaded Paint Unleaded Paint Intensity

9. Leaded Paint Calibration Using Fiber-Optic Probe 200 150 100 50 0 Intensity 0.100.080.060.040.020.00 Concentration of Lead (% w/w, Dry Basis) L.O.D.= 0.014% Pb (wt/wt) Dry Basis - 4 mJ/pulse, 2 Hz, 532 nm laser, avg. 5 replicate spectra

10. Fiber-Optic Transmission 120 110 100 90 80 70 60 50 40 30 20 10 0 Power Out of fiber (mJ) 150140130120110100908070605040302010 Power into Fiber (mJ) fiber breakdown 1 mm silica-clad 1 mm hard-clad 800  m hard-clad 600  m hard-clad

11. imaging fiber He:Ne Nd:YAG Ar + pellicle f/8 probe b&w CCD 6x macro lens 10x imaging fiber frame grabber excitation fiber ICCD LIBS/Raman collection fiber monitor pulser controllerspectrograph f/7 lens 10x imaging ex. w/GRIN spectral excit.

12. Imaged region Imaging fiber GRIN lens Filtered Raman excitation fiber (514.5 nm) LIBS excitation fiber (1064 nm) (632 nm pointer) Collection fiber (filtered for Raman) Region of interest Sample Video camera

13. Intensity 16 x10 3 Intensity 35x10 3 25 15 5 420416412408404 Fe Ca Fe b 14 10 6 2 420416412408404 Sr Ca Sr d Wavelength (nm) 5 mm Region of Interest Wavelength (nm) a c

14. 1000800600400200 Darkfield image of TiO 2 and Sr(NO 3 ) 2 on soil Raman spectrum of Sr(NO 3 ) 2 Raman spectrum of TiO 2 200x10 3 150 100 50 0 Intensity Wavenumber (cm -1 ) 200x10 3 150 100 50 1600140012001000800 Wavenumber (cm -1 ) Intensity a c b

15. TiO 2 @190 cm -1 Darkfield image of TiO 2 and Sr(NO 3 ) 2 on soil Raman Images Sr(NO 3 ) 2 @1055cm -1 a c b

16. Plasma Temperature Profile 2500 0 384382380378376374372370368366 Graph 7 (top of plasma) 2500 0 384382380378376374372370368366 Graph 6 Graph 5 2500 0 384382380378376374372370368366 Graph 2 2500 0 384382380378376374372370368366 Graph 1 (bottom of plasma) 2500 0 384382380378376374372370368366 Graph 3 Graph 4 2500 0 384382380378376374372370368366 2500 384382380378376374372370368366 0 7 6 5 4 3 2 1 Observed plasma region 70006000 Plasma temperature (K) Top Bottom Regions 7 6 5 4 3 2 1

17. LIBS Imaging Spectrometer sample ICCD lens beam stop AOTF RF generator collimating lens plasma laser 1064 nm mirror 1064 nm mirror

18. Background Subtracted 722.8 nm Lead Emission + Continuum 715.2 nm Continuum Background 2.64 mm Repetition Rate: 2 Hz, 2000 Shots, 2.5  s Delay Background Subtracted Lead Emission

19. Temporal Dependence of Lead Emission 50 ns675 ns 1. 3  s1. 9  s2. 5  s Pb emission at 722.8 nm Continuum background Background subtracted 2.5 mm

20. Lead Crater Depth and Plasma Height 0.38 mm 0.50 mm 0.63 mm 1.42 mm 2.75 mm 100 shots 2400 shots 960 shots

21. Plasma Height vs. Number of Laser Shots 2500 2000 1500 1000 200015001000500 Number of Laser Shots Plasma Height (microns) 2.5  s delay 1.0  s delay Rep Rate: 2 Hz

22. Using High Wavelength Resolution If the major source of noise is the continuum background –Eliminate the background by time resolution –Use wavelength resolution to distinguish the atomic lines from the continuum background

23. Echelle Spectrometer

24. Matrix effects Use binary alloy (brass samples) Examine signals from zinc (volatile) and copper (nonvolatile) Vary laser power Vary focal depth

25. Studying selective volatilization Measure zinc and copper emission from brass standards Perform measurements while varying laser power (Q-switch delay) See if ratio is independent of power and proportional to concentration

26. Effect of Laser Power 2.86% Zn

27. Effect of Laser Power 4.18 % Zn

28. Effect of Laser Power 24.8 % Zn

29. Effect of Laser Power 34.6 % Zn

30. Effect of Laser Power 39.7 % Zn

31. Calibration Plot

32. Effect of focus Measure Zn-to-Cu emission ratio –As a function of composition –As a function of focal point Negative: focal point below surface Zero: at surface Positive: above surface

33. Zn-to-Cu ratio as a function of focal point 2.86% Zn

34. Zn-to-Cu ratio as a function of focal point 4.18 % Zn

35. Zn-to-Cu ratio as a function of focal point 8.48 % Zn

36. Zn-to-Cu ratio as a function of focal point 24.8 % Zn

37. Zn-to-Cu ratio as a function of focal point 34.6 % Zn

38. Zn-to-Cu ratio as a function of focal point 39.7 % Zn

39. Conclusions LIBS is more complex than originally thought. Much of the data are consistent with a low- power heating mechanism and a high power dielectric vaporization mechanism. Can design experiments to decouple excitation and vaporization.

40. Segregate excitation effects from vaporization effects Brass samples, known composition Laser ablation into solution Dissolution Chemical analysis by ICP-MS Determine if materials vaporized in proportion to concentration Determine factors that affect selective and nonselective vaporization

41. Spectrometer High Spectral Resolution (7500) High Time Resolution (5 ns) Delivery?

42. Alternative Excitation Use laser system to vaporize solid sample. Direct vapor into microwave-excited plasma. Use emission from microwave plasma for chemical analysis.

43. Pulsed Nd:YAG Controller 1064nm mirror plasma sample Pulsed Nd:YAG Timing Control Spectrograph lens ICCD lens Pulser Optical Fiber Colinear Dual-Pulse LIBS Configuration

44. 25x10 3 20 15 10 5 Intensity (arb units) 530525520515510505500 Wavelength (nm) 0  s between lasers 1  1064 nm Laser 1 (100 mJ) Laser 2 (180 mJ) Colinear Dual-Pulse LIBS Enhancement for Copper

45. Signal-to-Bkg Optimum Delay Between Lasers for Copper Enhancement 16 14 12 10 8 6 4 2 5004003002001000 Time Between Lasers (  s)  Laser 1 = 100 mJ Laser 2 = 180 mJ Colinear Dual-Pulse LIBS

46. 0.38 mm 20  s  T Cu S/B  15 0.38 mm 1  s  T Cu S/B  14 0.38 mm 0  s  T Cu S/B  3 Copper Craters from Colinear Dual-Pulse LIBS

47. 100 Optimum Timing Between Lasers for Lead Enhancement 4.0 3.5 3.0 2.5 806040200 Pb SBR Time Between Lasers (  s)  T Colinear Dual-Pulse LIBS

48. Comparison of Lead Craters (colinear geometry) 0.60 mm Zero  s  TOne  s  T Pb S/B  6 Pb S/B  2.5

49. Orthogonal Dual-Pulse LIBS

50. Controller Nd:YAG plasma Nd:YAG Timing Control Spectrograph ICCD Pulser

51. 10 8 6 4 2 0 Intensity 530525520515510505500 Wavelength (nm) 0  s between lasers -1  s between lasers Orthogonal Dual-Pulse LIBS Enhancement for Cu

52. 14 12 10 8 6 4 2 0 Cu Sig-to-bkg -5-4-3-20 Time between lasers (  s) Enhancement of Copper Emission Using Non-Ablating Prespark

53. 150  m 176  m Orthogonal Dual-Pulse LIBS Geometry SEM Craters for Copper

54. 2.86% Zinc at Low Power 36.4 120.8 144.4 56.3 141.2

55. 2.86% Zinc at High Power 86.6 259.9 111.8 110.3

56. 4.18% Zinc at Low Power 88.9133.9 124.9 101.2 90.5 95.0

57. 4.18% Zinc at High Power 89.191.0 97.8 60.6 93.8 71.7 57.8

58. 24.8% Zinc at Low Power 130.0 7.8 62.0 75.4 88.0

59. 24.8% Zinc at High Power 101.3 89.1 57.9 93.3 100.0 106.7 100.8

60. 35.6% Zinc at Low Power 70.9 92.5 90.2 79.1 101.6

61. 34.6% Zinc at High Power 108.8 109.6 85.4 173.9 126.3 119.6 119.1 84.4

62. 34.6% Zinc at High Power Surface Effect 110.5 99.4

63. Targeted DOE Needs ID No: SR99-3025: Monitoring Technologies for Effectiveness of Solidification and Stabilization Systems  ID No: SR99-1003: Improvements to Physical, Chemical, and Radionuclide Quantification of Solid Waste  ID No: SR99-1004: Need for Continuous Emissions Monitors for Measurement of Hazardous Compound Concentrations in Incinerator Stack Gas

64. Targeted DOE Needs  ID No. RL-SS06 Improved, Real-Time, In-Situ Detection of Hexavalent Chromium in Groundwater  ID No. RL-DD038: Liquids Characterization for CDI  ID No. RL-SS15: Improved, In Situ Characterization to Determine the Extent of Soil Contamination of One or More of the Following Heavy Metals: Hexavalent Chromium, Mercury, and Lead