Ultraviolet Resonant Raman Enhancements in the Detection of ...

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A. OBJECTIVES VI. EXPERIMENTAL TECHNIQUES The goal of this research was to quantitatively determine resonance Raman enhancements in the absence of the frequency dependent enhancements for select high explosive (HE) materials by contrasting Raman measurements at 785, 244, and 229 nm excitation wavelengths using an internal standard. The internal standard (acetonitrile) exhibits no resonance or pre-resonance Raman effects and did not overly convolve the analyte Raman peaks. The experimental conditions between ultraviolet resonance Raman (UVRR) and near-infrared (NIR) Raman systems were matched to the greatest extent possible given experimental constraints, and the use of an internal standard allows quantitative comparison between measurements. Using this technique it is possible to determine the benefits of UV excited Raman compared to normal Raman techniques for the standoff detection of high explosives. B. EXPERIMENTAL SUMMARY UV-visible (UV-Vis) absorption measurements were performed to select solution concentrations for UVRR analysis and to collect required transmission data for Raman enhancement calculations and corrections. Sample solutions at a single fixed dilute solution (varying from 2.2 to 9.27 mM for different analytes) were placed in a 1.00 mm path length (sealable) quartz cell for UVRR analysis. UVRR measurements of sample solutions were made for three to five sample replicates at five different laser powers settings for each replicate ranging from 20 to 2.2 mW. The laser was rastered across the cell during the 180-second analysis time to prevent or minimize localized heating and photodegradation effects that could negatively influence the measurement. Three replicates of one fixed sample concentration between 100 to 150 mM were used for NIR Raman measurements at 50 mW. The higher concentration was necessary since the analyte Raman band intensities were weaker for NIR excitation; NIR excitation provides no resonance enhancements effects and Raman scattering power goes as ν 4 . The laser 37
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LLNL-TH-413751 Ultraviolet Resonant
Page 3 and 4:
NAVAL POSTGRADUATE SCHOOL MONTEREY,
Page 5 and 6: REPORT DOCUMENTATION PAGE Form Appr
Page 7 and 8: Approved for public release; distri
Page 9 and 10: ABSTRACT Raman-based spectroscopy i
Page 11 and 12: TABLE OF CONTENTS I.  INTRODUCTIO
Page 13 and 14: LIST OF FIGURES Figure 1.  Weight
Page 15 and 16: Figure 25.  Calculated Raman reso
Page 17 and 18: LIST OF TABLES Table 1. Table of se
Page 19 and 20: ACKNOWLEDGMENTS Foremost I wish to
Page 21 and 22: A. MOTIVATION I. INTRODUCTION The
Page 23 and 24: C. RESEARCH GOALS The primary goal
Page 25 and 26: II. DETECTION OF EXPLOSIVES A. SELE
Page 27 and 28: B. SPECTROSCOPY OF EXPLOSIVES Spect
Page 29 and 30: The presence of explosive related m
Page 31 and 32: While direct standoff detection of
Page 33 and 34: the explosive may be located in dif
Page 35 and 36: III. FUNDAMENTALS OF RAMAN SPECTROS
Page 37 and 38: thermal energy, a very small quanti
Page 39 and 40: Figure 5. Raman spectra of chlorofo
Page 41 and 42: Electronic State Virtual States n V
Page 43 and 44: Shot noise is a fundamental phenome
Page 45 and 46: IV. PREVIOUS RAMAN RESEARCH A. RAMA
Page 47 and 48: Sharma and collaborators at the Uni
Page 49 and 50: A. RAMAN CROSS SECTIONS V. METHOD T
Page 51 and 52: and ratioed to the same equation ev
Page 53 and 54: signal can be self-absorbed before
Page 55: enhancement multiplied by the frequ
Page 59 and 60: 1. NIR (785 nm) Raman System This R
Page 61 and 62: The manufacturer's wavelength calib
Page 63 and 64: A. SUMMARY OF RESULTS VII. RESULTS
Page 65 and 66: Figure 11. Calculated molar absorpt
Page 67 and 68: strong. Since most molecules absorb
Page 69 and 70: Figure 15. Raman spectra of PNT; 2,
Page 71 and 72: Figure 17. Raman spectra of RDX usi
Page 73 and 74: 40x10 3 Intensity (A.U.) 30 20 10 0
Page 75 and 76: scattering process, the Raman scatt
Page 77 and 78: Figure 24. Calculated Raman resonan
Page 79 and 80: as the internal standard. For solid
Page 81 and 82: The estimated total Raman enhanceme
Page 83 and 84: VIII. CONCLUSION A method was demon
Page 85 and 86: IX. RECOMMENDATIONS In order to con
Page 87 and 88: A. 785 NM SPECTRA 1. Standards APPE
Page 89 and 90: Figure 31. Raman spectra of 3,4-DNT
Page 91 and 92: Figure 33. Raman spectra of 3,4-DNT
Page 93 and 94: 30x10 3 Intensity (A.U.) 20 10 0 30
Page 95 and 96: APPENDIX B. MATLAB CODE This source
Page 97 and 98: B. PEAK AREA CALCULATIONS BASED ON
Page 99 and 100: LIST OF REFERENCES [1] National Res
Page 101 and 102: Spectra of 1,3,5-trinitro-1,3,5-tri
Page 103 and 104: INITIAL DISTRIBUTION LIST 1. Defens
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