Underwater Raman Sensor for Detecting High Explosives and Homemade Explosives (HMEs) Shiv K. Sharma* Hawaii Institute of Geophysics & Planetology, University of Hawaii (UH) at Manoa, Honolulu, Hawaii, USA Collaborators: Bruce Howe Anupam K. Misra John N. Porter Mark Rognstad *sksharma@soest.hawaii.edu Work supported in part by grants from ONR and NASA Presented at the ARL Winter 2016 Meeting, Jan 11, 2016
Introduction The marine environment can be affected by chemicals. Word-wide terroristic threats are also affecting coastal areas. Hydrocarbon benzene, toluene, ethyl benzene and xylenes isomers (BTEX) are present in gasoline (petrol). These BTEX compounds are ubiquitous contaminants in ground and surface waters. Because these compounds are known to be toxic to humans and aquatic life, their detection and identification is of critical importance. In recent years advances in solid state lasers, efficient spectrograph, CCD detectors and holographic optical filters and gratings have made it possible to develop small portable Raman systems which can also be used for measuring laser-induced native fluorescence (LINF). Fitting a Remotely Operated Vehicle (ROV) or glass bottom boat with a miniature telescopic Raman system could provide capability of investigating chemical pollution in deep and shallow waters.
OUTLINE Discuss briefly Raman spectroscopy Time-Resolved standoff Raman systems developed at the University of Hawaii (UH). Results of in situ remote Raman spectra of seawater as a function of depth in Snug Harbor, Oahu with a 203 mm (8-inch) diameter telescopic system. Results of TR Raman measurements of chemicals suspended in the ocean. Describe 76 mm (3-inch) diameter mirror lens (ML) based Raman Sensor has been developed at UH for underwater detection of HEs nd HMEs. Summary
SCATTERING OF LIGHT Virtual levels Raman Scattering involves polarizability of a molecule (induced dipole) the electric field of the molecule oscillates at the frequency of the incident wave (emits E.M. Radiation) if induced dipole is constant, scattering is elastic (Rayleigh-Mie) if induced dipole is not constant, inelastic (Raman) scattering is allowed Lifetime Raman process ~10-13 s In the Raman spectra the information about vibrations of molecules is obtained in visible part of the spectrum as a difference from the energy of the visible laser excitation. Raman spectra is complementary to IR spectra but the selection rules are different. For IR activity requires change in the permanent dipole moment.
Photographs of a Combined Remote Raman & LINF System in Coaxial Geometry Laser: pulsed Nd:YAG 1064 nm, doubled to 532 nm, 20 Hz, 35 mj/pulse Spectrograph: Kaiser HoloSpec commercial spectrograph Telescope: Meade ETX-125 125 mm Maksutov Cassegrain Detector = Princeton Instruments Intensified charge coupled device (ICCD) Sharma,S. K. et al (2002) Appl. Spectrosc., 56, 699-705.
Photograph of 76 mm (3-inch) Diameter Mirror Lens based Remote Raman Sensor IV I = Lens; II = Holographic transmission grating; III = lens; and IV = miniature ICCD detector Spectral resolution 15 cm -1 (0.43 nm) in the 100-2400 cm -1 and 13 cm -1 (0.37) in 2400-4000 cm -1 region; LINF spectral range 533-700 nm Spectrograph wt. = 631 g & ICCD wt. = 620 g (fabricated with aluminum body) dimension 10 cm (length) x 8.2 cm (width) x 5.2 cm (high) Miniaturized Raman-LINF spectrometer developed for Mars exploration is 1/14 in volume as compared to commercial Kaiser Raman spectrometer.
Underwater Raman Sensor
Underwater Raman Sensor computer ICCD Spectrograph Scanner
TR-Remote Raman Spectra of m-xylene at 10 m HoloPlex grating contains two holographic gratings that project spectrum in low- and high-frequency regions on ICCD.
TR-Remote Raman Spectra of 8% TNT at 8 m
TR-Remote Raman Spectra of 4% RDX at 8 m Intensity (Counts x10 4 ) 50 40 30 20 10 RDX 4% in silica glass inside a polystyrene (PS) petridish 334 408 463 PS 552 601 620 667 790 PS 842 883 948 PS 1000 PS 1030 PS 1156 1213 1273 1310 1344 1383 1437 PS 10 pulses 60 acc 1554 O 2 1600 PS 1/60 10 pulses 10 acc 10 pulses 1/10 0 1 pulse 400 600 800 1000 1200 1400 1600 1800 Raman shift cm -1
Remote Raman Spectroscopy of Seawater Detection of HEs and HMEs and Hazardous Chemicals in seawater.
Two Way Light Transmission in water (500-800 nm) 1 0.9 0.8 1 m 2 m 532 nm laser Two Way Transmission 0.7 0.6 0.5 0.4 5 m 10 m O-H 2 Raman band ~3425 cm -1 680 nm LIF Chlorophyall-a 0.3 15 m 0.2 20 m 0.1 25 m 30 m 0 500 550 600 650 700 750 800 Wavelength (nm)
Standoff Raman Testing in the Lab with 532 nm Laser Standoff Raman Sensor Lab Setup * 10 m distance * all lights on * 1 m fish tank with seawater at far end
Remote TR-Raman Spectra of Seawater (2320-4480 cm -1 ) in Snug Harbor, Honolulu, Hawaii D = 219 ns D = 216 ns D = 213 ns
Raman Detection of Ammonium Nitrate (NH 4 NO 3, AN) Through Seawater and 3 Plastic Bags SO 4 532 nm, 50 mj/pulse, 15 Hz, gate width 100 ns, slit 50 µm
Field Testing at Snug Harbor, Hawaii with 532 nm Standoff TR-Raman System
Single Shot Detection of Sulfur at 2 m Seawater Depth with 532 nm Laser * 3 as measured spectra shown 532 nm, 100 mj/pulse, slit 50 µm
Single Shot Detection of AN inside HDPE bottle at 2 m Seawater Depth with 532 nm Laser * 3 as measured spectra shown 532 nm, 100 mj/pulse, slit 50 µm
Single Shot Detection of KClO 4 inside Glass at 2 m Seawater Depth with 532 nm Laser-excited TR Raman system * 3 as measured spectra shown 532 nm, 100 mj/pulse, slit 50 µm
Summary * Described capability of TR- remote Raman systems for detecting Hes and HMEs chemicals * Developed compact time-resolved remote Raman sensor with 3-inch optics * It has range of detection in air to 50 m * Unambiguous detection of various chemicals both organic and inorganics * 2 m detection range for most chemicals in coastal seawater * Daytime/nighttime detection * The Raman Sensor will find applications in many DoD and Homeland Security as well as in marine environmental monitoring
Thank You for Your Attention Diamond Head UH Manoa