Shiv K. Sharma*Hawaii Institute of Geophysics & Planetology,

University of Hawaii (UH) at Manoa, Honolulu, Hawaii, USA

*sksharma@soest.hawaii.edu

Underwater Raman Sensor for Detecting High Explosives and Homemade Explosives (HMEs)

Presented at the ARL Winter 2016 Meeting, Jan 11, 2016

Work supported in part by grants from ONR and NASA

Collaborators:Bruce HoweAnupam K. Misra John N. PorterMark Rognstad

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

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.

SCATTERING OF LIGHT

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

Virtual levels

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/pulseSpectrograph: Kaiser HoloSpec commercial spectrographTelescope: Meade ETX-125 125 mm Maksutov CassegrainDetector = 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

Miniaturized Raman-LINF spectrometer developed for Mars exploration is 1/14 in volume as compared to commercial Kaiser Raman spectrometer.

IVIV

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 nmSpectrograph 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)

Underwater Raman Sensor

Underwater Raman Sensor

Scanner

computer Spectrograph

ICCD

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

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RDX 4% in silica glass inside a polystyrene (PS) petridish

TR-Remote Raman Spectra of 4% RDX at 8 m

Remote Raman Spectroscopy of Seawater

Detection of HEs and HMEs and Hazardous Chemicals in seawater.

500 550 600 650 700 750 8000

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532 nm laser

O-H2 Raman band~3425 cm-1

680 nm LIF Chlorophyall-a

Wavelength (nm)

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Two Way Light Transmission in water (500-800 nm)

Standoff Raman Sensor Lab Setup* 10 m distance* all lights on* 1 m fish tank with seawater at far end

Standoff Raman Testing in the Lab with 532 nm Laser

Remote TR-Raman Spectra of Seawater (2320-4480 cm-1) inSnug Harbor, Honolulu, Hawaii

D = 219 ns

D = 216 ns

D = 213 ns

Raman Detection of Ammonium Nitrate (NH4NO3, AN)Through Seawater and 3 Plastic Bags

532 nm, 50 mJ/pulse, 15 Hz, gate width 100 ns, slit 50 µm

SO4

Field Testing at Snug Harbor, Hawaiiwith 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 bottleat 2 m Seawater Depth with 532 nm Laser

* 3 as measured spectra shown532 nm, 100 mJ/pulse, slit 50 µm

* 3 as measured spectra shown

Single Shot Detection of KClO4 inside Glass at 2 m Seawater Depthwith 532 nm Laser-excited TR Raman system

532 nm, 100 mJ/pulse, slit 50 µm

* 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

Summary

UH Manoa

Diamond Head

Thank You for Your Attention