TERAHERTZ IMAGING and DETECTION OF SUICIDE BOMBERS*

1. TERAHERTZ IMAGING and DETECTION OF SUICIDE BOMBERS* J. F. Federici, D. Gary, B. Schulkin, F. Huang, H. AltanDepartment of Physics R. Barat Department of Chemical Engineering K. Walsh Picatinny Arsenal Federici@adm.njit.edu http://physics.njit.edu/~federici *Funded by US Army and NSF

2. Outline • THz Basics • Basics of Interferometric Imaging • Spectral Information • Spatial information • Simulated Images • cm resolution at 100m distances • Spectral Resolution of Explosives and Metals • Analysis of Images • Current and Future Work

3. What is Terahertz (THz)? Visible Radio Microwave T-rays Infrared UV X-rays 108 109 1010 1011 1012 1013 1014 1015 1016 1017 Frequency (Hz) 1 THz frequency = 300 m wavelength or 33 cm-1 or 4.1 meV or T = 48 K Also known as Far-Infrared or sub-millimeter

4. THz at NJIT • 1997-2001 Developed various THz sources, detectors, and imaging techniques • Two PhD students graduated, 9+ publications in THz technology • 2000-2001 Developed concept for Detection of explosives, chemical and biological weapons using new THz imaging methodology. • Spring 2001 - Proposal for cargo screening submitted to FAA • Post 9/11 - National Science Foundation and US Army Funding • 8 publications since 2002, 2 patents pending

5. Wide Area Surveillance • NJIT Team is developing THz imaging techniques for Stand-Off Detection of concealed Explosives, Chemical/Biological Agents • Development of Technique/ Hardware for Imaging • Development of Image Analysis

6. Comparison with Other Techniques • X-Ray, Neutron Scattering - Uses high energy radiation • damages biological systems - eg. damages DNA/ tissues • permissible exposure limited - more difficult for use on people. • THz - low energy radiation - “non-ionizing” • no damage to biological tissue • differentiation of target compounds based on THz “color” • Imaging and “color” information combination will reduce false alarm rate.

7. Metals are opaque to THz will reflect the THz THz strongly absorbed by water will not detect explosives inside the body THz scanners will likely be used in conjunction with other detection techniques. Not a forensic technique - looking for 1cm2 size blocks of material Disadvantages of THz for Scanning for Explosives / BioAgents

8. Application of High-Resolution X-Ray Raman Scattering to Homeland SecurityT. A. Tyson, Q. Qian (NJIT), Z. Zhong, C.-C. Kao and W. Caliebe (NSLS) X-ray absorption spectroscopy of is one method that can be used to identify chemical systems by threshold spectra. The resonance features in x-ray absorption spectra are uniquely related with the molecular structure enabling rapid chemical identification. Utilizing 100 KeV x-rays with high penetration power and a transmission x-ray analyzer system based on a working design (left), we will develop a system for detecting explosives and chemical weapons by fingerprinting their spectra. The upper and lower left panels show the full spectrometer and blow up of the analyzer array, respectively. Each of the nine x-ray focusing mirrors can be independently aligned with micro radian precision in the horizontal and vertical planes. The lower left panel show the carbon K-edge spectrum of graphite measured in energy loss mode (x-ray Raman spectrum) with a resolution of ~ 0.5 eV. Tyson@adm.njit.edu

9. THz transmits through most non-metallic materials: plastic, paper , clothing THz yields transmission / reflection spectra of targets* Advantages of THz for Scanning for Explosives / Bio and Chemical Agents Explosives Kemp (2003) Transmissive Bas.Sub. Spectra Woolard et al (2003) * See papers from Proc. SPIE5070, (2003)

10. Interferometric Imaging - Motivation • A THz digital camera would be ideal for THz imaging: • However • consumer digital cameras  imaging arrays of 1024 by 768 pixels or 780,000 individual detector elements in the array. • That high density of detectors in THz range not technologically possible. • Therefore • To image in the THz, one must generate images using only a few to a few hundred detector elements. • Possible Solution: Interferometric imaging

11. Sample Array Geometry Detector Distance to Origin: Exponential Distances Ensure Non-redundant Spacing of Detector Pairs 66 detector pair combinations Rotation of 90o with data acquired every 1o: 66*90 = 5940 points in u-v plane

12. Estimated Angular Resolution Field-of-View determined by either Field-of-View of individual Detectors or Bandwidth of Detectors. Angular (Spatial) Resolution determined by spacing between Detector Pairs. A 1m baseline array has a spatial resolution of 3cm at 100m! Scaling down to cargo unit or hand-held  size of smoke detector!

13. Simulation of THz Imaging Array RDX Detection of RDX and Metal at a distance of 30m Metal Objects 1.5cm in size Composite Image combination of THz images taken at 5 different frequencies  Spectral and Spatial Images Objects with spectral content of RDX colored Red Objects reflecting all THz radiation colored white Sidelobes

14. Focusing of Image Focal Length Object ImagingArray Single frequency, uncleaned image

15. Image Analysis - Neural Networks THz Image at 1 frequency Neural Network Analysis BLUE = metal coin PINK = bioagent GREEN = flour ORANGE = starch

16. Development of Benchtop model underway to demonstrate key technological components Detect C4 versus peanut butter hidden in clothing. Scale up to imaging system for suicide bombers (system size about 1m) Scale to hand-held/ cargo container unit (10cm size, battery operated unit) Present and Future Work