Applications of THz Radiation APS March Meeting, March 23, 2005 Homeland Security, Medical, Pharmaceutical and Non-destructive Testing Applications of Terahertz Radiation Colin Baker colin.baker@teraview.com mike.kemp@teraview.com
Overview Introduction to terahertz Techniques imaging and spectroscopy Applications of terahertz light Medical Non-destructive testing Pharmaceutical Security Conclusions
TeraView The Terahertz Company Founded April 2001 Cambridge, England Exclusive focus on terahertz technology and applications 30+ staff Close relationship with Cavendish Laboratory, Cambridge University Developed world s first portable terahertz imager & spectrometer Focus markets medical imaging, pharmaceuticals, security screening, non-destructive testing
TeraView s TPI range
What is Terahertz? X Ray Visible Terahertz gap Infrared Millimetre Ultraviolet Microwave and Radio 10 19 Hz 10 18 Hz 10 17 Hz 10 16 Hz 10 15 Hz 10 14 Hz 10 13 Hz 10 12 Hz 10 11 Hz 10 10 Hz Terahertz region 300 GHz 10 THz (1 mm 30 micron) Until recently inaccessible due to lack of sources and detectors Key properties: Penetrates clothing, leather, paper, plastics, packing materials Materials identification using characteristic Terahertz spectra 3-D imaging capability Non-ionizing - no damage to body or cells
Photoconductive THz generation V bias GaAs device 90 fs NIR laser pulse Emitted THz pulse
Photoconductive THz detection I GaAs device 90 fs NIR laser pulse THz pulse
Basics of THz Pulsed Imaging TPI provides for time of flight analysis, as well as producing spectral information. A proportion of the incident pulse will be reflected back whenever there is a change in the refractive index. Reconstruction of the multiple detected pulses permits depth profiling. X-Y raster scanning builds a 3D image.
Non-Destructive Testing 3-D Terahertz Imaging of integrated circuit package visible images Terahertz images seeing inside the chip top surface 1mm deep 2 mm deep
Medical Imaging Patient 9 (TPP 285) Applications Skin cancer imaging basal cell carcinoma Surgeon s aid tissue typing Endoscopy prostrate & other cancers Status y (mm) 0 0.20 0.40 0.60 0.80 Results very promising TPI Scan imager in use for clinical research Probe based systems under development x (mm) 1.00
Skin Cancer In vivo surface and depth information
Pharmaceuticals 5 Applications absorption 4 3 2 Crystalline form 1 1.6THz 1.3THz 1THz 1.8THz absorption 4 3 2 Crystalline form 2 1.2THz Process improvement Polymorph screening Tablet inspection Status Reflection imaging system Partnership with Bruker Range of products available including reflection and transmission spectrometers 1 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 frequency / THz 1 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 frequency / THz
TPI spectra 1000
10000 FFT frequency / THz 10 8 0.8 1.5 2.3 3.0 3.8 4.5 THz electric field / arb. units 8000 6000 4000 2000 0 reference sample signal / arb. units 10 7 10 6 10 5 10 4 10 3 10 2 10 1 crystalline phonon bands reference sample water vapour lines -2000 0 5 10 15 20 25 30 35 optical delay / ps 10 0 25 50 75 100 125 150 wavenumber / cm -1 Terahertz Pulse Profile
Form I Form II Form III Form IV Form V Absorbance (decadic) 7 6 5 4 3 2 1 Frequency/THz 0.6 1.2 1.8 2.4 400mg, 13mm diameter tablet 20% sulphathiazole in PE 0 20 40 60 80 Wavenumber/cm -1 Samples provided by Terry Threlfall, U. of Southampton
Using terahertz pulsed imaging as a tool to investigate coating integrities single incident THz pulse multiple return pulses Reflected THz pulses probe coating structure coated tablet
Non-destructive mapping of coating thickness in pharmaceutical tablets Terahertz pulses reflect from each coating layer Time of flight and scanning over surface allows mapping of coating layers
Security z z z z z Checkpoint people screening for hidden weapons & explosives Stand-off detection of explosives Baggage screening for explosives Screening for biological & chemical agents white powder detection
Terahertz & Security: Key Issues Signatures Do threat materials have characteristic signatures? Are they distinct from confusion materials? Barriers Will terahertz penetrate clothing and other barriers? Reflection Can signatures be detected in reflection? Distance Can we see (at least) 10 metres? Source power/ detector sensitivity Atmospheric absorption Systems Can we design practical systems? What sources and architectures should we use?
Terahertz spectra of explosives Absorption (offset for clarity) Semtex PE4 RDX PETN HMX TNT Terahertz transmission spectra Energetic compounds and explosives All show characteristic features at terahertz frequencies Note: Most features above 0.5 THz Barrier material absorption limits practical range to 3THz 0 1 2 3 4 Frequency (THz) Kemp et. al., Proc SPIE 5070, 44 (2003)
Semtex-H reference measurements Absorption and reflection spectra of Semtex calculated from measurements in transmission spectrometer 0.12 0.10 Reflectance Absorption 60 50 Reflectance 0.08 0.06 0.04 0.02 0.00 40 30 20 10 0 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Frequency/THz Absorption/cm -1 TeraView data November 2004
Measurements of potential confusion materials Absorbance (decadic) TeraView has measured a library of terahertz spectra of common materials - developed with support of UK Department of Trade & Industry Also includes many pharmaceutical compounds No significant confusion found between explosives and harmless materials 5 4 3 2 1 co-codamol (+3.0) milk chocolate 0 0 1 2 3 4 Frequency (THz) Absorbance (decadic) 4 3 2 1 Cocoa Washing Powder Aspirin Milk Chocolate Flour Ibuprofen Blusher Paracetamol Soap Sugar Vitamins 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Tribe et. al., Proc SPIE 5354, 168 (2004) Frequency/THz
Clothing & Barrier Materials Absorbance (decadic) 4 3 2 1 Cotton Silk Wool Leather Nylon Polyester Polyester/cotton All clothing materials are partially transparent Absorption increases with frequency Limits useful frequency range to 2-3 THz 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Frequency/THz Tribe et. al., Proc SPIE 5354, 168 (2004)
Detecting metals, non-metals and explosives hidden in clothing terahertz beam wool 2 layers cotton 4 layers hidden object subject s arm
Detecting metals, non-metals and explosives hidden in clothing image metal scalpel blade ceramic plastic sheet explosive depth profile Terahertz images of objects (approx 1cm across) hidden under 2 layers of wool and 4 layers of shirt material Kemp et al. Proc SPIE 5070, 2003
TeraView data March 2003 Terahertz detection of sheet explosive underneath clothing Image of 1cm square piece of SX2 sheet explosive against skin, hidden under two layers of woollen jumper and four layers of cotton shirt material
Ongoing development programmes Objective: move from proof-of-principle to prototype and then to fieldable system Two projects: People Screening Hand Wand Stand-off Explosives Detection
People Screening Wand Terahertz wand to detect metal & non-metallic weapons and explosives Marketing partnership with Smiths Detection Initial prototype under construction Detection techniques and algorithms being developed Smiths Detection
Terahertz reflection spectrum from Hand Wand raw data TeraView data January 2005
Stand-off Explosives Detection Stand-off Explosives Detection Programme funded by UK Home Office PSDB, with US participation Laboratory prototypes under construction Initial target 1m Source & detector development to achieve larger stand-off distances Development of detection techniques and algorithms
Experimental system Femtosecond pulsed laser Beamsplitter Delay stage Target Detector Emitter
Experimental System in Operation Response of stand-off THz system Target 1m Path Length over 2m Power 10 0 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 0 1 2 3 4 Frequency/THz
Water windows correspond to spectral features of explosives Semtex RDX Water absorption 0 1 2 3 Frequency (THz)
Semtex-H Stand-off spectrum at 1 metre THz spectrum of Semtex-H (composed of RDX and PETN) measured data at stand off distance of 1 m System purged with nitrogen gas to remove water vapour. Data collected in 70 ms, with a spectral range of 0.3 2 THz 0.08 Reflectance 0.06 0.04 Semtex-H System Purged Semtex-H Calculated 0.02 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Frequency/THz TeraView data November 2004
Semtex-H spectrum with water vapour THz spectrum of Semtex-H measured data at stand off distance of 1m in atmospheric air Note effect of water vapour absorption lines 0.08 Reflectance 0.06 0.04 0.02 Semtex-H at 1m (no purging) Semtex-H Calculated 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Frequency/THz TeraView data November 2004
Semtex-H spectrum corrected for water vapour effects Reflection spectrum at stand off distance of 1m, data collected in 70ms Water vapour absorption lines removed by data processing algorithm. 0.08 Reflectance 0.06 0.04 0.02 Semtex-H at 1m (no purging), after data processing Calculated 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Frequency/THz TeraView data November 2004
Semtex and SX-2 spectra Spectra of two different RDX based explosives showing same distinctive features Data collected at 1m stand-off through normal atmosphere with 70ms integration time water vapour lines removed Reflectance 0.08 SX-2 Semtex-H Calculated Semtex-H 0.06 0.04 0.02 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Frequency/THz TeraView data November 2004
Conclusion Terahertz is very promising technology for many applications Reflectance 0.08 0.06 0.04 Semtex-H at 1m (no purging), after data processing Calculated 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Frequency/THz Proof-of-principle confirmed with measurements and data Technology now moving forward to commercialisation
Acknowledgements Dr Bill Tribe Dr Tom Lo Dr Mike Kemp Dr Philip Taday Michael Withers Michael Evans Dr Bryan Cole Dr Ian Bradley Dr Simon Chandler