terahertz signature science: the second gap in the electromagnetic spectrum frank c. de lucia
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Penetration. Resolution. Spectroscopic Identification. Terahertz Signature Science: The Second Gap in the Electromagnetic Spectrum Frank C. De Lucia Department of Physics Ohio State University International Symposium on Spectral Sensing Research Bar Harbor, Maine June 1, 2006. - PowerPoint PPT PresentationTRANSCRIPT
Terahertz Signature Science:
The Second Gap in the
Electromagnetic Spectrum
Frank C. De Lucia
Department of Physics
Ohio State University
International Symposium on Spectral Sensing Research
Bar Harbor, Maine
June 1, 2006
The New York Times - July 11, 2005High-Tech Antiterror Tools: A Costly,
Long-Range Goal
Millimeter wave machines . . .use trace amounts of heat released by objects . . .to create images that can identify hidden bombs . . . from about 30 feet away.
Terahertz radiation devices can create images of concealed objects as well as identify the elemental components of a hidden item.
The terahertz devices may be more promising since they could sound an alarm if someone entering a subway or train station had traces of elements used in bombs on them.
Resolution
Spectroscopic Identification
Penetration
CONCEPTS ARE NICE
BUT THE NUMBERS MATTER
The Beginning Theses:
No ‘Public’ THz application has yet come to fruition - Why?
What do we need to do to remedy this?
1. We need ‘End-to-End’ systems analyses for the most widely discussed applications.
2. We need to consider appropriate figures of merit for the several technical approaches and choose the technology best suited for the application.
3. Often a lot more is known about the signatures and phenomenology than we consider as we propose applications.
(this leads to proposed applications which threaten our credibility)
4. But in other cases the phenomenology and signature science is only poorly know.
(this leads to missed opportunities)
From Mark Rosker
Two SMM/THz Legacy ‘Public’ Applications -- Clear, but Challenging Paths to Success --
IMAGING ANALYTICAL CHEMISTRY
Technical and Scientific R & D Impact The Breadth of Applicability
Why is there a ‘Clear Path’ to Imaging?Many special purpose imagers have been built over the last 40+ years
Detectors
- scientifically we understand
- in single element receivers we can approach well understood fundamental limits
Transmit power
- acceptable solid state sources for some applications exist
Propagation
-overall absorption generally known
-impact of fluctuations noise less clear
Recognition/targets/clutter
-preliminary studies completed
-nature of active images complex, but large contrast in images provides opportunities
-TIFT can start to do realistic end to end calculations
Where can we get to on sensitivity-speed-size-cost tradeoff?
Quantitatively, what are the target signatures, clutter, and phenomenology for scenarios of interest?
These are not show stoppers, but the answers will determine the Breath of Application
Why is there a ‘Clear Path’ to Analytical Chemistry?
A well understood spectroscopic foundation is in place
False alarm rates in complex environments have been studied and can be shown to be low because
of the number of resolution elements and ‘complex redundancy’ of molecular fingerprints
Background clutter/interference at trace levels have been studied and can be shown to be low
What we need to know/develop
Trade-offs among size, cost, sensitivity, power consumption
Speed of cost reduction from mass wireless market?
Development of a signature science for larger molecules
These are not show stoppers, but the answers will determine the Breath of Application
Quantitative end-to-end
designs
Parallel and On Going MM/SMM Science[Field Technology and Systems Grew out of Lab Science]
NASA JPL catalog
HITRAN, KOLN, GEISA data bases
Ongoing Data Base Development ALMA - Denmark
HITRAN
NASA
The GEISA/IASI spectroscopic database
Applications Matrix
as introduction to
Signature Science
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical) XMutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XClassical imaging XPoint gas detection
absolute specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XRemote gas detection
modest specificity X specificity in mixtures at 1km X
See through walls ~100 GHz >1 THz
Buried land mines> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
Cost? Size? Speed?
Breadth of Application?
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical) XMutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XClassical imaging XPoint gas detection
absolute specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XRemote gas detection
modest specificity XSee through walls ~100 GHz >1
THzBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
Legacy Applications
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical)Mutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificityClassical imaging XRemote gas detection X
modest specificityAstrophysics (>$2x109) XAtmospheric (>$n x 108) XSee through walls ~100 GHz >1
THzPoint gas detection
absolute specificity XBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method to be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical) XMutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XClassical imaging XRemote gas detection
modest specificity XPoint gas detection
absolute specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XSee through walls ~100 GHz >1
THzBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
“it could be used to scan for diseases, such as cancer, the cells of which have a vibrant terahertz signature.”“New-wave body imaging -
medical imaging using Terahertz radiation”
e20 attenuation in 1 mm
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical)Mutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XClassical imaging T&SRemote gas detection
modest specificity T&SSee through walls ~100 GHz >1
THzPoint gas detection
absolute specificity XBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill X
Explosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
“A camera that can see through clothes, skin and even walls without X-rays has been developed in what is being called one of the first great technological breakthroughs of the 21st century”
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical)Mutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XClassical imaging T&SRemote gas detection
modest specificity T&SSee through walls ~100 GHz >1
THzPoint gas detection
absolute specificity XBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
“Since cancerous tissue tends to have a higher water content than healthy tissue, terahertz radiation could be used to differentiate between the two.”
?
A Good Challenge
Signatures: Explosives Spectra
Clearly spurious results in both gas and
solids have been reported
The solid line shows the reflectivity of the meat part normalized of the reflectivity of the fat part of Black Forrest ham averaged on three points each.
From THz-Bridge
Are any of us willing to say that we are sure that the sharp lines are spurious?
Clutter and Noise
in the SMM/THz
The THz is VERY Quiet even for CW Systems in Harsh Environments
QuickTime™ and a Photo - JPEG decompressor are needed to see this picture.
Experiment: SiO vapor at ~1700 K
All noise from 1.6 K detector system
Good News - CW systems are ~1010
better than has been widely claimed
Signature, with perfect atmo model
Impact of Atmospheric Transmission on
Spectral Fingerprints - What’s a THz?
Signatures vs Pictures:Humans at 650 GHz
Active Image
Skin is close to specular - Hair really lights up
At least 40 db of dynamic range across this target
A high contrast target signature is very good for recognition if you have system sensitivity to observe Thermal Image: T/T = 0.1
Clutter Limits in Imaging
Temporal and Spatial Scales
When do we reach clutter limits as a function of frequency?
Systems: Remote Spectroscopic SensingGas Phase Example: 100 m, 1 ppm plume => 10-2 absorption fraction, with 10 GHz linewidth
sharp lines: 10-7 detectable (noise limits), 105 resolution elements
broad lines: 10-1 detectable (clutter limits), <102 resolution elements
Solids:
What is the concentration and absorption fraction (in reflection)?
What is the signature, the linewidths, the clutter?
Are their equivalent double resonance schemes for solids?
3-D Specificity Matrix
What are the Characteristics of Compact THz Technologies?
1. CW multiplied or fundamental oscillators
2. THz-TDS
3. FTFIR
How do these Relate to Signatures?
Quantifiable Figures of Merit
Spectroscopic Sensor Figures of Merit - ISensitivity - ‘Dynamic Range’ is widely abused
1. Only source power in the signature bandwidth (Brightness - W/Hz) is useful
- the rest often causes additional noise (a fundamental limit for FTFIR)
2. Detectors-NEP (W/Hz1/2) vs NEP’(W/Hz)
3. Noise and Dynamic Range Example: - 1 mW in a 100 Hz bandwidth, 3000K noise temperature =>dynamic range of >140 db
This is good for the imager because the bandwidth of the reciever can be matched to the source and frame rate of the imager
But people who build spectrometers never discuss dynamic range because the detection of a small amount of power in a narrow bandwidth is fundamentally different than the detection of a small change in a large amount of power.
- in ideal noise limited spectrometer, the minimum detectable absorption is only - 90 dbA 50 db Difference
Spectroscopic Sensor Figures of Merit - II
Specificity
1. Scenario Clutter must be understood - spectroscopic clutter is much more complex than radar clutter.
2. ‘A’ vs ‘B’ demonstrations relate to a relatively small fraction of the scenarios of interest
3. Calculation of scenario dependant PFA or ROC is useful
4 0 0
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3 6 03 5 03 4 03 3 0F re q u e n c y ( M H z )
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3 3 3 .1 0 x1 033 3 3 .0 83 3 3 .0 63 3 3 .0 43 3 3 .0 23 3 3 .0 0Frequency (MHz)
#09 Acrylontrile Library
Combined Spectrum
“Whispered Excitement about the THz”
Graham Jordan Opening Plenary Presentation SPIE Symposium: Optics/Photonics in Security and Defense Bruges, Belgium, 26 September, 2005
How do we Move Beyond
to
A Field with many ‘Public’ Applications?
What Needs to be Done to Enable the SMM/THz Spectral Region?
1. Classical penetrability, scatter, and specular reflection as a function of frequency and material.
2. What is the origin of linewidths in solids?
3. What are the signatures of solids and large molecules in the gas phase? Distribution in frequency relative to penetration?
4. What are the signatures of clutter for scenarios of interest?
5. Develop schemes for using time domain or other ‘X’ factors?
6. A closer connection between the technology community and the applications and science community.
A litmus test: A reproducible, well founded signature science catalogue