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

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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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#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