Terahertz Spectroscopy and Applications

Frank C. De LuciaDepartment of PhysicsOhio State University

IEEE International Frequency Control SymposiumJune 5 - 7, 2006 Miami, Florida

PEOPLE

Doug Petkie - Professor WSUEric Herbst - Professor OSU

Brenda Winnewisser - Adj. Professor OSUManfred Winnewisser - Adj. Professor OSU

Paul Helminger - Professor USAAtsuko Maeda - Research AssociateIvan Medvedev - Research AssociateAndrei Meshkov - Graduate StudentTJ Ronningen - Graduate Student

Laszlo Sarkozy - Graduate StudentDavid Graff - Graduate StudentCory Casto - Graduate Student

Kerra Fletcher - Graduate StudentBryan Hern - Undergraduate Student

Drew Steigerwald - Undergraduate StudentJohn Hoftiezer - Electrical Engineer

The Lay of the Land

What is the basic physics of the SMM/THz?

How does this impact technology and frequency control?

What physics does it lead us to naturally - What are the important applications?

Where is the excitement?

What is the Physics of the SMM/THz? The Energetics: h ≤ kT

The Classical Size Scale ≤ 1 mm

Noise

Interactions: Gases, Liquids, and Solids

Atmospheric Absorption

Classical Scattering and Penetration

Technology and Frequency Control

Solid-State THz Sources (CW)

0.001

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Frequency (GHz)

Po

wer

(mW

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What are the Field Applications?

Orion. IRAM 30-m telescope line survey

Atmospheric Chemistry

Astrophysics

Where is the New Excitement?

4 0 0

3 0 0

2 0 0

1 0 0

0

- 1 0 0

3 3 3 .1 03 3 3 .0 83 3 3 .0 63 3 3 .0 43 3 3 .0 23 3 3 .0 0x 1 0

3

3 0 0 0

2 0 0 0

1 0 0 0

0

- 1 0 0 0

3 7 0 x 1 03

3 6 03 5 03 4 03 3 0F re q u e n c y ( M H z )

4 0 0

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0

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3 3 3 .1 0 x1 03

3 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

Medical

New Physical RegimesAnalytical Applications

Active and Passive Imaging

Temperature

kT (300 K) = 200 cm-1

kT (1.5 K) = 1 cm-1

kT (0.001 K) = 0.0007 cm-1

Fields

qE (electron) >> 100000 cm-1

mE (1 D) ~ 1 cm-1

mB (electronic) ~ 1 cm-1

mB (nuclear) ~ 0.001 cm-1

The THz has defined itself broadly and spans kT

The Physics - The EnergeticsAtoms and Molecules

E (electronic) ~ 50000 cm-1

E (vibrational) ~ 1000 cm-1

E (rotational) ~ 10 cm-1

E (fine structure) ~ 0.01 cm-1

Radiation

UV/Vis > 3000 cm-1

IR 300 - 3000 cm-1

FIR 30 - 300 cm-1

THz 3 - 300 cm-1

MW 1 - 10 cm-1

RF < 1 cm-1

The ‘Gap’ in the Electromagnetic Spectrum

Solid-State THz Sources (CW)

0.001

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0.1

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10

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1000

10000

10 100 1,000 10,000 100,000

Frequency (GHz)

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[From Tom Crowe UVA/VDI]

Size

h/kT

Cooling

Tubes, a little more - Photomixers, a little less

PN ~ kT (Bmax )1

2 ~ kTmax

B

max

12

Blackbody Brightness [W/cm2-Hz]

Thermal Noise and Power in the THz

From E. Brown

Number of modes/cm2 ~ 1/(cm)

Blackbody Noise/mode

Thermal Noise below cutoff frequency max in integration bandwidth B

Thermal noise in bandwidth b with integration bandwidth B

PN kTb

PN kT (bB)1/2

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

1 mW/MHz -> 1014 K

1mW/100 Hz -> 1018 K

“Noise, detectors, and submillimeter-terahertz system performance in nonambient environments”

Frank C. De Lucia

J. Opt. Soc. B, 1275 (2004)

What is the Physics of Interactions?

Separate into Three Classes by Linewidth

Low pressure gases: Q ~ 106

Atmospheric pressure gases: Q ~ 102

Solids and Liquids: Q ~ 1 - 100

(are there useful signatures?)

(are these classical or QM?)

GHzCBA 25 Jmax 18

GHzCBA 10 Jmax 30

GHzCBA 3 Jmax 55

GHzCBA 1 Jmax 96

GHzCBA 1.0 Jmax 305

inertia of moment

1~constant Rotational

Spectra as a Function of Molecular Size

Population of levels

Atmospheric Propagation

Collisional Cooling: An Approach to Gas Phase Studies at Low Temperature

Atom Envy - Molecule Envy

Quantum Collisions

300 K 1 K_____________________

L ~ 30J ~ 10

L ~ 2J 1

Correspondence Principle

The predictions of the quantum theory for the behavior of any physical system must correspond to the prediction of classical physics in the limit in which the quantum numbers specifying the state of the system become very large.

hr ~ kT ~ Vwell

Typical Spectra - HCN

Sources and Metrology for the THzSynthesized Frequency Multiplication

Jumping the THz via Frequency SynthesisSpectroscopy via Photomixing

Fre

qu

ency

Ref

eren

ce

Sp

ectr

osc

op

ic M

easu

rem

ent

“Speed of Light from Direct Frequency and Wavelength Measurements of the Methane-Stabilized Laser,”

K. M. Evenson, J. S. Wells, F. R. Petersen, B. L. Danielson, G. W. Lay, R. L. Barger, and J. L. Hall,

Phys. Rev. Lett. 29, 1346-1349 (1972).

VCO FrequencyReference10.5 GHz

Mixer

X8 MultiplierW-band

W-band Amplifier75-110 GHz

X3 MultiplierW-band

AmplifierLow Pass Filter10kHz – 1MHz

Harmonic10 MHz Comb

GeneratorAmplifierMixer

Gas Cell Detector

Computer DAQ

FrequencyStandard

x24

The Multiplied FASSST Spectrometer

105 resolution elements/sec

The Fundamental FASSST Spectrometer

“Frequency and phase-lock control of a 3 THz quantum cascade laser.”

A. L. Betz, R. T. Boreiko, B. S. Williams, S. Kumar, Q. Hu, J. L. Reno.

Opt Lett. 30, 1837-9 (2005).

Frequency Control and Reference in the THz

“A Tunable Cavity-Locked Diode Laser Source for Terahertz Photomixing,”

S. Matsuura, P. Chen, G. A. Blake, J. C. Pearson, and H. M. Pickett,

IEEE Trans. Microwave Theory and Tech. 48, 380 (2000).

Frequency Synthesis via Femtosecond Demodulation

“Microwave generation from picosecond demodulation sources”

F. C. De Lucia, B. D. Guenther, and T. Anderson

Appl. Phys. Lett. 47, 894 (1985)

I(f)

f “Spectral Purity and Sources of Noise in Femtosecond-Demodulation Terahertz Sources Drive by Ti:Sapphire Mode-Locked Lasers”

J. R. Demers, T. M. Goyette, Kyle B. Ferrio, H. O. Everitt, B. D. Guenther, and F. C. De Lucia

IEEE J. Quant. Electron. 37, (2004).

“Optical frequency synthesis based on mode-locked lasers”

S. T. Cundiff, J. Ye, and J. L. Hall

Rev. Sci. Instrum. 72, 3749 (2001)

THz Synthesis from the Optical Comb

As with Evenson, THz mixer bandwidth and efficiency highly desirable

Atmospheric Remote Sensing

JPL - Microwave Limb Sounder

Ozone Destruction

Cycle

Microwave Limb Sounder

Image courtesy of NRAO/AUI and Computer graphics by ESO

“Generation and Distribution of the mm-wave Reference Signal for ALMA”M. Musha, Y. Sato, K. Nakagawa, K. Ueda, A. Ueda, and M. IshiguroNMIJ-BIPM Workshop, Tsukuba 2004

Orion. IRAM 30-m telescope line survey

“Whispered Excitement about the THz”

Graham Jordan Opening Plenary Presentation SPIE Symposium: Optics/Photonics in Security and Defense Bruges, Belgium, 26 September, 2005

‘New’ Applications - Holy Grails

How do we Move Beyond

to

A Field with many ‘Public’ Applications?

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

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

How do you look at THz images?

What is so favorable about the SMM/THz?What are the Opportunities?

The SMM/THz combines penetrability with -a reasonable diffraction limit -a spectroscopic capability -low pressure gases have strong, redundant, unique signatures

-solids can have low lying vibrational modes, especially at high THz frequencies

Rotational transition strengths peak in the SMM/THz

The SMM/THz is very quiet: 1 mW/MHz => 1014 K

The commercial wireless market will provide us with a cheap technology

It should be possible to engineer small (because of the short wavelength), high spectral purity (because we can derive via multiplication from rf reference) and low power (because the background is quiet/the quanta is small) devices and systems

What is so Challenging about the SMM/THz?

Efficient generation of significant tunable, spectrally pure power levels

Practical broadband frequency control and measurement

The need to develop systems without knowledge of the phenomenology

Impact of the atmosphere