Terahertz Spectroscopy and Applications
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Terahertz Spectroscopy and Applications Frank C. De Lucia Department of Physics Ohio State University IEEE International Frequency Control Symposium June 5 - 7, 2006 Miami, Florida. PEOPLE Doug Petkie - Professor WSU Eric Herbst - Professor OSU Brenda Winnewisser - Adj. Professor OSU

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Terahertz Spectroscopy and Applications Frank C. De Lucia Department of Physics

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Terahertz Spectroscopy and Applications

Frank C. De Lucia

Department of Physics

Ohio State University

IEEE International Frequency Control Symposium

June 5 - 7, 2006

Miami, Florida


PEOPLE

Doug Petkie - Professor WSU

Eric Herbst - Professor OSU

Brenda Winnewisser - Adj. Professor OSU

Manfred Winnewisser - Adj. Professor OSU

Paul Helminger - Professor USA

Atsuko Maeda - Research Associate

Ivan Medvedev - Research Associate

Andrei Meshkov - Graduate Student

TJ Ronningen - Graduate Student

Laszlo Sarkozy - Graduate Student

David Graff - Graduate Student

Cory Casto - Graduate Student

Kerra Fletcher - Graduate Student

Bryan Hern - Undergraduate Student

Drew Steigerwald - Undergraduate Student

John 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: hn ≤ kT

The Classical Size Scale ≤ 1 mm

Noise

Interactions: Gases, Liquids, and Solids

Atmospheric Absorption

Classical Scattering and Penetration


Technology and Frequency Control


What are the Field Applications?

Atmospheric Chemistry

Astrophysics

Orion. IRAM 30-m telescope line survey


Where is the New Excitement?

New Physical Regimes

Analytical Applications

Medical

Active and Passive Imaging


The Physics - The Energetics

Atoms 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

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


[From Tom Crowe UVA/VDI]

The ‘Gap’ in the Electromagnetic Spectrum

Tubes, a little more - Photomixers, a little less

hn/kT

Size

Cooling


Thermal Noise and Power in the THz

Blackbody Brightness

[W/cm2-Hz]

Blackbody Noise/mode

Thermal Noise below cutofffrequencynmax in integration bandwidth B

Thermal noise in bandwidth b with integration bandwidth B

From E. Brown

Number of modes/cm2 ~ 1/l2(cm)


The THz is VERY Quiet even for CW Systems in Harsh Environments

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?)


Spectra as a Function of Molecular Size

Population of levels

Jmax 18

Jmax 30

Jmax 55

Jmax 96

Jmax 305


Atmospheric Propagation


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

Atom Envy - Molecule Envy


Quantum Collisions

300 K 1 K

_____________________

hnr ~ kT ~ Vwell

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.


Typical Spectra - HCN


Sources and Metrology for the THzSynthesized Frequency Multiplication


Jumping the THz via Frequency Synthesis

Spectroscopy via Photomixing

“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).

Frequency Reference

Spectroscopic Measurement


The Multiplied FASSST Spectrometer

VCO

Frequency

Reference

10.5 GHz

Frequency

Standard

Mixer

X8 Multiplier

W-band

Harmonic

10 MHz Comb

Generator

Amplifier

Mixer

W-band Amplifier

75-110 GHz

Amplifier

Low Pass Filter

10kHz – 1MHz

x24

X3 Multiplier

W-band

Computer DAQ

Gas Cell

Detector

105 resolution elements/sec


The Fundamental FASSST Spectrometer


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 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).


I(f)

f

Frequency Synthesis via Femtosecond Demodulation

“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).

“Microwave generation from picosecond demodulation sources”

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

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


THz Synthesis from the Optical Comb

As with Evenson, THz mixer bandwidth and efficiency highly desirable

“Optical frequency synthesis based on mode-locked lasers”

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

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


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. Ishiguro

NMIJ-BIPM Workshop, Tsukuba 2004


Orion. IRAM 30-m telescope line survey


‘New’ Applications - Holy Grails

How do we Move Beyond

“Whispered Excitement

about the THz”

Graham Jordan

Opening Plenary Presentation

SPIE Symposium: Optics/Photonics in Security and Defense

Bruges, Belgium, 26 September, 2005

to

A Field with many ‘Public’ Applications?


Penetration

Resolution

Spectroscopic Identification

The New York Times - July 11, 2005

High-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.


Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP

($spent or $potential) best methodTo be demo

Cancer/deep(spectra)X

Cancer/surface(spectra)X

T-Ray (deep medical)X

Mutation(spectra)X

Broadband communications ~100 GHz>1 THz

Explosives

remote with specificityX

Classical imagingX

Point gas detection

absolute specificityX

Astrophysics (>$2x109)X

Atmospheric (>$n x 108)X

Remote gas detection

modest specificityX

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)X

Incapacitate and killX

Explosives/other solids

close, sm obstruct, mixturesX

Explosives

close, sort, sm obstructsome materials

Pharmaceuticals, bio

close, sort, sm obstruct some materials


Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP

($spent or $potential) best methodTo be demo

Cancer/deep(spectra)X

Cancer/surface(spectra)X

T-Ray (deep medical)X

Mutation(spectra)X

Broadband communications ~100 GHz>1 THz

Explosives

remote with specificityX

Classical imagingX

Point gas detection

absolute specificityX

Astrophysics (>$2x109)X

Atmospheric (>$n x 108)X

Remote gas detection

modest specificityX

See through walls~100 GHz>1 THz

Buried land mines

> 6”~100 GHz> 1THz

< 6”>1 THz

Cancer/surface (water)X

Incapacitate and killX

Explosives/other solids

close, sm obstruct, mixturesX

Explosives

close, sort, sm obstructsome materials

Pharmaceuticals, bio

close, sort, sm obstruct some materials

Legacy Applications

Cost? Size? Speed?

Breadth of Application?


Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP

($spent or $potential) best methodTo be demo

Cancer/deep(spectra)X

Cancer/surface(spectra)X

T-Ray (deep medical)

Mutation(spectra)X

Broadband communications ~100 GHz>1 THz

Explosives

remote with specificity

Classical imagingX

Remote gas detectionX

modest specificity

Astrophysics (>$2x109)X

Atmospheric (>$n x 108)X

See through walls~100 GHz>1 THz

Point gas detection

absolute specificityX

Buried land mines

> 6”~100 GHz> 1THz

< 6”>1 THz

Cancer/surface (water)X

Incapacitate and killX

Explosives/other solids

close, sm obstruct, mixturesX

Explosives

close, sort, sm obstructsome materials

Pharmaceuticals, 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 Orderdemonstrateddemonstratedclear pathPhenomenaVLP

($spent or $potential) best methodto be demo

Cancer/deep(spectra)X

Cancer/surface(spectra)X

T-Ray (deep medical)X

Mutation(spectra)X

Broadband communications ~100 GHz>1 THz

Explosives

remote with specificityX

Classical imagingX

Remote gas detection

modest specificityX

Point gas detection

absolute specificityX

Astrophysics (>$2x109)X

Atmospheric (>$n x 108)X

See through walls~100 GHz>1 THz

Buried land mines

> 6”~100 GHz> 1THz

< 6”>1 THz

Cancer/surface (water)X

Incapacitate and killX

Explosives/other solids

close, sm obstruct, mixturesX

Explosives

close, sort, sm obstruct some materials

Pharmaceuticals, bio

close, sort, sm obstructsome 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 Orderdemonstrateddemonstratedclear pathPhenomenaVLP

($spent or $potential) best methodTo be demo

Cancer/deep(spectra)X

Cancer/surface(spectra)X

T-Ray (deep medical)

Mutation(spectra)X

Broadband communications ~100 GHz>1 THz

Explosives

remote with specificityX

Astrophysics (>$2x109)X

Atmospheric (>$n x 108)X

Classical imagingT&S

Remote gas detection

modest specificityT&S

See through walls~100 GHz>1 THz

Point gas detection

absolute specificityX

Buried land mines

> 6”~100 GHz> 1THz

< 6”>1 THz

Cancer/surface (water)X

Incapacitate and killX

Explosives

close, sort, sm obstructsome materials

Pharmaceuticals, 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

Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP

($spent or $potential) best methodTo be demo

Cancer/deep(spectra)X

Cancer/surface(spectra)X

T-Ray (deep medical)

Mutation(spectra)X

Broadband communications ~100 GHz>1 THz

Explosives

remote with specificityX

Astrophysics (>$2x109)X

Atmospheric (>$n x 108)X

Classical imagingT&S

Remote gas detection

modest specificityT&S

See through walls~100 GHz>1 THz

Point gas detection

absolute specificityX

Buried land mines

> 6”~100 GHz> 1THz

< 6”>1 THz

Cancer/surface (water)X

Incapacitate and killX

Explosives/other solids

close, sm obstruct, mixturesX

Explosives

close, sort, sm obstructsome materials

Pharmaceuticals, bio

close, sort, sm obstruct some materials

?


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


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