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
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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
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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?
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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
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Technology and Frequency Control
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What are the Field Applications?
Atmospheric Chemistry
Astrophysics
Orion. IRAM 30-m telescope line survey
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Where is the New Excitement?
New Physical Regimes
Analytical Applications
Medical
Active and Passive Imaging
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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 gt 3000 cm-1 IR 300 - 3000 cm-1 FIR 30 - 300
cm-1 THz 3 - 300 cm-1 MW 1 - 10 cm-1 RF lt 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) gtgt 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
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The Gap in the Electromagnetic Spectrum
Tubes, a little more - Photomixers, a little less
hn/kT
Size
Cooling
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Thermal Noise and Power in the THz
Blackbody Brightness W/cm2-Hz
Blackbody Noise/mode Thermal Noise below cutoff
frequency nmax in integration bandwidth
B Thermal noise in bandwidth b with
integration bandwidth B
From E. Brown
Number of modes/cm2 1/l2(cm)
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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 -gt 1014 K 1mW/100 Hz -gt 1018 K
Noise, detectors, and submillimeter-terahertz
system performance in nonambient
environments Frank C. De Lucia J. Opt. Soc. B,
1275 (2004)
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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?)
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Spectra as a Function of Molecular Size
Population of levels
Jmax ? 18
Jmax ? 30
Jmax ? 55
Jmax ? 96
Jmax ? 305
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Atmospheric Propagation
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Collisional Cooling An Approach to Gas Phase
Studies at Low Temperature Atom Envy - Molecule
Envy
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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.
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Typical Spectra - HCN
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Sources and Metrology for the THzSynthesized
Frequency Multiplication
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Jumping the THz via Frequency Synthesis Spectrosco
py 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
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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
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The Fundamental FASSST Spectrometer
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Frequency Control and Reference in the THz
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).
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).
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Frequency Synthesis via Femtosecond Demodulation
Spectral Purity and Sources of Noise in
Femtosecond-Demodulation Terahertz Sources Drive
by TiSapphire 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)
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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)
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Atmospheric Remote Sensing
JPL - Microwave Limb Sounder
Ozone Destruction Cycle
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Microwave Limb Sounder
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Image courtesy of NRAO/AUI and Computer graphics
by ESO
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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
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Orion. IRAM 30-m telescope line survey
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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?
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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.
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Impact Order demonstrated demonstrated clea
r path Phenomena VLP (spent or potential) best
method To be demo Cancer/deep(spectra) X Ca
ncer/surface(spectra) X T-Ray (deep
medical) X Mutation(spectra) X Broadband
communications 100 GHz gt1 THz Explosives
remote with specificity X Classical
imaging X Point gas detection absolute
specificity X Astrophysics (gt2x109) X Atmosph
eric (gtn x 108) X Remote gas detection modest
specificity X specificity in mixtures at
1km X See
through walls 100 GHz gt1 THz Buried land
mines gt 6 100 GHz gt 1THz lt 6 gt1
THz Cancer/surface (water) X Incapacitate and
kill X Explosives/other solids close, sm
obstruct, mixtures X Explosives close,
sort, sm obstruct some materials Pharmaceuticals,
bio close, sort, sm obstruct some
materials
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Cost? Size? Speed? Breadth of Application?
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Impact Order demonstrated demonstrated clea
r path Phenomena VLP (spent or potential) best
method to be demo Cancer/deep(spectra) X Ca
ncer/surface(spectra) X T-Ray (deep
medical) X Mutation(spectra) X Broadband
communications 100 GHz gt1 THz Explosives
remote with specificity X Classical
imaging X Remote gas detection modest
specificity X Point gas detection absolute
specificity X Astrophysics (gt2x109) X Atmospheri
c (gtn x 108) X See through walls 100
GHz gt1 THz Buried land mines gt 6 100 GHz gt
1THz lt 6 gt1 THz Cancer/surface
(water) X Incapacitate and kill X Explosives
/other solids close, sm obstruct,
mixtures X Explosives close, sort, sm
obstruct some materials Pharmaceuticals, bio
close, sort, sm obstruct some materials
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Impact Order demonstrated demonstrated clea
r path Phenomena VLP (spent or potential) best
method To be demo Cancer/deep(spectra) X Ca
ncer/surface(spectra) X T-Ray (deep
medical) Mutation(spectra) X Broadband
communications 100 GHz gt1 THz Explosives
remote with specificity X Astrophysics
(gt2x109) X Atmospheric (gtn x 108) X Classical
imaging TS Remote gas detection modest
specificity TS See through walls 100
GHz gt1 THz Point gas detection absolute
specificity X Buried land mines gt 6 100
GHz gt 1THz lt 6 gt1 THz Cancer/surface
(water) X Incapacitate and kill X Explosives
close, sort, sm obstruct some
materials Pharmaceuticals, bio close, sort,
sm obstruct some materials
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Impact Order demonstrated demonstrated clea
r path Phenomena VLP (spent or potential) best
method To be demo Cancer/deep(spectra) X Ca
ncer/surface(spectra) X T-Ray (deep
medical) Mutation(spectra) X Broadband
communications 100 GHz gt1 THz Explosives
remote with specificity X Astrophysics
(gt2x109) X Atmospheric (gtn x 108) X Classical
imaging TS Remote gas detection modest
specificity TS See through walls 100
GHz gt1 THz Point gas detection absolute
specificity X Buried land mines gt 6 100
GHz gt 1THz lt 6 gt1 THz Cancer/surface
(water) X Incapacitate and kill X Explosives/
other solids close, sm obstruct,
mixtures X Explosives close, sort, sm
obstruct some materials Pharmaceuticals, bio
close, sort, sm obstruct some materials
?
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Signatures Explosives Spectra
Clearly spurious results in both gas and solids
have been reported
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How do you look at THz images?
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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 gt 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
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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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