WMD

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WMD

• Science and Technology in the Submillimeter/Terahe
  rtz Spectral Region
• Frank C. De Lucia
• Ohio State University
• Department of Physics
• Columbus, OH, 43210

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Overview
Whats a THz? Whats a Killer Ap? Physics of
the SMM/THz Specific Applications Solids
Gases Opportunities - THz X Conclusions and
Questions
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Whats a THz? (With a broad definition, what
properties are available at a particular choice
of frequency?)
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There are Established SMM/THz Killer Aps
Technologies which approach fundamental
limits Fundamental Molecular Studies -
Spectroscopy, Dynamics Laboratory
Astrophysics Science in the Field/Remote
sensing Interstellar medium, stellar
formation Upper atmospheric chemistry
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Two Old, but New, Killer Aps Identify Need -
Competitive SMM/THz Solution? - Do it --
Clear, but Challenging Paths to Success --
IMAGING ANALYTICAL
CHEMISTRY
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Widely Promoted Killer Aps are working on a
T-ray imaging system that can look through walls,
doors, and window curtains to locate people and
weapons within a building has also produced a
THz method for long-distance sensing of object
buried in soil. Cancer cells, especially
melanoma tissues, also vibrate in THz and lend
themselves to early detection by doctors equipped
with THz devices . . . Have already
demonstrated . . Passive THz-wave techniques can
detect concealed nuclear materials, as well as
detect and make images of chemical and
radioactive plumes. THz waves interact well
with biological molecules, making it possible to
remotely detect biological aerosols in less than
a minutes with low false-alarm rate. They used
envelopes containing various white powders
flour, sugar, talcum powder and spores of a
benign species of bacterium, which acted as a
surrogate for anthrax and found that they could
detect a characteristic absorption signature for
the spores. T-rays can detect breast cancer and
see underground toxins better than other
technologies, such as conventional
x-rays. These so-called t-rays can, like
x-rays, see through most materials. But t-rays
are believed to be less harmful than x-rays. And
different compounds respond to terahertz
radiation differently, meaning a terahertz-based
imaging system can discern a hidden objects
chemical composition. Stage 1 These are
powerful public Killer Aps. What do we need to
do to convince the public that we can do
them? Stage 2 Show that there is a competitive
SMM/THz Solution. What phenomenology do we need
to demonstrate? Stage 3 What technology do we
need to develop to demonstrate?
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Physics in the SMM/THz Degrees of Freedom - What
is the Physics? Energetics and Temperature
hn/kT System and Ambient Noise Linewidths (Qs),
Specificity, Signatures, and Clutter Illustrative
Examples -solids -gases
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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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Does Thermal Noise Plague cw Submillimeter
Spectroscopy (Imaging) Experiments?
SiO vapor at 1700 K
Amplifier noise in 4 K detector
No - You Cant Even Observe it with a 4 K
detector!
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Phenomenology What is the Physics of
Interactions? Separate into Three Classes
According to 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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FASSST Spectrometer Diagram
VCO 10.3 10.8 GHz
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
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Gas Identification in Mixture of 20 Gases
Blow-ups of Combined Spectrum
Library Identification of Acrylonitrile
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1 second sweep time over whole spectrum 300
seconds integration on resonance X 107
sensitivity plus absolute specificity
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How can this be? Source Brightness!
10-2 photons/pulse/MHz
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THE STEALTH KILLER APCOMMUNICATIONS - WIRELESS
TECHNOLOGY
The government alone cant afford to develop the
THz, only the market can make us mature
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THz X - A search for new approaches to
significant problems Frank C. De Lucia,
Department of Physics, Ohio State University,
Columbus, OH 43210 Douglas T. Petkie, Department
of Physics, Wright State University, Dayton, OH
45435 Robert K. Shelton, Sarah L. Westcott, and
Brian N. Strecker, Nomadics, Inc., 1024
Innovation Way, Stillwater, OK 74074
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• The Importance of X
• THz is unique because of the infancy of its
  commercial and military applications
• Much of this infancy due to the difficulties of
  generating and detecting radiation
• However, enormous numbers of important
  applications in the other spectral regions have
  resulted from their large investment in systems
  and applications development often an
  additional X factor. X can be worth Nobel
  Prize!
• RF MRI (rf X shaped magnetic
• fields, rf pulse sequences, and
• signal processing)
• Visible Night Vision (light X
• electron multiplication and
• fluorescence)

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• An Example X for SMM/THz Gas Analysis
• 1. Gas/Particle Capture and Concentration
• 2. System Strategy
• Frequency control and measurement
• Signal recovery/dynamic range/noise spectra
• 3. Spectroscopic Theory/Libraries
• 4. Clutter analysis
• 5. Information theory

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WHY WE NEED INFORMATION THEORY THE SPECTRUM OF
A 20 GAS MIXTURE
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X Rydberg Atom Photocathode What is the
photocathode problem in the SMM/THz? 1. There
are no materials with a cutoff wavelength this
long. 2. If there were, for a room
temperature device, the infrared flux would
overwhelm the photocathode
The Physics of a Solution 20d - 18f is strongly
allowed sensitive detector of SMM/THz Because of
selection rules, not energetics, 20d is not
sensitive to IR radiation (or for that matter to
other SMM/THz) 18f can be selectively field
ionized against 20d to produce photoelectron Most
importantly, it has been possible to subject his
general idea to a detailed analysis that has led
to the solution of the challenges and a rather
detailed design concept
The Technology There is no interconnect problem,
either look directly at phosphor screen or use
CCD array Quantitative analysis is
favorable Laser requirements favorable in
comparison to SMM/LO Discharge plasma
excitation may be possible Solid state
photocathodes might be possible With Professor
Douglas Schumacher
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Conclusions and Questions
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What is so favorable about the SMM/THz? The
SMM/THz is very quiet 1 mW/MHz gt 1014
K Rotational transition strengths peak in the
SMM/THz The SMM/THz combines penatrability 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 In
comparison to the MW, the SMM/THz has a lot of
bandwidth The commercial wireless market will
provide us with a cheap technology It should be
possible to engineer small (because of the short
wavelength) and low power (because the background
is quiet/the quanta is small) devices and systems
- e.g. like miniature GC-MS
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What is so Challenging about the
SMM/THz? Efficient generation of significant
tunable, spectrally pure power levels. The
difficulty of the physics which produces
signatures in solids. Need to find a public
Killer Ap that can allow us to rapidly develop
X like other fields. Impact of the atmosphere
on measurements.
What do We Wish We Knew? What are the signatures
of the aforementioned Killer Aps? Can we
develop a reliable spectroscopic catalog? What is
the science that underlies the spectroscopy? How
do the time and spatial scales of atmospheric
fluctuations impact SMM/THz images and
spectroscopy?
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Frontispiece Armys Near-Millimeter Wave
Technology Base Study, November 1979
The interest of the Navy and other services in
this field is so great that the generation,
propagation, and detection of such waves are the
subject of an expanding research program in the
Department of Defense today. Rear Admiral R.
Bennett, ONR Symposium on Millimeter
Waves Polytechnic Institute of Brooklyn 31
March 1959 Now is the time for you workers in
the field to come out of hiding and be counted!
All is forgiven! Leonard R. Weisberg,
OUSDRE Proceedings of the Sixth
DARPA/Tri-Service Millimeter Wave Conference 29
November 1977
Now, 25 years later we have gone through a second
cycle. Will there be a third? Or, are we ready
to be a mature field?
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PEOPLE Frank C. De Lucia - Professor OSU Eric
Herbst - Professor OSU Brenda Winnewisser - Adj.
Professor OSU Manfred Winnewisser - Adj.
Professor OSU Paul Helminger - Professor USA Doug
Petkie - Professor WSU Markus Behnke - Research
Associate Atsuko Maeda - Research
Associate Andrei Meshkov - Graduate Student Ivan
Medvedev - Graduate Student TJ Ronningen -
Graduate Student Laszlo Sarkozy - Graduate
Student David Graff - Graduate Student Bryan Hern
- Undergraduate Student Drew Steigerwald -
Undergraduate Student John Hoftiezer - Electrical
Engineer
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REFERENCES
Optics and Photonics News (August 2003)
Spectroscopy in the Terahertz Region, in
Sensing with Terahertz Radiation, D. Mittleman,
ed. Springer, Berlin (2003).