P1246990920XyUjT

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Opportunities in the THz (A discussion) Frank
C. De Lucia Department of Physics Ohio State
University Air Force Research
Laboratory Wright-Patterson AFB July 6, 2006
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State - of - the - Art There are well
established SMM/THz Specialist applications -
largely based on low pressure gases - whose
technology approaches fundamental limits There
are two applications - imaging and gas analysis -
for which clear (but challenging) paths to
Public applications exist System development
for Holy Grail applications is ahead of
knowledge of the signature phenomenology and
often not based on the optimum technological
approach Much of the fundamental phenomenology
(e.g. atmospheric fluctuations, transmissivity,
physics of target signatures) is also not well
understood
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DoD Applications IEDs Spectroscopic Detection of
Explosives Gases (remote atmospheric
pressure, upper atmosphere, point) Biological
Materials Images of Concealed
weapons/materials (clothes, packaging)
Navigation (dust, clouds) Upper atmosphere
objects Enabling Technology QCLs, photomixers,
e-beam devices Detectors, cooling
methodologies Frequency control Leverage Commercia
l market for wireless communications
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Organizational Interest
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DoD Meetings and Workshops
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Professional Organizations
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Submillimeter Applications
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Atmospheric Attenuation
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The Terahertz Gap Solid-State SourcesFrom Tom
Crowe UVA/VDI
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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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Low noise background in the SMM/THz enables
active imaging and many other applications
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LOW TEMPERATURE SCIENCE LOW TEMPARATURE TECHNOLOGY
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WHAT DOES LOW TEMPERATURE BUY? hn kT 300 K
black body is a strong source relative to a 0.1 K
detector High Q passive components for
resolution Interaction strengths (1/T)n, n
large Reduction in sample linewidths Sensitive
focal plane arrays w/o need for local
oscillators Cryogenics on a chip is cheap,
small, . . . .
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Transmission Loss of common Building Materials
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Signatures Explosives Spectra
Clearly spurious results in both gas and solids
have been reported
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RPI
THz EXPLOSIVE SPECTRA
PSI
TeraView
Wisconsin
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Signature of Explosive through 1 m of Atmosphere
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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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A BETTER CHEAPER( 1 week effort) OLDER (early
80s) SUBMILLIMETER IMAGE
BETTER NAMES
First Image from Revolutionary T-ray Camera Sees
through Fog, Clothing and into Deep Space
(www.space.com) By Robert Roy Britt Senior
Science Writer posted 0130 pm ET 11 February
2003
As seen on TV Q-ray Ionized Bracelet
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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 DT/T 0.1
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The Power of Logarithmic Active Images
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Sensitivity of SMM/THz to Small Lines and Cracks
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What is so favorable about the SMM/THz? The
SMM/THz is very quiet 1 mW/MHz 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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MM and THz Science Along the Critical Path What
are the spectral signatures of solids? a. What
is the physics? Is it more difficult than that
of gas phase phenomena? b. How do transmission
and reflection/scattering signatures differ? c.
How narrow are the spectral features? d. Are
there schemes for resolution/specificity
improvement? e. Is it possible to develop
reproducible and well founded spectral
catalogues? What is the nature of clutter for
solids? More specifically, most of the
published fingerprints of explosives and some
biological chemicals consist of a few very broad
lines. These might still be useful fingerprints
IF most common materials (dirt, clothing,
ordinary powders (soap, sugar, starch. etc.)) do
not have similar features. a. What are the
clutter spectra due to these common materials?
b. How complex are the spectra due to mixtures
of these materials? c. How do systems separate
the broad spectral features of solids from
background effects and clutter?
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Science Along the Critical Path
(continued) What do we know about the
penetration of materials (clothing, building
materials, particulates, etc.)? a. How does
it vary with frequency? b. How do regions of
good transmission compare with the frequencies of
fingerprint spectra and high spatial resolution?
Whats a THz? c. How do we define and
characterize the materials (e. g. water content
and density of weave)? What is the impact of the
atmosphere? a. What are the time and spatial
scales of atmospheric fluctuations? b. How do
they compare with the corresponding scales of
imaging systems? c. How many
information points (windows) are available as a
function of range?
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Technology Along the Critical Path Because a
very large number of THz technology solutions
have been detailed in the literature, we will not
attempt to be exhaustive. Focal Plane
Arrays - SPEED (Power) Technology based on
commercial wireless developments This
approach appears to be the only technology in the
foreseeable future that will provide sources at a
price that will allow THz applications to move to
the public - Only the market can afford THz,
not the government. Low Temperatures a.
Many of the source power limitations are
dramatically reduced with cooled detectors. b.
Many signatures in solids become stronger and
more specific. c. Cooling is also a strong
enabler for focal plane arrays. What is the time
line for fieldable cooling approaches, for
quantum cooling on a chip? How might these
coolers compare in power and size with the size
and power requirements for THz local oscillators
or drive lasers? A rediscovery of FTFIR
technology a. FTFIR is a very
competitive and cost effective in many
applications
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Franks Top Ten Technical 1 Electron beam
sources of radiation 2 Cooled detector/source
technology for the field 3 Convenient frequency
control 4 Methods to utilize the gas phase
spectra of very large molecules 5 Logarithmic
THz Images for active heterodyne
imagers Signatures and Phenomenology 1
Quantitative spectra of materials of interest 2
Atmospheric deconvolution 3 Co-, by-, and
decomposition- products of materials of
interest 4 X - Factors 5 Non-destructive
testing and evaluation
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REFERENCES
Optics and Photonics News (August 2003)
and Spectroscopy in the
Terahertz Region, in Sensing with Terahertz
Radiation, D. Mittleman, ed. Springer, Berlin
(2003).
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Recent Terahertz Images from the Web 80s
Submillimeter Image
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