WMD Science and Technology in the Submillimeter/Terahertz Spectral Region Frank C. De Lucia Ohio State University Department of Physics Columbus, OH, 43210
Jan 07, 2016
WMD
Science and Technology in the Submillimeter/Terahertz Spectral Region
Frank C. De Lucia
Ohio State UniversityDepartment of PhysicsColumbus, OH, 43210
Overview
What’s a THz?
What’s a ‘Killer Ap’?
Physics of the SMM/THz
Specific Applications Solids Gases
Opportunities - THz + ‘X’
Conclusions and Questions
What’s a THz?
(With a broad definition, what properties are available at a particular choice of frequency?)
There are Established SMM/THz ‘Killer Aps’ Technologies which approach fundamental limits
Fundamental Molecular Studies - Spectroscopy, DynamicsLaboratory AstrophysicsScience in the Field/Remote sensingInterstellar medium, stellar formationUpper atmospheric chemistry
2.5
2.0
1.5
1.0
0.5
0.0
Ab
sorp
tio
n i
n c
m-1
x10
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260240220200180
Frequency [GHz]
- atm - atm + 0.8 atm of N2
Two Old, but New, ‘Killer Aps’Identify Need - Competitive SMM/THz Solution? - Do it
-- Clear, but Challenging Paths to Success --
IMAGING ANALYTICAL CHEMISTRY
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 object’s 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?
Physics in the SMM/THz
Degrees of Freedom - What is the Physics?
Energetics and Temperature: h/kT
System and Ambient Noise
Linewidths (Qs), Specificity, Signatures, and Clutter
Illustrative Examples -solids -gases
TemperaturekT (300 K) = 200 cm-1
kT (1.5 K) = 1 cm-1
kT (0.001 K) = 0.0007 cm-1
FieldsqE (electron) >> 100000 cm-1
E (1 D) ~ 1 cm-1
B (electronic) ~ 1 cm-1
B (nuclear) ~ 0.001 cm-1
The THz has defined itself broadly and spans kT
The Energetics
Atoms and MoleculesE (electronic) ~ 50000 cm-1
E (vibrational) ~ 1000 cm-1
E (rotational) ~ 10 cm-1
E (fine structure) ~ 0.01 cm-1
RadiationUV/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
Does Thermal Noise ‘Plague’ cw Submillimeter Spectroscopy (Imaging)
Experiments?
SiO vapor at 1700 K
Amplifier noise in 4 K detector
No - You Can’t Even Observe it with a 4 K detector!
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?)
VCO10.3 – 10.8 GHz
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
FASSST Spectrometer Diagram
400
300
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100
0
-100
333.10333.08333.06333.04333.02333.00x10
3
3000
2000
1000
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-1000
370x103
360350340330Frequency (MHz)
#09 Acrylonitrile Library
Combined Spectrum
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333.10x103
333.08333.06333.04333.02333.00Frequency (MHz)
Gas Identification in Mixture of 20 Gases
Blow-ups ofCombined Spectrum
Library Identificationof Acrylonitrile
1 second sweep time over whole spectrum
300 seconds integration on resonance
X 107 sensitivity plus
‘absolute’ specificity
How can this be? Source Brightness!
10-2 photons/pulse/MHz
THE STEALTH ‘KILLER AP’COMMUNICATIONS - WIRELESS TECHNOLOGY*
*The government alone can’t afford to develop the THz, only the market can make us mature
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
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)
•To grow to maturity, the THz needs not only to optimize its technology for native applications (imaging through obscuration, chemical sensing, etc.), but to integrate its attributes with other technologies to address a broader range of challenges competitively.
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
3000
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370x103
360350340330Frequency (MHz)
3000
2000
1000
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-1000
335x103
334333332331330Frequency (MHz)
1000
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-500
332.1x103
332.0331.9331.8Frequency (MHz)
WHY WE NEED INFORMATION THEORY: THE SPECTRUM OF A 20 GAS MIXTURE
‘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
input window
Atom source
micro-channel plates
phosphor screen
viewing window
grids
T
vacuum can
6p3/2
6s1/2
20d
18d
22d
852 nm
518 nm
18f
0.52 THz
16f
20f
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
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
Conclusions and Questions
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
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?
“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, ONRSymposium on Millimeter WavesPolytechnic Institute of Brooklyn31 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, OUSDREProceedings of the Sixth DARPA/Tri-ServiceMillimeter Wave Conference29 November 1977
Frontispiece: Army’s Near-Millimeter Wave Technology Base Study, November 1979
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?
PEOPLEFrank C. De Lucia - Professor OSU
Eric Herbst - Professor OSUBrenda Winnewisser - Adj. Professor OSUManfred Winnewisser - Adj. Professor OSU
Paul Helminger - Professor USADoug Petkie - Professor WSU
Markus Behnke - Research AssociateAtsuko Maeda - Research AssociateAndrei Meshkov - Graduate StudentIvan Medvedev - Graduate StudentTJ Ronningen - Graduate Student
Laszlo Sarkozy - Graduate StudentDavid Graff - Graduate Student
Bryan Hern - Undergraduate StudentDrew Steigerwald - Undergraduate Student
John Hoftiezer - Electrical Engineer
Optics and Photonics News (August 2003)
“Spectroscopy in the Terahertz Region,” in Sensing with Terahertz Radiation, D. Mittleman, ed. Springer, Berlin (2003).
REFERENCES