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![Page 1: The Physics and Chemistry of Analysis in the Submillimeter/Terahertz Spectral Region Frank C. De Lucia The Microwave Laboratory Ohio State University Columbus,](https://reader030.fdocuments.us/reader030/viewer/2022032806/56649f085503460f94c1d0cf/html5/thumbnails/1.jpg)
The Physics and Chemistry of Analysis in the
Submillimeter/Terahertz Spectral Region
Frank C. De Lucia
The Microwave LaboratoryOhio State UniversityColumbus, OH 43210
August 30, 2005
American Chemical SocietyWashington, DC
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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 AssociateIvan Medvedev - Research AssociateAndrey Meshkov - Graduate Student
TJ Ronningen - Graduate StudentLaszlo Sarkozy - Graduate Student
David Graff - Graduate StudentBryan Hern - Undergraduate Student
Drew Steigerwald - Undergraduate StudentJohn Hoftiezer - Electrical Engineer
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SMM Analytical GapA
tte
nu
ati
on
(d
B/k
m)
10 GHz
3 cm
0.1 THz
3 mm
1 THz
0.3 mm
10 THz
30 m
100 THz
3 m
1000 THz
300 nm
Millimeter/Submillimeter Infrared Visible0.01
0.1
1
10
100
H2O CO2
H2O
O2H2O
H2O
CO2
O3
H2O
CO2
H2O
FrequencyWavelength
RFMicrowave
Bo e-
International Light
Bruker FTIR’s
Bruker BioSpin MRI
THERE ARE NO ‘PUBLIC’
APPLICATIONS OF THE THz
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Overview
What do Analytical Chemists Care About?
SMM/THz Technology - pulsed and cw Noise
Brightness
SMM/THz Systems in ‘Scientific’ Applications
A Clear Path to a ‘Public’ Application Fast Scan Submillimeter Spectroscopy Technique (FASSST) Gas Analysis
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What do Analytical Chemists Care About?
Specificity
Sensitivity
Generality
Size
Cost
Speed
Ease of Use
Comparison with Alternatives
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There are Established SMM Applications 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
-5
260240220200180
Frequency [GHz]
- atm - atm + 0.8 atm of N2
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A CLEAR PATH TO GAS ANALYSISHP ~1975 Opt. Lett. 14, 1128-1130(1989)
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TRANSMIT POWER
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+05
0.1 1 10
Frequency (THz)
CW
Po
we
r (
W) Fundamental
IMPATTsVaractorMultipliers
GaAsPhotomixers
FundamentalRTDs
SemiconductorLasers
CW
Po
we
r (
W)
Kindly provided by E. Brown
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The THz is VERY Quiet even for CW Systems in Harsh Environments
QuickTime™ and a Photo - JPEG decompressor are needed to see this picture.
Experiment: SiO vapor at ~1700 K
All noise from 1.6 K detector system
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3000
2000
1000
0
-1000
370x103
360350340330Frequency (MHz)
3000
2000
1000
0
-1000
335x103
334333332331330Frequency (MHz)
1000
500
0
-500
332.1x103
332.0331.9331.8Frequency (MHz)
‘Absolute’ Specificity in a Mixture of 20 Gases
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400
300
200
100
0
-100
333.10333.08333.06333.04333.02333.00x10
3
3000
2000
1000
0
-1000
370x103
360350340330Frequency (MHz)
#09 Acrylonitrile Library
Combined Spectrum
400
200
0
-200
333.10x103
333.08333.06333.04333.02333.00Frequency (MHz)
Gas Identification in Mixture of 20 GasesBlow-ups of
Combined SpectrumLibrary Identification
of Acrylonitrile
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1 10 100 1000 Number of Lines(Fingerprint Elements)
500 Molecules
50 Molecules
2 MoleculesPFA=10-12
PFA=10-9
PFA=10-6
PFA=10-3
PFA=10-12
PFA=10-9
PFA=10-6
PFA=10-3
PFA=10-12
PFA=10-9
PFA=10-6
PFA=10-3
THz Rotational SpectroscopyG
C/M
S/I
MS
IR-Vibration
Log
of N
umbe
r of
Res
olut
ion
Ele
men
tsFamilies of False Alarm Rates
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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
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COMMUNICATIONS WIRELESS TECHNOLOGY*
[can make, very small, low power, and very cheap]
*The government alone can’t afford to develop the THz, only the market can make us mature
+ commodity microwave chips
+ 3 (very special) diodes
= cw THz module
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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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This is Great, But What About Real Problems in the Real World?
To this end we’ve:
Built the compact solid state system (but not cheaply yet!).
Developed appropriate control and calibration software.
Built the automated identification and quantification software and used it successfully on challenging complex mixtures.
Considered sensitivity, sampling, and preconcentration strategies.
Considered in detail issues of background and clutter, especially that expected from the atmosphere.
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USACHPPM Toxic Industrial Chemical List* in Atmospheric Clutter Background
Allyl alcoholAcroleinAcrylonitrileAmmoniaArsineEthylene oxideFormaldehydeHydrogen bromideHydrogen chlorideHydrogen cyanideHydrogen fluorideHydrogen selenideHydrogen sulfideMethyl hydrazineMethyl isocyanateMethyl mercaptanNitrogen dioxideNitric AcidPhosgenePhosphineSulfur dioxideToluene diisocyanate (2,4)
*Excludes gases without dipole or vapor pressure: Chlorine, diborane, hydrazine, parathion, sulfuric acid
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x3 multiplier x8 multiplierW-band amplifier
HRL Chip Set
0.5 cm
AT THIS POINT IN TIME -- GAS ANALYSIS EMERGES FROM A CONFLUENCE OF SCIENCE AND TECHNOLOGY
Physics Always Favorable (1955) HP 40 GHz MW Spectrometer(1974) OSU BWO Based 300 GHz FASSST (1998)
Microfabrication => small, inexpensive in quantity (2004) Solid StateWaveguide Block Components (2001)
Growth in computing power to handle information
Broadband wireless market
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What do Analytical Chemists Care About?
Specificity ‘Absolute’, Even in Complex Mixtures
Atmospheric/Background Clutter Minimal
Sensitivity 10-15 - 10-18 Moles
Generality Requires Dipole Moment, Vapor Pressure
Size Now: <<1 ft3; potential for a few in3
Cost (in quantity): ‘Wireless’ Chips, 3 Diodes, Small Vacuum System, Data Analysis
Speed 10-6 s to 3+ s
Ease of Use Automated Quantification in Complex Mixtures
Comparison with Alternatives ???
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Research and Development Issues
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
6. Extreme miniaturization
7. Large molecule limit
8. Specialized monitors
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Source Brightness!
10-2 photons/pulse/MHz
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(0.02223482)(0.18331000)(0.38019757)(0.44800137)0.55693607(0.62070183)0.75203305(0.91617141)(0.97031518)0.987926861.097364631.113343501.153125571.162914461.207642611.228790891.41062289
THz Spectroscopy SMM/FIR Spectroscopy
Phys. Rev. A5, 487 (1972).Int. J. Infrared and Millimeter Waves 4, 505 (1983).Appl. Phys. Lett. 42, 309 (1983).
Opt. Lett. 14, 1128-1130 (1989).
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GHzCBA 25 Jmax 18
GHzCBA 10 Jmax 30
GHzCBA 3 Jmax 55
GHzCBA 1 Jmax 96
GHzCBA 1.0 Jmax 305
inertia of moment
1~constant Rotational
Spectra as a Function of Molecular Size
Population of levels
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Optics and Photonics News (August 2003)
and
“Spectroscopy in the Terahertz Region,” in Sensing with Terahertz Radiation, D. Mittleman, ed. Springer, Berlin (2003).
REFERENCES
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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
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 ENERGETICSAtoms 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
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PHYSICS AND THz SOURCE REQUIREMENTS
Source Brightness
Doppler Width ~ 1 MHz
1 mW in 1 MHz has same
brightness as 1 kW in 1 THz
10-10 W in 1 MHz has same
brightness as 10-4 W in 1 THz
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THE ‘NATIVE’ THz APPLICATION:
GAS SENSING WITH ‘ABSOLUTE’ SPECIFICITYIn the context of DARPATECH 2004, our laboratory’s work in this area was highlighted as a part of their presentation as:
“One such opportunity is the identification of chemical threats. Low-pressure gases have astonishingly selective signatures in this region. In MTO’s recently completed Terahertz Technology for Sensing and Satellite Communications program, a relatively compact chemical sensor was developed and shown to have incredible absolute specificity even when dealing with very complicated mixtures. Further advances could lead to very inexpensive and portable systems.”
A PROBLEM: This is such a natural application that many really bad systems have been proposed/sold that are completely incapable of living up to their claims.
EVEN WORSE: It is widely claimed that systems like our cw submillimeter system are ‘plagued by noise’ and that only THz-TDS systems are viable.
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VERY REMOTE SUBMILLIMETER SENSING
Spectrum of the 325 - 360 GHz survey of the Orion molecular cloud taken by the CSO instrument on Mauna Kea.
Details of the 338 - 339 GHz portion of the 325 - 360 GHz survey of the Orion molecular cloud taken by the CSO instrument on Mauna Kea.
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Phenomenology and SMM/THz Technology
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?)
How does the Physics interact with the Technology Where are the interactions? What is a THz?
Source brightness, time dependence
Detector sensitivity, background noise