Transcript delucia-062313 Spectroscopic Engineering

Spectroscopic Engineering in the
Submillimeter
Frank C. De Lucia
Department of Physics
Ohio State University
June 19, 2013
Columbus, Ohio
Submillimeter Spectrum of Nitric Acid
Even Better - Perturbations
Outline
The Underlying Physics
Two Examples: Microwave Limb Sounder and ALMA
Other Examples
Opportunities/The Submillimeter Engineer’s Tool Kit
Two legacy applications: Sensors and Imaging
Engineering non-ambient environments
Cold molecules
Molecular ions
Plasmas
Mass market technology to enable powerful ~ ‘free’
systems
From Where Did We Come?
Giants of Spectroscopic Science:
Hertzberg
Wilson
Dennison
Nielsen
Townes
The First Submillimeter Engineer
Motivation for development of the maser:
Molecular generator to address the submillimeter source problem
Molecules as engineering medium to accomplish this
Last 150 pages of his book devoted to engineering
Frequency standards, analytical chemistry, spectrometers, . .
Where Are We Going?
With Whom Are We Going There?
The Three Cultures*
THz/Optical
Optical Society of America,
“THz Spectroscopy and Imaging Applications”
Toronto, June 14, 2011
Millimeter/Electronic (Engineering)
IEEE International Microwave Show 2011
“Workshop on MM-Wave and Terahertz Systems”
Baltimore, MD, June 6, 2011
Submillimeter/Electronic (Scientific)
International Astronomical Union,
“The Molecular Universe”
Toledo Spain, June 2, 2011
__________________
With apologies to C. P. Snow, “The Two Cultures”
Do We Know Each Other?
Radiation and Interactions: Orders of Magnitude
In
100 GHz
1013 K
1012 K
1011 K
1010 K
109 K
108 K
107 K
106 K
In
1 MHz
kT
1018 K
1017 K
1016 K
1015 K
1014 K
1013 K
1012 K
1011 K
kT(300 K) = 6000 GHz => thermal emission from both atmospheric and astronomical sources
kT (3 K) = 60 GHz => thermal emission from space/cryogenic sources
For samples in thermal equilibrium, Doppler broadening is proportional to frequency
Optimum sample quantity is then proportional to frequency
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 -> 1014 K
ABSORPTION COEFFICIENTS
Number
Density
 mn
NFm

c
Boltzmann
Factor
1  e
Einstein Photon
Coefficient Size
h  mn / kT
B
mn
h mn
2  1
8 3 
m g n 

2
3h 
g x, y, z
 
h mn / kT
(in long wavelength limit)
Frequency and Temperature Factors
mn
2 

8 2 N Fm
2

 mn   m g n 
3ck  T
g x, y, z


1
mn 
3
T5 /2
 mn
T
5 /2
(Partition function and degeneracy)
(Pressure broadening = Doppler broadening)
10 GHz - 1000 GHz: 106
300 K - 3 K:
105
1000 K - 1 K:
3 x 107
Low Atmospheric Clutter Background
[The miracle of the Microwave]
Nitric acid at ~ 1 ppb is first ‘clutter molecule’ in low pressure sample
The Physics is very Favorable:
Simple, but powerful systems to study
small, fundamental molecules are possible
Today
Commercial availability of
submillimeter components
makes possible much more
sophisticated and flexible
systems
This talk is about the
spectroscopic engineering
that involves these systems
Epitome of Spectroscopic Engineering:
JPL’s Microwave Limb Sounder
A Priori Predicted Spectral Signature of the Atmosphere
Needed, Sought, and Achieved ‘Complete’ Spectroscopic Model via
Quantum Mechanical Models:
The ‘Pickett’ Program
http://spec.jpl.nasa.gov/
___________________
Required careful knowledge of atmospheric concentrations and temperatures
An engineered spectroscopic data base: (1) selection of molecules and states,
(2) table of results for use by non-experts
Employed a generation of spectroscopist -> accomplished atmospheric scientists
Enabled a Complete Spectroscopic Model of
the Atmosphere in the
Millimeter/Submillimeter
The ALMA Spectroscopy Problem is
Much More Challenging:
A Spectroscopic Engineering Work in
Progress
Completeness and Intensity
Calibration in Orion
No a priori catalog of Orion
Many more detectable species
Narrower lines
Larger molecules with complex
perturbations
Four full sessions at this meeting
Requires a different kind of
engineering than MLS
_____________
Figure courtesy of NSF
A Contribution to the Engineering:
Complete Experimental Models
Challenges for Quantum Mechanical Models
Completeness: Excited Vibrational States (hard to analyze perturbed states)
Frequency calculations: Extrapolations in J and K
Intensities: Especially in flexible molecules
Completeness in Ethyl Cyanide
Experimental
QM Catalog
ALMA
CES Simulation at 190 K
Frequency Calculation
[perturbed states are hard to calculate]
QM
Vinyl Cyanide
Intensities in Methanol
[and other flexible molecules?]
Other Examples of
Spectroscopic Engineering
Gordy: Brought spectroscopic technology to astronomy/engineering problem
Flygare: Electronic time domain techniques for spectroscopy
Claude Woods: Brought spectroscopic insight, to engineering problem, and launched
ion spectroscopy in the mm/submm
Krupnov, Burenin: Backward Wave Oscillator techniques for submillimeter
spectroscopy
Belov et al.: BWO lamb dip spectroscopy
RAD-3 Spectrometer
Liebe: Propagation models
Pate: Modern digital implementation of electronic time domain techniques
Crowe, Hesler (VDI): A commercial, broadband mm/submm technology
Herschel and SOFIA:
A piece of Spectroscopic Engineering History:
The First mm/submm Astronomy
Accomplished new science
Used heterodyne third harmonic mixer
for receiver (technology from
spectroscopy)
Humidity in Durham ended astronomy at
Duke, but graduate student (Burrus) at
time went on to build the receivers for
the Bell Labs Penzias/Wilson millimeter
wave astronomy group
What is in the Submillimeter
Spectroscopic Engineer’s Tool Kit?
What is the Physics?
Strong molecular interactions
Small Doppler widths
Highly specific fingerprints (Erot << kT)
Very quiet background
Low diffraction relative to microwave
Penetration of materials and hostile environments
What are the enablers?
Very bright electronic sources
Flexible and agile control
Potential for very low cost
Some Submillimeter Opportunities
Well known and well represented at this meeting
Astronomy and Astrophysics
Gas sensors and process control
Remote sensing of the upper atmosphere
Well known in other communities
Imaging
Non-ambient environments
Cold molecules (hv/kT ~ 1)
Non-thermal (e.g. plasmas) (quiet and transparent in SMM)
Laser diagnostics
Ions and free radicals
Impact of mass market technologies
A black art commercial (expensive)
almost FREE
Two SMM/THz Legacy ‘Public’ Applications
-- Clear, but Challenging Paths to Success -IMAGING
ANALYTICAL CHEMISTRY
50 cm
Reservoir
Continuous LHe Fill Line
Sample Gas Injector
Cell/Pot
Non-ambient Environments
4K and 77K Heat Shields
40 cm
Pot Pumping
Line
Low temperature environments
Millimeter Wave
Probe Path
Buffer Gas Line
Expeimental Cell
Traps and beams
Sample Gas
Injector
Plasmas
Molecular ions
Liquid Helium Pot
Cold Molecules: Quantum Collisions
L
300 K
1K
_________________________________
L ~ 30
L~2
J ~ 10
J 1

b
2Em
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.
An Experimentalist’s History and Perspective
Pioneering Theory of Green and Thaddeus
COLLISIONAL COOLING APPARATUS
Buffer Gas Line
Pot Pumping Line
LN 2
Reservoir
Explore New Experimental Regimes
What is the physics in the regime where kT ~ hvr ~Vwell?
Vacuum
Jacket
LHe
Reservoir
50 cm
Continuous LHe Fill Line
Sample Gas Injector
Cell/Pot
Erot ~ Ewell ~ kT
4K and 77K Heat Shields
40 cm
Pot Pumping
Line
Millimeter Wave
Probe Path
Buffer Gas Line
Expeimental Cell
Sample Gas
Injector
Liquid Helium Pot
Typical Spectra – HCN
Pressure broadening by Helium
Engineering of Plasmas for Spectroscopy
J. Chem. Phys. 78, 2312 (1983).
Minimal Electron Beam Heating
Molecular Ions at
Low Temperature
11.2 K
28 K
MA01 Low Temperature Trapping: From
Reactions to Spectroscopy
S. Schlemmer, O. Asvany, and S. Brunken
Universitat zu Koln
Traps can be a powerful and flexible tool in the submillimeter
23 K
Plasma Diagnostics in a Discharge Laser*
In the submillimeter plasmas are transparent and quiet
Experimental arrangement for the measurement of number density
and temperatures in the plasma of an HCN discharge laser.
Relaxation of excited
vibrational state population
that leads to the HCN laser
Vibrational temperatures of HCN (100) and CO (v=1). Gas
mixture was N2:CH4:CO = 1:2:2 for a total pressure of 200 mTorr.
__________________________________
*D. D. Skatrud and F. C. De Lucia, "Dynamics of the HCN Discharge Laser," Appl. Phys. Lett., Vol. 46, pp. 631-633, 1985.
Semiconductor Plasma Diagnostics
CF2 Concentration
Applied Materials
Semiconductor
Plasma Reactor
Temperature
Y. Helal, et al. WH09
The Technology Future
High resolution, easily calibrated, and flexible submillimeter technology
from the wireless community will become essentially free.
These will not be ‘toy’ systems.
This technology can also require little space and little power.
How close are we?
Wireless HDTV communications link at 60/240 GHz
Custom integrated CMOS Rx/Tx in 200 – 300 GHz region
Off the shelf family of chips/modules to 100 GHz
A SiGe BiCMOS 16-Element Phased-Array
Tx/Rx for 60GHz Communications*
Combined Tx/Rx 16 Channel
Evaluation Board
•Integration includes synthesizer, modulator, and steered phased array
•Applications include wireless HDTV
•Single ‘engine’ flexible enough for communications, imaging, spectroscopy
•Extension to 240 GHz under discussion
*Courtesy of Alberto Valdes-Garcia and Arun Natarajan, Watson Laboratory, IBM
CMOS Integrated Engine for 200-300 GHz
Antennas: Rashaunda Henderson (UT-D)
Receiver: Bhaskar Banerjee (UT-D)
Transmitter: Kenneth O (UT-D)
•With integrated synthesizer
•Currently less microwave power (~0.1
mW) than III-V
(Prototype: Summer 2013)
Off the Shelf System Hardware
Wireless Components: To 100 GHz - Chip costs <$100
Symbiosis among Spectroscopy and
Spectroscopic Engineering
Type 1: Submillimeter spectroscopic analysis is a key component of
system designed to address broader problems
Astronomy, Atmospheric Science, Chemistry, Sensors, . . .
Type 2: Submillimeter spectroscopists develop technology of
importance to other fields
Astronomy, Imaging, Communications, . . .
Type 3: Molecules/spectroscopy provide engineering building blocks
Lasers, Masers, . . .
Type 4: Engineer molecular environments for spectroscopy
Molecular ions, traps, cold molecules, . . .
Summary
We love the science of spectroscopy
A mature submillimeter spectroscopy makes spectroscopic engineering
possible. Well defined (but sometimes complex) theory.
Favorable physics in submillimeter
Rotational fingerprint is strong, specific, and ubiquitous
Available technology – go from hardest to easiest
Wireless technology promises to make the submillimeter particularly
interesting because the inexpensive technology can also be very
powerful
Absolute frequency calibration and spectral agility
‘Zero’ instrument width
High brightness temperatures
Quiet, low clutter backgrounds
Systems can be very small and low power – photons are small
Spectroscopic engineering in the submillimeter is
many faceted and provides an accelerating symbiotic
family of opportunities
Acknowledgements
Students, Coworkers, and Colleagues
The Spectroscopic Community