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

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

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

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

What do Analytical Chemists Care About?

Specificity

Sensitivity

Generality

Size

Cost

Speed

Ease of Use

Comparison with Alternatives

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

A CLEAR PATH TO GAS ANALYSISHP ~1975 Opt. Lett. 14, 1128-1130(1989)

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

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

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

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

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

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

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

1 second sweep time over whole spectrum

300 seconds integration on resonance

X 107 sensitivity plus

‘absolute’ specificity

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.

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

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

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 ???

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

Source Brightness!

10-2 photons/pulse/MHz

(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).

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

Optics and Photonics News (August 2003)

and

“Spectroscopy in the Terahertz Region,” in Sensing with Terahertz Radiation, D. Mittleman, ed. Springer, Berlin (2003).

REFERENCES

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

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

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.

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.

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