CHIRPED-PULSE TERAHERTZ SPECTROSCOPY FOR BROADBAND

TRACE GAS SENSING

Eyal Gerecht, Kevin O. Douglass, David F. Plusquellic

National Institute of Standards and Technology Optical Technology Division, Gaithersburg, MD

Multi-Component Gas MonitorGHGs, VOCs, or breath analysis

Formaldehyde

CO

MethanolAcetone

Ethanol

CO2 (18O)

N2O

NO

0.805 0.875THzL.S. Rothman et al, “The HITRAN 2004 molecular spectroscopic database,” J. Quant. Spectrosc. Radiat. Transf. 96, 139-204 (2005).

Current Multiplier Chain Coverage

255 – 315 GHz 4 mW520 – 630 GHz 0.8 mW850 – 945 GHz 0.1 mW

x48

White Cell

9 GHz Source

Mix AMCx48

YIG

YIG

AWG 12 GS/s

Chirped-Pulse THz Spectrometer

E. Gerecht, K.O. Douglass, D.F. Plusquellic, Optics Express, April 22, 2011, Vol. 19, Issue 9, pp. 8973-8984 (2011)Field group (MIT): 70-100 GHz,G.B. Park et al., 64th ISMS, 2009, RH07

LO

High Purity MW Chirped Pulse

100 ns - 10 GHz Chirped THz pulse

Time (ns)0 100

Fre

quen

cy (

GH

z)0

12

550 – 560 GHz

High Speed Data Transfer

360 MB/s 26.66 MS/sRecord and Transfer 80 MS in 3 s

At 40 GS/s:4000 records in 3 s80,000 averages in 60 sec.

Remote Data TransferWired x4 PCI Express

White Cell

M

3

M5

M1

M

2

M4

M

6

Power Transmission ~20%Currently aligned for 25 meter path length

V. B. Podobedov, D. F. Plusquellic, and G. T. Fraser, J. Quant. Spectrosc. Radiat. Transf. 91(3), 287–295 (2005).V. B. Podobedov, D. F. Plusquellic, K. E. Siegrist, G. T. Fraser, Q. Ma and R. H. Tipping, J. Quant. Spectrosc. Radiat. Transf. 109(3), 458-467 (2008).

0.5 m

Artifact of White Cell Alignment 50 Meter path pulse

SignalBackground

Subtracted

Artifact of White Cell Alignment 50 Meter path pulse

SignalBackground

Subtracted

Artifact of White Cell Alignment 50 Meter path pulse

SignalBackground

Subtracted

Time (ns)0 100

Fre

quen

cy (

GH

z)

012

25 ns - 10 GHz Chirped THz pulse 550 – 560 GHz

Direct Absorption of a 5 Component Gas Mix

L.S. Rothman et al, “The HITRAN 2004 molecular spectroscopic database,” J. Quant. Spectrosc. Radiat. Transf. 96, 139-204 (2005). H. M. Pickett, R. L. Poynter, E. A. Cohen, M. L. Delitsky, J. C. Pearson, and H. S. P. Muller, "Submillimeter, Millimeter, and Microwave Spectral Line Catalog," J. Quant. Spectrosc. Radiat. Transf. 60, 883-890 (1998).

Absorption - N2O at 853.3553 GHz

0 50 100 150 200 250 3000

0.5

1

1.5

2

2.5

f(x) = 0.00893065835605766 xR² = 0.99669476297959

Inte

nsity

Pressure (mTorr)

Absorption Data Results

Correcting Simulated Intensities for FID Response

FID Detection of a 5 Component Gas Mix

0.54600 0.55666THz

FID

Sig

nal

(a.

u.)

0.55133 0.553990.54866

N2O170 ppb

OCS280 ppb

EtOH1600 ppb MeOH

100 ppb

Acetone8000 ppb

H2O2 ppbx5

00

100,000:1

x500

L.S. Rothman et al, “The HITRAN 2004 molecular spectroscopic database,” J. Quant. Spectrosc. Radiat. Transf. 96, 139-204 (2005). H. M. Pickett, R. L. Poynter, E. A. Cohen, M. L. Delitsky, J. C. Pearson, and H. S. P. Muller, "Submillimeter, Millimeter, and Microwave Spectral Line Catalog," J. Quant. Spectrosc. Radiat. Transf. 60, 883-890 (1998).

10.6 GHz in 500 nsec – 80K averages in 60 sec

FID Detection of MeOH 10 GHz Bandwidth

Field Magnitude

Intensity

*

**

*

In between limits

541060 552505ν / GHz

2.5 mTorr Pure

Signal Scaling?

779.760 869.760ν / GHz

Extending to Higher Bandwidths

Please See Justin Neil

RC06

90 GHz FID near 850 GHzMeOH -1.2 mTorr Pure

2ms acquisition time

Measuring lineshapes from the FID

See RB08

ConclusionsDemonstrated Chirped pulse THz spectrometer

operating in 530 – 630 GHz and 780 – 870 GHz regions

Demonstrated phase stable operation

Demonstrated high sensitivity and rapid throughput for both absorption and FID emission measurements

We continue to make progress on the quantification of FID signals and sensitivities

Acknowledgements

Virginia L. Perkey – SURF student Eric M. Vess - SURF student Tektronix – equipment loan

NIST National Research Council ProgramPost Doctoral Research Opportunities

http://www.nist.gov/pml/div685/grp08/biophysics-group-research-opportunities.cfm

5 Component Gas Mix – 3 GHz Section

N2O

EtOH

MeOH

Acetone