Mid-IR ethene detection using

a quasi-phase matched

LiNbO3 waveguide

Mid-IR ethene detection using

a quasi-phase matched

LiNbO3 waveguide

• 64th OSU International Symposium on Molecular Spectroscopy

• 23rd June 2009

Biogenic sources

- Plant Hormone 'ripening hormone'

Anthropogenic sources

- Organic chemical industry (polyethylene products)

- Vehicle exhaust

(Ethene as indicator of UV-induced lipid peroxidation)

OH ~ 20 hoursO3 ~ 9.7 daysNO3 ~ 5.2 months

Why ethene?

Urban Area ~ few ppbv

Remote Area < 1 ppbv

2900 3000 3100 3200 6148 6152

0.0

0.2

0.4

0.6

0.8

1.0

1.2

line

/ 10-2

0 cm2 m

olec

ule-1

cm

-1

Wavenumber /cm-1

C2H4

A.M.Parkes et al., Phys. Chem. Chem. Phys., 6 (2004) 5313-53178HITRAN Database, 2008

Mid-IR vs Near-IR

Mid-IR Near-IR

DFG (2 to 5m)

QCLs (5 to 11m)

3080.9 3081.0 6150.2 6150.3 6150.4-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

/

10-1

8 cm

2 mo

lecu

le-1

wavenumber /cm-1

C2H4

HITRAN Database, 2004

3081.002 cm-1 6150.300 cm-1

cm-1 (FWHM) 0.00717 0.01432

line / cm2 molecule-1 cm-1 1.124 10-20 5.08 10-22

Gain ~ 46

Mid-IR vs Near-IR

ELECTRONICS LETTERS 17th August 2006 Vol. 42 No. 17Applied Physics Letters 88, 061101, 2006

ps

ips

i

Frequency mixing and phase matchingPerfect phase matchingQuasi-phase matchingWithout phase-matching

deff= 17 pm/V

0i

i

s

s

p

p nnn

ks

kp

ki

1

2k

01

Bulk vs waveguide

Applied Physics Letters 88, 061101, 2006

Waveguide structure improves conversion efficiency with respect to bulk

WGBulk

300

PZT

Experimental set-up (OA-CEAS)

90 mW

28 mW

~ 200 W

Characterization of the laser source

Conversion efficiency = 12.3 % W-1

Experimental phase matching curve in good agreement with the simulated one

Beam profile analysis gave a Gaussian beam waist of ~2 mm.

30 40 50 60 70 80

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Con

vers

ion

Eff

icie

ncy

TCrystal

/ oC

2

sin 2 Lkc

3220 3225 3230 3235 3240 3245 3250 3255 32600

2

4

6

8

10

12

14

pump

/nm

1062.0671062.3561062.7031063.1101063.3601063.6501064.0041064.150

Con

vers

ion

Effi

cien

cy %

/W

Idler

/nm

Tunability of the laser sourceWide tunability range of 35 cm-1

FWHM ~ 7 cm-1

Multi-pass absorption + WMS

3080.94 3080.96 3080.98 3081.00 3081.02 3081.04

-0.2

0.0

0.2

0.4

0.6

WM

S S

igna

l a.u

.

Wavenumber /cm-1

Upper-state Local Quanta

Lower-state

Local Quanta

Molecule /cm-1

Term Symbol

Integrated cross section /cm2 cm-1

J' Ka' Kc' J'' Ka'' Kc''

C2H4 3081.0016 RP0(14) 1.09 · 10-20 13 1 13 14 0 14

C2H4 3081.0016 PR6(10) 1.64 · 10-22 11 5 6 10 6 5

C13CH4 3081.0016 PQ3(10) 1.76 · 10-22 10 2 8 10 3 7

1.29 Torr of C2H4 in Ar (500 ppmv)

Slow modulation = 1 Hz

Fast modulation = 20 kHz

c = 5 ms

Idler power = 193 W

L = 56 m

Modulation depth → b = 2

min (BW)= 1.63 x 10-8 cm-1 Hz-1/2 (2)

3080.96 3080.98 3081.00 3081.02 3081.04 3081.06

0.00

0.04

0.08

0.12

0.16

c = 5 ms

c = 50 ms

3080.96 3081.00 3081.04

0.0

0.1

0.2

(I0-I

)/I

/cm-1

(Io-I

)/I

/cm-1

OA-CEAS

1.8 Torr of C2H4 in Ar (21.8 ppmv)

Slow modulation = 0.8 Hz

Chopper frequency = 2.6 kHz

= 0.01232 cm-1

= 0.00717 cm-1

3080.97 3081.00 3081.03 3081.06 3081.09

0.0

0.1

0.2

0.3

0.4

0.5

0 1 2 3 40

2

4

6

area

/ 10

-3 c

m-1

[C2H

4] / 1012 molecule cm-3

(Io-I

)/I

/ cm-1

OA-CEAS

R = 99.901 ± 0.002 % min (BW)= 1.6 x 10-8 cm-1 Hz-1/2 (2)

L = 1110 ± 20 m

Conclusions and future work

Mid-IR light has been characterized. The CONVERSION EFFICIENCY of the

waveguide, the BEAM PROFILE and the TUNABILITY of the system have been

tested.

Applications of the DFG spectrometer as a new laser sources @ 3.2 m for

ethene detection have been proved using MULTI-PASS ABSORPTION coupled

with WMS, and OA-CEAS.

A.M.Parkes et al., Phys. Chem. Chem. Phys., 6 (2004) 5313-53178

Technique[C2H4]min

/ molecule cm-3 (in air)Mixing ratio

/ ppbv (in air)

Near-IR(@ 1.6 m)

cw-CRDS 1.6 1012 64

cw-CRDS + preconc. 4.7 1010 1.9

Mid-IR(@ 3.2 m)

MPA + WMS 5.4 1011 21.8

OA-CEAS 2.2 1011 8.9

Acknowledgements

Prof. Andrew Orr-Ewing

Dr. Mike Nix

Keith Rosser

Dr James Smith

Charles Murray

Bristol Laser Group

Prof. Gus Hancock

Dr Grant Ritchie

Dr Rob Peverall

Luca Ciaffoni

10 15 20 25 30 35

Inte

nsit

y / a

rb. u

nits

Frequency / MHz

EDFA Pump 1 ( = 980 nm) Pump 2 ( = 1480 nm) Both Pumps

FWHM ~ 0.5 MHz

10 15 20 25 30 35

1583 nm DFB Diode LaserFWHM ~ 1.1 MHz

inte

nsity

/ ar

b. u

nits

Frequency /MHz50 100 150 200-85

-80

-75

-70

-65

-60

N

oise

(dB

VR

MS)

Frequency / kHz

Pseed

= 0 mW P

seed = 0.4 mW

Pseed

= 0.8 mW P

seed = 1.2 mW

Spectrum analysis of the EDFA output- Fabry-Perot spectrum analyzer → laser bandwidth ~ 500 kHz- 1480 nm pump more noisy than 980 nm- FFT spectrum analyzer → ASE at seeding powers < 1 mW

Characterization of the laser source

Noise Analysis

330-370 kHz

0 20 40 60 80 100

0

100

200

300

400

500

600

shot-noise

background

N = a0 + a

1 I + a

2 I2

a

0 = 147.1 ±7.6

a1 = 0.32 ±0

a2 = 0.0355 ±0.0016

No

ise

N (

pA

2 /Hz)

Detector Current I (A)

Noise Analysis

Applied Physics B 76, 473-477 (2003)

0.025 (200-500kHz)

N 2

B2eI

N 2eIB

cw-CRDS with Laser Detuning Technique

Cavity

Signal

Laser

Cur

rent